A recent study (published November 10, 2026, in Nature Communications) found that dissolved organic matter (DOM) in Antarctic waters remains remarkably stable in both amount and molecular composition as water forms Antarctic Bottom Water on the continental shelf, despite intense biological activity.
The press release and related coverage (often under titles highlighting “unexpected stability” or “vanished without a trace”) come from the Alfred Wegener Institute (AWI).
The lead author is Dr. Gonzalo V. Gomez- Saez (formerly at AWI, now leading a group at Ludwig- Maximilians- Universität München), with joint senior authors Dr. Moritz Holtappels (AWI) and Prof. Dr. Thorsten Dittmar (University of Oldenburg/ICBM). Folke Mehrtens is associated with the AWI communications and press release.
Researchers analyzed water samples from two Polarstern expeditions (2016 and 2021) in the southern Weddell Sea. They used advanced molecular techniques (including ultrahigh-resolution mass spectrometry at ICBM) and radiocarbon dating (via AWI’s MICADAS facility).
Despite seasonal phytoplankton blooms producing labile (easily degradable) organic matter and significant changes in water masses, the concentration and chemical makeup of the vast DOM reservoir showed almost no detectable change as dense water sank into the deep ocean. Shelf processes left essentially no “fingerprint”.
The explanation is residence time: dense waters stay on the Weddell Sea shelf (including under the Filchner- Ronne Ice Shelf) for 6- 12 years. This gives microbes enough time to fully remineralize newly produced surface organic carbon into dissolved inorganic carbon before the water exits the shelf.
DOM is highlighted as a stable component of the regional Southern Ocean carbon cycle. Because this large organic carbon reservoir is largely unaffected by shelf processes, it may remain relatively buffered against climate change impacts in this region (even as warming reaches Antarctic shelf seas). Other carbon pools (e.g., sinking particulate organic matter or dissolved inorganic carbon) may respond more strongly to temperature, sea-ice, and biological changes.
The paper is: Gomez-Saez et al., “Conserved molecular properties of dissolved organic matter during Weddell Sea Deep Water formation,” Nature Communications (2026), DOI: 10.1038/s41467-026-79040-4.
Further work is planned under initiatives like Antarctica InSync, including a 2028 Polarstern winter expedition to the Weddell Sea.
Antarctic Bottom Water (AABW) is the coldest, densest water mass in the open ocean. It forms primarily around the Antarctic continental margin and sinks to the abyssal depths, where it spreads northward as a key part of the global overturning circulation (the “great ocean conveyor belt”). It ventilates the deep ocean by supplying oxygen and helps sequester heat and carbon for centuries to millennia.
Main Formation Regions
AABW forms mainly in a few key areas:
- Weddell Sea (the largest contributor, often producing the densest component, called Weddell Sea Bottom Water)
- Ross Sea
- Adélie Coast (off East Antarctica)
- Cape Darnley region
Step- by- Step Formation Process
- Cooling and Sea- Ice Formation in Polynyas
Strong, cold katabatic winds blow off the Antarctic continent, pushing sea ice away from the coast and creating persistent open- water areas called coastal polynyas. In these “sea- ice factories”, seawater is continuously exposed to the frigid atmosphere, freezes rapidly, and is then blown away, allowing more ice to form. - Brine Rejection and Density Increase
When seawater freezes, most of the salt is rejected (left behind) in the remaining liquid water. This process, combined with intense surface cooling, creates extremely cold, high- salinity water near the freezing point (around- 1.9 °C). This is known as High- Salinity Shelf Water (HSSW) or, more broadly, Dense Shelf Water (DSW). - Interaction with Ice Shelves (in some regions)
In places like the Weddell and Ross Seas, some of this dense water flows under floating ice shelves (e.g., Filchner- Ronne or Ross Ice Shelf). Contact with the ice base further cools it, sometimes producing Ice Shelf Water (ISW) that is supercooled (colder than the surface freezing point, typically below -2 °C). - Overflow and Descent Down the Continental Slope
The dense shelf water becomes dense enough to spill over the continental shelf break. It cascades down the steep continental slope as gravity- driven plumes (overflows). - Mixing and Entrainment
As the dense plumes descend, they mix with and entrain surrounding waters, primarily warmer, saltier Circumpolar Deep Water (CDW, also called Warm Deep Water) and some Antarctic Surface Water. This mixing modifies the original shelf water, producing the final AABW properties: typically, colder than 0 °C with high density (neutral density greater than about 28.27 kg m⁻³).
