Author Archive for mmaheigan

OCB2025 – registration paused

Posted by mmaheigan 
· Monday, April 21st, 2025 

We are paused for in person registrations due to unexpected budget uncertainties. Please hold on making travel arrangements.
-->If you have already registered and we are able to continue in person you will not lose your place.
If we need to change to a virtual workshop all paid registration fees will refunded.
-->We will hold the workshop on these same dates virtually if unable to proceed with an in person workshop.
-OCB Team

The OCB2025 Summer Science Workshop will take place Tuesday, June 3 to Friday, June 6, 2025.

In person location (on hold) NASA Ames Conference Center (Mountain View, CA)

OCB2025 Plenary Sessions

Constraining the dark ocean carbon cycle: Implications for ocean carbon budgets? (Co-chairs: Anne Dekas, Anela Choy, Jeff Bowman, Randie Bundy)

Rivers to coasts: Biogeochemical linkages and environmental resilience (joint with North American Carbon Program) (Co-chairs: Fei Da, Kanchan Maiti, Shaily Rahman, Libby Larson, David Butman)

Rapidly changing systems (Co-chairs: Kristen Krumhardt, Rachel Stanley, Melissa Melendez)

Bridging scales in the ocean carbon cycle (Co-chairs: Zachary Erickson, Tim DeVries, Roo Nicholson, Daniel Whitt, Dreux Chappell)

Learn more and register

Leaky Deltas workshop summary

Posted by mmaheigan 
· Thursday, April 10th, 2025 

The Leaky Deltas OCB workshop was held 17-20 March 2025 at Louisiana State University, in Baton Rouge, USA, which is situated within the Mississippi River delta. We brought together 57 members of the research community who study river deltas in the context of the global carbon cycle. The goal of the workshop was to create a community consensus on the state of delta carbon cycle science, identify critical knowledge gaps, and brainstorm opportunities and priorities for future research efforts. Participants ranged in career stage from graduate student to senior scientist, and from disciplines ranging from biogeochemistry to geomorphology, river scientists to oceanographers; and scientists using a variety of methodological approaches.

The workshop included five oral sessions, four breakout sessions, numerous opportunities for discussion over meals and coffee breaks, a trip to the LSU Center for River Studies, and a workshop dinner. The breakout sessions were formatted to encourage discussion among interdisciplinary groups of scientists at different career stages. During breakout session 1, participants were randomly assigned to groups that spanned career stages and expertise. This session was aimed at identifying grand challenges in delta carbon cycle science. Breakout session 2 had a disciplinary focus, where we broke out into groups of biogeochemistry, geomorphology, modeling, and ecosystems. Breakout session 3 was broken out into groups based on physical domains of the delta: river, wetlands, subaqueous delta, shelf, and continental slope. A highlight of day three was a field trip to the LSU Center for River Studies, where workshop participants were guided on a tour of the historical changes of the Mississippi River Delta, as well as the large-scale physical model of the delta. On the fourth and final day of the workshop, we had short break-out sessions and reconvened as a whole to synthesize ideas and circle back to the workshop objectives.

In summary, the workshop resulted in a consensus on the key knowledge gaps and research grand challenges, which included constraining the composition of organic matter, the timescales of geomorphic processes, biogeochemical reaction rates, impacts of human perturbations and extreme events, and challenges in monitoring deltaic processes. Workshop participants now have the task of writing a position paper that summarizes these grand research challenges, identifies the data needed to address these challenges, and recommends a framework and directions for future research. One outcome of the workshop included the structure and organization for this paper. The early career workshop participants will also lead an early-career-led perspective paper that discusses ideas for integrating new technologies and methodologies to address these grand challenges and identifies future challenges for the delta science community.

