Tag: Atlantic meridional overturning circulation (AMOC)

Ice Age Climate Shifts Were Much Slower Than We Thought

Researchers from Xi’an Jiaotong University’s Institute of Global Environmental Change (led by first author Xiyu Dong, with contributions from Hai Cheng, Xu Zhang, and others) analyzed high- resolution oxygen isotope (δ¹⁸O) records from annually laminated speleothems.

In short, abrupt climate change is a well- established feature of Earth’s past climate system, driven by internal thresholds and feedback, and remains a key concern for understanding both historical variability and potential future surprises.

Illustration of an icy coastline and ocean currents with charts showing slow Ice Age climate shifts, AMOC circulation, speleothem records, and North Atlantic temperatures.
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A new study published in Science (DOI: 10.1126/science.aed4270) on November 5, 2026, finds that abrupt climate shifts during the last ice age, specifically Dansgaard- Oeschger (DO) events linked to the Atlantic Meridional Overturning Circulation (AMOC), took substantially longer than previously inferred from Greenland ice- core records.

Researchers from Xi’an Jiaotong University’s Institute of Global Environmental Change (led by first author Xiyu Dong, with contributions from Hai Cheng, Xu Zhang, and others) analyzed high- resolution oxygen isotope (δ¹⁸O) records from annually laminated speleothems.

These came from Cherrapunji Cave (northeast India) and Shuixi Cave (southwest China), combined with published data from Zhangjia Cave. The records cover DO events 1 through 8.

Key findings:

  • Transitions in the Asian monsoon speleothem records consistently lasted longer than 100 years and averaged about 180 years.
  • This is far slower than the decadal- scale shifts seen in Greenland ice -core δ¹⁸O records, which had been used as the main proxy for the speed of AMOC strengthening.⁠

The annual laminae in the speleothems provided precise relative timing of transition durations (complementing absolute U– Th ages).

Modeling indicates a two- stage process: rapid retreat of sea ice in the northeastern North Atlantic quickly adjusted regional atmospheric circulation, producing the sharp Greenland δ¹⁸O rise.

Full AMOC strengthening and further northwestern North Atlantic sea- ice retreat followed more gradually, without major additional changes in atmospheric circulation modes or moisture pathways that would further alter Greenland δ¹⁸O.

Asian monsoon speleothem records capture the complete AMOC strengthening process.⁠

Implications: Natural AMOC transitions were not as rapid as ice- core data alone suggested. When discussing potential future AMOC tipping risks, the duration of any transition is as important as the climatic impacts.

The study highlights the value of combining high- quality, annually resolved paleoclimate records with process- based (isotope- enabled) Earth system models.

The authors note that additional high- quality speleothem records of DO events, better North Atlantic sea- ice reconstructions, and models that incorporate ice- sheet processes will further improve understanding.⁠

This revises the view of how quickly these past high- latitude Northern Hemisphere warmings (5- 16 °C) and associated AMOC changes unfolded, offering a more measured perspective for interpreting both past and potential future abrupt climate shifts.

Rapid Warming Could Tip the AMOC at Just 2°C — Slow the Pace and It May Survive Beyond 5°C

Rapid Warming Could Tip the AMOC at Just 2°C — Slow the Pace and It May Survive Beyond 5°C – Climate- Science.press

Abrupt climate change refers to large- scale shifts in the climate system that occur much faster than the gradual external forcing (such as orbital changes or rising greenhouse gases) that triggers them.

These transitions happen on timescales of years to a few decades, persist for decades or longer, and can cause major disruptions to ecosystems and human societies.

Two complementary definitions are commonly used:

  • Physical: The climate system crosses a threshold or tipping point and switches to a new state at a rate set by internal dynamics (e.g., feedbacks involving ocean circulation, sea ice, or ice sheets), faster than the forcing itself.
  • Impacts- based: A change so rapid and unexpected that natural or human systems struggle to adapt.

The best- documented cases come from the last glacial period (~120,000–11,700 years ago):

  • Dansgaard- Oeschger (DO) events: Repeated abrupt warmings of 5- 16 °C over Greenland (and the North Atlantic region), often within decades according to ice- core records, followed by gradual cooling. These occurred roughly every 1,000- 1,500 years. They are strongly linked to strengthening of the Atlantic Meridional Overturning Circulation (AMOC), which transports heat northward.⁠
  • Heinrich events: Massive iceberg discharges into the North Atlantic that disrupted ocean circulation, often associated with the coldest phases of DO cycles.
  • Younger Dryas (~12,900- 11,700 years ago): A sudden return to near- glacial conditions in the Northern Hemisphere during the last deglaciation, ending with rapid warming.

Other examples include the end of the Carboniferous rainforest collapse and possibly the Paleocene- Eocene Thermal Maximum.

Abrupt changes typically involve nonlinear feedbacks and thresholds:

  • Changes in AMOC strength (weakening or collapse reduces heat transport to the North Atlantic).
  • Sea -ice and ice- sheet dynamics (ice- albedo feedback amplifies warming or cooling).
  • Freshwater input from melting ice that stratifies the ocean and suppresses deep- water formation.
  • Atmospheric reorganization (shifts in monsoons, storm tracks, and the Intertropical Convergence Zone).

A recent Science study (November 2026) used annually laminated speleothems from Asia to show that the full AMOC strengthening during DO events 1- 8 actually took longer than previously thought, consistently over 100 years and averaging ~180 years, rather than the decadal scale suggested by Greenland ice- core δ¹⁸O alone.

Modeling indicates a two-stage process: rapid northeastern North Atlantic sea- ice retreat drives the sharp Greenland signal, while the complete AMOC recovery and further sea- ice loss occur more gradually. Asian monsoon records capture the fuller transition.⁠

This revises the view of how quickly these past “abrupt” ocean- circulation shifts unfolded and underscores that transition duration is as important as the magnitude of change when assessing future risks.

Modern climate models and observations raise concerns about possible abrupt shifts under anthropogenic warming, including:

  • Weakening or collapse of the AMOC.
  • Rapid ice- sheet mass loss (Greenland, West Antarctica) and associated sea-level rise.
  • Permafrost thaw releasing additional greenhouse gases.
  • Amazon rainforest dieback or other ecosystem tipping points.

While the current warming is primarily gradual and forced by greenhouse gases, the climate system can still exhibit nonlinear, abrupt responses once thresholds are crossed.

Paleoclimate records remain the primary evidence for such behavior, informing risk assessments for the coming decades to centuries.

In short, abrupt climate change is a well- established feature of Earth’s past climate system, driven by internal thresholds and feedback, and remains a key concern for understanding both historical variability and potential future surprises.

Rapid Natural Warming Spikes Occurred 25 Times — Last Ice Age Edition

Rapid Natural Warming Spikes Occurred 25 Times — Last Ice Age Edition – Climate- Science.press

The linked Science paper is titled “Glacial abrupt transitions in ocean circulation were much slower than ice-core records imply” (DOI: 10.1126/science.aed4270), published 5 November 2026.

It is a peer- reviewed research article from researchers including Xiyu Dong (first author), Xu Zhang, Hai Cheng, and co-authors from Xi’an Jiaotong University and collaborating institutions. The full text is behind Science’s paywall and subscriber access, but detailed summaries, the dataset, and press materials are publicly available.

Dansgaard– Oeschger (DO) events involved rapid high- latitude Northern Hemisphere warmings of 5- 16 °C, tightly linked to strengthening of the Atlantic Meridional Overturning Circulation (AMOC).

Prior estimates of AMOC transition speeds (often within decades) relied heavily on Greenland ice-core δ¹⁸O records, which reflect both temperature and moisture- source changes.

Using high- resolution δ¹⁸O records from annually laminated speleothems (cave deposits) that more directly track AMOC- driven changes in the Asian monsoon:

  • Two new records from Cherrapunji Cave (northeast India) and Shuixi Cave (southwest China), plus published data from Zhangjia Cave.
  • Coverage of DO events 1- 8.

Results: The transitions consistently lasted >100 years and averaged ~180 years, substantially longer than the decadal- scale shifts in Greenland ice- core δ¹⁸O.⁠

Annual laminae enabled precise relative dating of transition durations (complementing absolute U– Th ages).

Modeling supports a two- stage process:

  1. Rapid sea- ice retreat in the northeastern North Atlantic quickly adjusted regional atmospheric circulation, producing the sharp Greenland δ¹⁸O rise.
  2. Further AMOC strengthening and northwestern North Atlantic sea- ice retreat occurred more gradually, without major additional shifts in atmospheric circulation or moisture pathways that would further change Greenland δ¹⁸O.

Asian monsoon speleothem δ¹⁸O records capture the full AMOC strengthening process.

Natural AMOC transitions were slower than previously inferred from ice cores alone. The authors note that discussions of future AMOC tipping risks should emphasize transition duration alongside potential impacts.

Supporting data (U- Th dates, δ¹⁸O time series, annual lamina thicknesses, anchored ice- core records, stacked series, and lamina- counting code) are archived on Dryad (doi:10.5061/dryad.xgxd254wx).⁠

The study underscores the value of combining annually resolved speleothem records with isotope- enabled Earth- system modeling for quantifying rates of past abrupt climate change.

Milankovitch Cycles, the Last Glacial Period, and Why Earth Is Still in an Ice Age

Milankovitch Cycles, the Last Glacial Period, and Why Earth Is Still in an Ice Age – Climate- Science.press

Journal: Science, Vol 394, Issue 6824

DOI: 10.1126/science.aed4270.

Provided: Xi’an Jiaotong University

Authors: Xiyu Dong, Xu Zhang, Yuchen Sun, Gayatri Kathayat, Youwei Li, Sune O. Rasmussen, Anders Svensson, Christo Buizert, Ashish Sinha , Stephen Barker, Carlos Pérez-Mejías, Gregor Knorr, Rishui Chen , Kan Zhao, Wenjing Du, Haiwei Zhang, Hanying Li, Andrea Columbu, Liangcheng Tan , Yuao Zhang, Youfeng Ning, Martin Werner, Yongjin Wang, R. Lawrence Edwards and Hai Cheng

Abstract

Dansgaard-Oeschger (DO) events during the last ice age are thought to reflect rapid shifts in the Atlantic Meridional Overturning Circulation (AMOC). Greenland ice cores suggest warming transitions within only a few decades—or even just over 10 years. Using precisely dated speleothem oxygen-isotope records from the Asian monsoon region, we have shown that the same DO warmings unfolded over more than a century. Isotope modeling revealed that Greenland records primarily capture a rapid atmospheric reorganization triggered by the initial sea-ice retreat in the northeastern North Atlantic, whereas the parallel AMOC recovery and hemispheric thermal adjustment proceeded much more slowly. These findings reveal that natural AMOC transitions evolved more slowly than the rapid North Greenland oxygen-isotope shifts would imply, thereby refining our understanding of “abruptness” during DO events.

AMOC Collapse Would Be Catastrophic: And Ice- Age Records Show It’s Happened Before

Potential Catastrophe: The Impact of AMOC Collapse on Climate

North Atlantic’s Cold Blob Reveals Complex, Shifting Link to Weakening Ocean Current

North Atlantic Cold Blob Reveals AMOC Weakening Is Complex

Ocean Circulation Continues for Centuries Even After Key AMOC Engine Shuts Down

How Ocean Circulation Endures After Key AMOC Shutdown

North Atlantic’s Cold Blob Reveals Complex, Shifting Link to Weakening Ocean Current

Penn State researchers report that the link between the North Atlantic “cold blob” (also called the North Atlantic warming hole) and the Atlantic Meridional Overturning Circulation (AMOC) is more complex and phase- dependent than previously assumed.

The North Atlantic “cold blob” (also called the North Atlantic warming hole) is a region south and southeast of Greenland that has cooled or lagged substantially behind global ocean warming over the past century (by up to ~1– 1.8°F / ~0.5– 1°C in some estimates).

Illustration of ocean currents swirling around Greenland and the North Atlantic, with orange and blue flow arrows.
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Penn State researchers report that the link between the North Atlantic “cold blob” (also called the North Atlantic warming hole) and the Atlantic Meridional Overturning Circulation (AMOC) is more complex and phase- dependent than previously assumed.

The cold blob is a roughly 965,000- square- mile region south and southeast of Greenland that has cooled by as much as 1.8°F over the past century while most other ocean waters have warmed.

It has long been linked to a weakening AMOC, the ocean “conveyor belt” that transports warm surface water northward and denser cold water southward in the deep ocean. A sustained AMOC decline (influenced by climate change) is viewed as a key driver of the cooler surface temperatures there.⁠

In a Nature Communications paper, a team led by Laifang Li (assistant professor of meteorology and atmospheric science) and including lead author Yifei Fan (doctoral candidate) used climate model simulations across many scenarios.

These incorporated varying greenhouse- gas levels, past and present climate conditions, ocean heat transfer, ocean– atmosphere heat exchange, and atmospheric radiation (including low -cloud effects). The work builds on their 2025 finding that atmospheric radiation also helps keep the region cooler.

The cooling effect of a weakening AMOC on surface temperatures is not constant:

  • When the current weakens from its greatest strength, surface temperatures drop only modestly.
  • When it weakens from mid- range strength, the temperature drops roughly triples, and the cold blob expands across the subpolar basin.
  • When the current weakens further from an already diminished state, the cooling effect fades; the cold blob shifts northeast toward Iceland and the Norwegian Sea. Variable atmospheric heat radiation and low- cloud reflections contribute to these shifts.

Models project that AMOC will move from its current higher- strength phase toward its lowest- strength phase by 2100. The cold blob’s most significant temperature shift could occur as late as 2067 or could already have begun as early as 2021.

Earlier peaks in temperature change would correspond to an earlier fading of the cool patch. Once AMOC is weak enough, the ocean is expected to absorb more heat from the atmosphere and approach its capacity to buffer climate change, increasing uncertainty in future surface temperatures, currents, weather and climate effects.

Heat map of the Atlantic Ocean and surrounding continents with a large blue cold region near Greenland and warm red-orange areas elsewhere.
The 965,000-square -mile area in the North Atlantic Ocean south and southeast of Greenland, the so- called cold blob, cooled by as much as 1.8 degrees Fahrenheit over the past century as other ocean waters warmed. Credit: NASA.

The North Atlantic “cold blob” (also called the North Atlantic warming hole) is a region south and southeast of Greenland that has cooled or lagged substantially behind global ocean warming over the past century (by up to ~1–1.8°F / ~0.5– 1°C in some estimates).

