ocean carbon uptake and storage :: Ocean Carbon & Biogeochemistry

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Archive for ocean carbon uptake and storage

The North Atlantic’s microscopic carbon traffic controllers

Posted by mmaheigan

· Friday, August 14th, 2026

Each year, as the North Atlantic transitions from turbulent spring mixing to layered summer stratification, a key question emerges: How do these seasonal changes reshape bacterial host-virus interactions and control carbon flux?

In a recent study published in Microorganisms, researchers show that seasonal stratification regulates viral activity by modulating encounter rates between viruses and distinct bacterial hosts. They found that one viral group (V1) is tightly coupled with high nucleic acid (HNA) bacteria in stratified surface waters, whereas another (V2) preferentially interacts with low nucleic acid (LNA) cells in the deeper, well-mixed layers. These patterns indicate that physical layering structures viral dynamics by regulating host distribution and ecological traits. Importantly, the study reveals a growth-dependent shift in viral infection strategy. The induction of temperate viruses increases with host growth rate up to a metabolic threshold (~0.1 d⁻¹), then declines as lytic infection becomes dominant. This finding challenges the traditional paradigm that lysogeny is favored under low-productivity conditions, instead suggesting that lysogeny may play a key role in fast-growing, r-selected host-virus systems.

These results highlight how viruses act as microscopic carbon traffic controllers, regulating the balance between microbial recycling and carbon export across seasonal transitions. During the shift toward stronger stratification, virus-driven lysis redirects up to 47% of bacterial carbon into dissolved pools each day, reinforcing the dominance of the microbial loop. Yet, under certain conditions, viral lysis may also inject carbon into deeper waters, enhancing export and the efficiency of the biological carbon pump. It is essential to understand these shifting pathways to predict how ocean stratification reshapes carbon cycling in a changing climate.

Authors:
Yean Das (The University of Southern Mississippi)
Corina P. D. Brussaard (NIOZ Royal Netherlands Institute for Sea Research & University of Amsterdam)
Kristina D. A. Mojica (The University of Southern Mississippi)

Citation:
Das, Y., Brussaard, C. P. D, & Mojica, K. D. (2025). Heterotrophic Prokaryote Host–Virus Dynamics During Spring in the Northeast Atlantic Ocean. Microorganisms, 13(11), 2474. https://doi.org/10.3390/microorganisms13112474

Impacts of warming and circulation slowdown on future ocean carbon cycle feedback

Posted by mmaheigan

· Friday, August 14th, 2026

The ocean has absorbed a quarter of anthropogenic CO₂ emissions, mitigating changes. However, predicting the future fate of this ‘sink’ is challenging as marine carbon is regulated by a complex set of interacting processes that respond differently to warming. Our recent study teases apart these interactions with a novel mechanistic carbon decomposition and attribution framework applied to an ocean biogeochemical model driven by output from a climate model, to quantify the impact of changes in different forcing factors, such as warming and circulation, on marine carbon storage and the consequent feedback on atmospheric CO₂.

Figure: (a) Waterfall chart attributing changes in atmospheric CO2 (pCO2atm) (relative to a simulation with no climate change; NCC) to different carbon components for the SSP5-8.5 high-emission scenario. Each bar represents a component with its height corresponding to the (positive or negative) change in pCO2atm due to that component. The cumulative change in pCO2atm as successive components are added is shown from left to right. Subscripts are: sat=saturation, dis=disequilibrium, soft=soft tissue remineralization, caco3=CaCO3 dissolution, phy=physical process, and bio=biological process. (b) Compensation ratio of change (∆) in preformed to regenerated carbon with respect to NCC in the Temperature (solid lines) and Circulation (dashed lines) attribution experiments for the four emission scenarios studied as a function of time. (c) Change in carbon components with respect to NCC in year 2500 due to temperature under the SSP1-2.6 low-emission scenario. (d) Change in carbon components with respect to NCC in year 2500 due to circulation under SSP5-8.5.

