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).

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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.

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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.