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Archive for New OCB Research

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.

Do ecological feedbacks matter in a changing world?

Posted by mmaheigan

· Friday, August 14th, 2026

Interactions among organisms shape ecological dynamics, while exchanges with the environment alter physical and chemical conditions. Examples of these include predator-prey dynamics (biotic interaction), the release of nutrients through excretion (chemical changes), or the development of coral reefs (physical changes). Together, these processes can generate feedback loops, which may amplify or buffer the impacts of environmental change. We know such processes are important in ecosystems, but do ecological feedbacks really matter at larger scales and in the wider Earth system? To address this question, authors of a recent study published in Earth’s Future, compiled what is known about how ecological feedbacks operate, drawing on examples from ecosystems in marine, terrestrial and freshwater habitats across the world.

Figure caption: A wide range of ecological feedbacks influence the functioning of coral reef systems, affecting the structure and functioning of the ecosystem and associated physical and biogeochemical processes. Figure modified from Murphy et al. (2025), originally published in Earth’s Future, © The Authors, published by the American Geophysical Union under a Creative Commons license.

The synthesis highlights that ecological feedbacks are ubiquitous within and across ecosystems, yet remain a major gap in Earth system science. Ecological feedbacks can affect ecosystem structure and resilience, tipping points, global biogeochemical cycles, and the structure and dynamics of the physical environment. The study emphasises that current Earth System models often underrepresent these processes, despite their importance for carbon cycling, climate regulation, and ecosystem stability. Representing them appropriately is not trivial. Feedbacks operate across spatial (local to global) and temporal (seconds to centuries) scales, and are integral in multiple Earth system processes. A systematic approach is needed to both develop our understanding of ecological feedbacks and refine models, which will require increased integration of ecosystem and Earth system research. Overall, these findings matter because failing to account for ecological feedbacks could lead to inaccurate climate projections, misguided policy decisions, and unanticipated ecological losses.

Authors
Eugene Murphy (British Antarctic Survey)
Jessica Williams (Imperial College London)
Emma Cavan (Imperial College London)

Follow and learn more:
www.bas.ac.uk, IMBeR, ICED, SCOR, Future Earth, imber-youtube

@britishantarcticsurvey, @imber, @scor-int.bsky.social, @futureearth

https://www.bas.ac.uk/profile/ejmu/

https://profiles.imperial.ac.uk/jessica.williams15

https://profiles.imperial.ac.uk/e.cavan/about

Some extra background:
The study developed from scientific activities of the Integrating Climate Ecosystem Dynamics in the Southern Ocean (ICED) programme and the Integrated Marine Biosphere Research Project (IMBeR). ICED is a regional programme of IMBeR, which is a Large-Scale Ocean Research Project under the Scientific Committee on Oceanic Research (SCOR) and a Global Research Network under Future Earth. Improving understanding of ecological feedbacks in the Earth system was developed as an Innovation Challenge of IMBeR, with a conference session on the topic held at the Future Oceans 2 conference. Following subsequent discussions, and a recognition of the connected nature of ecosystems across the world, the study expanded to develop an integrated view encompassing marine, terrestrial and freshwater systems.

Citation: Murphy, E. J., Williams, J. J., Myers-Smith, I. H., Groner, V. P., Jacoby, D. M. P., Kwiatkowski, L., Melbourne-Thomas, J., Ransome, E., Banks-Leite, C., Bopp, L., Gehlen, M., Hofmann, E. E., Hoogakker, B., Johnston, N. M., Malhi, Y., & Cavan, E. L. (2026). Ecological Feedbacks in the Earth System. Earth’s Future, 14(2), e2025EF006478. https://doi.org/10.1029/2025EF006478

Beyond carbonate chemistry: Biogenic silica dissolution may weaken carbon sequestration under ocean alkalinity enhancement

Posted by mmaheigan

· Friday, August 14th, 2026

Ocean alkalinity enhancement (OAE) is a promising carbon dioxide removal strategy, yet evaluating its net carbon removal potential requires understanding not only seawater carbonate chemistry, but also biological feedbacks that may influence long-term carbon sequestration. While most OAE studies focus on resolving immediate responses during biomass production, much less attention is paid to processes occurring during particle sinking.