We find that under a high-emission scenario, global warming reduces marine carbon storage and raises atmospheric CO₂ in 2500 by ~270 ppm (Fig panel a), a positive feedback. This is due to a decrease in ocean CO₂ uptake (C_sat,phy), compensated in part by an increase in biologically regenerated carbon (C_soft & C_caco3). While previous studies have also found this compensation, they have ascribed it largely to a slowdown in ocean circulation. Our attribution experiments instead show that the degree of compensation depends strongly on the process and emission scenario (Panel b). Reduced CO₂ uptake due to a slower circulation is half-compensated by increased regenerated carbon under high emissions, but almost exactly compensated for under the lowest emission scenario (dashed lines). On the other hand, temperature-driven changes in uptake and regeneration are mostly uncompensated (solid lines); the direct effects of warming thus dominate under low-emission, high-mitigation scenarios, while also contributing a third of the decrease in carbon storage at the highest emissions. Air-sea disequilibrium, as revealed by the carbon decomposition, provides an explanation. Warming enhances physical disequilibrium because of an increase in the meridional sea surface temperature gradient; this is the leading cause of the decrease in carbon storage under low emissions (Panel c). In contrast, for high emissions (Panel d) a slowdown in circulation decreases physical disequilibrium, amplifying the impact of increased biological carbon sequestration in compensating for reduced CO₂ uptake. In summary, temperature dominates the climate-carbon cycle feedback for low emission scenarios, and circulation for high emission scenarios. This study provides new mechanistic insights into how the marine carbon cycle responds to change, and highlights the need for accurate partitioning of carbon components in Earth System Models.

Authors:
Samar Khatiwala (Waseda University)
Olivia Strachan (Independent Researcher)
Andreas Schmittner (Oregon State University)

Citation: Khatiwala, S., O. Strachan and A. Schmittner (2026). Multi-centennial response of marine carbon pumps to global warming, Nature Climate Change, https://doi.org/10.1038/s41558-026-02686-x.

Research Briefing (accompanying the main article): Warming dominates over circulation slowdown in reducing marine carbon storage under high-mitigation scenarios, Nature Climate Change, https://doi.org/10.1038/s41558-026-02687-w.

BGC-Argo floats reveal shifting nitrogen cycling in the Eastern Tropical North Pacific

Posted by mmaheigan

· Friday, August 14th, 2026

Oxygen-deficient zones are regions of the ocean where microbes consume nitrate in lieu of oxygen. This drives major losses of biologically available nitrogen. In a recent study, we used a BGC-Argo float in the Eastern Tropical North Pacific to remotely observe these processes over nearly three years. Using a new method to extract nitrite from UV nitrate sensor spectra (Bif and Johnson, 2025), the float captured a progressive decline in the secondary nitrite maximum over time, revealing a shift in microbial nitrogen cycling through time.

By combining float observations with a stoichiometric biogeochemical model, we found that nitrogen transformations reorganized in response to changing organic matter supply and redox conditions. The results show that oxygen-deficient zones are highly dynamic environments rather than stable systems. This also demonstrates how autonomous observing platforms can now monitor hidden nitrogen and carbon cycling processes across the global ocean in near real time.

Figure. BGC-Argo float observations in the Eastern Tropical North Pacific oxygen-deficient zone. (a) Float WMO#5906484 trajectory. (b) Time-series distribution of nitrite concentrations. The white contour indicates the upper boundary of low-oxygen waters of less than 1 µmol/kg. (c) Nitrate concentrations over the same period. (d–e) Relative contributions of anammox and denitrification estimated with a stoichiometric mass-balance model under contrasting biogeochemical conditions.

Authors:
Mariana B. Bif (University of Miami)
Colette Kelly (Woods Hole Oceanographic Institution, now
Mark A. Altabet (University of Massachusetts Dartmouth)
Annie Bourbonnais (University of South Carolina)
Claire Elbon (University of Washington)
Edgart Flores (University of Colorado Boulder
Alanna Mnich (University of Massachusetts Dartmouth)
Josh Plant (Monterey Bay Aquarium Research Institute (MBARI))
Kenneth S. Johnson (Monterey Bay Aquarium Research Institute (MBARI))

Citations:

Bif, M.B., & Johnson, K.S., 2025. BGC-Argo floats reveal nitrite and thiosulfate dynamics in the oceans with high spatiotemporal resolution. Global Biogeochemical Cycles, 39, e2024GB008473. https://doi.org/10.1029/2024GB008473

Bif, M.B., Kelly, C., Altabet, M.A., Bourbonnais, A., Elbon, C., Flores, E., Mnich, A., Plant, J. and Johnson, K.S., 2026. BGC-Argo float reveals shifts in nitrogen-carbon cycling in an oxygen-deficient zone. Communications Earth & Environment, 7(1), p.294. https://www.nature.com/articles/s43247-026-03410-5

What happens when marine snow and oil mix?

