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Archive for ocean carbon uptake and storage – Page 2

Marine plant metabolites give marine microbes gas

Posted by mmaheigan

· Friday, October 17th, 2025

A recent study in Nature Geosciences observed high concentrations of methane overlying permeable (sand) sand sediments in bays in Denmark and Australia. These environments are not one would expect to see methane because they are highly oxygenated and the high concentrations of sulfate in seawater typically inhibit methanogenesis. The authors showed that the methane was not being imported from local groundwater using geochemical methods. Using a combination of biogeochemical, microbial isolation, culturing and genomic approaches, revealed that methane was being produced by fast growing microbes resistant to oxygen exposure using plant produced substrates such as dimethylsulfide and amines. This work shows that where marine plants such as seaweed and seagrass grow and accumulate there may be high and sporadic production of methane. This has implications for how we account for the carbon sequestering capacity of coastal environments and the climate impact of increasing algal blooms such as coastal Ulva and the great sargassum bloom.

Authors
Perran Cook (Monash University)
Ning Hall (University of free spirit)

How does a persistent eddy impact the biological carbon pump?

Posted by mmaheigan

· Friday, September 26th, 2025

The Lofoten Basin Eddy (LBE) is a unique and persistent anticyclonic feature of the Norwegian Sea that stirs the water column year-round. However, its impact on biogeochemical processes that influence region carbon storage, including carbon fixation, particle aggregation and fragmentation, and remineralization, has remained largely unknown.

Figure caption: (a) Map of the Lofoten Basin Eddy study region including locations of 1886 profiles from 22 Biogeochemical-Argo floats (2010–2022) and a heatmap showing the relative extent of the LBE influence zone over the timeseries. (b–d) Mean monthly profiles and the difference (Δ) determined as inside minus outside the LBE influence zone of the mass concentration of particulate organic carbon in small particles (POC_s). Arrows indicate key mechanisms regulating the regional biological carbon.

Using 12 years of data from Biogeochemical-Argo floats and satellite altimetry to track eddy movements, Koestner et al. (2025) examined how the LBE influences the seasonal transport of organic carbon from surface waters to the deep ocean. While the LBE can enhance carbon export during certain months, like during spring shoaling and late autumn subduction, it generally reduces the efficiency of the biological carbon pump. Inside the eddy, warmer subsurface waters and slower-sinking particles often lead to more respiration and remineralization, meaning less carbon reached the deep sea.

The LBE’s persistent influence on organic carbon cycling could affect regional climate feedbacks and marine ecosystems, including key fisheries in Norway. Understanding how features like the LBE modulate carbon sequestration is vital for improving climate models and managing ocean resources in a warming Arctic.

Authors
Daniel Koestner (University of Bergen)
Sophie Clayton (National Oceanography Centre)
Paul Lerner (Columbia University)
Alexandra E. Jones-Kellett (MIT & WHOI)
Stevie L. Walker (University of Washington)

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)

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)

OA could boost carbon export by appendicularia

Posted by mmaheigan

· Wednesday, December 4th, 2024

Gelatinous zooplankton comprise a widespread group of animals that are increasingly recognized as important components of pelagic ecosystems. Historically understudied, we have little knowledge of how much key taxa contribute to carbon fluxes. Likewise, there’s a critical knowledge gap of the impact of ocean change on these taxa.

Appendicularia are the most abundant gelatinous zooplankton in the world oceans. Their population dynamics display typical boom-and-bust characteristics, i.e. high grazing rates in combination with a short generation time and life cycle, results in intense blooms. The most prominent feature of appendicularians is their mucous feeding-structure (“house”), which is produced and discarded several times per day. These sinking houses can contribute substantially to carbon export.

Figure 1: Influence of ocean acidification on the Appendicularia Oikopleura dioica and carbon export. Appendicularian populations display typical boom-and-bust characteristics, resulting in intense blooms. The sinking of appendicularians’ discarded mucous feeding-structure several times per day can contribute substantially to carbon export. Low pH conditions (as expected for future ocean acidification extreme events) enhanced its population growth and contribution to carbon fluxes shown above (red lines/diamonds) vs ambient (blue lines/diamonds).
(Figure sources: Picture by Jean-Marie Bouquet, data plots from Taucher et al. (2024): The appendicularian Oikopleura dioica can enhance carbon export in a high CO2 ocean. Global Change Biology, doi:10.1111/gcb.17020)

A recent study in Global Change Biology quantified how much appendicularia can contribute to carbon export via the biological pump, and how this carbon flux could markedly increase under future ocean acidification and associated extreme pH events.