It stands out as one of the few areas resisting the broader warming trend.

The Atlantic Meridional Overturning Circulation (AMOC) acts as a major “conveyor belt”: it carries warm, salty surface water northward into the subpolar North Atlantic, where the water cools, becomes denser, sinks, and returns southward at depth. A weakening AMOC reduces northward ocean heat transport (OHT) into this region, which is widely hypothesized as the primary cause of the cold blob.

Recent observational analyses (including full- depth ocean heat content data back to the 1950s and satellite records) support this view.

They show that the cooling extends below the surface, surface heat loss from the region has actually decreased in recent decades, and multidecadal heat-content variations correlate more strongly with horizontal ocean heat transport changes than with atmospheric surface fluxes.

This points to reduced heat delivery by the AMOC rather than increased atmospheric extraction of heat.

Climate models and reconstructions generally link the blob’s emergence to anthropogenic forcing (primarily greenhouse gases, with contributions from aerosols and Greenland meltwater freshening that inhibits deep convection).

Direct AMOC measurements (e.g., RAPID array since ~2004) and indirect indicators also indicate a weakening trend over recent decades, though natural variability remains significant.

A 2026 Nature Communications study (Fan, Chan, Zhang, Li et al., using large ensembles of CESM2 simulations across paleoclimate to future scenarios, plus other CMIP6 models) demonstrates that the AMOC- subpolar SST relationship is not stationary.

It shifts across three regimes defined by AMOC strength (change points near ~20 Sv and ~11.5 Sv):⁠

  • Regime 1 (strong AMOC, > ~20 Sv): Low sensitivity (~0.09 °C per Sv). Classic dipole fingerprint—cooling in the central subpolar basin paired with warming along the Gulf Stream extension. The cold blob begins to emerge. Oceanic, clear-sky radiative, and cloud processes contribute roughly equally and modestly.
  • Regime 2 (intermediate AMOC, ~11.5– 20 Sv): Sensitivity more than triples (~0.31 °C per Sv). Cooling intensifies and expands across the entire subpolar basin (strongest in the Irminger and Labrador Seas). This is the “maturing” stage of the warming hole. The amplification is driven primarily by atmospheric radiative processes: reduced clear- sky longwave radiation (from cooler and drier troposphere) and increased shortwave reflection by low- level clouds. Ocean heat transport changes are largely offset by compensating turbulent fluxes.
  • Regime 3 (weak AMOC, < ~11.5 Sv): Sensitivity drops again (~0.12 °C per Sv). The canonical cold blob decays or shifts northeastward toward Iceland and the Norwegian Sea. Radiative amplifiers weaken and relocate; the subpolar region can begin absorbing more heat from the atmosphere.

These regimes map onto historical-to-future trajectories in models (e.g., CESM2 transitions through them from the late 20th century into the 21st). The year of peak AMOC- SST sensitivity can help predict the shift into the weak regime and associated decay of the classic warming hole. Atmospheric radiative processes dominate the regime shifts; oceanic processes contribute more indirectly via air– sea coupling.

Implications

  • The cold blob is a useful but imperfect and non- stationary indicator of AMOC strength. Its presence or intensity does not map linearly to AMOC decline, and its future disappearance would not necessarily signal AMOC recovery.
  • Models project continued AMOC weakening under greenhouse- gas forcing, with the system potentially moving from the current stronger and intermediate regimes toward the weak regime by 2100. The timing of major shifts in the blob carries uncertainty (model-dependent estimates range from the early 2020s to the 2060s).
  • Broader climate effects of a weaker AMOC (and associated blob) include potential influences on the jet stream, storm tracks, European and North American weather extremes, and regional sea- level patterns. A full AMOC collapse remains a low- probability but high- impact tipping- point risk this century under high- emissions scenarios; most assessments project substantial weakening rather than abrupt shutdown.
  • Improved monitoring (satellites, ocean arrays, sustained heat- content observations) and model constraints that account for regime dependence will reduce projection uncertainties.

In short, the cold blob is tightly linked to AMOC weakening via reduced ocean heat transport, but the strength of that coupling, and the resulting SST pattern- depends strongly on the background AMOC state and is mediated importantly by atmospheric radiation and clouds. This adds important nuance to interpreting both past observations and future projections.

Scatter plot of AMOC versus WHSST across three regimes, with colored climate model data, change points, fitted lines, and an inset North Atlantic map.
AMOC– North Atlantic SST relationship in model simulations. Credit: Nature Communications (2026). DOI: 10.1038/s41467-026-76149-4

Regime shifts of AMOC- sea surface temperature relationship

The Atlantic Meridional Overturning Circulation (AMOC) regulates climate, and subpolar North Atlantic sea- surface temperature (SST) patterns are commonly used as proxies for its strength.

This study shows the AMOC- SST relationship is state- dependent, not stationary.

Using Community Earth System Model (CESM2) simulations across diverse climate states plus a multi- model ensemble, the authors identify three distinct regimes:

  • Strong AMOC: typical dipole SST fingerprint.
  • Intermediate AMOC: amplified subpolar SST anomalies.
  • Weak AMOC: muted North Atlantic signals.

These regimes arise primarily from changes in atmospheric radiative processes (ocean processes contribute more indirectly via air–sea interactions).

The year of peak AMOC- SST sensitivity can predict the transition into the weak- AMOC regime and the associated decay of the North Atlantic warming hole (“cold blob”).

This provides a physically based constraint on model uncertainties in climate projections and implies that SST- based AMOC indicators must account for state dependence.

AMOC is indexed as maximum overturning transport below 500 m at 40°N. The warming- hole SST index (WHSST) is the difference between subpolar North Atlantic mean SST (roughly 45°- 60°N, 20°- 50°W) and the global mean.

Objective change-point detection on CESM2 simulations (paleoclimate to future scenarios) yields two change points (~20.0 Sv and ~11.5 Sv), defining three regimes:

RegimeAMOC strengthWHSST sensitivity to AMOCSpatial SST pattern with weakening AMOC
1 (strong)> ~20 SvLow (~0.09 °C Sv⁻¹)Classic dipole: cooling in central subpolar basin and warming along Gulf Stream extension
2 (intermediate)~11.5- 20 SvHigh (~0.31 °C Sv⁻¹; >3 times Regime 1)Intensified cooling across the entire subpolar basin (strongest in Irminger and Labrador Seas)
3 (weak)< ~11.5 SvLow again (~0.12 °C Sv⁻¹)Cooling shifts northeast into the Norwegian Sea and Iceland basin; canonical warming hole decays

The pattern is robust across alternative SST and AMOC metrics and appears in at least four additional CMIP6 models.

These regimes correspond to stages of the North Atlantic warming hole: emerging (Regime 1), maturing (Regime 2), and decaying (Regime 3).

Historical and 21st- century CESM2 trajectories cross these regimes between ~1985 and 2100.

A partial temperature-change decomposition attributes WHSST anomalies mainly to:

  1. Oceanic processes (ocean heat transport convergence and local heat storage, largely balanced by turbulent heat fluxes).
  2. Surface downward clear- sky radiation (dominated by longwave).
  3. Cloud radiative effects.
  • Regime 1: All three process groups contribute roughly equally (modest net cooling).
  • Regime 2: Sensitivity tripling is radiatively driven. Clear- sky longwave (linked to tropospheric cooling and reduced water vapor) supplies ~2/3 of the increase; enhanced shortwave reflection by low- level clouds supply most of the rest. Oceanic terms stay nearly neutral.
  • Regime 3: Radiative amplifiers (clear- sky longwave and cloud shortwave) weaken and shift northeast, so the canonical subpolar warming hole fades even as AMOC continues to decline. Oceanic contributions remain secondary.

Ocean heat transport changes scale with AMOC but are largely offset by compensating turbulent fluxes, so they do not drive the regime shifts directly.

Implications

  • SST fingerprints of AMOC are non- stationary; interpreting the observed cold blob (or its future evolution) as a simple AMOC proxy requires regime awareness.
  • The timing of peak AMOC- SST sensitivity offers a useful predictor for when the system enters the weak- AMOC regime, and the warming hole begins to decay.
  • This framework helps explain and constrain inter- model spread in 21st-century North Atlantic SST projections.

The paper builds directly on the authors’ prior work linking atmospheric radiation to the cold blob and aligns with the Penn State news summary discussed previously.

Full text, figures, methods, and supplementary material are available at the Nature Communications page and PDF.

Journal: Nature Communications, volume 17, Article number: 9416 (2026)

DOI: 10.1038/s41467-026-76149-4, Open access

Published: 05 August 2026

Provided: Pennsylvania State University

Authors: Yifei Fan,
Duo Chan,
Gokhan Danabasoglu,
Who M. Kim,
Pengfei Zhang&
Laifang Li (corresponding), among others

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) plays critical roles in regulating climate, and subpolar North Atlantic sea-surface temperature (SST) patterns are widely used to infer changes in its strength. Yet the stationarity of their relationship remains unclear. Here, using Community Earth System Model simulations spanning various climate states and a multi-model ensemble, we show that this relationship is state-dependent. We identify three distinct regimes: strong AMOC with the typical dipole fingerprint; intermediate AMOC with amplified subpolar SST anomalies; and weak AMOC with muted North Atlantic signals. These regimes arise primarily from changes in atmospheric radiative processes, while ocean processes contribute indirectly through air–sea interactions. The year of peak AMOC–SST sensitivity emerges as a predictor of the transition into the weak-AMOC regime and associated decay of the North Atlantic warming hole, offering a physically-based constraint on model uncertainties in climate projections. Our findings also imply that SST-based AMOC indicators must account for state dependence.

Antarctic Sea Ice Collapse Triggers Abrupt Reversal in Key Southern Ocean Layer, Threatening Heat and Carbon Storage

New research from the University of Melbourne (with the Indian Institute of Science and University of Southampton), published in Nature Climate Change (October 2026), shows that the Antarctic Intermediate Water (AAIW), a vast, relatively fresh ocean layer spanning much of the Southern Hemisphere, has abruptly reversed long- term trends in salinity, density, and depth since around 2016, linked to major Antarctic sea ice loss.

Illustration depicting the collapse of Antarctic sea ice and its impact on the Southern Ocean, highlighting ocean layer reversal, with labels for fresh, warmer surface layer, denser, saltier deep water, and associated risks to heat and carbon storage.
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New research from the University of Melbourne (with the Indian Institute of Science and University of Southampton), published in Nature Climate Change (October 2026), shows that the Antarctic Intermediate Water (AAIW), a vast, relatively fresh ocean layer spanning much of the Southern Hemisphere, has abruptly reversed long- term trends in salinity, density, and depth since around 2016, linked to major Antarctic sea ice loss.

What is the AAIW and why does it matter?

The AAIW is a layer typically found roughly 500- 1,500 meters (or more specifically ~700- 1,200 m in some descriptions) below the surface. It forms partly from Antarctic surface waters influenced by sea ice melt and spreads northward into the Atlantic, Indian, and Pacific Oceans.

It helps:

  • Store and redistribute heat, freshwater, and carbon.
  • Supply oxygen.
  • Support parts of the global ocean overturning circulation (a key climate regulator).⁠

The ocean absorbs over 90% of excess heat from human activities (mostly in the upper ocean) and a large share of CO₂ emissions, acting as a climate buffer.

The observed shift

  • Pre- 2016 (roughly 1990s and 2004- 2015): Antarctic summer sea ice melt supplied large volumes of freshwater (estimated at ~triple the Amazon River’s annual discharge, or ~17,400 gigatons in some accounts). This made the AAIW progressively fresher, lighter, and shallower.
  • 2016- 2024: Record- low Antarctic sea ice sharply reduced this meltwater input (dropping toward roughly double the Amazon’s flow). The AAIW rapidly became saltier, denser, and deeper across multiple ocean basins. This is the first direct observational evidence of such a change, detected via Argo floats (thousands of robotic ocean profilers), satellite data, and other records.⁠

Researchers note the last comparable major switch in AAIW properties occurred at the end of the previous interglacial period (~130,000 years ago), when Antarctic ice was minimal, but that transition unfolded over thousands of years, not roughly a decade or two.

Implications for heat and carbon storage

  • A denser and weaker or altered AAIW could reduce the effectiveness of the density barrier (pycnocline) that limits vertical mixing, potentially allowing more excess heat to move into deeper ocean layers. Climate models may therefore be underestimating deep-ocean warming, regional sea- level rise, and longer- term surface temperature responses.⁠
  • Changes in how surface water is subducted could affect the ocean’s capacity to lock away atmospheric carbon, though the magnitude and timing remain uncertain.
  • As the altered water mass spreads north, it forms part of the upper limb of the global overturning circulation and could eventually influence systems like the Atlantic Meridional Overturning Circulation (AMOC), as well as Southern Hemisphere atmospheric circulation, storm tracks, rainfall, and weather patterns over years to decades. Effects could cascade more widely.⁠

The lead researchers (including Associate Professor Bishakhdatta Gayen and PhD student Kaushik Mishra) describe this as revealing a critical missing feedback and an urgent signal that the ocean is responding faster than previously appreciated.

Ongoing monitoring (especially Argo data) and improved climate model representation of these processes are highlighted as priorities, particularly while Antarctic sea ice remains at record lows.

In short, the findings raise important questions about whether current projections fully capture the ocean’s evolving role in heat and carbon storage under rapid polar change.

The study itself focuses on the observational reversal rather than detailed future projections or quantified environmental impacts.

A snowy mountain under a blue sky, with a foreground of ice and snow texture.
Sea ice off Victoria Land, Antarctica, with Mount Melbourne in the background. Credit: Alberto C Naveira Garabato

Antarctic Intermediate Water (AAIW) plays a key role in oceanic carbon storage and redistribution as part of the Southern Ocean’s contribution to the global carbon cycle.

AAIW forms in the polar Southern Ocean (primarily in the Polar Frontal Zone, between the Subantarctic and Polar Fronts). Surface waters there are influenced by sea-ice processes, winds, and mixing.

These waters exchange gases with the atmosphere, absorbing substantial amounts of CO₂ (both natural and anthropogenic) through air- sea gas exchange. Cold temperatures enhance CO₂ solubility, aiding uptake.

Once formed, AAIW is subducted (sunk) to intermediate depths, typically around 500–1,500 meters (often cited as ~700– 1,200 m), and spreads northward into the Atlantic, Indian, and Pacific Oceans as part of the upper limb of the global overturning circulation. This process isolates the absorbed carbon from the atmosphere for decades to centuries.