In a 39-day mesocosm experiment in the North Sea, a recent study investigated how phytoplankton bloom development and the composition of sinking particles responded to CO₂-unequilibrated OAE (ΔTA_max = 1250 μmol kg^-1). Although phytoplankton blooms were delayed, their overall magnitude and organic carbon export remained largely unchanged across the OAE gradient. In contrast, elevated pH (up to 9.25) enhanced the dissolution of diatom-derived silica during particle sinking, reducing silica ballasting ratios (BSi:POC) by up to 60%. This response is consistent with the well-established pH sensitivity of biogenic silica dissolution. Following bloom senescence, the degradation of protective organic coatings surrounding diatom frustules exposes biogenic silica to naturally undersaturated seawater, where elevated pH further accelerates dissolution.

Figure caption: A conceptual illustration of the North Sea mesocosm experiment investigating CO₂-unequilibrated OAE across a broad alkalinity gradient generated through different dilution scenarios. Original treatment colours and symbols are retained for transparency, although dilution treatments were pooled for the final analysis. Elevated pH enhanced the dissolution of diatom-derived biogenic silica during particle sinking, reducing silica ballasting ratuis (BSi:POC). The inset compares bloom-averaged water column (dashed regression, R2 = 0.56, p < 0.01) and deposition-averaged sediment trap (solid regression, R2 = 0.74, p < 0.01) silica ballasting ratios, illustrating that silica loss intensified during particle sinking. Graphics adapted from Integration and Application Network, University of Maryland Center for Environmental Science, https://ian.umces.edu/symbols/.

Because silica ballasting influences the depth at which sinking organic matter is remineralized, reduced silica preservation may shoal carbon remineralization and shorten carbon sequestration timescales, even when export production remains unchanged. The study highlights an export-phase process that has received little attention in OAE research and should be considered in future field observations and Earth system models evaluating the net carbon sequestration efficacy of OAE.

Authors
Philipp Suessle (University of the Azores)
Kai Georg Schulz (Southern Cross University, Geomar Helmholtz-Centre for Ocean Research)
Joana Barcelos e Ramos (University of the Azores)
Nico Manuel Sievers (Geomar Helmholtz-Centre for Ocean Research)
Julieta Schneider (Southern Cross University, Geomar Helmholtz-Centre for Ocean Research)
Juliane Katharina Tammen (Geomar Helmholtz-Centre for Ocean Research)
Leila Kittu (Geomar Helmholtz-Centre for Ocean Research)
Laura Marín-Samper (University of Las Palmas de Gran Canaria)
Maarten Boersma (Alfred-Wegener-Institute, Helmholtz-Centre for Polar- and Marine Research)
Ulf Riebesell (Geomar Helmholtz-Centre for Ocean Research)

Citation: Suessle, P., Schulz, K. G., Barcelos e Ramos, J., Sievers, N. M., Schneider, J., Tammen, J. K., Kittu, L., Marín-Samper, L., Boersma, M., and Riebesell, U. (2026) Ocean alkalinity enhancement reduces silica ballasting during export due to amplified dissolution, Biogeosciences, 23, 4691–4710, https://doi.org/10.5194/bg-23-4691-2026.

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

Phytoplankton respond more consistently to nutrient pulses than marine heat waves

Posted by mmaheigan

· Monday, June 29th, 2026

How do phytoplankton respond to short-term changes in temperature and nutrient availability, and how does this response vary under different baseline conditions?

A recent study perturbed a summer plankton community by manipulating nutrient concentrations and temperature (±4°C) in short-term controlled microcosms to assess the relative impacts of each factor on phytoplankton physiology and community structure. Nutrient amendments rapidly shifted the phytoplankton community towards larger cells, altered elemental stoichiometry, and reduced microzooplankton grazing. Conversely, temperature changed community composition, but had no impact on size or stoichiometry. These results paralleled a similar spring incubation and regional field studies, which together suggest that over short time scales (days) nutrient amendments may produce more consistent and significant impacts on phytoplankton composition and physiology than temperature or grazing. Though temperature is a significant driver of phytoplankton dynamics globally, the impacts of short-term temperature changes, like marine heat waves, may depend on baseline thermal conditions, the starting plankton community, and the availability of nutrients to cope with increased metabolic demands. Understanding baseline conditions will be central to deciphering how short-term temperature changes may impact phytoplankton communities and the ecosystems they support.