The resulting AABW then spreads along the seafloor into the Atlantic, Indian, and Pacific Ocean basins, forming the deepest layer of the global ocean.
Importance and Sensitivity to Change
AABW formation drives a major branch of the global thermohaline circulation. It is highly sensitive to changes in sea- ice production, wind patterns, and freshwater input from glacial melt. Recent observations show declines in the densest components in some regions (e.g., reduced volume of the densest Weddell Sea Bottom Water), linked to decreased sea-ice formation and increased meltwater.
This process was central to the recent study on dissolved organic carbon stability in the Weddell Sea: the long residence time of dense waters on the shelf (years) allows biological processes to fully process organic matter before the water sinks as AABW.
The regional Southern Ocean carbon cycle refers to the processes controlling the exchange, transformation, transport, and long- term storage of carbon (both inorganic and organic) specifically in the Southern Ocean, particularly its Antarctic sectors such as the Weddell Sea.
This region is disproportionately important for the global carbon cycle.
The Southern Ocean (south of ~30- 35°S) accounts for a large share of the ocean’s uptake of anthropogenic CO₂ and heat. It currently acts as a net carbon sink of roughly 0.4- 1.1 Pg C yr⁻¹ (estimates vary by method and time period), helping offset a significant portion of human emissions.
Key reasons for its outsized role:
- Upwelling of deep water brings CO₂- and nutrient- rich water to the surface.
- Biological production (phytoplankton photosynthesis) converts some of that CO₂ into organic matter.
- Deep- water formation (especially Antarctic Bottom Water) returns carbon to the abyss, where it can be sequestered for centuries to millennia.
Main Components of the Regional Cycle
- Air- Sea Gas Exchange
CO₂ enters or leaves the surface ocean depending on the difference in partial pressure (pCO₂). Upwelling tends to cause natural outgassing, while biological uptake and the rising atmospheric CO₂ drive net anthropogenic uptake. - Biological Carbon Pump
Phytoplankton convert dissolved inorganic carbon into particulate organic carbon (POC) and dissolved organic carbon (DOC/DOM).- Much of the organic matter is remineralized (broken down by microbes) back to inorganic forms in the upper ocean.
- A fraction is exported to depth as sinking particles or as dissolved organic matter.
- Physical Circulation and Deep- Water Formation
Dense shelf waters form on the Antarctic continental shelf (especially the Weddell and Ross Seas) through sea- ice formation (brine rejection) and cooling under ice shelves. These waters overflow and sink, mixing with Circumpolar Deep Water to form Antarctic Bottom Water (AABW) and its precursor Weddell Sea Deep Water (WSDW). This process ventilates the deep ocean and carries carbon (both inorganic and organic) into long- term storage. - Dissolved Organic Matter (DOM) Reservoir
DOM is the largest pool of organic carbon in the ocean. In the Weddell Sea, recent research shows that the molecular composition and amount of solid-phase extractable DOM remain remarkably stable during dense- water formation. Shelf processes leave almost no molecular “fingerprint” on the DOM exported into WSDW/AABW because long residence times (6- 12 years) on the shelf allow efficient microbial remineralization of newly produced labile organic carbon. This makes DOM a relatively stable component of the regional Southern Ocean carbon cycle.
Regional Specifics (Weddell Sea Focus)
In the southern Weddell Sea:
- Intense seasonal phytoplankton blooms occur on the shelf.
- Dense waters have unusually long residence times, allowing thorough processing of organic matter.
- An estimated ~0.155 Pg C of organic carbon is transferred annually into AABW via this pathway, with conserved molecular properties.
- Climate- driven weakening of AABW formation may reduce the efficiency of carbon sequestration in this region, even if the molecular character of the exported DOM stays similar.
Climate Sensitivity
The Southern Ocean carbon cycle is highly sensitive to changes in:
- Sea- ice cover and formation rates
- Wind patterns (which affect upwelling and polynyas)
- Glacial meltwater input (which can freshen shelf waters and inhibit dense-water formation)
- Iron supply (which limits phytoplankton growth in large areas)
Changes here can influence atmospheric CO₂ levels on both short (decadal) and long (centennial- millennial) timescales.