Learn more about this workshop

New: Connecting Observations to Models

Posted by mmaheigan 
· Thursday, April 10th, 2025 

Ombres, E., H. Benway, K. Bisson, A. Larkin, L. Perotti, L. Wright-Fairbanks (eds.) (2024). Connecting Observations to Models: Biogeochemical Observing and Modeling Workshop, 2024 Summary Report and Suggested Steps Forward. Published Date: 2024 Series: NOAA technical memorandum OAR-OAP ; 6, DOI: https://doi.org/10.25923/wpdj-ja69

Microbial Iron limitation in the ocean’s twilight zone

Posted by mmaheigan 
· Monday, March 31st, 2025 

How deep in the ocean do microbes feel the effects of nutrient limitation? Microbial production in one third of the surface ocean is limited by the essential micronutrient iron (Fe). This limitation extends to at least the bottom of the euphotic zone, but what happens below that?

In a study that recently published in Nature we investigated the abundance and distribution of siderophores, small metabolites synthesized by bacteria to promote Fe uptake. When environmental Fe concentrations become limiting and microbes become Fe deficient, some bacteria release siderophores into the environment to bind iron and facilitate its uptake. Siderophores are therefore a window into how microbes “see” environmental Fe. We found that siderophore concentrations were high in low Fe surface waters, but surprisingly we also found siderophores to be abundant in the twilight zone (200-500 m) underlying the North and South Pacific subtropical gyres, two key ecosystems for the marine carbon cycle. In shipboard experiments with siderophores labeled with the rare 57Fe isotope, we found rapid uptake of the label in twilight zone samples. After removing 57Fe from the 57Fe-siderophores complex, bacteria released the now unlabeled siderophores back into seawater to complex additional Fe (Figure. 1).

Figure 1: Iron-siderophore cycling in the twilight zone. When the seawater becomes Fe-deficient, some bacteria are able to synthesize siderophores and release them into the environment (middle left). These metabolites bind Fe (middle right) and the Fe-siderophore complex is taken up by bacteria using specialized TonB dependent transporters (TBDT; bottom right). Inside the cell, Fe is recovered from the Fe-siderophore complex (bottom left) and the siderophore excreted back into the environment to start the cycle anew.

Our results show that in large parts of the ocean microbes feel the effects of nutrient limitation deep in the water column, to at least 500 m. This greatly expands the region of the ocean where nutrients limit microbial metabolism. The effects of limitation this deep in the water column are unexplored, but twilight zone Fe deficiency could have unanticipated consequences for the efficiency of the ocean’s biological carbon pump.

 

Authors
Jingxuan Li, Lydia Babcock-Adams and Daniel Repeta
(all at Woods Hole Oceanographic Institution)

How do ocean microbes share the job of denitrification?

Posted by mmaheigan 
· Monday, March 31st, 2025 

Denitrification is a crucial multi-step process for ecosystem productivity and sustainability because some of its steps can result in the loss of the essential nutrient nitrogen or the production of greenhouse gas nitrous oxide. We do not understand why microbial functional groups conducting different steps of denitrification can coexist in the ocean and why certain groups are more abundant than others.

In a recent study published in PNAS, we uncover ecological mechanisms that govern the coexistence of these microbes. For the microbial groups utilizing different nitrogen substrates, the “stronger” groups rely on the “weaker” groups to feed them nitrogen (with respect to the organic substrates that they compete for), enabling them to coexist. For the groups competing for the same nitrogen substrates, microbes that invest more to build longer denitrification steps win the competition when nitrogen is limiting, but lose the game when nitrogen is repleted and organic carbon is limiting. The spatial and temporal variability of nutrients in the ocean allows these microbes to be observed in the same water mass.

Figure caption: Temporal and spatial heterogeneity in nutrients promotes the coexistence of functionally diverse denitrifiers in the ocean.

These hypothesized coexistence patterns help us predict where and when nitrogen loss and nitrous oxide production may occur. As human activities continue to alter marine nutrient balances, these predictions help us better anticipate ocean responses and design better strategies for mitigating negative anthropogenic impacts on the ocean.