Posted by mmaheigan

· Friday, May 22nd, 2026

The Deepwater Horizon oil spill (April-July 2010) in the NE Gulf of Mexico provided researchers with an opportunity to explore what happens when marine snow and oil mix. Marine snow are detrital particles or aggregates consisting of inorganic and organic components, such as bacteria, phytoplankton cells, zooplankton fecal pellets, and mucous feeding webs, and are important in the biological pump and export of carbon to deep water. It is now known that marine snow and oil interact to form marine-oil-snow (MOS) which sediments to the seafloor, supported by observations from experiments, sediment traps, and sediment cores.

In a recent study published in the Journal of Geophysical Research Oceans, the authors provide additional analyses of the impact of oil on marine snow. The SIPPER camera imaging system was deployed on 13 cruises between May 2010 and August 2014 (during and after the oil spill), collecting more than 117 million images of aggregates. Analyses of these images indicated that diatom chains and Acantharian (small animals) spines were relatively common components of aggregates. The oil spill, combined with high Mississippi River outflow, resulted in marine snow concentrations that were significantly higher with larger-sized particles during the oil spill than in follow-on years. The shape of particles was consistently elongated in all years compared to the spherical shape assumed for simulations of particle sinking speeds. Analysis of the fractal dimension or surface roughness of particles indicated that during the oil spill (May 2010) aggregates had significantly higher fractal dimensions, suggesting that oil droplets in the marine-oil-snow reduced the amount of empty space within aggregates, thereby increasing particle density and increasing the sedimentation of oil. Fractal dimensions also increased with particle size in all years and, therefore, was not an impact of the oil spill. These data provide a baseline for future biogeochemical studies in the northern Gulf of Mexico and for model development for future oil spill response scenarios.

Figure caption. The abundance and distribution of marine snow was spatially variable, but unusually high in the upper 20 m of the water column during the summer following the Deepwater Horizon (DWH) oil spill (upper panel). Previously reported concentrations were 1,000 – 6,000 particles m-3. High concentrations occurred at the DWH platform site and shelf edge stations (lower right panel). Smaller sized particles were abundant near surface with larger particles (up to 1 cm) observed deeper in the water column (lower left panel). Examples of marine snow images are shown at the bottom. nVd is the normalized particle volume spectra, d is the median diameter within each particle size bin.

Authors:
Kendra L. Daly (University of South Florida)
George Jackson (Texas A&M University)
Andrew Remsen (Bureau of Ocean Energy Management)
Kurt Kramer (OceanSpace Sensors)
Palak Dave (Moffitt Cancer Center and Research Institute)
Dmitry B. Goldgof (University of South Florida)
Lawrence Hall (University of South Florida)

Citation:

Daly, K. L., Jackson, G., Remsen, A., Kramer, K., Dave, P., Goldgof, D. B., & Hall, L. (2026). Marine snow dynamics in the NE Gulf of Mexico: Particle abundance, characteristics, and impacts on Deepwater Horizon oil sedimentation. Journal of Geophysical Research: Oceans, 131, e2025JC023316. https://doi.org/10.1029/2025JC023316

When plastics slip into the carbon cycle

Posted by mmaheigan

· Wednesday, April 29th, 2026

What if a tiny amount of plastic could make the ocean’s carbon appear thousands of years older than it really is?

For decades, oceanographers have relied on routine measurements of particulate organic carbon to understand how carbon moves through the ocean, how long it persists, and how it shapes Earth’s climate. These measurements, based on combusting or oxidizing environmental samples and measuring the carbon released as CO₂, assume that the carbon being measured comes from natural biological sources. But what if that assumption is no longer safe?

Microplastics are now pervasive throughout the ocean, from coastal waters to the open sea. These tiny fragments originate from the breakdown of larger plastic debris or are manufactured directly for commercial and industrial uses. Once they enter marine systems through rivers, wastewater, or runoff, they mix seamlessly with natural particles and are easily captured during routine sampling of particulate organic matter. Critically, the analytical tools used to quantify carbon in these samples cannot distinguish plastic-derived carbon from carbon produced by living organisms.

