mmaheigan :: Ocean Carbon & Biogeochemistry

Studying marine ecosystems and biogeochemical cycles in the face of environmental change

Author Archive for mmaheigan

Remembering Dr. Jorge Sarmiento

Posted by mmaheigan

· Friday, July 10th, 2026

The global climate science community mourns the passing of Dr. Jorge Sarmiento in May 2026. In addition to co-authoring the first decadal U.S. Carbon Cycle Science Plan (Sarmiento and Wofsy, 1999) and leading the historic push to develop the U.S. Carbon Cycle Science Program and its carbon science coordination entities, OCB and NACP, Jorge stood as a pioneering “giant” in ocean biogeochemistry whose visionary leadership fundamentally shaped the trajectory of Earth system science. From his early steering of JGOFS to his profound contributions within OCB and his groundbreaking work heading the SOCCOM initiative, Jorge unraveled the critical complexities of the Southern Ocean and global marine ecosystems. Yet, beyond his extraordinary scientific accolades, including his shared recognition in the 2007 Nobel Peace Prize, his ultimate legacy lives on through his selfless mentorship, his infectious enthusiasm for new ideas, and the generations of brilliant scientists he inspired and guided. We owe an immeasurable debt of gratitude to Jorge for his career of profound discovery, collaborative spirit, and enduring dedication to understanding our planet. He will be deeply missed, but his scientific legacy remains a guiding light for all future carbon cycle research.

GLODAPv3 – A new version release

Posted by mmaheigan

· Wednesday, July 8th, 2026

On behalf of the GLODAP Reference Group and hundreds of seagoing oceanographers who have tirelessly collected data all over the ocean for several decades, it is our pleasure to announce the release of the new Global Ocean Data Analysis Project version 3, GLODAPv3!

Use this link for direct access: GLODAPv3 OCADS landing page and check out our webpage.

GLODAPv3 provides surface-to-bottom ocean biogeochemical observations determined through chemical analysis of discrete bottle samples. This new version comprises data from 1181 cruises, spanning more than 50 years of observations (1972 – 2023). It includes all data from the previous GLODAPv2.2023, together with an additional 57 new cruises. All data have been evaluated for systematic differences and adjusted appropriately. The result is the most comprehensive and rigorously quality controlled ocean interior data product for marine biogeochemistry studies. Its analysis will allow for quantitative assessment of biogeochemical changes and feedbacks between climate change and the ocean.

GLODAPv3 Cruises

GLODAPv3 consists of:

a data base with original cruise data, as submitted by individual data providers but updated to WOCE Exchange format
a merged data product, with systematic measurement differences removed for key biogeochemical variables

The original data, their documentation and DOIs are available at the Ocean Carbon Data System of NOAA NCEI.

GLODAPv3 is the result of a multi-year global team effort funded by the EU Horizon Europe project OceanICU, US NOAA, the SCOR-IOC International Ocean Carbon Coordination Project (IOCCP) and many other projects, programmes and organisations.

The procedures and results are extensively documented in:

Nico Lange, Siv K. Lauvset, Brendan R. Carter, Matthew P. Humphreys, Ryan J. Woosley, Are Olsen, Henry C. Bittig, Alex Kozyr, Marta Álvarez, Kumiko Azetsu-Scott, Susan Becker, Peter J. Brown, Leticia Cotrim da Cunha, Larissa Dias, Mario Hoppema, Masao Ishii, Emil Jeansson, Akihiko Murata, Jens Daniel Müller, Fiz F. Pérez, Carsten Schirnick, Reiner Steinfeldt, Adam Ulfsbo, Anton Velo, and Toste Tanhua. Submitted.
Matthew P. Humphreys, Siv K. Lauvset, Nico Lange, Henry C. Bittig, Brendan R. Carter, Mario Hoppema, Akihiko Murata, Are Olsen, Toste Tanhua, Adam Ulfsbo, Antón Velo, Ryan J. Woosley, Kumiko Azetsu-Scott, Jens D. Müller, and Fiz F. Pérez. 2026.
https://doi.org/10.5194/egusphere-2026-3063

This work was funded by the European Union under grant agreement no. 101083922 (OceanICU) and UK Research and Innovation (UKRI) under the UK government’s Horizon Europe funding guarantee [grant number 10054454, 10063673, 10064020, 10059241, 10079684, 10059012, 10048179]. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Research Executive Agency. Neither the European Union nor the granting authority can be held responsible for them.

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)

Celebrating 20 years of OCB + OCB2027 dates

Posted by mmaheigan

· Monday, June 22nd, 2026

Save the dates for OCB2027 in person June 22-25, 2027

2026 marks 20 years since the OCB Project Office began in 2006 to support science, community, and connection across a globally distributed network of scientists! To celebrate all the accomplishments of the community across these two decades, OCB is convening a one-day virtual symposium on November 18, 2026. The symposium will highlight scientific discoveries, game-changing technologies, and lessons learned from the perspective of OCB community members.