The findings are based on a large-volume in situ experimental approach that allowed observing natural plankton populations and carbon export under close-to-natural conditions for almost two months. Thereby, O. dioica population dynamics could be directly linked to sediment trap data to quantify the influence of this key species on carbon fluxes at unprecedented detail. During the appendicularia bloom up to 39% of total carbon export was attributed to them.

The most striking finding was that high CO₂ conditions elevated carbon export by appendicularia increased by roughly 50%. Appendicularians physiologically benefit from low pH conditions, giving them a competitive advantage over other zooplankton, allowing them to contribute to a disproportionally large role in carbon export from the ecosystem.

Authors
Jan Taucher (GEOMAR)
Anna Katharina Lechtenbörger (GEOMAR)
Jean-Marie Bouquet (University of Bergen)
Carsten Spisla (GEOMAR)
Tim Boxhammer (GEOMAR)
Fabrizio Minutolo (GEOMAR)
Lennart Thomas Bach (University of Tasmania)
Kai T. Lohbeck (University of Konstanz)
Michael Sswat (GEOMAR)
Isabel Dörner (GEOMAR)
Stefanie M. H. Ismar-Rebitz (GEOMAR)
Eric M. Thompson (University of Bergen)
Ulf Riebesell (GEOMAR)

The fate of the 21st century marine carbon cycle could hinge on zooplankton’s appetite

Posted by mmaheigan

· Wednesday, September 11th, 2024

Both climate change and the efforts to abate have the potential to reshape phytoplankton community composition, globally. Shallower mixed layers in a warming ocean and many marine CO₂ removal (CDR) technologies will shift the balance of light, nutrients, and carbonate chemistry, benefiting certain species over others. We must understand how such shifts could ripple through the marine carbon cycle and modify the ocean carbon reservoir. Two new publications in Geophysical Research Letters and Global Biogeochemical Cycles highlight an often over looked pathway in this response: The appetite of zooplankton.

We have long known that the appetite of zooplankton—i.e. the half-saturation concertation for grazing—varies dramatically. This variability is largely based on laboratory incubations of specific species. An open-ocean perspective has been much more elusive. Using two independent inverse modelling approaches, both studies reached the same conclusion: Even at the community level, the appetite of zooplankton in the open-ocean is incredibly diverse.

Moreover, variability in zooplankton appetites maps well onto the biogeography of phytoplankton species. As these phytoplankton niches evolve, the composition of the zooplankton will likely follow. To help understand the impact of this response on the biological pump, we compared two models, one with only two types of zooplankton, and another with an unlimited amount, each with different appetites, all individually tuned to their unique environment. Including more realistic diversity reduced the strength of the biological pump by 1 PgC yr^-1.

Figure Caption. A) Variability in the abundance and characteristic composition of phytoplankton drives B) large differences in the associated appetite and characteristic composition of zooplankton in two independent inverse modelling studies. C) When more realistic diversity in the appetite of zooplankton is simulated in models, the strength of biological pump is dramatically reduced.

That is the same order as the most optimistic scenarios for ocean iron fertilization. This means that when simulating the efficacy of many CDR scenarios, the bias introduced by insufficiently resolved zooplankton diversity could be just as large as the signal. Moving forward, it is imperative to improve the representation of zooplankton in Earth System Models to understand how the marine carbon sink will respond to inadvertent and deliberate perturbations.

Authors (GRL):
Tyler Rohr (The University of Tasmania; Australian Antarctic Program Partnership)
Anthony Richardson (The University of Queensland; CSIRO)
Andrew Lenton (CSIRO)
Matthew Chamberlain (CSIRO)
Elizabeth Shadwick (Australian Antarctic Program Partnership; CSIRO)

Authors (GBC):
Sophie Meyjes (Cambridge)
Colleen Petrick (Scripps Institute of Oceanography)
Tyler Rohr (The University of Tasmania; Australian Antarctic Program Partnership)
B.B. Cael (NOC)
Ali Mashayek (Cambridge)

Inorganic carbon outwelling as important blue carbon sink

Posted by mmaheigan

· Wednesday, May 29th, 2024

Blue carbon ecosystems—mangroves, saltmarshes, and seagrass meadows—carbon sequestration powerhouses that can help us mitigate climate change. For many years, our community has focused on studying and quantifying organic carbon storage in the soils of these ecosystems and crediting it as Blue Carbon in carbon markets.