Specific contributions to carbon storage

  • Major anthropogenic CO₂ sink: Modern AAIW is a significant reservoir for anthropogenic carbon. Its associated carbon inventory has been estimated to exceed ~20 Pg C (petagrams of carbon).⁠
  • Redistribution and transport: AAIW acts as a lateral conduit, carrying carbon (along with nutrients and oxygen) from high-latitude Southern Ocean uptake regions to lower latitudes. This links Southern Ocean air- sea CO₂ exchange with biogeochemical processes in subtropical and tropical oceans.⁠
  • Physical and biological pumps: It participates in the solubility pump (temperature- and salinity- driven CO₂ uptake and isolation at depth) and supports aspects of the biological pump by transporting nutrients that fuel productivity elsewhere. Stratification and density structure associated with AAIW help regulate how effectively carbon is retained versus returned to the surface.
  • Broader Southern Ocean context: The Southern Ocean as a whole dominates global oceanic uptake of anthropogenic heat and carbon. AAIW (together with Subantarctic Mode Water) is central to the rate of water- mass formation and subduction that determines how much CO₂ is taken up and sequestered.

Relevance to recent changes

In the context of the recent research (the abrupt post- 2016 shift toward saltier, denser, and deeper AAIW due to reduced Antarctic sea- ice meltwater), scientists note that alterations to AAIW properties or the way surface water is carried into deeper layers could change how much carbon the ocean locks away.

The magnitude and timing of any such effect remain uncertain, but it raises questions about the future efficiency of this carbon storage pathway.⁠

In summary, AAIW functions as both a direct storage reservoir for absorbed atmospheric CO₂ at intermediate depths and a key transporter that redistributes carbon within the global ocean, helping moderate atmospheric CO₂ levels on multi- decadal to centennial timescales.

Its effectiveness depends on formation rates, surface conditions (temperature, salinity, ice melt), stratification, and circulation.

An expanse of icy water with numerous irregularly shaped ice floes floating on its surface, alongside a snowy edge.
Sea ice floes from a marine voyage. Credit: Alberto C Naveira Garabato

Reversal of Antarctic Intermediate Water trends triggered by sea ice decline

Abstract

Antarctic Intermediate Water (AAIW), a key component of the global overturning circulation and a major regulator of pycnocline structure, forms in the polar Southern Ocean, where sea-ice processes shape its properties. Sustained sea-ice expansion over several decades up to 2015 enhanced summertime meltwater input, stratifying the upper polar ocean and freshening AAIW. However, since 2016, repeated record sea-ice losses have reversed these trends. Using Argo-derived ocean observations supplemented by satellite and re-analysis datasets, we reveal that the abrupt post-2015 shift in sea-ice conditions is on course to alter hemispheric-wide water-mass properties. We estimate a net decline in sea-ice meltwater input of nearly 36 mSv per decade, relative to a pre-2016 increase of 14 mSv per decade. This unprecedented sea-ice loss has triggered densification and salinification of AAIW, whose core has salinified at 4.8×10−3±1.7×10−34.8×10−3±1.7×10−3 g kg−1−1 per decade. These changes signal that a hemispheric-scale reconfiguration of the pycnocline is underway.

Key points from the paper

  • Pre- 2016 trend: Decades of Antarctic sea- ice expansion increased summertime meltwater, which freshened and lightened AAIW while helping stratify the upper ocean.
  • Post- 2016 reversal: Record sea- ice losses sharply reduced meltwater input. This caused AAIW (and related Winter Water) to become saltier, denser, and deeper across the Southern Hemisphere.
  • Quantitative estimates:
    • Net decline in sea- ice meltwater input: ~36 mSv per decade (vs. a prior increase of ~14 mSv per decade).
    • AAIW core salinification rate: 4.8×10−3±1.7×10−3 per decade.
  • Methods: Primarily Argo float data (upper-ocean profiles), combined with satellite sea- ice observations, reanalysis products, and supporting datasets (e.g., EN4, IAP, CFC- 11 tracers).
  • Broader implication: The shift indicates an ongoing hemispheric- scale reconfiguration of the ocean’s pycnocline (the density gradient layer that regulates vertical mixing, heat, and carbon exchange).

Figures (titles)

  1. Climatological state of Winter Water (WW) and AAIW
  2. Evolution of Antarctic sea ice and northward transport of sea- ice meltwater
  3. Evolution of WW and AAIW core salinity anomalies
  4. Evolution of WW core density and depth
  5. Evolution of AAIW core density and depth
  6. Schematic of AAIW regime shift linked to changes in Antarctic sea-ice cover

Data and code

The full text is behind a paywall (institutional access, Nature+, or purchase required). The abstract and supporting materials above capture the core findings. This is the primary research paper underlying the University of Melbourne press coverage discussed earlier.

Journal: Nature Climate Change, (2026)

DOI: 10.1038/s41558-026-02758-y

Provided: University of Melbourne

Published: 28 October 2026

Authors: Kaushik Mishra,
Bishakhdatta Gayen&
Alberto C. Naveira Garabato

Comparison of Antarctic sea ice trends before and after 2016, illustrating changes in Antarctic Intermediate Water (AAIW) characteristics and their impact on ocean dynamics.
Antarctic Intermediate Water shifted from freshening before 2016 to becoming saltier, denser and deeper afterward. Credit: Kaushik Mishra

CBC’s “Climate Change” False Spook Story About Canadian Pumpkin Harvests Is All Trick and No Treat

A recent article from CBC News, titled “Climate change brings unpredictability, and it’s haunting the pumpkin harvest in N.L.,” claims that unusually wild swings between weather extremes in recent years in Newfoundland and Labrador is endangering pumpkin harvests, both being symptoms of climate change. This is false. Pumpkin production is doing just fine, weather variations from one year to the next are the norm and are not unusual, nor is there evidence in the local station data that there is a trend towards greater weather variability.

A scenic autumn landscape featuring a harvest of pumpkins in a foggy field, with hay bales, trees in a fall color palette, and a barn in the background.
AI generated by Meta

From ClimateRealism

By Linnea Lueken

A carved Halloween pumpkin with a glowing face, surrounded by smoky mist.

A recent article from CBC News, titled “Climate change brings unpredictability, and it’s haunting the pumpkin harvest in N.L.,” claims that unusually wild swings between weather extremes in recent years in Newfoundland and Labrador is endangering pumpkin harvests, both being symptoms of climate change. This is false. Pumpkin production is doing just fine, weather variations from one year to the next are the norm and are not unusual, nor is there evidence in the local station data that there is a trend towards greater weather variability.

The CBC piece is not a particularly scientific article, despite quoting one climatologist from Memorial University. It relies largely on farmers claiming that climate is clearly changing because the weather of one season can be “so different” from the previous. Farmers have dealt with changes in the quality of growing seasons from one year to the next forever, literally since the humans have been intentionally growing and harvesting crops.

They focus on the past two years, where “this past summer was particularly cold and wet, especially compared to 2025 when the province experienced record high temperatures and not a lot of rain.”

Because of the weather, pumpkin harvests for some farmers were either behind or the yields suppressed. In a change from the usual pumpkin doom and gloom articles we normally get this time of year, the CBC article admits that “both farmers said that the pumpkins that did grow were great quality.”

CBC News goes on to talk to climatologist Joel Finnis, who they paraphrase as saying “the drastic weather difference between summer 2025 and summer 2026 is evidence of a changing climate — because the warmer the climate gets the more variation in weather conditions.”

This is incorrect. It is surprising that a climatologist would make such a claim when data shows no emerging weather trend of worsening or inconsistent weather. It’s possible this is a misquote or oversimplified to the point of being somewhat ridiculous, but two years of very different weather are not evidence of a trend of any kind. They cannot be, especially with regards to climate change, which is a long-term phenomenon occurring over decades.

Regional weather naturally has at times very large variations from one year to the next, these variations can be the result of natural patterns like the El Niño Southern Oscillation (ENSO) and more directly for Eastern Canadian provinces, the Atlantic Meridional Overturning Circulation (AMOC) and the influence of the Gulf Stream.

When it comes to summertime temperature, the IPCC doesn’t even predict large changes in variability for the entire world in its AR6 report. Models attempting to predict changes in Newfoundland especially show low agreement, and what estimates that exist there show little to no change. That is using RCP8.5 – a since-abandoned scenario that overestimated warming to an impossible degree.

Using Environment and Climate Change Canada’s adjusted temperature record for St. John’s, which goes back to 1874 and up to 2020, comparing mean summer temperatures over the decades shows no trend whatsoever in temperature swings from one year to the next. I focused on a station nearest to where the most pumpkins are grown in Newfoundland, the St. John’s Adjusted and Homogenized Canadian Climate Data (AHCCD)  station, (downloaded here, then processed using Claude.ai). If there is any trend, it is declining. (See figure below)

Graph showing year-to-year summer mean temperatures in St. John's, NL from 1874-2020, indicating no significant increase. Includes a smoothed trend line.

When it comes to precipitation, again relying on RCP8.5 because it is the only scenario that reaches the very high warming levels that the IPCC wants to fearmonger over, the IPCC does claim that eventually there will be an increase in year-to-year variability. Under lower and more realistic emissions pathways, that change will take a whole lot longer.

Again we should anchor the model-based predictive estimate to real world data. The fact of the matter is that the station data representing St. John, which has been tracked 1874 to 2011, show absolutely no trend towards increased variability in summer rainfall. If there is a trend in that period, there is a downward trend in so-called “weather whiplash” from one summer to the next. (See figure below)

Line graph depicting summer total precipitation in St. John's, NL from 1874 to 2011, showing fluctuations without significant increase.

Note the swing between 1967, the hottest and driest summer in this record, and the following summer, 1968, which was the coldest. This is very similar to the 2025-2026 pattern which CBC and their climatologist claimed was evidence of climate change.

This is data from just one station, mind, but it should give anyone trying to claim that recent weather patterns are evidence of increasing volatility some pause.

Much of the northern hemisphere has seen a slight increase in average annual precipitation, but again this is a very mild trend. Still, the CBC article itself quotes a farmer as saying that good precipitation in summer is great for the pumpkin quality.

If all of this wasn’t enough, data from the Canadian agriculture statistics service show no trend in Newfoundland and Labrador pumpkin harvests declining amid climate change. The data only goes from 2007 to 2025, but it certainly shows no evidence that the pumpkin industry in the province is in any danger. Production saw its lowest year in 2010, its highest in 2013, and second highest tied repeatedly in each of the most recent three years on record.

Similarly, United Nations Food and Agriculture Organization data show Canadian pumpkin, squash and gourd production has been fairly stable over the past decade, after having risen gradually since the 1990s. (See figure below)

Line graph showing the production and yield of pumpkins, squash, and gourds in Canada from 1992 to 2022. Blue line represents production, while red line indicates yield.

Data provides no reason for Canadians to fear that pumpkins in Labrador and Newfoundland, nor Canada more generally, and definitely not globally, are endangered by climate change. CBC should have had done a little more homework and showed more discernment when making claims about long term climate change based on two years of pumpkin harvests.

Ice Age Humans in New Mexico Endured Sudden Climate Chaos 23,000 Years Ago

New research from White Sands National Park in New Mexico shows that early humans were present during the Last Glacial Maximum (roughly 23,500- 21,700 years ago) and lived through repeated, rapid climate shifts, including drought and major landscape changes.

Dansgaard- Oeschger (D-O) events are abrupt, large- scale climate oscillations that occurred repeatedly during the last glacial period (roughly the past 120,000- 11,000 years). They are named after Danish geophysicist Willi Dansgaard and Swiss geophysicist Hans Oeschger, who identified them in Greenland ice-core records.

D -O event 2 (also called Greenland Interstadial 2 or GI- 2) is one of the later events in the sequence. It began around 23.3- 23.2 thousand years ago (ka), during the Last Glacial Maximum (the coldest phase of the last ice age, ~26.5- 19/20 ka).

A group of prehistoric people walking along a muddy riverbank with mountains in the background under a dramatic sky.
AI generated by Grok

New research from White Sands National Park in New Mexico shows that early humans were present during the Last Glacial Maximum (roughly 23,500- 21,700 years ago) and lived through repeated, rapid climate shifts, including drought and major landscape changes.

The findings come from an October 2026 Science Advances paper (and a related popular article by co-authors Matthew Robert Bennett and Sally Christine Reynolds in The Conversation). Expanded excavations identified 20 distinct sediment layers (horizons) containing human footprints, spanning nearly 2,000 years at the height of the last ice age. This builds on earlier (2021 and later) dating of the famous White Sands footprints that placed people in North America thousands of years earlier than many traditional models allowed.

Environmental reconstruction

Sediments, pollen, and plant- leaf waxes (biomarkers) reveal a dynamic setting quite unlike today’s desert:

  • Early in the record, a large perennial lake (Lake Otero) filled much of the basin. Nearby mountains held conifer forests, and average temperatures were about 4°C colder than today.
  • From around 23,600 years ago the lake began shrinking as temperatures rose. Conifers declined and were replaced by oak and sagebrush steppe; the basin grew drier due to higher evaporation.
  • Around 23,200 years ago a short but severe drought struck: rainfall dropped, the lake became more saline, and drought- tolerant plants expanded. This local aridification matched a rapid Northern Hemisphere climate shift (Dansgaard- Oeschger event 2) recorded in Greenland ice cores.

People were present during these transitions, the earliest expanded footprint horizons appear around the drought/climate shift, and tracks continue at intervals as the lake retreated.

Interpreting the footprint record

The authors caution against over- interpreting the pattern.

An agent- based computer model of people moving around a fluctuating lake showed that preservation is highly selective: footprints survive mainly when mud is exposed (e.g., during drying) and then quickly buried by rising water or sediment.

As a result:

  • Footprint- rich surfaces tend to cluster around climatic and hydrological transitions (exactly the pattern seen at White Sands).
  • Gaps between layers do not prove people were absent, and dense tracks do not necessarily mean a population boom, a few people crossing soft mud repeatedly can leave many prints.
  • The record therefore interleaves a human history (repeated use of the landscape amid changing conditions) with a geological filter that preserved only certain moments.⁠

In short, the study strengthens evidence that humans occupied the southern United States during the peak of the ice age and demonstrates they experienced abrupt, noticeable environmental change (lake recession, vegetation turnover, centennial- scale wet, dry swings) over roughly two millennia. It does not claim people only appeared during droughts, but shows they were resilient in a rapidly shifting world.

