SOLAS Update — Newsletter March 2025
The Influence of Natural, Anthropogenic, and Wildfire Sources on Iron and Zinc Aerosols Delivered to the North Pacific Ocean
Global Carbonate Chemistry Gradients Reveal a Negative Feedback on Ocean Alkalinity Enhancement
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
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)
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.
3-7 August 2025
University of Maryland Baltimore County (UMBC)
Learn more and apply by March 24
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!
The global ocean dampens the anthropic CO2 increase in the atmosphere by absorbing around 25% of the carbon emitted each year. Of the processes involved in exchanges of energy and mass between ocean and atmosphere that may impact this carbon sink, rainfall has never been systematically and comprehensively quantified. A study recently published in Nature Geosciences suggests that about 6% of the global ocean CO2 sink is mediated by rainfall.
Figure 1. Histograms of 2008-2018 global ocean (60°S-60°N) CO2 sink increase due to rain-induced turbulence only, rain-induced dilution only, the resultant of turbulence and dilution (named the interfacial effect), the wet deposition of CO2 absorbed during the raindrops fall and the total (interfacial plus wet deposition) using 1-h rain rates from IMERG (blue) and ERA5 (red). The rain-induced dilution is diagnosed from a satellite-derived empirical relationship (full) or a 1D physical model (stripes). Figure based on Parc et al. (2024) Table 1.
The exchange of CO2 at the ocean interface is controlled by chemical, physical, and biological properties and processes. Rainfall, one of these processes, can alter the properties of the ocean surface and perturb the carbon exchange in three ways:
(i) Turbulence: Raindrops increase the momentum transfer to the ocean and generate turbulence enhancing the renewal of interfacial water (first column in Fig. 1). This tends to increase both in- and out-gassing. The impact of this effect alone is weak because wind dominates the generation of turbulence in the ocean;
(ii) Dilution + Interfacial: Rain dilutes and cools the near surface waters, which perturbs chemical equilibria and leads the ocean to absorb more CO2 (second column in Fig. 1). The result of dilution and turbulence effects of rain, which is named “Interfacial”, is a clear increase in global CO2 sink (third column in Fig. 1);
(iii) Wet deposition: Finally, raindrops directly inject CO2 molecules into the ocean that they absorbed during their fall through the atmosphere (fourth column in Fig. 1).
Using two rainfall datasets (the satellite-derived product IMERG and the ERA5 reanalysis) and two ways to quantify the rain-induced dilution, the authors show that rain increases the ocean carbon sink by 140 to 190 million tonnes of carbon per year, equivalent to 5% to 7% of the 2.66 billion tonnes of carbon absorbed annually by the oceans. Because rainfall amounts and patterns will change in the future, impacting the ocean carbon sink, these results call for explicitly including rain effects in the annual global carbon budget estimates.
Authors
Laëtitia Parc (Laboratoire de Météorologie Dynamique)
Hugo Bellenger (Laboratoire de Météorologie Dynamique)
Laurent Bopp (Laboratoire de Météorologie Dynamique) @bopplaurent.bsky.social
Xavier Perrot (Laboratoire de Météorologie Dynamique)
David T. Ho (University of Hawaii at Manoa; [C]Worthy) @davidho.bsky.social
Parc, L., Bellenger, H., Bopp, L., Perrot, X., and Ho, D. T. Global ocean carbon uptake enhanced by rainfall.Nat. Geosci. 17, 851–857 (2024). https://doi.org/10.1038/s41561-024-01517-y
What drives carbon from the atmosphere to the deep ocean? The journey of phytoplankton-derived carbon is critical in the global carbon cycle, yet the influence of interacting bacteria in degrading lipid-rich particles during their descent has remained a mystery—until now.
Using an innovative combination of nano-scale lipidomics and microscopy, researchers investigated how bacteria target and degrade diverse lipid molecules in sinking oceanic particles. The study, published in Science, revealed that bacteria exhibit distinct dietary preferences, governed by their lipid-degrading genes rather than taxonomic affiliation. Interactions among bacteria influenced both degradation rates and timing, together reshaping our view on the efficiency of lipid transport to the ocean depths. These findings were incorporated into a mathematical model, revealing how microbial communities could regulate the carbon transfer efficiency.
This research enhances our understanding of the ocean’s carbon pump, highlighting the pivotal role of bacterial communities in carbon sequestration. By uncovering how microbial interactions affect carbon transfer, these findings improve climate models and support the development of strategies to mitigate atmospheric CO2.
Authors
Lars Behrendt (Uppsala University, Sweden)
Benjamin van Mooy (Woods Hole Oceanographic Institution)
Twitter: LarsBehrendt4
Bluesky: @belab1.bsky.social
Marine microeukaryotes are important players in ocean biogeochemistry, contributing to primary production and respiration. Their diversity and function is generally better understood in coastal regions, and harder to study in offshore locations, especially at depth. The CASHEW (Clio Atlantic Sectional Hoedown Ending at Woods Hole) expedition aimed to characterize microeukaryotic community composition and functionality along a gradient in the western North Atlantic Ocean.
Autonomous underwater vehicle (AUV) Clio is a refrigerator sized robot that was used to collect biological material throughout the water column (see photo). This cruise was Clio’s first ocean transect, before this expedition Clio was in a testing phase. Clio was used to survey the upper 1 km of the water column. At one station, Clio was successfully sent 4.1 km down to the sea floor! We used the biomass collected to analyze metatranscriptomes and metaproteomes, which allowed us to examine the identity and metabolic profiles of marine microorganisms.
One of the most interesting aspects of this study was the similarities and differences in biological patterns based on whether transcripts or proteins were considered. While eukaryotic community breakdown was generally consistent between transcripts and proteins, there were more clear signs of heterotrophic taxa at depth in the protein fraction. Transcripts also indicated nitrate stress in continental margin waters with phosphate stress offshore, potentially a result of aerosol dust introducing iron and nitrogen. This study highlights the value of complementary omic datasets when reconstructing microbial community metabolism and showcases the degree of omic resolution possible with AUV efforts.
Authors
Natalie Cohen (University of Georgia Skidaway Institute of Oceanography)
Mak Saito (Woods Hole Oceanographic Institution)
Leaky Deltas webinar
Speakers: Gerrit Trapp-Müller ( SoMAS, Stony Brook University), Fei Da (Princeton University), Gabriella Akpah Yeboah (University of Ghana)
February 4, 10a eastern REGISTER
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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.