Figure caption. Illustrative diagram showing the impacts of short-term nutrient amendments on phytoplankton communities, and the factors that influence the thermal response. Frequency distribution plots show how the community size structure <20 µm differed between the nutrient amended treatment (solid) and the control (white) on day 4 of the incubation experiments, as discerned via flow cytometry forward scatter (FSC).

Authors
Stephanie I. Anderson (University of Rhode Island)
Gayantonia Franzè (University of Rhode Island & Institute of Marine Research)
Joshua D. Kling (University of Southern California)
Paul Wilburn (Michigan State University)
Colin T. Kremer (University of Connecticut)
Susanne Menden-Deuer (University of Rhode Island)
Elena Litchman (Michigan State University)
David A. Hutchins (University of Southern California)
Tatiana A. Rynearson (University of Rhode Island)

Bluesky
@drplankton.bsky.social
@quant-ecology.bsky.social
@elenalitchman.bsky.social
@stephanieianderson.bsky.social

Detecting the ocean’s eddy carbon pump globally—it’s smaller than we thought.

Posted by mmaheigan

· Monday, June 29th, 2026

How much carbon do ocean eddies actually pump into the ocean interior? A decade ago, a landmark study (Omand et al, 2015) showed that turbulent eddies at ocean fronts can grab carbon-rich surface water and plunge it hundreds of meters down in a matter of days—back-of-the-envelope extrapolations suggest this “eddy subduction pump” could export as much as 2 Pg of carbon per year (Boyd et al, 2019), roughly a fifth of the entire biological carbon pump. But because these events are small, short-lived, and scattered across every ocean basin, constraining the pump’s true size at the global scale has remained elusive. The authors of a recent study built an algorithm that detects individual subduction events from coincident anomalies in salinity, oxygen, and particulate organic carbon, and applied this algorithm to 126,591 profiles from 941 BGC-Argo floats, identifying 1,333 carbon subduction events concentrated in springtime hotspots in the Southern Ocean and the subpolar North Atlantic. The resulting global export below 200 m is about 0.05 [<0.01–0.28] Pg C yr⁻¹, orders of magnitude smaller than the earlier upper bound, and less than 5% of the total biological pump. The result is in close agreement with an independent global estimate derived from a four-dimensional POC budget (Bellacicco et al., 2025), giving us added confidence that the pump’s true magnitude is modest. This is, somewhat counterintuitively, reassuring news for global carbon budgets. Current Earth System Models cannot resolve the kilometer-scale dynamics behind eddy subduction, but our results suggest they are not missing a first-order term in the ocean carbon cycle.

Figure caption : Spatial distribution of total annual mean POC flux below 200 m from the eddy subduction pump, assuming a constant vertical velocity W = 200 m day⁻¹. Strongest export occurs in the Southern Ocean and subpolar North Atlantic. White stippling marks 5° grid cells without Argo profiles (insufficient coverage).

Authors
Maxime Keutgen De Greef
Laure Resplandy
Mathieu A. Poupon
(all Princeton Univ)

A small pH bias can make Southern Ocean CO₂ uptake look too weak

Posted by mmaheigan

· Friday, May 22nd, 2026

The Southern Ocean is one of the most important regions for absorbing anthropogenic CO₂, and it is one of the most challenging places to observe, until Biogeochemical (BGC) Argo floats began to monitor this remote region year-round. Yet, CO₂ uptake estimates based on float data have suggested a much weaker uptake Southern Ocean than estimates from ships and aircraft observations. This strongly challenges the conventional view of Southern Ocean carbon sink and raises questions about the float pH data. Could this disagreement come from a bias in the pH measurements used to calculate float-derived pCO₂?

A study published in Scientific Reports, tested this by comparing BGC Argo float data with high-quality ship-based observations across the Southern Ocean. Rather than focusing only on the surface or on a small number of float-ship crossover points, we carried out a basin-scale, multi-variable, whole-profile comparison using GLODAP as a reference, and then checked the surface signal independently with OceanSODA.

First, we focused on old subsurface waters with minimal anthropogenic carbon, where ship and float data collected at different times are comparable. Float temperature, salinity, nitrate, oxygen, and algorithm-estimated total alkalinity (TA) were consistent with ship data. pH from floats, in contrast, was systematically lower (by ~ 0.021 units), leading to higher derived pCO₂ (by ~ 20 µatm) and dissolved inorganic carbon (DIC). At the surface, two independent approaches suggest that float-derived pCO₂ is biased high by 15 ± 3 µatm on average. This bias is larger than previously recognized and is large enough to help explain why float-based estimates have made Southern Ocean CO₂ uptake appear weaker than estimates from other observing platforms.