Footprints imprinted on a sandy surface, showing distinct toe and heel outlines.
Footprints found at White Sands, New Mexico, were dated to the height of the last ice age. Credit: National Park Service

Dansgaard- Oeschger (D-O) events are abrupt, large- scale climate oscillations that occurred repeatedly during the last glacial period (roughly the past 120,000- 11,000 years). They are named after Danish geophysicist Willi Dansgaard and Swiss geophysicist Hans Oeschger, who identified them in Greenland ice-core records.

General characteristics

Each D- O event typically features:

  • A very rapid warming phase (over decades, sometimes just a few years to decades) in the North Atlantic region, especially Greenland. Temperatures there could rise by 5- 15 °C (9- 27 °F), roughly half the full glacial- to- interglacial difference.
  • This is followed by a more gradual cooling over centuries to millennia, often ending with a sharper drop back into cold (stadial) conditions.

These produce a characteristic “sawtooth” pattern in temperature proxies (especially oxygen isotope ratios, δ¹⁸O) from Greenland ice cores. About 25 such events are recognized over the last glacial cycle; roughly 13 well- dated ones fall between ~45,000 and 11,600 years ago, with an average spacing near 1,470 years (though exact regularity is debated).

They are most strongly expressed around the North Atlantic but have global or hemispheric effects, appearing in records from Europe, Asia, the Americas, and the Southern Hemisphere (often with some lag or opposite polarity via ocean and atmospheric teleconnections).

Causes

The precise triggers remain uncertain, but the leading explanation involves shifts in the Atlantic Meridional Overturning Circulation (AMOC), the large- scale ocean current system that transports heat northward.

Weakened AMOC (linked to expanded sea ice, freshwater input from melting ice, or other factors) produces cold stadials; a sudden reinvigoration produces the abrupt warmings. Sea- ice extent in the North Atlantic, atmospheric circulation changes, and possible external pacing (e.g., solar or orbital influences) are also implicated. Exact mechanisms are still actively researched.

Dansgaard- Oeschger event 2 specifically

D -O event 2 (also called Greenland Interstadial 2 or GI- 2) is one of the later events in the sequence. It began around 23.3- 23.2 thousand years ago (ka), during the Last Glacial Maximum (the coldest phase of the last ice age, ~26.5- 19/20 ka).

In Greenland ice cores (on the GICC05 timescale), it marks a relatively short interstadial warming. Recent high-resolution work, including from White Sands National Park in New Mexico, places its peak or expression at approximately 23.2 ± 0.3 ka.

At White Sands, this interval coincided with a short but severe regional drought: reduced rainfall, increased lake salinity in ancient Lake Otero, expansion of drought- tolerant vegetation, and shrinkage of the lake that exposed shoreline areas. This local aridification is interpreted as a teleconnected response to the broader Northern Hemisphere climate shift associated with D- O 2.

D- O 2 is notable because it occurred deep within the Last Glacial Maximum, when large ice sheets still dominated the Northern Hemisphere, yet it still produced detectable, rapid environmental changes far from Greenland, including in the American Southwest.

In short, D- O events illustrate that even during full glacial conditions the climate system could flip rapidly between cold and warmer states on human- relevant timescales, driven largely by ocean- atmosphere interactions centered on the North Atlantic. Event 2 is a specific instance of this behavior dated to ~23.2 ka.

A prehistoric scene depicting a group of early humans observing mammoths by a river at sunset, with grass and mountains in the background.
Reconstruction of life at White Sands at the height of the last ice age. Credit: Davide Bonadonna, Bournemouth University

Dansgaard- Oeschger (D- O) events, including event 2 (~23.2 ka), produced rapid, widespread climate impacts far beyond Greenland and the North Atlantic, though the strongest signals occurred in the Northern Hemisphere.

These effects arose mainly from changes in the Atlantic Meridional Overturning Circulation (AMOC), shifts in atmospheric circulation (including the Intertropical Convergence Zone, or ITCZ, and storm tracks), and interhemispheric heat redistribution via the bipolar seesaw.

Northern Hemisphere

  • Europe and western Mediterranean: Interstadial (warm) phases brought warmer and wetter conditions. Vegetation expanded (more temperate forests or woodland), and lake levels or precipitation proxies often rose. Stadials were colder and drier. Temperature swings were smaller than in Greenland but still significant (several degrees).
  • Eurasia (including central and eastern Europe, western Asia): Largest land- based warming during interstadials occurred here according to pollen- based reconstructions. Winters warmed more than summers, reducing seasonality. Moisture responses varied but often included wetter conditions in many areas.
  • East Asia and Asian monsoon regions: Northern Hemisphere summer monsoons typically strengthened during interstadials (more rainfall in China and surrounding areas, recorded in speleothem δ¹⁸O). Southern Hemisphere monsoons weakened in a seesaw pattern.
  • North America: Patterns were spatially complex. Eastern or more continental areas often warmed and sometimes became wetter during interstadials. Western North America (including the Southwest) frequently showed cooling or increased aridity in some reconstructions. For D- O event 2 specifically, multiproxy evidence from White Sands (New Mexico) and other southwestern U.S. sites records a short but severe aridification: reduced rainfall, higher lake salinity, recession of Lake Otero, and a shift toward drought- tolerant vegetation (conifer forest giving way to sagebrush/oak steppe). This matched the Greenland timing of D- O 2 and allowed humans and megafauna to traverse newly exposed lake margins.⁠

Tropics and low latitudes

The ITCZ shifted northward during Northern Hemisphere interstadials. This increased rainfall in northern tropical regions (e.g., Caribbean, northern South America, parts of Africa and Asia) and decreased it in southern tropical areas. Speleothem and lake records across the tropics consistently show these hydroclimate flips, often with little lag relative to Greenland.

Southern Hemisphere

  • Antarctica and Southern Ocean: Temperature changes were typically out of phase with Greenland (the bipolar seesaw). Antarctic warming (Antarctic Isotope Maximum events) often led or lagged Greenland warmings by centuries, driven mainly by slower oceanic heat transport changes. Atmospheric teleconnections were faster: mid- latitude storm tracks and westerly winds shifted within decades of North Atlantic changes, altering moisture sources for Antarctic precipitation (seen in deuterium- excess records).
  • Southern extratropics more broadly often cooled or showed muted/opposite responses relative to northern warming.

Spatial and temporal patterns

Impacts diminished with distance from the North Atlantic but remained detectable globally. Warming was strongest in northern extratropics (especially Eurasia), with antiphasing between northern and southern extratropics.

In North America a west- east contrast (cooling and aridity in the west, warming farther east) appears in some pollen syntheses. Moisture (precipitation) changes did not always mirror temperature changes and were regionally specific. Most teleconnections outside the high southern latitudes operated rapidly (decades or less) via the atmosphere; oceanic links to Antarctica were slower (centuries).

These patterns hold across multiple D- O events, including weaker ones like event 2 during the Last Glacial Maximum, although signal strength and coherence are greatest for the larger events. Proxy records (ice cores, speleothems, pollen, marine sediments, lake levels) and climate models consistently support this global reorganization of atmospheric and oceanic circulation.

Map showing early archaeological sites in North America with locations and estimated ages, including Coopers Ferry, Paisley Caves, Clovis, White Sands, Meadowcroft Rockshelter, Debra L Friedkin Site, and Page-Ladson Site.
Map of early archaeological sites in North America. Credit: The Conversation

Humans experienced abrupt environmental changes at White Sands during the Last Glacial Maximum

Key findings

Expanded excavations at White Sands National Park (WHSA) Locality 2 (Tularosa Basin, New Mexico) uncovered 20 stratigraphic horizons containing in situ human footprints, megafaunal trackways (mammoth/Proboscidea, ground sloth, canids, possible ursids, rare birds), and linear features interpreted as travois (drag marks from poles used to transport resources).

Refined chronology (using improved radiocarbon dating of conifer pollen and aquatic Ruppia seeds, plus supporting OSL ages):

  • Footprint- bearing sequence spans 23.5 to 21.7 thousand years ago (ka).
  • Firmly within the Last Glacial Maximum (LGM).

Paleoenvironmental reconstruction (pollen, leaf- wax biomarkers and hydrogen isotopes, stratigraphy):

  • The setting began as a shallow perennial lake (pluvial Lake Otero) with surrounding conifer forests and cooler temperatures.
  • It underwent a complete environmental overturn to a lake- margin and wet- playa system.
  • A major aridification episode at ~23.2 ka coincided with Dansgaard- Oeschger event 2 (a rapid Northern Hemisphere climate oscillation recorded in Greenland ice cores). Rainfall declined, the lake shrank and became more saline, and vegetation shifted toward drought- tolerant sagebrush and oak steppe.
  • Centennial- scale swings in hydroclimate continued afterward.
  • Lake recession during the aridification exposed shoreline areas that humans and megafauna repeatedly traversed for nearly two millennia.

This provides a high-resolution terrestrial record showing that early humans in North America experienced marked, abrupt environmental changes (including severe drought) during the height of the last ice age. The earliest track horizons occur around the D- O 2 transition.

The paper strengthens the LGM age of the White Sands footprints (previously debated) and demonstrates human presence and activity (including possible resource transport with travois) amid a dynamic glacial climate.

Journal: Science Advances, 14 October 2026, Vol. 12, Issue 42, eaeh0707

DOI: 10.1126/sciadv.aeh0707

PMC full text: PMC13666055

Provided: The Conversation

Authors: Kathleen B. Springer, Jeffrey S. Pigati, Jessica E. Tierney, et al. (including Sally C. Reynolds and Matthew R. Bennett)

Abstract

Expanded excavations at White Sands National Park have unearthed 20 stratigraphic horizons containing in situ human footprints, megafaunal trackways, and linear features created by travois. Advances in radiocarbon dating of conifer pollen, combined with ages of aquatic seeds, refines the chronology of the footprint-bearing sequence to between 23.5 and 21.7 thousand years ago (ka). Biomarker, pollen, and stratigraphic evidence indicate a complete overturning of the environment from a perennial lake to a playa and capture a large aridification episode coincident with Dansgaard-Oeschger event 2 at 23.2 ka, which shrank pluvial Lake Otero and allowed people to traverse the former shoreline area for nearly two millennia. This well-dated and highly resolved paleoclimate record provides compelling evidence that humans in North America experienced marked environmental changes during the Last Glacial Maximum.

An archaeological excavation site featuring exposed layers of soil with various labeled markers and tools in the background.
People repeatedly crossed this landscape for almost two millennia while the regional climate swung between wetter and exceptionally dry conditions. Credit: National Park Service

Seasonal CO₂ Swings Amplify in the Indian Ocean as Climate Warms

New research suggests that climate- driven changes are amplifying seasonal CO₂ exchange patterns in parts of the Indian Ocean, which could influence its role as a climate buffer, though this does not automatically mean greater overall carbon absorption.

The Indian Ocean plays a significant but regionally complex role in the global carbon cycle.

It acts as a modest net sink for atmospheric CO₂ overall, absorbing a portion of human- caused emissions and helping buffer climate change, though its behavior differs sharply between northern and southern regions and is strongly modulated by the monsoon system, ocean circulation, temperature, biology, and climate variability.

Infographic showing seasonal CO2 swings in the Indian Ocean, illustrating increased carbon uptake in summer and lower uptake in winter, alongside climate warming effects and monsoon wind patterns.
AI generated by Grok

New research suggests that climate- driven changes are amplifying seasonal CO₂ exchange patterns in parts of the Indian Ocean, which could influence its role as a climate buffer, though this does not automatically mean greater overall carbon absorption.

Published on Phys.org on October 18, 2026, and written by Hannah Bird, the article covers a study in Geophysical Research Letters (Joshi et al., 2026; DOI: 10.1029/2026GL123472) led by Dr. Apurva Padamanbh Joshi of the Indian National Center for Ocean Information Services. It analyzes data from 1980- 2019 on how seasonal air- sea CO₂ exchange has evolved across Indian Ocean regions.

Key findings

  • Seasonal variation in CO₂ exchange increased by 48% in the equatorial Indian Ocean and 23% in the southern Indian Ocean (greater contrast between seasonal highs and lows).
  • It decreased by 14% in the Arabian Sea and rose modestly (~7%) in the Bay of Bengal.
  • Average CO₂ release to the atmosphere decreased in the Arabian Sea, Bay of Bengal, and equatorial Indian Ocean, while absorption increased in the southern Indian Ocean. Larger seasonal swings do not necessarily equal higher net carbon uptake.

Drivers

  • In the equatorial and southern Indian Ocean, changes in the CO₂ partial- pressure difference between surface water and the atmosphere were key.
  • In the Arabian Sea and Bay of Bengal, shifts in wind speed (which affect gas transfer across the air-sea interface) played a larger role.
  • Similar seasonal amplification has been noted in parts of the Pacific and Atlantic, indicating broader ocean responses.

Context and implications

Oceans absorbed roughly 26% of human- caused CO₂ emissions from 2014- 2023 (per the Global Carbon Budget 2024), but capacity growth has slowed since around 2016 amid rising climate variability.

Temperature, winds, circulation, and existing dissolved CO₂ levels all influence the exchange: cooler water tends to absorb more, while warming can favor release, modulated by currents and other factors.⁠

The study focuses on historical changes rather than future projections. It highlights that seasonal processes are being reshaped regionally, which matters for accurate carbon- budget estimates (annual averages can miss timing shifts) and for marine ecosystems.

Greater CO₂ absorption increases ocean acidification, reducing carbonate ions needed by corals and shell-forming organisms; repeated seasonal extremes could stress recovery and affect biodiversity and productivity.

Overall, the findings provide a finer picture of the Indian Ocean’s evolving contribution to the global carbon cycle and its buffering of atmospheric CO₂. Further work is needed to determine long- term effects on storage capacity as warming continues.

Illustration of the carbon cycle, showing various carbon reservoirs such as the atmosphere, vegetation, soils, oceans, and fossil fuels, along with fluxes of carbon measured in gigatons per year.
Diagrammatic representation of the global carbon cycle. Credit: Wikimedia Commons/ PD-USGov-NASA.

The Indian Ocean plays a significant but regionally complex role in the global carbon cycle.

It acts as a modest net sink for atmospheric CO₂ overall, absorbing a portion of human- caused emissions and helping buffer climate change, though its behavior differs sharply between northern and southern regions and is strongly modulated by the monsoon system, ocean circulation, temperature, biology, and climate variability.