In our study, we set out to test how much this hidden overlap matters. Using controlled experiments, we demonstrate that even very small amounts of fossil fuel–derived plastic can substantially bias standard measurements of organic matter composition. When microplastics contribute as little as ~1% of a sample’s mass, they introduce large isotopic errors, shifting Δ¹⁴C values by approximately −258‰ and δ¹³C values by −3.65‰. In radiocarbon terms, this translates into organic matter appearing roughly 4,000 years older than it actually is.

Figure: Relationship between δ¹³C, C:N, and radiocarbon (¹⁴C) age for sedimentary organic matter – polyethylene sediment admixtures. Colored boxes denote typical δ¹³C ranges of major carbon reservoirs (POC, DOC, terrestrial). Pie charts show measured positions of polyethylene admixtures (percent polyethylene by mass in parentheses), with yellow and blue sectors representing apparent marine and terrestrial contributions inferred from a two-endmember mixing model. Even 1% polyethylene contamination (red outline) substantially shifts apparent source attribution and radiocarbon age (red values). The black curve shows the modeled δ¹³C–C:N relationship

These findings reveal a quiet but consequential problem. Radiocarbon measurements are widely used to estimate how long carbon persists in the ocean and how resistant it is to degradation. If microplastics are inadvertently included in samples, natural organic carbon can appear artificially older and more stable than it truly is. Because most carbon biogeochemistry studies do not routinely account for the presence of microplastics, existing datasets and models may already be influenced by this contamination to unknown degrees.

Carbon isotope measurements are crucial for estimates of oceanic carbon budgets, inform climate models, and shape our understanding of how the ocean moderates atmospheric CO₂. If microplastics have been altering these measurements for years, then some interpretations of carbon cycling and climate feedbacks may need to be revisited. Recognizing microplastics not only as pollutants, but also as analytical interlopers, is an essential step toward improving the accuracy of ocean carbon science and ensuring that future observations reflect the ocean’s true biological signal.

Authors
Luis E. Medina Faull
Gordon T. Taylor
Steven R. Beaupré
(all at School of Marine and Atmospheric Sciences, Stony Brook University)

Citation: Medina Faull LE, Taylor GT, Beaupré SR (2025) Microplastic contaminants potentially distort our understanding of the ocean’s carbon cycle. PLoS One 20(10): e0334546. https://doi.org/10.1371/journal.pone.0334546

New unified interface for existing ocean carbonate chemistry data products

Posted by mmaheigan

· Tuesday, March 24th, 2026

The paper provides a comprehensive synthesis of 68 existing ocean carbonate chemistry data products and data product sets, including cruise-based compilations, time-series datasets, gap-filled observational products, and model-based reconstructions. The authors highlight the diversity of available products, noting differences in spatial coverage, temporal resolution, methodologies, and intended scientific applications. By systematically cataloguing and comparing these datasets, the study helps researchers identify which products are most suitable for specific scientific questions related to ocean carbon cycling and ocean acidification.