A new paper in Nature Communications reveals that much of that carbon sequestered by mangroves and saltmarshes is actually exported as inorganic carbon to the ocean. Inorganic carbon export dominates blue carbon budgets and rivals or even surpasses carbon stored in soils. Inorganic carbon exports had an alkalinity: dissolved inorganic carbon ratio of 0.8 ± 0.2, impacting the carbonate system and carbon cycling along the coast. Most of the inorganic carbon is exported as bicarbonate which stays permanently dissolved in the ocean and is therefore a permanent atmospheric carbon sink. When we ignore inorganic carbon export, we highly underestimate the potential of mangroves and saltmarshes to mitigate climate change. Consequently, inorganic carbon export should be integrated into blue carbon frameworks to adequately inform carbon markets, which encourage landowners to restore and preserve mangrove and saltmarsh ecosystems.

Authors
Gloria M. S. Reithmaier (University of Gothenburg) Twitter: @GReithmaier@Barefoot_Lab
Alex Cabral (University of Gothenburg)
Anirban Akhand (Hong Kong University of Science and Technology)
Matthew J. Bogard (University of Lethbridge)
Alberto V. Borges (University of Liège)
Steven Bouillon (KU Leuven)
David J. Burdige (Old Dominion University)
Mitchel Call (Southern Cross University)
Nengwang Chen (Xiamen University)
Xiaogang Chen (Westlake University)
Luiz C. Cotovicz Jr (Leibniz Institute for Baltic Sea Research)
Meagan J. Eagle (U.S. Geological Survey)
Erik Kristensen (University of Southern Denmark)
Kevin D. Kroeger (U.S. Geological Survey)
Zeyang Lu (Xiamen University)
Damien T. Maher (Southern Cross University)
Lucas J. Pérez-Lloréns (University of Cádiz)
Raghab Ray (University of Tokyo)
Pierre Taillardat (National University of Singapore)
Joseph J. Tamborski (Old Dominion University)
Rob C. Upstill-Goddard (Newcastle University)
Faming Wang (Chinese Academy of Sciences)
Zhaohui Aleck Wang (Woods Hole Oceanographic Institution)
Kai Xiao (Southern University of Science and Technology)
Yvonne Y. Y. Yau (University of Gothenburg)
Isaac R. Santos (University of Gothenburg)

Carbon sequestration by the biological pump is not exclusive to the deep ocean

Posted by mmaheigan

· Tuesday, April 16th, 2024

The biological carbon pump plays a key role in ocean carbon sequestration by transporting organic carbon from the upper ocean to deeper waters via three broad processes: the sinking of organic particles, vertical migration of organisms, and physical mixing. Most studies assume that century-scale carbon sequestration occurs only in the deep ocean, thus have missed sequestration that happens in the water column above 1,000m.

A recent publication reassessed the biological pump’s century-scale (≥100 years) carbon sequestration fluxes throughout the water column, by implementing the concept of ‘continuous vertical sequestration’ (CONVERSE). The resulting CONVERSE estimates were up to three times higher than those estimated at 1,000 m. This method shows that not only are these fluxes higher than previously thought, but also that vertical migration and physical mixing, which are generally neglected, make a significant contribution (20-30%) to carbon sequestration.

The CONVERSE method provides a new metric for calculations of the biological pump’s century-scale carbon sequestration flux that can be used to diagnose future changes in carbon sequestration fluxes in prognostic models of ocean biogeochemistry.

Interested in learning more? View more results and figures here.

Authors
Florian Ricour (Institute of Natural Sciences, Belgium)
Lionel Guidi (CNRS and Sorbonne University, France)
Marion Gehlen (CEA, CNRS and Paris-Saclay University, France)
Timothy Devries (University of California at Santa Barbara, USA)
Louis Legendre (Sorbonne University, France)

@LionelGuidi
@ComplexLov
@CNRS_INSU

Tiny parasites, big impact: Species networks and carbon recycling in an oligotrophic ocean

Posted by mmaheigan

· Tuesday, March 12th, 2024

Parasites are everywhere in the ocean. Including the microbial realm where a diverse, widespread group of protist parasites (Syndiniales) infect and kill a range of hosts, such as dinoflagellates, radiolarians, and even larger zooplankton. A complete Syndiniales infection cycle is only 2-3 days. First, the parasite is a free-living spore. Once inside a host, the parasite consumes the host’s carbon and becomes a larger multicellular organism (a trophont) eventually causing the host to burst open and release hundreds of new spores.

Like viruses, parasite lysis is expected to reroute organic carbon to the microbial loop, potentially decreasing the amount of carbon available for export to the deep sea. Yet, the role of Syndiniales in carbon cycling has been hard to define, as depth-specific infection dynamics and links to carbon export remain poorly understood.