Overview of the Ocean Carbon Cycle (Relevant to the Indian Ocean)

Oceans exchange CO₂ continuously with the atmosphere. When the partial pressure of CO₂ in surface seawater (pCO₂) is lower than in the air, the ocean absorbs CO₂ (a sink); when higher, it releases CO₂ (a source).

Key controls include:

  • Solubility pump: Cooler water holds more CO₂. Warming reduces solubility and can promote outgassing.
  • Biological pump: Phytoplankton take up CO₂ via photosynthesis; some organic carbon sinks to deeper waters, sequestering it.
  • Physical factors: Winds enhance gas transfer across the air-sea interface; upwelling brings CO₂-rich deep water to the surface; currents and stratification redistribute carbon; freshwater inputs (e.g., rivers) affect alkalinity and pCO₂.
  • Anthropogenic influence: Rising atmospheric CO₂ drives net ocean uptake, but also causes ocean acidification (lower pH) as CO₂ forms carbonic acid.

Globally, oceans absorb roughly 25- 28% of anthropogenic CO₂ emissions. The Indian Ocean contributes a share of this, estimated at a net uptake of about −0.07 to −0.19 PgC/yr (petagrams of carbon per year; negative = sink) north of ~37.5°S for recent decades.

Regional Patterns in the Indian Ocean

The basin is not uniform:

  • Northern Indian Ocean (north of ~15–18°S): Generally a net source of CO₂ to the atmosphere.
    • Arabian Sea (northwestern): Strong perennial source, especially due to intense upwelling during the Southwest Monsoon that brings carbon-rich deep waters to the surface.
    • Bay of Bengal (northeastern): Often a moderate net sink, influenced by large freshwater inputs from rivers that lower salinity and can suppress pCO₂.
  • Southern Indian Ocean (south of ~15- 18°S, especially 15- 50°S): A significant sink. Cooler temperatures, subduction of surface waters, and biological activity favor CO₂ absorption. This region helps make the overall Indian Ocean a weak net sink.⁠

The equatorial Indian Ocean is closer to neutral (neither strong source nor sink) due to relatively deep thermocline and weaker upwelling compared to the equatorial Pacific.

Seasonal and Interannual Variability

The Indian Ocean’s carbon cycle is strongly seasonal because of the reversing monsoon winds and currents:

  • Large seasonal swings in pCO₂ and air- sea CO₂ flux are linked to monsoon- driven changes in temperature, winds, upwelling, and biological production.
  • Recent research (1980- 2019 data) shows these seasonal variations have amplified: +48% in the equatorial Indian Ocean and +23% in the southern Indian Ocean, with a decrease (−14%) in the Arabian Sea and a modest increase (~7%) in the Bay of Bengal. Drivers include changes in the air-sea pCO₂ difference (especially equatorial and southern regions) and wind speeds (Arabian Sea and Bay of Bengal). Average outgassing has decreased in northern and equatorial areas while southern uptake has increased.⁠

Interannual variability is strongly influenced by the Indian Ocean Dipole (IOD) and its interactions with El Niño- Southern Oscillation (ENSO). Positive IOD events can enhance outgassing in parts of the southeastern tropical Indian Ocean via upwelling and changes in dissolved inorganic carbon (DIC) and alkalinity. Circulation changes (e.g., Indonesian Throughflow, Southern Ocean inflows) can also cause large interior carbon accumulation anomalies.

Biological and Other Processes

  • Primary production (photosynthesis) is substantial, with satellite- based estimates around 8 Gt C/yr for the basin.
  • Respiration in deeper (aphotic) layers recycles carbon, influencing DIC distributions.
  • Dust and iron deposition from the atmosphere can stimulate biological uptake in some areas, though effects vary north- south.
  • The Indian Ocean is relatively undersampled compared to other basins, leading to greater uncertainty in flux estimates

Climate Change Impacts and Buffering Role

Warming, changing monsoons, and rising atmospheric CO₂ are altering the cycle. Amplifying seasonal CO₂ exchange does not automatically increase the net annual sink, but it reshapes when and how strongly exchange occurs.

This matters for accurate carbon budgets (annual averages can miss timing shifts) and for marine ecosystems: greater CO₂ uptake increases acidification, which reduces carbonate availability for corals, shellfish, and other calcifiers. Extreme seasonal conditions may hinder ecosystem recovery.⁠

Overall, the Indian Ocean continues to act as a climate buffer by taking up anthropogenic CO₂, with evidence of a strengthening sink in some analyses (~0.02 PgC/yr per decade in certain periods).

However, its capacity and reliability depend on ongoing physical and biological changes. Continued observations and modeling are essential, especially given data sparsity in parts of the basin.

_____________________________________________________________________________________

The Indian Ocean and Atlantic Ocean both act as net sinks for atmospheric CO₂ and contribute meaningfully to the global ocean carbon sink, but they differ substantially in magnitude, regional patterns, drivers, seasonal behavior, and efficiency of carbon storage.

Net CO₂ Flux (Air-Sea Exchange)

  • Indian Ocean: A relatively modest net sink, typically estimated at about −0.07 to −0.19 PgC/yr (north of ~37.5°S) for recent multi- decadal periods (e.g., 1985- 2018). Northern areas (especially the Arabian Sea) are sources, while the southern subtropical region is a stronger sink. One reconstruction puts the full Indian Ocean sink near −0.30 PgC/yr.⁠
  • Atlantic Ocean: A stronger net sink overall, with basin- wide estimates around −0.36 to −0.47 PgC/yr (1985- 2018, including the Mediterranean in some assessments). The North Atlantic (particularly subpolar regions) is an intense sink; the tropical Atlantic is a moderate source due to upwelling. The North Atlantic alone (a small fraction of global ocean area) can account for a disproportionately large share of global uptake.

In relative terms, the Atlantic often contributes a larger share of the global ocean sink relative to its size than the Indian Ocean. Both basins show evidence of a strengthening sink over recent decades in response to rising atmospheric CO₂, though interannual variability (e.g., linked to ENSO and IOD in the Indian Ocean or AMOC changes in the Atlantic) can modulate this.

Regional Contrasts

  • Indian Ocean: Strong north- south contrast driven by the monsoon. The northwestern Arabian Sea is a perennial source (strong summer upwelling brings CO₂- rich deep water to the surface). The Bay of Bengal is closer to neutral or a mild sink (influenced by large river freshwater inputs that lower salinity and pCO₂). The equatorial region is near neutral. The southern Indian Ocean (south of ~15- 18°S) is the main sink region.⁠
  • Atlantic Ocean: Stronger high- latitude sink in the North Atlantic due to cooling of poleward- flowing waters (increasing solubility) and biological drawdown, combined with deep convection and the Atlantic Meridional Overturning Circulation (AMOC). The tropical Atlantic is a source (upwelling), while the South Atlantic is a sink. Coastal and open-ocean differences exist, but the North Atlantic’s efficiency is notable.

Unlike the equatorial Pacific (a major source) or equatorial Atlantic (a source), the equatorial Indian Ocean is closer to neutral because of its unique wind patterns and deeper thermocline.

Drivers and Physical Processes

  • Indian Ocean: Dominated by seasonal monsoon wind reversal, upwelling (especially Arabian Sea), riverine freshwater inputs (Bay of Bengal), and connections via the Indonesian Throughflow and Southern Ocean inflows. Both solubility and biological pumps matter, with solubility more influential in the north and both important in the south. Climate modes like the Indian Ocean Dipole strongly affect interannual flux variability.
  • Atlantic Ocean: Strongly influenced by the AMOC, which ventilates deep waters and efficiently transfers anthropogenic carbon (Cₐₙₜ) into the interior. The North Atlantic is a key entry point for Cₐₙₜ into the deep ocean. Heat loss, biological export, and western boundary currents (e.g., Gulf Stream cooling) enhance uptake. A significant fraction of Atlantic Cₐₙₜ accumulation comes from lateral transport from the Southern Ocean.

The Atlantic stores a large share of global oceanic anthropogenic carbon relative to its area (historically ~23% despite covering ~15% of the ocean), thanks to deep ventilation. The Indian Ocean stores less efficiently in its northern (landlocked) portion but receives carbon via throughflow and Southern Ocean connections.

Seasonal Variability

Both oceans show pronounced seasonal cycles in CO₂ exchange, with cooler seasons favoring stronger sinks.

  • In the Indian Ocean, monsoon-driven changes produce large seasonal swings in pCO₂ and flux; recent studies show these seasonal amplitudes have increased substantially in equatorial and southern regions (e.g., +48% equatorial, +23% southern from 1980- 2019).
  • In the Atlantic, seasonal amplitude is also significant (especially subtropics and high latitudes), with winter cooling and biological activity enhancing uptake. Amplification of seasonal pCO₂ cycles due to anthropogenic carbon accumulation is a broader ocean phenomenon observed in both basins.

Climate Change and Buffering Role

Both basins help buffer atmospheric CO₂ rise and are experiencing acidification.

The Atlantic’s deep ventilation makes it particularly important for long- term sequestration of anthropogenic carbon.

The Indian Ocean’s role is more surface- and intermediate- depth oriented in many areas, with greater sensitivity to monsoon and IOD changes.

Warming reduces solubility in both, but circulation changes (e.g., potential AMOC weakening vs. monsoon shifts) will affect future uptake differently. The Indian Ocean remains more undersampled than the Atlantic in many datasets (e.g., SOCAT), adding uncertainty to its estimates.

In summary: The Atlantic is generally a more efficient and stronger net CO₂ sink per unit area (especially in the North Atlantic), with superior deep- ocean carbon storage via overturning circulation.

The Indian Ocean is a weaker overall sink with sharper regional contrasts (northern sources vs. southern sink) tightly coupled to monsoon dynamics.

Both are critical components of the global ocean carbon cycle, and ongoing changes in their seasonal and interannual behavior will influence how reliably they continue to act as climate buffers.

_____________________________________________________________________________________

The Pacific Ocean is the largest ocean basin and plays a dual role in the global carbon cycle: it is the world’s biggest oceanic source of CO₂ in its equatorial region, yet overall, it functions as a net sink of comparable magnitude to the Atlantic (and larger than the Indian Ocean in absolute terms), thanks to strong uptake in its subtropical and higher- latitude zones.

Net CO₂ Flux (Air- Sea Exchange)

  • Pacific: Basin- wide net uptake is typically estimated at roughly −0.4 to −0.5 PgC/yr (e.g., −0.41 ± 0.12 PgC/yr from observation- based pCO₂ products and −0.51 ± 0.16 PgC/yr from models for (−0.7 PgC/yr), offsetting substantial natural outgassing. The net sink has been strengthening at rates around −0.08 to −0.09 PgC/yr per decade.
  • Comparison: This places the Pacific’s net sink in a similar range to the Atlantic (−0.36 to −0.47 PgC/yr) and larger in absolute terms than the Indian Ocean (−0.07 to −0.30 PgC/yr depending on the exact domain). Despite covering nearly half the global ocean area, the Pacific’s net contribution is moderated by its powerful equatorial source. In some climatologies, the three basins contribute roughly similarly to global open- ocean uptake when coastal zones are included (Pacific and Atlantic each ~25%, Indian ~20%).

Regional Patterns

  • Equatorial Pacific: The dominant global oceanic CO₂ source. Strong upwelling of carbon-rich deep water (especially in the eastern “cold tongue”) releases ~0.4- 0.7 PgC/yr or more on average, often accounting for a large fraction of total oceanic outgassing. This far exceeds the tropical Atlantic source and the more localized northern Indian Ocean sources (e.g., Arabian Sea). The western equatorial Pacific is closer to neutral or occasionally a weak sink.⁠
  • Subtropical Pacific: Strong sinks, particularly in the North Pacific subtropical gyre, driven by cooling of waters and biological activity. These help offset equatorial outgassing.
  • Higher latitudes: Uptake occurs in subpolar regions, though less intense per unit area than the North Atlantic’s deep-convection zones. The North Pacific lacks the Atlantic’s vigorous deep-water formation, so anthropogenic carbon (Cₐₙₜ) penetration is shallower (mainly intermediate depths).

In contrast:

  • The Atlantic has intense high- latitude (especially North Atlantic) sinks and efficient deep ventilation via the AMOC.
  • The Indian Ocean shows a clear north– south divide (northern sources vs. southern sink) tightly tied to the monsoon, without a single dominant equatorial source like the Pacific’s.

Drivers and Variability

  • Pacific: Dominated by the El Niño- Southern Oscillation (ENSO). During El Niño, equatorial upwelling weakens and outgassing decreases sharply (sometimes nearly shutting off the source); during La Niña, outgassing intensifies. This makes the tropical Pacific the largest contributor to interannual variability in the global ocean carbon sink. Subtropical and higher -latitude uptake is influenced by gyre circulation, seasonal temperature changes, and biology.
  • Seasonal cycles: Present but often secondary to interannual ENSO- driven swings in the tropics. Seasonal amplification of pCO₂ cycles (linked to anthropogenic carbon accumulation) occurs, similar to other basins.
  • Comparison: The Indian Ocean’s variability is more monsoon- and IOD- driven with strong seasonal signals that have recently amplified. The Atlantic has notable seasonal cycles (especially high latitudes) and is influenced by AMOC strength and North Atlantic Oscillation variability but lacks the Pacific’s extreme interannual equatorial swings.

Anthropogenic Carbon Storage and Efficiency

The Pacific stores a large absolute amount of Cₐₙₜ due to its size, but less efficiently per unit area than the Atlantic. The North Atlantic’s deep convection allows deeper and more rapid sequestration. Pacific Cₐₙₜ is mostly confined to intermediate depths via mode and intermediate water subduction. The Southern Ocean (shared influence) is a major entry point for all basins, with subsequent redistribution.

Climate Change Context

All three basins are experiencing rising uptake of anthropogenic CO₂, ocean acidification, and changes in seasonal and interannual patterns. The Pacific’s equatorial source region is particularly sensitive to ENSO changes and warming (which can affect upwelling and solubility). Its large area means even modest per-area changes have global impact. Data coverage in the Pacific is generally better than in the Indian Ocean but still sparse in some southern regions.

Summary comparison:

  • Pacific: Largest source region (equatorial) and large subtropical sinks → moderate- to- strong net sink; high interannual variability (ENSO).
  • Atlantic: Strongest high latitude sinks and efficient deep storage (AMOC) → strong net sink relative to size.
  • Indian: Modest net sink with sharp monsoon- driven north– south contrast and growing seasonal amplitude.