ESSD Paper

Interface for the most updated list of products

Submission interface

Authors
Li-Qing Jiang (University of Maryland; NOAA National Centers for Environmental Information; Scripps Institution of Oceanography)
Amanda Fay (Columbia University / Lamont-Doherty Earth Observatory)
Jens Daniel Müller (ETH Zürich; Carbon to Sea Initiative)
Luke Gregor (ETH Zürich; Swiss Data Science Center)
Alizée Roobaert (Flanders Marine Institute, VLIZ)
Lydia Keppler (Vycarb Inc.)
Dustin Carroll (Moss Landing Marine Laboratories; NASA Jet Propulsion Laboratory)
Siv K. Lauvset (NORCE Research / Bjerknes Centre for Climate Research)
Tim DeVries (University of California, Santa Barbara)
Judith Hauck (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research)
Christian Rödenbeck (Max Planck Institute for Biogeochemistry)
Nicolas Metzl (Sorbonne Université / LOCEAN)
Andrea J. Fassbender (NOAA Pacific Marine Environmental Laboratory)
Jean-Pierre Gattuso (Sorbonne Université / CNRS; Laboratoire d’Océanographie de Villefranche)
Peter Landschützer (Max Planck Institute for Meteorology)
Rik Wanninkhof (NOAA Atlantic Oceanographic and Meteorological Laboratory)
Christopher Sabine (University of Hawaii at Mānoa)
Simone R. Alin (NOAA Pacific Marine Environmental Laboratory)
Mario Hoppema (Alfred Wegener Institute)
Are Olsen (University of Bergen / Bjerknes Centre for Climate Research)
Matthew P. Humphreys (University of East Anglia)
Kunal Chakraborty (National Institute of Oceanography, India)
Ana C. Franco (University of Miami)
Kumiko Azetsu-Scott (Bedford Institute of Oceanography / Fisheries and Oceans Canada)
Dorothee C. E. Bakker (University of East Anglia)
Leticia Barbero (NOAA Atlantic Oceanographic and Meteorological Laboratory)
Nicholas R. Bates (Bermuda Institute of Ocean Sciences / Arizona State University)
Nicole Besemer (University of Natural Resources and Life Sciences Vienna)
Henry C. Bittig (GEOMAR Helmholtz Centre for Ocean Research Kiel)
Albert E. Boyd (University of Tasmania)
Daniel Broullón (Spanish Institute of Oceanography, IEO-CSIC)
Wei-Jun Cai (University of Delaware)
Brendan R. Carter (University of Washington)
Thi-Tuyet-Trang Chau (LSCE, CEA-CNRS-UVSQ)
Chen-Tung Arthur Chen (National Sun Yat-sen University)
Frédéric Cyr (Fisheries and Oceans Canada)
John E. Dore (University of Hawaii)
Ian Enochs (NOAA Atlantic Oceanographic and Meteorological Laboratory)
Richard A. Feely (NOAA Pacific Marine Environmental Laboratory)
Hernan E. Garcia (NOAA National Centers for Environmental Information)
Marion Gehlen (LSCE, CEA-CNRS-UVSQ)
Prasanna Kanti Ghoshal (CSIR-National Institute of Oceanography, India)
Lucas Gloege (Princeton University)
Melchor González-Dávila (University of Las Palmas de Gran Canaria)
Nicolas Gruber (ETH Zürich)
Debby Ianson (Fisheries and Oceans Canada / Institute of Ocean Sciences)
Yosuke Iida (Japan Meteorological Agency)
Masao Ishii (Meteorological Research Institute, Japan)
Apurva Padamnabh Joshi (CSIR-National Institute of Oceanography, India)
Esther Kennedy (NOAA Pacific Marine Environmental Laboratory)
Alex Kozyr (NOAA National Centers for Environmental Information)
Nico Lange (GEOMAR Helmholtz Centre for Ocean Research Kiel)
Claire Lo Monaco (Sorbonne Université / LOCEAN)
Derek P. Manzello (NOAA Atlantic Oceanographic and Meteorological Laboratory)
Galen A. McKinley (Columbia University / Lamont-Doherty Earth Observatory)
Natalie M. Monacci (NOAA Pacific Marine Environmental Laboratory)
Xosé A. Padin (Spanish Institute of Oceanography, IEO-CSIC)
Ana M. Palacio-Castro (Instituto de Investigaciones Marinas, CSIC)
Fiz F. Pérez (Spanish Institute of Oceanography, IEO-CSIC)
J. Magdalena Santana-Casiano (University of Las Palmas de Gran Canaria)
Jonathan Sharp (University of Delaware)
Adrienne Sutton (NOAA Pacific Marine Environmental Laboratory)
Jim Swift (Scripps Institution of Oceanography)
Toste Tanhua (GEOMAR Helmholtz Centre for Ocean Research Kiel)
Maciej Telszewski (International Ocean Carbon Coordination Project, IOCCP)
Jens Terhaar (University of Bern)
Ruben van Hooidonk (University of Miami / NOAA Coral Reef Watch)
Anton Velo (Spanish Institute of Oceanography, IEO-CSIC)
Andrew J. Watson (University of Exeter)
Angelicque E. White (Oregon State University)
Zelun Wu (University of Delaware)
Liang Xue (Xiamen University)
Hyelim Yoo (University of Maryland / NOAA NCEI)
Jiye Zeng (National Institute for Environmental Studies, Japan)
Guorong Zhong (Xiamen University)

How much carbon do fish move towards the seafloor as they feed and migrate in the water column?