Figure caption: Conceptual summary of how a small negative bias in float pH can propagate into a positive bias in derived surface pCO₂. In this study, basin-scale float–ship comparisons and surface checks against OceanSODA suggest that float-derived Southern Ocean surface pCO₂ is biased high by 15 ± 3 µatm, which would make CO₂ uptake by the Southern Ocean appear weaker than it actually is.

These findings do not diminish the value of BGC Argo float data. Instead, they show how essential careful calibration is when autonomous observations are used to quantify air-sea CO₂ exchange. We suggest that future float pH adjustment should use multiple reference depths, rather than rely on a single deep reference point. Combining improved float calibration with continued ship-based measurements will significantly strengthen our ability to quantify the Southern Ocean carbon sink and its role in the global carbon cycle.

Authors:
Chuqing Zhang (University of Southampton; National Oceanography Centre Southampton)
Yingxu Wu (Polar and Marine Research Institute, Jimei University)
Peter J. Brown (National Oceanography Centre)
David Stappard (University of Southampton; National Oceanography Centre Southampton)
Amavi N. Silva (University of Southampton; National Oceanography Centre Southampton; GEOMAR Helmholtz Centre for Ocean Research Kiel)
Toby Tyrrell (University of Southampton; National Oceanography Centre Southampton)

Citation: Zhang, C., Wu, Y., Brown, P.J. et al. A systematic bias in float pH leads to overestimation of derived pCO₂ and underestimation of carbon uptake by the Southern Ocean. Sci Rep 16, 13929 (2026). https://doi.org/10.1038/s41598-026-43863-4

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

El Niño-driven changes in the tropical Pacific O2 content and structure

Posted by mmaheigan

· Wednesday, April 29th, 2026

What drives the year-to-year variability of dissolved oxygen (O₂) in the tropical Pacific? A recent study explored this question using a global high-resolution model with active ocean biogeochemistry along with a machine learning based estimate of dissolved oxygen from Argo floats. El Niño and La Niña events play a major role in regulating the O₂ content and distribution in the tropical Pacific. El Niño events result in excess O₂ in the eastern tropical Pacific and reduced O₂ in the west. La Niña yields opposite patterns. In contrast to previous speculations that lower model resolution leads to an underestimate of observed O₂ variability in this region, we find little difference in the amplitude of the O₂ content change between models of different resolution (~1º vs 0.1º) and the observations-based machine learning estimate. ENSO-driven variability of O₂ in the eastern tropical Pacific is driven by large opposing physical and biological contributions: reduced upwelling of low-O₂ waters and weaker O₂ consumption at depth due to suppressed biological productivity during El Niño dominate over the reduction in O₂ ventilation by vertical turbulent mixing and the Equatorial Undercurrent, and the opposite occurs during La Niña. This subtle balance between competing processes suggests that future changes in O₂ in the tropical Pacific are likely to be sensitive to local changes in equatorial Pacific circulation and productivity, in addition to changes in large scale O₂ supply from the mid and high latitude basins as the ocean warms and stratifies. These O₂ changes have important implications for understanding and predicting marine ecosystem health and fisheries productivity throughout the tropical Pacific.

Figure: ENSO impacts on temperature and O₂ shown as regression of Nino 3.4 index on a) temperature anomalies, and b) O₂ anomalies in a high resolution simulation of CESM. Panel c) illustrates the main mechanisms governing the O₂ response to El Niño events.

Authors
Yassir A. Eddebbar (Scripps Institution of Oceanography)
M L. Hoffman (Scripps Institution of Oceanography)
Jonathan D. Sharp (UW/NOAA)
Daniel B. Whitt (NASA Ames)
Aneesh C. Subramanian (CU Boulder)
Sam Stevenson (UC Santa Barbara)

@NCAR_CGD @CUBoulderATOC @Scripps_Ocean @aneeshcs @CLIVAR @USCLIVAR

Citation: Eddebbar, Y. A., Hoffman, E. L., Sharp, J. D., Whitt, D. B., Subramanian, A. C., & Stevenson, S. (2026). ENSO-Driven Variability of Oxygen Content and Distribution in the Tropical Pacific. Journal of Climate, 39(5), 1333-1353. https://doi.org/10.1175/JCLI-D-25-0476.1

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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