Together, the three major ocean basins (plus the Southern Ocean) form the backbone of the oceanic carbon sink that absorbs roughly a quarter of human CO₂ emissions each year.

The Pacific’s unique combination of a massive natural source and extensive sink regions makes its behavior especially important for understanding global carbon- cycle variability.

Graph comparing δpCO2 (μatm) across four regions: AS, BoB, EIO, and SIO, showing trends from 1980-89 and 2010-19 with three data series: Thermal (red), Non-Thermal (blue), and δpCO2 (black).
Changes in surface CO₂ levels and the factors driving them across four Indian Ocean regions—the Arabian Sea (AS), Bay of Bengal (BoB), Equatorial Indian Ocean (EIO) and Southern Indian Ocean (SIO)—during the 1980s and 2010s. Black lines show CO₂ changes, while red and blue lines represent the effects of temperature and non-temperature related factors, respectively. Dashed lines represent the 1980s and solid lines the 2010s. Credit: Joshi et al, 2026.

Climate Change Induced Seasonal Amplification of the Indian Ocean CO2 Sink

Key findings from the paper (based on available summaries)

The study analyzed air- sea CO₂ exchange across the Indian Ocean from 1980 to 2019, focusing on changes in seasonal variability:

  • Seasonal amplitude increased by:
    • 48% in the equatorial Indian Ocean
    • 23% in the southern Indian Ocean
    • ~7% in the Bay of Bengal
    • It decreased by 14% in the Arabian Sea
  • Mean CO₂ release to the atmosphere decreased in the Arabian Sea, Bay of Bengal, and equatorial Indian Ocean.
  • CO₂ absorption increased in the southern Indian Ocean.
  • Drivers differed by region:
    • Equatorial and southern Indian Ocean → mainly changes in the air-sea difference in CO₂ partial pressure (ΔpCO₂).
    • Arabian Sea and Bay of Bengal → primarily changes in wind speed (affecting gas-transfer velocity).

Important caveat emphasized in the work: Larger seasonal swings do not automatically mean a stronger net annual carbon sink. The amplification reshapes the timing and intensity of exchange within the year rather than necessarily increasing total uptake.

The paper frames these changes as a response to climate change (warming, altered circulation and monsoon patterns, and rising atmospheric CO₂) and notes implications for marine ecosystems (via acidification) and for carbon- budget estimates that rely only on annual averages.

Context

This is one of the more detailed observational analyses of seasonal CO₂ flux changes specifically in the Indian Ocean. It complements broader findings that seasonal pCO₂ amplitudes are increasing across much of the global ocean due to anthropogenic carbon accumulation (which reduces the ocean’s buffer capacity and makes pCO₂ more sensitive to temperature and biology).

Journal: Geophysical Research Letters, (2026)

DOI: 10.1029/2026gl123472

First published: 30 September 2026

Authors: A. P. Joshi, Kunal Chakraborty, V. V. S. S. Sarma, Prasanna Kanti Ghoshal, B. Sridevi, Zouhair Lachkar

Abstract

This study investigates changes in the mean and seasonal states of oceanic carbon uptake across the Indian Ocean (IO) using an improved, high-resolution, observationally constrained long-term (1980–2019) surface ocean pCO2 data product. The Arabian Sea shows a ∼14% decline in CO2 flux amplitude along with reduced mean source strength. In contrast, the Equatorial IO exhibits the largest increase in seasonal amplitude (∼48%), followed by the Southern IO (∼23%), while the Bay of Bengal shows only a modest change (∼7%). Despite these differences, mean source strength decreases in both the Bay of Bengal and Equatorial IO, whereas the Southern IO shows an enhanced carbon sink. Amplitude changes in the Arabian Sea and Bay of Bengal are driven by shifts in flux sensitivity to wind speed and evolving seasonality of the ocean-atmosphere pCO2 gradient, whereas in the Equatorial and Southern regions, they are primarily controlled by the evolving pCO2 gradient alone.

Ocean Circulation Continues for Centuries Even After Key AMOC Engine Shuts Down

The Ocean Circulation That Persists Even After a Key AMOC Component Fails, by Nathaniel Scharping (Eos, American Geophysical Union, published 13 October 2026), is a research spotlight summarizing a study in AGU Advances.

Community Earth System Model 2 (CESM2) is a fully coupled, open- source global Earth system model developed collaboratively by the National Center for Atmospheric Research (NCAR) and the broader research community. It simulates Earth’s past, present, and future climate and Earth-system states and served as a major contributor to the Coupled Model Intercomparison Project Phase 6 (CMIP6).

Model output from preindustrial control, historical, and other experiments is publicly available (e.g., via ESGF). CESM2 has been applied in diverse studies, including AMOC behavior under CO₂ quadrupling, ice-sheet coupling, sub seasonal prediction, and chemistry- climate interactions.

Map illustrating the Atlantic Meridional Overturning Circulation (AMOC), showing warm surface currents in red/orange flowing northward and cold deep currents in blue returning southward at depth.
AI generated by Grok

The Ocean Circulation That Persists Even After a Key AMOC Component Fails, by Nathaniel Scharping (Eos, American Geophysical Union, published 13 October 2026), is a research spotlight summarizing a study in AGU Advances.

It covers work by Shantong Sun and Andrew F. Thompson showing that a cross-hemispheric overturning circulation can continue for centuries even after North Atlantic Deep Water (NADW) formation, the sinking branch of the Atlantic Meridional Overturning Circulation (AMOC), shuts down under extreme warming.

Key points from the study

  • Climate models disagree on the AMOC’s future under warming. The researchers used a hierarchy of models, including the Community Earth System Model 2 (CESM2) under a CO₂- quadrupling scenario and an idealized reduced- gravity ocean model.
  • In the CESM2 simulation, NADW formation fully ceases, yet the cross- hemispheric overturning transport slows only gradually and persists for centuries.
  • This residual circulation is not driven by a steady balance of sinking and rising water (diapycnal processes). Instead, it arises from a transient adjustment: progressive deepening of density layers (isopycnal surfaces) that rearranges the ocean’s stratification.
  • The same behavior appears in the idealized model, confirming the mechanism.
  • The circulation is therefore temporary; it may last several centuries until the ocean reaches a new density distribution, after which it could change further. Predicting the AMOC’s ultimate fate remains difficult.

Broader implications

The continued interbasin flow leads to a clockwise overturning circulation in the Indo- Pacific. This redistributes heat (shifting more into intermediate depths and potentially keeping the surface cooler), biogeochemical tracers, and ventilation. Expected effects include reduced nutrient- rich water in the upper ocean and substantially older ventilation ages in the deep Atlantic, with possible wide- ranging consequences for marine ecosystems and global climate.

The original research article is “Transient Global Overturning Following the Shutdown of North Atlantic Deep Water Formation” (Sun & Thompson, AGU Advances, 2026; DOI: 10.1029/2026AV002462).

_____________________________________________________________________________________

Community Earth System Model 2 (CESM2) is a fully coupled, open- source global Earth system model developed collaboratively by the National Center for Atmospheric Research (NCAR) and the broader research community. It simulates Earth’s past, present, and future climate and Earth-system states and served as a major contributor to the Coupled Model Intercomparison Project Phase 6 (CMIP6).

Overview and purpose

CESM2 is the successor to CESM1 and includes substantial scientific and infrastructure improvements. It is maintained primarily by the Climate and Global Dynamics (CGD) Laboratory at NSF NCAR, with primary support from the U.S. National Science Foundation. The model is widely used for climate research, including studies of ocean circulation (such as AMOC responses under extreme forcing), paleoclimate, and future projections.⁠

Official site: https://www.cesm.ucar.edu/models/cesm2

Main components

CESM2 couple’s interactive models for multiple Earth system components that exchange states and fluxes:

  • Atmosphere: Community Atmosphere Model (CAM6; low-top ~40 km with limited chemistry, or high-top Whole Atmosphere Community Climate Model/WACCM6 extending to ~130- 140 km with comprehensive chemistry).
  • Ocean: Parallel Ocean Program version 2 (POP2).
  • Land: Community Land Model (CLM).
  • Sea ice: Community Ice CodE (CICE).
  • Land ice: Community Ice Sheet Model (CISM).
  • River runoff: Model for Scale Adaptive River Transport (MOSART).
  • Waves: WaveWatch III (WW3).

Key improvements and performance relative to CESM1

CESM2 shows better agreement with observations in several areas, including reduced low- latitude precipitation and shortwave cloud forcing biases, improved representation of the Madden- Julian Oscillation, better El Niño- Southern Oscillation teleconnections, and a more realistic global land carbon accumulation trend.

Climate sensitivity (a measure of long- term global temperature response to doubled CO₂):

  • Equilibrium climate sensitivity (ECS): approximately 5.1- 5.3 °C (higher than CESM1, largely due to changes in cloud microphysics and boundary- layer parameters).
  • Transient climate response (TCR): about 1.9- 2.0 °C (comparable to CESM1).⁠

These higher ECS values have been noted in the literature; some studies examine whether they affect 21st- century projections or paleoclimate simulations.

Current releases (as of recent information)

  • Supported production release: CESM 2.1.5 (recommended for most science applications, especially CMIP6- related work).
  • Developmental release: CESM 2.2.2 (includes newer features but is not yet scientifically supported with long validated simulations).⁠

Model output from preindustrial control, historical, and other experiments is publicly available (e.g., via ESGF). CESM2 has been applied in diverse studies, including AMOC behavior under CO₂ quadrupling, ice-sheet coupling, sub seasonal prediction, and chemistry- climate interactions.

_____________________________________________________________________________________

Transient Global Overturning Following the Shutdown of North Atlantic Deep-Water Formation

Abstract summary

The Atlantic Meridional Overturning Circulation (AMOC) is projected to weaken under climate warming, raising concerns about a possible collapse. Recent work has suggested that wind- driven upwelling in the Southern Ocean may prevent a full AMOC collapse even under extreme forcing.

This study analyzes a climate model (CESM2) under CO₂ quadrupling and shows that North Atlantic Deep Water (NADW) formation can completely cease under extreme warming. Despite this shutdown, a cross-hemispheric overturning circulation persists for centuries.

This residual circulation is a transient adjustment of the global ocean caused by progressive deepening of isopycnal (density) surfaces, rather than sustained diapycnal (across- density) downwelling in the interior ocean. The same adjustment explains the emergence of a clockwise overturning circulation in the Indo-Pacific even without deep- water formation there.

These features are reproduced in an idealized 1.5- layer reduced- gravity model. The transient overturning has important climate implications: it redistributes heat into intermediate depths (helping mitigate surface warming) and reorganizes ocean tracers, altering global patterns of nutrients and ventilation that may feed back onto the climate system.

Key findings (from the paper and the Eos research spotlight)

  • In the CESM2 CO₂- quadrupling experiment, NADW formation shuts down, but cross- hemispheric overturning transport only slows gradually and continues for centuries.
  • A buoyancy- budget analysis shows that the apparent downwelling in the Atlantic and Indo- Pacific after NADW cessation is mainly adiabatic (linked to the deepening of density layers) rather than diabatic.
  • The continued circulation is therefore temporary: it reflects the ocean adjusting toward a new stratification state and may last several centuries before further change.
  • One consequence is the development of clockwise overturning in the Indo- Pacific, which redistributes heat, nutrients, and ventilation. Expected effects include more heat stored at intermediate depths (keeping the surface relatively cooler), reduced nutrient concentrations in the upper ocean, and substantially older ventilation ages in the deep Atlantic.

Data and models

  • CESM2 output from the Earth System Grid Federation (CMIP6 node).
  • Idealized reduced- gravity model code available on figshare.

The full PDF (and supporting files including the original manuscript and peer-review history) is freely available via CaltechAUTHORS: https://authors.library.caltech.edu/records/26z4c-48×90.

This paper is the scientific source highlighted in the Eos article “The Ocean Circulation That Persists Even After a Key AMOC Component Fails” by Nathaniel Scharping (13 October 2026).

Journal: AGU Advances, Volume 7, Issue 5, e2026AV002462

DOI: 10.1029/2026av002462

Provided: American Geophysical Union

Published: 22 August 2026 (online)

Open access under Creative Commons Attribution- NonCommercial- NoDerivs License.

Authors: Shantong Sun, (Laoshan Laboratory, Qingdao, China) and

  Andrew F. Thomps, (California Institute of Technology)

Peer Review :The peer review history for this article is available as a PDF in the Supporting Information.

The 8.2 ka Cold Snap: How a Catastrophic Lake Drainage Weakened the AMOC and Cooled the Planet

The 8.2- kiloyear (ka) event (also called the 8.2 ka BP event or 8k event) was an abrupt global cooling episode around 8,200 years before present (BP; present ≈ 1950 CE), lasting roughly 150- 400 years (most precisely ~160 years in Greenland ice cores, with a ~60-70- year coldest central phase).

The 8.6- kiloyear (ka) interval is not a distinct, sharply defined abrupt climate event equivalent to the well-known 8.2 ka event. Instead, it marks the approximate onset of a broader, multi- centennial (centennial-scale) cooling anomaly in the early Holocene that lasted roughly from ~8.6- 8.5 ka to ~8.0 ka BP, within which the sharper ~8.2 ka cold event is superimposed.

Infographic illustrating the 8.2 ka Cold Snap events, highlighting the catastrophic drainage of Glacial Lake Agassiz and Ojibway, the effects on the AMOC, and global cooling impacts.
AI generated by Grok

The 8.2- kiloyear (ka) event (also called the 8.2 ka BP event or 8k event) was an abrupt global cooling episode around 8,200 years before present (BP; present ≈ 1950 CE), lasting roughly 150- 400 years (most precisely ~160 years in Greenland ice cores, with a ~60-70- year coldest central phase).

It is the most prominent abrupt climate anomaly of the Holocene (the current interglacial epoch) and marks the start of the Northgrippian stage. It was milder than the preceding Younger Dryas but more severe than the later Little Ice Age.

Timing and Magnitude

  • Onset in central Greenland: ~8,175 BP, with rapid cooling of ~3.3 °C (decadal average) in under 20 years.
  • Full event duration in Greenland ice cores: ~160.5 years (central cold phase ~69 years); temperatures then recovered in steps.
  • Broader estimates: 100- 200 years near the North Atlantic, up to ~400 years for some tropical monsoon impacts.
  • Cooling estimates: 1- 5 °C regionally (strongest in the North Atlantic and Greenland; ~1- 1.5 °C over Europe); atmospheric methane dropped by ~80 ppb (~15% reduction), indicating hemispheric drying and cooling.