Posted by mmaheigan

· Tuesday, March 24th, 2026

Ocean organisms transfer carbon via many natural processes from surface to seafloor. These include the passive sinking of carbon-rich particles and the active transport of carbon as animals swim downward. A recent study in GBC modeled how carbon stored in fish biomass moves from the sea surface to the seafloor in shelf–slope–abyssal systems through feeding interactions alone. This transport occurs as large fish eat smaller fish while occupying different vertical habitats in the water column. On average, this process delivers an amount equivalent to 5% of all carbon that reaches the seafloor—through sinking organic particles from phytoplankton and zooplankton. Yet, this can be as high as 20% in some shelf areas. On continental slopes, midwater fishes play a key role as a stepping-stone for carbon transfer (up to 50%) to the seafloor. Overall, the study reveals that the vertical movement of fish is an important pathway for delivering carbon to groundfish species, particularly on shelf areas where most commercially valuable fisheries operate.

Caption: Schematic of a shelf-slope-abyssal system with hypothesized fluxes of carbon among major functional groups (top panel); and model-estimated fluxes of carbon from functional groups to demersal fishes (bottom panel). Solid and dotted lines are mean fluxes for Eastern and Western North Atlantic systems, respectively, and shaded areas are standard deviations. Values are proportional.

Authors

Daniel Ottmann (Technical University of Denmark (DTU-Aqua); Institute of Marine Sciences of Andalusia)
Ken H. Andersen (Technical University of Denmark (DTU-Aqua))
Yixin Zhao (Technical University of Denmark (DTU-Aqua))
Colleen M. Petrik (Scripps Institution of Oceanography)
Charles A. Stock (Scripps Institution of Oceanography)
Clive Trueman (University of Southampton)
P. Daniël van Denderen (Technical University of Denmark (DTU-Aqua))

Follow the authors:
bluesky: @danielottmann.bsky.social; @kenandersen.bsky.social
LinkedIn accounts: Ottman; Andersen; Truman
X: @daniel_ottmann; @69kno; @OceanLifeCenter; @van_denderen; @clivetrue;

Active Transport of Carbon to Demersal Fish Communities in Shelf-Slope-Abyssal Systems of the North Atlantic Ocean
Global Biogeochemical Cycles, Vol 40:2, e2025GB008861. https://doi.org/10.1029/2025GB008861

The ocean is the largest natural carbon sink for atmospheric CO2

Posted by mmaheigan

· Friday, January 23rd, 2026

Only about half of human-made CO2 emissions remain in the atmosphere and drive global warming. The other half has so far been said to be taken up in roughly equal amounts by the biosphere on land and by physical-chemical processes in the ocean. In equal amounts?

In a new assessment, Friedlingstein et al. reassess the various components of the Global Carbon Budget. Major changes were suggested for the land and ocean sinks. For the land, the prior assumption of a preindustrial land-cover in the Dynamic Global Vegetation Models (DGVM) led to an overestimation of the natural land sink in previous studies. The land sink is further revised downwards by accounting for an anthropogenic perturbation of lateral carbon export to the ocean. For the ocean, adjustments were made for the known underestimation of the ocean sink from Global Ocean Biogeochemical Models and the cool and salty skin effect in surface fCO₂-observation-based estimates. As a result, the ocean is now estimated to have taken up 29% of anthropogenic CO₂ emissions in the last decade 2015-2024, while the land sink has taken up 21%. In this revised estimate with virtually no budget imbalance over the last decade and no significant trend in the budget imbalance since 1960, climate-driven impacts on the natural sinks are quantified: Land and ocean sinks would be 25% and 7% higher, respectively, without this carbon-climate feedback. Since 1960, the carbon-climate feedback has already contributed 8 ppm (8%) to the rise in atmospheric CO₂ concentration.

The negative imprints of earth system changes (e.g., warming, droughts, changes in wind patterns and ocean circulation, etc.) on these important carbon sinks is worrisome and is expected to intensify as warming continues. The most effective way to protect these sinks is to drastically reduce CO₂ emissions from fossil fuels and land-use changes, ultimately to net zero.