In short, the regional Southern Ocean carbon cycle, especially around Antarctica, links surface biological activity, air- sea exchange, and deep- ocean sequestration through the formation and export of dense waters, with dissolved organic matter acting as a surprisingly stable reservoir within that system.
Antarctic Bottom Water (AABW) volume is decreasing due to climate change, with implications for long-term abyssal carbon storage. The study investigates solid-phase extractable dissolved organic matter (SPE-DOM) in the Weddell Sea (source of ~50% of AABW).
- Molecular and structural properties of SPE-DOM remain essentially unchanged during dense-water formation on the shelf.
- Shelf biogeochemical processes have minimal impact on the organics exported to the deep sea.
- This is attributed to efficient remineralization of newly produced organic carbon to inorganic forms, enabled by the long residence time (6–12 years) of dense waters on the Weddell Sea shelf.
- The dominant SPE-DOM signature in Weddell Sea Deep Water (WSDW, the precursor to AABW) is largely established before dense shelf waters mix with warmer offshore waters.
- An estimated 0.155 ± 0.03 PgC of organic carbon is transferred annually from the Weddell Sea into AABW.
- The molecular composition of this exported DOM is expected to remain conserved even as AABW formation weakens under ongoing climate change.
Researchers analyzed 178 water samples from two Polarstern expeditions (2016 and 2021) across seven water masses involved in WSDW/AABW formation (from surface to >4,000 m).
They used:
- Quantitative DOC measurements
- Ultrahigh- resolution FT- ICR- MS (molecular formulas)
- ¹H- NMR spectroscopy (structural features)
- Radiocarbon (¹⁴C) dating of SPE- DOC
Results:
- SPE- DOM was highly similar across all water masses at both the molecular-formula and structural levels (low Bray- Curtis dissimilarities).
- Apparent ¹⁴C ages of SPE-DOC were consistently old (~5,400- 6,800 years), indicating a predominance of aged, recalcitrant material everywhere.
- No systematic molecular imprint from intense biological activity or shelf processes was detected in the exported deep water.
- DOC and SPE- DOC concentrations showed little systematic change with depth or water- mass transformation.
This supports the idea that the large oceanic reservoir of recalcitrant dissolved organic carbon behaves as a relatively stable component of the Southern Ocean carbon cycle in this region.
While AABW formation itself is weakening, the organic carbon that does get exported via this pathway carries a conserved molecular signature.
The paper is open access on Nature.com.
Title: Conserved molecular properties of dissolved organic matter during Weddell Sea Deep Water formation
Journal: Nature Communications, volume 17, Article number: 11455, 2026
DOI: 10.1038/s41467-026-79040-4
Provided: Alfred Wegener Institute
Authors: Gonzalo V. Gomez-Saez,
Sarah K. Bercovici,
Marit Renken,
Sahithya P. B. Vemulapalli,
Andreas Rogge,
Hendrik Grotheer,
F. Alexander Haumann,
Moritz Holtappels &
Thorsten Dittmar
Abstract
Antarctic Bottom Water (AABW) is decreasing in volume due to climate change with potential consequences for abyssal carbon storage, where carbon is locked away from the atmosphere for centuries. Understanding the formation and export of dissolved organic matter (DOM) on the Antarctic shelf is therefore essential to determine how organic carbon enters this deep-sea reservoir. Here, we investigate solid-phase extractable DOM (SPE-DOM) transformations in the Weddell Sea, where half of AABW forms. Molecular and structural properties of SPE-DOM remain unchanged during dense-water formation. Shelf processes minimally affect exported organics into the deep-sea, likely due to remineralization to inorganic carbon enhanced by long residence times on the shelf. Consequently, the dominant SPE-DOM signature in Weddell Sea Deep Water (WSDW) is established before dense shelf waters mix with warmer off-shelf waters. We estimate that 0.155 ± 0.03 PgC are transferred annually from the Weddell Sea to AABW, and that its molecular composition is expected to remain conserved despite ongoing climate-driven weakening of AABW.
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