Evidence comes from Greenland ice cores (strongest signal), speleothems (caves across Eurasia, Mediterranean, South America, southern Africa), lake and ocean sediments, and other proxies, showing the event was globally synchronous or near synchronous.

Cause

The leading explanation is a massive freshwater pulse from the catastrophic drainage of proglacial Lakes Agassiz and Ojibway (formed by meltwater from the retreating Laurentide Ice Sheet in northeastern North America) into Hudson Bay and then the Labrador Sea/North Atlantic around ~8.47 ka BP.

This reduced the density of surface waters, weakening the Atlantic Meridional Overturning Circulation (AMOC) by an estimated 55- 62%. Reduced northward heat transport led to North Atlantic cooling, expanded sea ice, and atmospheric teleconnections that propagated the signal globally. Some researchers note it may have been superimposed on a longer cooler interval lasting up to several centuries.

Associated sea- level rise from the meltwater pulse is estimated at ~0.4- 2.2 m (or higher in some delta records).

Global Impacts

  • Cooling: Strongest around the North Atlantic; milder elsewhere in the Northern Hemisphere.
  • Hydrology: Widespread drying in Northern Hemisphere tropics and monsoon regions (e.g., weakened Asian/Indian monsoons, droughts in parts of Southeast Asia, Near East, and Africa); some wetter conditions or shifts in the Southern Hemisphere consistent with a southward displacement of the Intertropical Convergence Zone (bipolar seesaw pattern). Impacts on monsoons sometimes lagged the North Atlantic cooling by ~100 years and lasted longer.
  • Other: Reduced snow accumulation in Greenland; possible increased storminess in places like coastal California; atmospheric circulation changes.
  • Human societies: Linked to stresses on early Neolithic farming communities in the Near East (e.g., changes at sites like Çatalhöyük), possible accelerated migrations, and shifts in settlement and food strategies.

The event serves as a key analogue for testing climate models’ sensitivity to North Atlantic freshwater forcing under near- interglacial conditions, relevant to potential future AMOC weakening from Greenland ice- sheet melt.

It is also known regionally as the Misox oscillation (Switzerland) or Finse event (Norway).

World map illustrating the regional distribution of meltwater release, with color-coded levels indicating varying amounts of meltwater across different regions.
The sea level rise of the 8.2 ka event simulated by the iCESM1.3 | Climate Dynamics | Springer Nature Link

The 8.6- kiloyear (ka) interval is not a distinct, sharply defined abrupt climate event equivalent to the well-known 8.2 ka event. Instead, it marks the approximate onset of a broader, multi- centennial (centennial-scale) cooling anomaly in the early Holocene that lasted roughly from ~8.6- 8.5 ka to ~8.0 ka BP, within which the sharper ~8.2 ka cold event is superimposed.

Relationship to the 8.2 ka Event

Many paleoclimate records (ice cores, speleothems, marine sediments, and others) show climate anomalies spanning 400- 600 years that begin around 8.6- 8.5 ka. The rapid, high- amplitude cooling centered near 8.2 ka (lasting ~150-160 years in Greenland ice cores) appears as a sudden “spike” or intensification within this longer cooler interval.

Some studies explicitly refer to a cooling event spanning ~8.6- 8.2 ka, often linked to progressive freshwater inputs into the North Atlantic from the decaying Laurentide Ice Sheet.

Causes and Context

Freshwater forcing: Early meltwater pulses, including the collapse of the Hudson Bay Ice Saddle (around 8.6- 8.5 ka) and initial drainage phases of proglacial Lakes Agassiz and Ojibway, contributed to surface- water freshening. This preceded the larger catastrophic lake drainage timed closer to the peak 8.2 ka cooling. These inputs likely weakened the Atlantic Meridional Overturning Circulation (AMOC) over an extended period.

Other factors: Possible contributions from solar variability minima and volcanic activity (including a large sulphate peak near ~8.6 ka, potentially linked to Icelandic eruptions such as the Þjórsá lava flow). Freshwater routing and ice- margin dynamics were complex and evolving.

The broader anomaly is viewed by some as part of a repeating pattern of Holocene climate variability, rather than solely a response to a single flood.

Impacts and Evidence

Proxy records indicate cooler and often drier conditions across parts of the Northern Hemisphere during this interval, with regional hydroclimate shifts (e.g., monsoon weakening in some tropical areas). The signal is clearer and more coherent in North Atlantic and European records but appears more variable or muted farther afield. Sea- level data also show periods of rapid rise around this time related to ice- sheet melt.

In summary, references to “8.6 ka” typically point to the start of this longer cooling phase that frames the classic 8.2 ka event. The sharp 8.2 ka anomaly remains the most prominent and best- defined feature of the early Holocene in high- resolution records such as Greenland ice cores.

Diagram illustrating the Atlantic Meridional Overturning Circulation (AMOC), showing ocean currents like the Gulf Stream and their impact on temperature regulation in the Northern Hemisphere.
Ocean currents: AMOC, the Atlantic Ocean’s conveyor belt.

The Atlantic Meridional Overturning Circulation (AMOC) is widely regarded as the primary oceanographic mechanism linking freshwater forcing from the Laurentide Ice Sheet region to the climate anomalies of the ~8.6- 8.0 ka interval and the sharper 8.2 ka event.

Background on AMOC

The AMOC is a major system of ocean currents that transports warm, salty surface water northward in the Atlantic and returns colder, denser deep water southward. It plays a key role in northward heat transport (contributing significantly to the relatively mild climate of northwest Europe and the North Atlantic region). Weakening reduces this heat transport, leading to cooling in the North Atlantic and associated atmospheric teleconnections.

Connection to the 8.6 ka / 8.2 ka Events

Broader ~8.6- 8.0 ka cooling: Proxy records and reconstructions indicate a multi-centennial period of generally cooler conditions starting around 8.6- 8.5 ka. This is linked to progressive meltwater inputs, including early drainage phases, the collapse of the Hudson Bay Ice Saddle (~8.6- 8.5 ka), and sustained freshwater fluxes from the retreating Laurentide Ice Sheet. These inputs freshened surface waters in the Labrador Sea and North Atlantic, reducing density and inhibiting deep-water formation, thereby weakening the AMOC over an extended interval.

Sharp 8.2 ka event: The most prominent Holocene cooling anomaly (onset ~8.25- 8.17 ka in Greenland ice cores, lasting ~150- 160 years overall with a colder central phase of ~60- 70 years) is strongly associated with the final catastrophic drainage of proglacial Lakes Agassiz and Ojibway into Hudson Bay and then the Labrador Sea and North Atlantic (dated around 8.47 ± 0.3 ka, with final stages closer to the cooling onset). This large freshwater pulse is thought to have caused a more abrupt AMOC slowdown.

Estimates of AMOC weakening during the 8.2 ka event vary:

  • Model simulations commonly show reductions of ~10- 50% (or more in some hosing experiments), with Wikipedia and related sources citing figures of 55- 62% in certain reconstructions or models.
  • Proxy-based estimates (e.g., from sediment cores tracking deep- water flow speed, chemistry, or 231^{231}Pa/230^{230}Th ratios) often indicate more modest changes, such as ~10- 15% or up to a few Sverdrups (Sv; 1 Sv = 106^6^6 m3^3) relative to pre- industrial strength, sometimes as part of a broader weakening between ~9.2- 8 ka.
  • The response typically involved reduced North Atlantic Deep Water (NADW) formation, possible shoaling of the overturning cell, and recovery over decades to a couple of centuries after the main freshwater pulse ended.

Climate Consequences of the AMOC Weakening

Reduced northward heat transport produced strong cooling around the North Atlantic (e.g., ~3.3 °C in central Greenland within decades; ~1- 1.5 °C or more in parts of Europe). Atmospheric teleconnections then propagated the signal globally: southward shift of the Intertropical Convergence Zone (ITCZ), weakened Northern Hemisphere monsoons (Asia, India, Africa), drier conditions in many tropical regions, and some opposing (wetter) signals in parts of the Southern Hemisphere. Methane concentrations also dropped, consistent with widespread cooling and drying.

The 8.2 ka event (and the surrounding 8.6- 8.0 ka interval) is considered a key natural analogue for testing AMOC sensitivity to freshwater forcing under near- interglacial boundary conditions, with relevance to potential future weakening from Greenland ice- sheet melt under anthropogenic warming.

In short, the AMOC acted as the critical intermediary: meltwater freshening → reduced overturning and heat transport → North Atlantic cooling → global climate anomalies. The broader 8.6 ka- onset cooling reflects more gradual or multi- pulse forcing, while the 8.2 ka peak reflects the most intense disruption.

AMOC Collapse Would Be Catastrophic: And Ice- Age Records Show It’s Happened Before

Yeah, a full collapse of the Atlantic Meridional Overturning Circulation (AMOC) would produce severe, far- reaching climate disruptions that scientists widely describe as catastrophic for large regions, especially northwestern Europe, the U.S. East Coast, and monsoon-dependent areas in Africa, Asia, and South America.

The AMOC has switched states in the past, that is well- supported by paleoclimate records.

During the last glacial period (roughly 115,000- 11,700 years ago), the climate system exhibited repeated abrupt shifts closely linked to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC). The two most prominent examples are Dansgaard-Oeschger (D-O) events and Heinrich events.

Illustration depicting the potential catastrophic collapse of the AMOC, with visual elements like ice, oceans, and geographic outlines showing past ice-age records.
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Yeah, a full collapse of the Atlantic Meridional Overturning Circulation (AMOC) would produce severe, far- reaching climate disruptions that scientists widely describe as catastrophic for large regions, especially northwestern Europe, the U.S. East Coast, and monsoon-dependent areas in Africa, Asia, and South America.

The AMOC is a major system of ocean currents (part of the broader thermohaline “conveyor belt”) that transports enormous amounts of heat northward in the Atlantic, on the order of 1 petawatt, far exceeding total human energy use. It helps keep northwestern Europe milder than other regions at similar latitudes. A collapse (or very strong weakening into a near-shutdown state) would sharply reduce this heat transport.

Main projected impacts

Cooling and weather extremes in Europe: Models show rapid cooling of several degrees to 5- 15°C (or locally more) in northwestern Europe over decades, with particularly harsh winters. Sea ice could expand southward (in some simulations toward the UK or Netherlands coasts). Summers might remain relatively warm due to ongoing greenhouse forcing, but year-round drier conditions, intensified droughts (especially in southern Europe), stronger winter storms, and wild temperature swings would severely damage agriculture, for example, one estimate reduces UK arable land from ~32% to ~7%.

Sea- level rise along the U.S. East Coast: Dynamic effects from the circulation change would add tens of centimeters to over half a meter (or more in places) of regional sea- level rise on top of global thermal expansion and ice melt, increasing coastal flooding risk.

Tropical and monsoon disruptions: A southward shift of the Intertropical Convergence Zone (ITCZ) would reduce rainfall in West Africa (potentially ~30%) and parts of India (~20%), disrupt Amazon seasonality (dry and wet seasons flipping in some models), and alter precipitation across other tropical regions. This threatens food systems for hundreds of millions of people.

Broader effects: Changes in storm tracks, marine ecosystems and fisheries (via altered nutrient upwelling and temperatures), Arctic sea- ice expansion, possible modest additional atmospheric CO₂ release from ocean carbon changes (with small net global warming after regional cooling offsets), and potential cascading stresses on other systems. Northern Hemisphere cooling would contrast with some Southern Hemisphere warming (a bipolar seesaw pattern seen in paleoclimate records).

These changes would unfold over decades to about a century once a tipping threshold is crossed, abrupt on human and societal timescales, though not instantaneous. Paleoclimate evidence (e.g., Dansgaard-Oeschger and Heinrich events) shows the AMOC has switched states in the past with major global repercussions, including large shifts in tropical rainfall.

Likelihood and uncertainty

A full collapse is not certain this century.

The IPCC AR6 assessed medium confidence that an abrupt collapse would not occur before 2100, while projecting overall weakening.

More recent studies are mixed: some identify early- warning signals (increasing variance/autocorrelation, freshwater- transport indicators, or “cold blob” patterns) suggesting the system is losing stability and could approach a tipping point this century under continued high emissions; constrained model ensembles project stronger weakening (~40- 50% by 2100 in some analyses) than the multi- model mean; other work finds resilience due to Southern Ocean upwelling, with collapse unlikely this century or reversible if forcing is reduced.

The risk is commonly framed as low- to-medium probability but very high impact. Weakening is already observed or inferred in various datasets, and continued high greenhouse- gas emissions plus Greenland meltwater increase the chance of further decline or eventual tipping. Reducing emissions lowers the risk.

In short, the statement is consistent with the scientific literature: a collapse would not freeze the planet as in fiction, but it would impose abrupt, multi- decadal regional climate shifts severe enough to strain agriculture, infrastructure, ecosystems, and societies across the North Atlantic sector and beyond. Monitoring improved early- warning systems, and mitigation remain the practical responses.

Map depicting ocean currents in the North Atlantic region, including the East Greenland Current, Polar Front, and North Atlantic Current, with Iceland and surrounding areas marked.
Arctic freshwater forcing of the Younger Dryas cold reversal | Nature

The AMOC has switched states in the past, that is well- supported by paleoclimate records.

During the last glacial period (roughly 115,000- 11,700 years ago), the climate system exhibited repeated abrupt shifts closely linked to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC). The two most prominent examples are Dansgaard- Oeschger (D- O) events and Heinrich events.

Dansgaard- Oeschger events

These were rapid warmings recorded in Greenland ice cores, with temperature increases of about 5-16°C occurring over decades (sometimes as little as a decade), followed by more gradual cooling over centuries. They occurred repeatedly during marine isotope stages 2- 4 under intermediate glacial conditions.

Proxy evidence (including Pa/Th ratios and benthic δ¹³C in ocean sediments, plus ice- core isotopes) indicates that the warm phases (interstadials) corresponded to a relatively strong AMOC, with active deep-water formation in the Nordic Seas, while the cold phases (stadials) featured a weaker AMOC.

The shifts involved reorganization of atmospheric circulation, including northward movements of the Intertropical Convergence Zone (ITCZ) and associated rainfall belts during the warmings. Global effects appear in speleothem records (e.g., Asian and South American monsoons), European fluvial systems, and other archives, though the amplitude of change generally decreases with distance from the North Atlantic.