This 20th anniversary symposium will feature the following four topics, which have seen a lot of growth in OCB, particularly in the last decade:

Air-Sea Interactions
Biological Carbon Pump
Ocean Carbon Removal
Ocean Metabolism (featuring programmatic developments across GEOTRACES, OCB, and the newly emerging BioGeoSCAPES)

Speakers and panelists will be announced soon.

The November 18 event will start at 11 am (Eastern Standard Time) and run approx. 7 hours with numerous breaks.

Learn more and register

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

Register for the 7th DMS(P) Symposium: Sulfur Carbon Nexus in the SOLAS Sphere

Posted by mmaheigan

· Monday, May 18th, 2026

A joint workshop with SCOR, SOLAS, and Schmidt Sciences: Climate

October 12-15, 2026 in person at Bigelow Laboratory (Boothbay Harbor, Maine) and online.

The organosulfur compound dimethylsulfoniopropionate (DMSP) ignited an entire subfield of biogeochemistry to investigate the precursor of the “anti-greenhouse gas” dimethylsulfide (DMS). Since then, decades of research have unveiled the importance of DMS(P), and related compounds, to carbon cycling and air-sea interactions, and ultimately an outsized contribution to global climate. This Symposium will bring together a diversity of researchers interested in synthesizing the inextricable link of the sulfur and carbon cycles from cellular to global scale processes. OCB will provide partial support for this workshop, to be held at the Bigelow Laboratory later this year in partnership with Schmidt Sciences: Climate, SOLAS, and SCOR.

Leads: Stephen Archer (Bigelow Laboratory for Ocean Sciences), Erin McParland (Oregon State University), David Kieber (State University of New York) and Patricia Matrai (Bigelow Laboratory for Ocean Sciences), Katherina Petrou (University of Technology Sydney) and Elisabeth Deschaseaux (Institut de Ciènces del Mar).

This will be the first DMS(P) Symposium gathering since the 6th Symposium, held in Barcelona, Spain, in 2014! More information will continue to be updated on the Symposium webpage.

The sessions are:
Atmosphere: carbon – sulfur chemistry and aerosols
Air-sea exchange of carbon – sulfur compounds
Carbon-sulfur ocean processes: molecular to ecosystem to global
Translating observations into models: biogeochemistry to climate

Registration is now open.

Learn more and register

New OCSIF Subcommittee

Posted by mmaheigan

· Thursday, May 14th, 2026

This new OCSIF OCB subcommittee focused on identifying and addressing uncertainties in the seawater carbonate system and increasing measurement inter-comparability, now has a full membership – see the new members and more info here.

Benthic Models & Data Synthesis

Posted by mmaheigan

· Friday, May 8th, 2026

New OCB Sediment Biogeochemistry Model Intercomparison Project (SedMIP) Working Group seeking input

Do you use and/or build benthic models? With the goal of designing a MIP for benthic models, OCB’s SedMIP WG is conducting an inventory of existing benthic models and would benefit from your feedback on model applications, components, and inputs/outputs to inform our planning process. Please take a few moments to share your input.

Two papers published by the OCB Benthic Ecosystem & Carbon Synthesis (BECS) WG

Schultz, C., Luo, J. Y., Brady, D. C., Fulweiler, R. W., Long, M. H., Petrik, C. M., Testa, J. M., Benway, H. M., Burdige, D., Cecchetto, M. M., Elegbede, I., Evans, N., Frenzel, A., Gillen, K., Herbert, L. C., Hirsh, H. K., Lessin, G., Levin, L., Maiti, K., Malkin, S., Mincks, S. L., Nmor, S., Pham, A., Pinckney, J., Rabouille, C., Rahman, S., Rakshit, S., Ray, N. E., Sasaki, D. K., Siedlecki, S. A., Somes, C., Stubbins, A., Sulpis, O., Trevisan, C., Xu, Y., Yin, H. (2025). Elucidating the role of marine benthic carbon in a changing world. Global Biogeochemical Cycles, 39, e2025GB008643. https://doi.org/10.1029/2025GB008643.

Siedlecki, S., Nmor, S., Lessin, G., Kearney, K., Rakshit, S., Petrik, C., Luo, J., Schultz, C., Sasaki, D., Gillen, K., Pham, A., Somes, C., Brady, D., Testa, J., Rabouille, C., Elegbede, I., and Sulpis, O. (2025). Sediment Biogeochemistry Model Intercomparison Project (SedBGC_MIP): motivation and guidance for its experimental design, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-1846.

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.

Author Archive for mmaheigan

New OCB Sediment Biogeochemistry Model Intercomparison Project (SedMIP) Working Group seeking input

Two papers published by the OCB Benthic Ecosystem & Carbon Synthesis (BECS) WG

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