Authors
Judith Hauck (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, University of Bremen)
Peter Landschützer (VLIZ)
Corinne Le Quéré (University of East Anglia)
Pierre Friedlingstein (University of Exeter)

Bluesky: @pfriedling @jhauck @clequere

A heat burp breaks the assumed relationship of cumulative CO2 emissions and warming

Posted by mmaheigan

· Friday, January 23rd, 2026

The ocean stores vast amounts of heat and carbon under anthropogenic CO₂ emissions, but its behavior under net-negative emission scenarios remains poorly understood. Here we use an Earth System Model of intermediate complexity and show results of an idealized future climate scenario that includes sustained net-negative emissions over centuries. After gradual global cooling, the model produces an abrupt “heat burp,” in which heat previously stored in the deep Southern Ocean resurfaces through deep convection, temporarily reversing the cooling and causing renewed warming. The release of heat is not accompanied by a comparable release of CO₂. The heat burp represents a breakdown of the assumed linear relationship between cumulative CO₂ emissions and warming, a metric that is used to calculate the remaining carbon budget. We call for assessing the robustness of how models forced with net-negative CO₂ emissions simulate durability of ocean storage of heat and CO₂, and pathways and time scales of loss to the atmosphere.

Fig caption: The temporal evolution of (a) global heat and carbon uptake and release; (b) surface air temperature (SAT) anomaly relative to preindustrial conditions; (c) Southern Ocean temperature anomaly relative to preindustrial conditions; gray shading/black bar indicate the period of comparatively abrupt ocean heat release that warms SAT, representing a climate feedback.

Authors
(all at GEOMAR)

Ivy Frenger
Svenja Frey (and Univ Copenhagen)
Andreas Oschlies
Julia Getzlaff
Torge Martin
Wolfgang Koeve

Frenger, I., Frey, S., Oschlies, A., Getzlaff, J., Martin, T., & Koeve, W. (2025). Southern Ocean heat burp in a cooling world. AGU Advances, 6, e2025AV001700. https://doi.org/10.1029/2025AV001700

A Microbial Conveyor Belt Beneath the South Pacific

Posted by mmaheigan

· Friday, October 17th, 2025

Global overturning circulation is a planetary conveyor belt: dense waters sink around Antarctica, spread through the deep ocean for centuries, and eventually rise elsewhere, redistributing heat, nutrients, and carbon. But how does this slow, pervasive movement of water impact marine microbes?

To find out, researchers collected over 300 water samples spanning the full depth of the ocean along the GO-SHIP P18 line in the South Pacific. They found that microbial genomes cluster into six spatial cohorts that are not only delineated by depth, but also circulatory features, like Antarctic Bottom Water formation, and ventilation age. Distinct functional signatures also emerged across these circulation-driven zones. For example, genes for light harvesting and iron uptake dominate in surface waters, while adaptations for cold, high pressure, or anaerobic metabolism characterize deep and ancient waters. Antarctic Bottom Water communities also carry hallmarks of rapid genetic exchange, suggesting horizontal gene transfer may help microbes adapt as they sink into the deep ocean. Even in waters isolated from the atmosphere for over a thousand years, many microbial genomes have coverage patterns that imply active replication, demonstrating that long-isolated water masses still support active microbial populations. In considering patterns of microbial diversity, researchers also identified a pervasive “prokaryotic phylocline” in which richness spikes just below the surface mixed layer and remains high to full ocean depth, only dipping slightly in very old water.

These results demonstrate that physical circulation, not just temperature or nutrients, partitions the ocean into microbial biomes. Understanding this linkage is critical because microbes determine the amount of carbon that is recycled or stored long-term in the deep ocean. As climate change alters overturning circulation, the functioning of these hidden microbial ecosystems and their role in regulating atmospheric CO₂ may shift in unexpected ways.

Authors
Bethany C. Kolody (University of California San Diego; UC Berkeley; J. Craig Venter Institute)
Rohan Sachdeva (UC Berkeley)
Hong Zheng (J. Craig Venter Institute)
Zoltán Füssy (UC San Diego; J. Craig Venter Institute)
Eunice Tsang (UC Berkeley)
Rolf E. Sonnerup (University of Washington)
Sarah G. Purkey (UC San Diego)
Eric E. Allen (UC San Diego)
Jillian F. Banfield (UC Berkeley; Lawrence Berkeley National Laboratory; Monash University)
Andrew E. Allen (UC San Diego; JCVI)

Social media
Twitter/X: @science_doodles, @Scripps_Ocean, @JCVenterInst
Bluesky: @banfieldlab.bsky.social, @bethanykolody.bsky.social, @scrippsocean.bsky.social, @jcvi.org

https://www.science.org/doi/10.1126/science.adv6903
Overturning circulation structures the microbial functional seascape of the South Pacific
Science

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.

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