Heinrich events

These involved massive discharges of icebergs (primarily from the Laurentide Ice Sheet) into the North Atlantic, marked by distinct layers of ice- rafted debris (IRD) in sediment cores. They typically occurred during some of the longer, colder stadials that preceded certain D- O warmings.

The large freshwater input from melting icebergs is widely interpreted as having caused strong weakening or near- collapse of the AMOC by reducing surface density and suppressing deep convection. Consequences included:

  • Pronounced cooling across the North Atlantic and adjacent continents.
  • A bipolar “seesaw” pattern, with gradual warming in the Southern Hemisphere (visible in Antarctic ice cores).
  • Southward displacement of the ITCZ and rainfall belts, producing severe droughts or major hydroclimate anomalies across large parts of the northern tropics and subtropics (including Afro- Asian monsoon regions), while some southern tropical areas became wetter.

These tropical rainfall shifts are documented in a wide range of continental and marine proxies and occurred close in time (within dating uncertainties of hundreds of years) to the North Atlantic IRD layers. Similar AMOC reductions and associated climate impacts are also inferred for events such as Heinrich Stadial 1 and the Younger Dryas during the last deglaciation.

Overall significance

Together, these records demonstrate that the AMOC has existed in multiple states and can transition relatively rapidly between them, producing large regional- to- global climate repercussions, especially in heat transport, sea ice, and the position of tropical rain belts.

The glacial boundary conditions (large ice sheets, lower CO₂, different freshwater budgets) differ from today, so the exact thresholds and rates are not identical to modern projections. Nonetheless, the paleoclimate evidence establishes that AMOC state changes are a real mechanism capable of driving abrupt, widespread climate shifts, including major alterations in tropical rainfall patterns that affected monsoon systems on which large human populations now depend.

This past behavior is one reason climate scientists treat potential future AMOC weakening or collapse as a high- impact risk, even while the precise likelihood and timing under current anthropogenic forcing remain subjects of active research.

Polar Bears Once Roamed Northern Europe – Fossils Confirm Southern Expansion During the Ice Age

Polar bears (Ursus maritimus) were present in parts of Europe during the late Pleistocene (Ice Age) and earliest Holocene, primarily along northern coastal areas where sea ice extended farther south, but there is no confirmed fossil evidence from Germany or most of central/southern continental Europe.

Researchers have found suggestive evidence from Ice Age fossils in Scotland’s Inchnadamph (Assynt) Bone Caves that some bears may have been polar bears (or a closely related form with a similar ecology), based mainly on diet rather than definitive DNA confirmation of species.

A snowy landscape featuring polar bears and a large animal skull, with icebergs and a cloudy sky in the background. The text overlay discusses polar bears' historical presence in Northern Europe during the Ice Age.
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Polar bears (Ursus maritimus) were present in parts of Europe during the late Pleistocene (Ice Age) and earliest Holocene, primarily along northern coastal areas where sea ice extended farther south, but there is no confirmed fossil evidence from Germany or most of central/southern continental Europe.

Fossil records show polar bears reached the southwestern margin of the Scandinavian Ice Sheet during the last deglaciation:

Scandinavia (Denmark, Sweden, Norway) and Iceland: Remains date mainly from about 15,000 to 11,000 years ago (Late Glacial to earliest Holocene). They include finds from the western coasts. A nearly complete skeleton from Finnøy, Norway (~12,000- 12,400 years old), is among the best- preserved Ice Age examples. A mandible from northern Denmark has been dated to ~11,100 years BP. These indicate a temporary southern Scandinavian population that became regionally extinct by ~11,500 years ago as the climate warmed and sea ice retreated.

Oldest known European (and global) fossil: A jawbone from Svalbard (Norway) dated to ~130,000-115,000 years ago (Eemian interglacial), confirming the species already had polar-bear adaptations by that time.

These southern extralimital finds (farther south than the modern range) align with periods of expanded North Atlantic sea ice, such as the Younger Dryas cold interval.

Possible or Suggestive Evidence Elsewhere in Europe

British Isles (including Scotland): Suggestive but not definitive. Isotope analysis of bear bones from Scotland’s Inchnadamph Bone Caves (~30,000- 50,000 years old) shows a near- exclusive marine/seafood diet, matching modern polar bears rather than typical brown bears. A skull from the same area has some polar- bear- like traits (though earlier dating has been questioned). DNA analysis is ongoing to confirm species identity (polar bear, specialized brown bear, or hybrid). A fragmentary ulna from Kew Bridge, London (~70,000 years ago, early Weichselian), was proposed as a large polar bear (Ursus maritimus tyrannus) but is disputed and may represent a large brown bear.

Genetic evidence indicates past hybridization between polar and brown bears in northwestern Europe (including areas near Ireland), implying overlapping ranges at times during the Late Pleistocene.

Germany and Other Continental European Countries

There is no confirmed polar bear fossil evidence from Germany or most of central/southern Europe. German Paleolithic sites (e.g., Schöningen, Bilzingsleben, Salzgitter- Lebenstedt) yield remains of brown bears, cave bears (Ursus spelaeus), and other Ice Age mammals (mammoth, reindeer), but Arctic specialists like polar bears are noted as absent in some faunal lists. Polar bears are strongly tied to sea ice and marine mammal prey, so their presence was limited to coastal zones with suitable ice conditions rather than inland or more southerly continental areas.

Polar bear fossils are rare overall because many individuals die on sea ice (where remains are less likely to be preserved on land). Their range expanded and contracted with Arctic temperatures and sea-ice extent. They survived warmer Holocene periods in high- Arctic refugia (e.g., near the East Siberian Sea, northern Greenland, Canadian Archipelago) and re- expanded during cooler phases.

In summary, polar bears did inhabit parts of northern Europe (especially Scandinavian coasts and possibly the British Isles) during colder phases of the last Ice Age, but they did not range into Germany or deeper continental Europe based on current evidence. Further discoveries or DNA work could refine this picture.

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Researchers have found suggestive evidence from Ice Age fossils in Scotland’s Inchnadamph (Assynt) Bone Caves that some bears may have been polar bears (or a closely related form with a similar ecology), based mainly on diet rather than definitive DNA confirmation of species.

The Daily Galaxy article (March 2025) reports on re- examination of bones (including material linked to earlier finds) by scientists from National Museums Scotland and the universities of Aberdeen and Edinburgh.

It highlights radiocarbon dating and analysis pointing to a marine/seafood- heavy diet in some specimens, consistent with modern polar bears, in an environment that included glacial conditions in northern Scotland. The caves have long yielded Ice Age remains of brown bears, lynx, reindeer, and other species; a 1927 bear skull had previously been noted for some polar- bear- like traits.

More precise reporting from late 2024 (BBC, The Times, and others) describes the key evidence as stable isotope analysis of three samples dated roughly 30,000- 50,000 years ago. These showed diets composed almost entirely of marine fish or other seafood, very different from the typical terrestrial (meat/plant, occasionally salmon) diet of brown bears, including other prehistoric Scottish bears. This was published in the journal Annales Zoologici Fennici.

Professor Kate Britton (University of Aberdeen) noted the samples “stick out like a sore thumb” relative to expected brown- bear diets.

The findings reopen the possibility of polar bears in Scotland during colder periods of the last Ice Age, when sea ice extended farther south in the North Atlantic, potentially allowing excellent swimmers like polar bears to reach the region.

Researchers emphasize it is not conclusive species identification: it could represent polar bears, a marine- specialized brown- bear subspecies/population, or overlapping ranges (polar and brown bears can interbreed). An older skull previously suggested as a possible polar bear had dating and isotope issues that weakened the case.

In short, the dietary evidence is genuine and interesting, it strengthens the case that polar-bear-like ecology occurred in Ice Age Scotland, but it does not yet constitute definitive proof of Ursus maritimus fossils there. Further DNA work has been discussed as a next step in related coverage. Polar- bear fossils are overall rare because many die on sea ice.

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The Last Ice Age in Europe refers to the most recent major glacial period of the Quaternary, commonly called the Last Glacial Period (LGP) or, regionally, the Weichselian glaciation (northern Europe), Devensian (British Isles), and Würm (Alps).

Timeline

  • Began: Roughly 115,000- 110,000 years ago (end of the previous interglacial, the Eemian).
  • Peak (Last Glacial Maximum, LGM): Approximately 26,500- 19,000 years ago.
  • Ended: Around 11,700 years ago, marking the start of the current Holocene epoch (with a brief cold snap called the Younger Dryas just before the final warming).

Ice Cover and Landscape in Europe during the LGM:

A massive Scandinavian Ice Sheet covered Scandinavia, Finland, the Baltic region, much of northern Germany, Poland, and parts of the British Isles (including Scotland and northern England/Ireland).

Alpine glaciers expanded significantly across the Alps, Pyrenees, and other mountain ranges.

Sea levels dropped by about 120- 130 meters, exposing land bridges (e.g., Doggerland connecting Britain to continental Europe) and extending coastlines.

Much of northern and central Europe was tundra, steppe- tundra, or permafrost- covered; southern Europe had more open grasslands and refugia for forests in milder areas (Iberia, Italy, Balkans).

Ecological and Human Context

Cold- adapted animals thrived, including woolly mammoth, woolly rhinoceros, reindeer, Arctic fox, and (in coastal/northern areas) species with polar- bear- like ecology. Brown bears were widespread; polar bears may have ranged farther south along sea- ice margins in the North Atlantic, as suggested by some Scottish fossil evidence from this period.

Early modern humans (Cro-Magnon) and Neanderthals (earlier in the period) adapted with specialized hunting technologies, clothing, and shelters. Human populations were concentrated in southern and ice-free refugia during the coldest phases.

Rapid warming after ~19,000- 15,000 years ago caused ice retreat, rising sea levels, and the return of forests. The transition included abrupt climate oscillations (e.g., Bølling- Allerød warming followed by Younger Dryas cooling).

This is the glacial stage most relevant to recent paleontological finds (such as the Scottish Bone Caves remains dated ~30,000- 50,000 years ago).

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Ice Age climate impacts refer primarily to the environmental, ecological, and human consequences of the Last Glacial Period (roughly 115,000- 11,700 years ago), with the most extreme phase being the Last Glacial Maximum (LGM) around 26,000- 19,000 years ago.

Global Climate Changes

Cooling: Global average temperatures dropped by about 4- 6°C relative to the pre- industrial Holocene (some estimates range higher locally). High latitudes cooled far more (polar amplification), with winter cooling often stronger than summer.

Ice sheets and sea level: Massive ice sheets covered northern North America (Laurentide), northern Europe (Scandinavian), and parts of Asia. Sea levels fell by ~120- 130 meters, exposing continental shelves, creating land bridges (e.g., Beringia, Doggerland), and extending coastlines.

Drier and dustier conditions: Many regions became more arid. Atmospheric dust levels rose dramatically (up to 20- 25 times modern values) due to reduced vegetation, stronger winds, and less precipitation to clear the air.

Ocean and circulation shifts: Weakened Atlantic Meridional Overturning Circulation (AMOC) during cold phases reduced heat transport to the North Atlantic, amplifying regional cooling. Storm tracks shifted southward.

These changes were driven by lower greenhouse gases (CO₂ ~180–200 ppm), orbital forcing (Milankovitch cycles), and ice- albedo feedback.

Impacts in Europe

Europe experienced particularly strong effects due to proximity to the Scandinavian Ice Sheet:

  • Temperature and precipitation: Cooling of 10- 14°C in many areas compared to today, with greater winter severity. Western/coastal regions were moderated by the ocean; areas southeast of the Alps saw stronger cooling and drying. Southwestern Europe (Iberia) was relatively wetter in some reconstructions, while Central and Eastern Europe were drier.
  • Vegetation and landscapes: Forests retreated to southern refugia (Iberian, Italian, and Balkan peninsulas). Much of central and northern Europe became open steppe- tundra or permafrost-covered loess landscapes. Solifluction, wind- blown loess deposits, and expanded deserts/arid zones occurred.
  • Abrupt climate swings: Dansgaard-Oeschger (D-O) events brought rapid warmings and coolings on millennial timescales. Heinrich stadials (massive iceberg discharges) caused sharp Atlantic cooling and vegetation crashes, especially near the western margin. The Younger Dryas (~12,900- 11,700 years ago) was a final intense cold snap before the Holocene.

Regional heterogeneity (e.g., Alps as a barrier) influenced local conditions strongly.

Ecological Impacts

  • Ecosystems and biomes: Shift from forests to open grasslands/steppe- tundra favored cold- adapted grazers. Mammoth- steppe habitats expanded across Eurasia. Reduced forest cover and lower CO₂ stressed woody plants.
  • Megafauna: Climate- driven habitat changes (expansion then contraction of open landscapes) caused range shifts and population stresses. Rapid interstadial warmings are linked to genetic turnover and local extinctions in some studies. This interacted with human pressures in the late Quaternary extinctions (e.g., woolly mammoth, woolly rhino). Polar bears expanded southward along sea- ice margins into Scandinavia and possibly the British Isles during colder phases with extended ice.
  • Other fauna and flora: Arctic species (reindeer, Arctic fox) moved south; temperate species contracted. Biodiversity patterns were reshaped by repeated habitat fragmentation and recolonization.

Human Impacts

  • Population declines and genetic bottlenecks occurred during the coldest phases (especially LGM and Late Pleniglacial), with western European groups facing severe reductions or local extinction/replacement.
  • Hunter- gatherers were pushed into southern and ice- free refugia. Cultural developments (e.g., Châtelperronian, Uluzzian) show regional divergences possibly linked to climatic heterogeneity.
  • Resource base changed with shifting prey (large herds on steppes) and vegetation.

Landscapes were reshaped by glaciation (moraines, fjords, outwash plains), lower sea levels created migration corridors, and the eventual rapid deglaciation (~19,000–11,700 years ago) caused sea- level rise, forest recolonization, and further ecological turnover. The transition into the Holocene featured the Younger Dryas cooling followed by abrupt warming.

These Ice Age dynamics demonstrate high climate sensitivity and the cascading effects of cooling, ice growth, and circulation changes on every level of the Earth system, from oceans and atmosphere to ecosystems and human societies. Modern paleoclimate research uses pollen, ice cores, marine sediments, and models to refine these reconstructions, highlighting both gradual orbital drivers and abrupt millennial-scale events.