 

Authors
Xin Sun (Carnegie Institution for Science) @xinsun-putiger.bsky.social
Emily Zakem (Carnegie Institution for Science) @carnegiescience.bsky.social

Read the latest SOLAS eNews

Posted by mmaheigan 
· Monday, March 10th, 2025 

SOLAS Update — Newsletter April 2025

Launch of the SOLAS Europe Regional Panel

Read this and more here

The ocean is shifting toward phosphorus limitation

Posted by mmaheigan 
· Friday, February 28th, 2025 

Biogeochemical models predict that ocean warming is weakening the vertical transport of nutrients to the upper ocean, with severe implications for marine productivity. However, nutrient concentrations across the ocean surface often fall below detection limits, making it difficult to observe long-term changes.

In a recent study in PNAS, we analyzed over 30,000 nitrate and phosphate depth profiles observed between 1972 and 2022 to quantify nutricline depths, where nutrient concentrations are reliably detected. These depths accurately represent nutrient supplies in a global model, allowing us to assess long-term trends. Over the past five decades, upper ocean phosphate has mostly declined worldwide, while nitrate has remained mostly stable. Model simulations support that this difference is likely due to nitrogen fixation replenishing upper ocean nitrate, whereas phosphate has no equivalent biological source.

Figure caption: Five decades of global and regional nutricline depth data reveal declining phosphate-to-nitrate trends. Nutricline depths were defined based on threshold concentrations of 3 μmol kg−1 nitrate (TNO3) and 3/16 μmol kg−1 phosphate (TPO4). Site-specific trends were quantified for each unique pair of geographic coordinates where sufficient data was available (TNO3, n = 1,859 sites; TPO4, n = 1,641 sites). Shown are 95% confidence intervals (CI95%) calculated for each median trend by generating 10,000 bootstrap samples. The curves over the histograms depict the kernel densities. The sets of error bars from top to bottom are the interquartile ranges of TNO3 and TPO4 from a monthly climatology, the total observations, and the total observations with added measurement error.

These findings suggest that the ocean is becoming more limited in phosphorus. This decline could make phytoplankton less nutritious for marine animals. Fish larvae growth rates correlate with phosphorus availability in the ecosystem, so intensifying phosphorus limitation may greatly impact fisheries worldwide.

 

Authors
Skylar Gerace (University of California, Irvine)
Jun Yu (University of California, Irvine)
Keith Moore (University of California, Irvine)
Adam Martiny (University of California, Irvine)

@UCI_OCEANS

Persistent bottom trawling impairs seafloor carbon sequestration

Posted by mmaheigan 
· Friday, February 28th, 2025 

Bottom trawling, a fishing method that uses heavy nets to catch animals that live on and in the seafloor, could release a large amount of organic carbon from seafloor into the water, that metabolizes to CO2 then outgasses to the atmosphere. The magnitude of this indirect emission has been heavily debated, with estimates spanning from negligibly small to global climate relevant. Thus, a lack of reliable data and insufficient understanding of the process hinders management of bottom trawling for climate protection.

We set out to solve this problem in two steps. First, we analyzed a large field dataset containing more than 2000 sediment samples from one of the most intensely trawled regions globally, the North Sea. We identified a trawling-induced carbon reduction trend in the data, but only in samples taken in persistently intensively trawled areas with multi-year averaged swept area ratio larger than 1 yr-1. In less intensely trawled areas, there was no clear effect. In a second step, we applied numerical modelling to understand the processes behind the observed change (Fig. 1). Our model results suggest that bottom trawling annually releases one million tonnes of CO2 in the North Sea and 30 million tonnes globally. Along with sediment resuspension in the wake of the trawls, the main cause for altered sedimentary carbon storage is the depletion of macrofauna, whose locomotion and burrowing effectively buries freshly deposited carbon into deeper sediment layers. By contrast, macrofauna respiration is reduced owing to trawling-caused mortality, partly offsetting the organic carbon loss. Following a cessation of trawling, the simulated benthic biomass can recover in a few years, but the sediment carbon stock would take several decades to be restored to its natural state.

Figure 1. (a) Benthic–pelagic coupling in a natural system. (b) Processes involved in bottom trawling. (c) Model-estimated source and sink terms of organic carbon in surface sediments in the No-trawling (solid fill, n = 67 annual values for 1950–2016) and trawling (pattern fill, n = 67 ensemble-averaged values for 1950–2016) scenarios of the North Sea. © 2024, Zhang, W. et al., CC BY 4.0.