Parasites are everywhere in the ocean. Including the microbial realm where a diverse, widespread group of protist parasites (Syndiniales) infect and kill a range of hosts, such as dinoflagellates, radiolarians, and even larger zooplankton. A complete Syndiniales infection cycle is only 2-3 days. First, the parasite is a free-living spore. Once inside a host, the parasite consumes the host’s carbon and becomes a larger multicellular organism (a trophont) eventually causing the host to burst open and release hundreds of new spores.

Figure 1. The mean relative abundance of Syndiniales (purple) in the photic zone (<140 m) is negatively correlated with particulate organic carbon (POC) flux at 150 m (p-value < 0.001). Similar correlations are not significant (p-values > 0.05) for other major 18S taxonomic groups, like Dinophyceae (red) and Arthropoda (green).

In a recent study published in ISME Communications, authors analyzed an 18S rRNA gene metabarcoding dataset from the Bermuda Atlantic Time-series Study (BATS) site that included 4 years (2016-2019) and twelve depths (1-1000 m). Syndiniales were the most dominant 18S group at BATS, present throughout the photic and aphotic zones. These parasites were prominent in species networks constructed with 18S sequence data, with significant associations with dinoflagellates and copepods in the surface, and with radiolarians in the aphotic zone. In addition, Syndiniales were the only major 18S group to be significantly (and negatively) correlated to particulate carbon flux (at 150 m), which was estimated from sediment trap data collected concurrently at BATS (Figure 1). This is in situ evidence of flux attenuation among Syndiniales, as they recycle host carbon that would otherwise transfer up to larger organisms (e.g., via grazing). Lastly, authors found 19% of the Syndiniales community is linked between photic and aphotic zones, indicating that parasites are sinking on particles and/or are recirculated via diel vertical migration. Overall, these findings elevate the role of Syndiniales in microbial food webs and further emphasize the importance in quantifying parasite-host dynamics to inform ocean carbon models.

Authors
Sean Anderson (University of New Hampshire / Woods Hole Oceanographic Institution)
Leocadio Blanco-Bercial (Bermuda Institute of Ocean Sciences / Arizona State University)
Craig Carlson (University of California, Santa Barbara)
Elizabeth Harvey (University of New Hampshire)

A suite of CO2 removal approaches modeled for the 1.5 ˚C future

Posted by mmaheigan

· Thursday, August 31st, 2023

Carbon dioxide removal (CDR) is “unavoidable” in efforts to limit end-of-century warming to below 1.5 °C. This is because some greenhouse gas emissions sources—non-CO₂ from agriculture, and CO₂ from shipping, aviation, and industrial processes—will be difficult to avoid, requiring CDR to offset their climate impacts. Policymakers are interested in a wide variety of ways to draw down CO₂ from the atmosphere, but to date, the modeling scenarios that inform international climate policies have mostly used biomass energy with carbon capture and storage (BECCS) as a proxy for all CDR. It is critical to understand the potential of a full suite of CDR technologies, to understand their interactions with energy-water-land systems and to begin preparing for these impacts.

Figure caption: Each of the six carbon dioxide removal approaches identified in recent U.S. legislation and modeled for this study could bring unique benefits and tradeoffs to the energy-water-land system. This image depicts afforestation, direct ocean capture, direct air capture, biochar, enhanced weathering, and bioenergy with carbon capture and storage in clockwise order. Floating carbon dioxide molecules hover above the landscape (image credit: Nathan Johnson, PNNL).

A recent study published in the journal Nature Climate Change was the first to model six major CDR pathways in an integrated assessment model. The modeled pathways range from bioenergy with carbon storage and afforestation (already represented by most models), also direct air capture, biochar and crushed basalt spreading on global croplands, and electrochemical stripping of CO₂ from seawater aka direct ocean capture. The removal potential contributed by each of the six pathways varies widely across different regions of the world. Direct ocean capture showed the smallest removal potential but has important potential synergies with water desalination. This method could help arid regions such as the Middle East meet their water needs in a warming world. Enhanced weathering has much larger (GtCO₂-yr^-1) removal potential and could potentially help ameliorate ocean acidification. Overall, similar total amounts of CO₂ are removed compared to other modeling scenarios, but broader set of technologies lessens the risk that any one of them would become politically or environmentally untenable.

Authors:
Jay Fuhrman (Joint Global Change Research Institute)
Candelaria Bergero (Joint Global Change Research Institute)
Maridee Weber (Joint Global Change Research Institute)
Seth Monteith (ClimateWorks Foundation)
Frances M. Wang (ClimateWorks Foundation)
Andres F. Clarens (University of Virginia)
Scott C. Doney (University of Virginia)
William Shobe (University of Virginia)
Haewon McJeon (Joint Global Change Research Institute )

Twitter: @pnnlab @climateworks @uva

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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