Marine conservation strategies traditionally favor hard bottoms, such as reefs, that are biologically diverse but accumulate limited amounts of organic carbon. Our results indicate that carbon in muddy sediments is more susceptible to trawling impacts than carbon in sand and point out a need to safeguard muddy habitats for climate protection. Our methods and results might be used in the context of marine spatial planning policies to gauge the potential benefits of limiting or ending bottom trawling within protected areas.

 

Zhang, W., Porz, L., Yilmaz, R. et al. Long-term carbon storage in shelf sea sediments reduced by intensive bottom trawling. Nat. Geosci. 17, 1268–1276 (2024). https://doi.org/10.1038/s41561-024-01581-4

Authors
Wenyan Zhang (Hereon)
Lucas Porz (Hereon)
Rümeysa Yilmaz (Hereon)
Klaus Wallmann (GEOMAR)
Timo Spiegel (GEOMAR)
Andreas Neumann (Hereon)
Moritz Holtappels (AWI)
Sabine Kasten (AWI)
Jannis Kuhlmann (BUND)
Nadja Ziebarth (BUND)
Bettina Taylor (BUND)
Ha Thi Minh Ho-Hagemann (Hereon)
Frank-Detlef Bockelmann (Hereon)
Ute Daewel (Hereon)
Lea Bernhardt (HWWI)
Corinna Schrum (Hereon)

PACE Hackweek

Posted by mmaheigan 
· Friday, February 28th, 2025 

The NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) Project and Ocean Carbon & Biogeochemistry (OCB) Program are hosting a second PACE Data Hackweek. This is a one-week social coding event that will include a combination of lectures, tutorials, and project work (data processing and analysis) that will kick-start research using the Earth science data streams generated by the OCI, SPEXone, and HARP2 instruments on board the observatory. Other projects that combine PACE data with other satellite data, such as from EarthCARE, TROPOMI, or SWOT are also encouraged. Participants will gain behind-the-scenes access to all aspects of PACE.

  • Data and compute resources will be provided on an AWS cloud platform, and tutorials will be conducted in Python. Participants must have some experience (i.e. able to work independently) with Python in order to benefit from this Hackweek. *We will also consider applicants who are proficient in a different programming language who are transitioning to Python.*
  • We anticipate accepting ~40 participants (from student to professional career stages).
  • All lectures and tutorials will be recorded and made available on the course web page.

3-7 August 2025
University of Maryland Baltimore County (UMBC)

Learn more and apply by March 24

Welcoming new SSC members!

Posted by mmaheigan 
· Friday, February 14th, 2025 

Welcome to the four new and one continuing SSC members!

Jason Graff (Oregon State Univ.) (2027) Biooptics, satellite remote sensing

Bror Jönsson (Univ. New Hampshire) (2027) – biological production across land-open ocean continuum, coastal ocean acidification, interactions between physical dynamics in the upper ocean and biological production, phytoplankton dynamics, and air-sea exchange, connectivity combining observations, analysis of large dataset, remote sensing and algorithm development

Jonathan Lauderdale (Massachusetts Inst. of Technology) (2027) –  biogeochemistry, global carbon, nutrient, and trace metal cycles, past climates, physical oceanography, and processes occurring in high latitude regions such as the Southern Ocean.

Sarah Mincks (Univ. Alaska Fairbanks) (2027) benthic-pelagic coupling, marine organism-mediated carbon cycling

Shaily Rahman (Univ Colorado, Boulder) (2027, second term) – marine biogeochemistry and sedimentary processes

Thank you to Jeff Bowman (SIO), Susanne Craig (NASA GSFC), Tim DeVries (UCSB), and Zachary Erickson (NOAA PMEL) for your OCB work over the past three years!

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Copyright © 2025 - OCB Project Office, Woods Hole Oceanographic Institution, 266 Woods Hole Rd, MS #25, Woods Hole, MA 02543 USA Phone: 508-289-2838  •  Fax: 508-457-2193  •  Email: ocb_news@us-ocb.org

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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.