Schmidt Ocean Institute Completes Two Expeditions Probing Ocean's Role in Global Carbon Cycle

Scientists supported by the Schmidt Ocean Institute and the Schmidt Sciences Ocean Biogeochemistry Virtual Institute have completed two transformative research expeditions in the Southwest Atlantic Ocean aimed at filling major gaps in the understanding of the biological pump, the process by which the ocean transfers carbon from the surface to the deep sea. The expeditions, conducted aboard research vessel Falkor (too) between January and April, examined the role of the world's largest animal migration and subsurface phytoplankton in the Southeastern Atlantic Gyre in regulating the global carbon cycle.

 

Strategic Importance of the Biological Pump

 

The biological pump is one of the central mechanisms by which the ocean regulates atmospheric carbon dioxide, transporting organic carbon from surface waters into the deep sea where it can remain sequestered for centuries. Understanding the efficiency, drivers, and variability of this process is essential for accurate climate modelling, since the ocean absorbs approximately one-third of the carbon dioxide produced by human activity. Despite that scale, the underlying biological and chemical mechanisms remain incompletely characterised, particularly in the dimly lit and deep portions of the water column where direct observation is logistically and technically demanding. The two expeditions reflect a deliberate effort to address that gap with high-resolution biogeochemical and biological sampling at sites where the relevant processes are most active.

 

Animals as Living Bioreactors Expedition

 

The first expedition, Animals as Living Bioreactors, took place in January and February under the leadership of Anitra Ingalls of the University of Washington. The team operated in waters off the east coast of South America, from Argentina to Brazil, focusing on the digestive systems of fish, jellies, and other animals that participate in the world's largest daily migration. Billions of animals undertake this diel vertical migration, swimming up from the depths to feed at the surface each night and returning to deep waters before dawn to avoid predators. Despite the sheer scale of this movement, the contribution of these animals to carbon export remains poorly quantified, and the expedition is among the most ambitious recent efforts to address that uncertainty.

 

Carbon Transport and Microbiome Hypotheses

 

According to Ingalls, the migrating animals effectively capture carbon at the surface and transport it in their guts down to depths of 1,500 metres, where it is eventually excreted. This active transport pathway has historically been overlooked in carbon export models, which have tended to focus on the passive sinking of organic particles. By quantifying the contribution of vertical animal migration to deep ocean carbon delivery, the expedition aims to refine the understanding of how the biological pump operates at scale. A second research question the team aims to address is whether the gut microbiomes of these migrating animals are transforming food into essential nutrients such as vitamin B12, which would support deep-water ecosystems and add another layer to the ecological role of the migration.

 

Sample Collection and Biodiversity Findings

 

The expedition collected an extensive set of animal samples for continued scientific analysis, including specimens that will be donated to museum collections. Several of the species observed have not previously been recorded in the South Atlantic, and others are likely to represent new species entirely. The biodiversity findings are significant in their own right, since they expand the documented species inventory of the South Atlantic and provide reference material for future taxonomic and ecological work. They also illustrate the dual scientific value of biogeochemistry-focused expeditions, which often generate biological discoveries alongside their primary climate-relevant findings.

 

SUBSEA Expedition in the Southeastern Atlantic Gyre

 

The second expedition, the Subtropical Underwater Biogeochemistry and Subsurface Export Alliance, took place in March and April under the leadership of Matthew Church of the University of Montana. SUBSEA operated more than 200 miles off the coast of Brazil and focused on how nutrients and carbon are cycled by phytoplankton living in the Southeastern Atlantic Gyre. Ocean gyres are vast and nutrient-poor systems that cover some of the largest contiguous habitats on Earth, and their surface conditions are among the few that can be observed continuously from satellites. However, the activity of phytoplankton at depths of around 100 metres, where sunlight begins to dim, lies beyond satellite observational range and represents a critical knowledge gap.

 

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Subsurface Phytoplankton and the Compost Hypothesis

 

The SUBSEA team caught the tail end of a major phytoplankton bloom that was beginning to die and decay, providing an opportunity to study how decaying surface plankton may serve as a nutrient source for phytoplankton living at greater depths. The hypothesis under investigation is that decaying surface phytoplankton effectively act as compost for subsurface communities, sustaining phytoplankton growth in regions where the surface waters are otherwise nutrient-poor. Open questions remain about the precise sources of the iron, phosphorus, and nitrogen needed to sustain that subsurface productivity, and resolving those questions could meaningfully improve the understanding of how nutrient cycling and carbon export operate in the largest oceanic ecosystems.

 

Scientific Significance and Knowledge Gaps

 

According to Church, the processes that sustain subsurface phytoplankton remain largely unknown, and the SUBSEA expedition was specifically designed to improve understanding of the biological and chemical interactions taking place in the dimly lit portion of the upper ocean. The implications extend well beyond the gyre system being studied, since subsurface phytoplankton are a global feature of low-nutrient ocean regions and contribute to global carbon export in ways that current models do not fully capture. Improvements in the characterisation of these processes feed directly into the next generation of climate and ocean biogeochemical models, with implications for projections of how the ocean's carbon uptake capacity may evolve in a warming climate.

 

Institutional Context and Long-Term Programme Support

 

Both expeditions are part of long-term research projects supported by Schmidt Sciences through the Ocean Biogeochemistry Virtual Institute programme. Schmidt Ocean Institute executive director Jyotika Virmani has framed the work as part of a broader mission to fill major research gaps in the global carbon cycle that have been understudied for decades because they are difficult to quantify. The institutional model behind the expeditions, combining a dedicated research vessel, advanced ROV and net sampling systems such as MOCNESS, and multi-year programmatic funding, reflects the level of resourcing required to make sustained progress on these questions. Long-term funding structures are particularly important for biogeochemical research, where seasonal variability and process complexity require multi-cruise data collection over extended periods.

 

Implications for Climate Science and Ocean Policy

 

The findings from these expeditions are likely to feed into a wide range of downstream scientific and policy applications. Improved characterisation of the biological pump strengthens the empirical foundation of climate models used by the Intergovernmental Panel on Climate Change and other authoritative bodies. It also informs ocean-based carbon dioxide removal research, which is increasingly being explored as a complement to conventional emissions reduction strategies. As governments and investors evaluate the credibility and scalability of ocean carbon solutions, high-resolution scientific data on natural carbon transport pathways becomes a critical reference point. The Falkor (too) expeditions therefore contribute not only to fundamental ocean science but also to the broader debate on the role of the ocean in long-term climate strategy.

 

Outlook for Ocean Biogeochemistry Research

 

The two expeditions illustrate how advances in research vessel capability, ROV technology, sensor systems, and biological sampling are enabling more precise characterisation of processes that have historically been beyond reach. As ocean observation capabilities continue to expand, including through autonomous platforms, advanced moorings, and integrated satellite and in-situ data systems, the ability to constrain key parameters of the biological pump is expected to improve substantially. For the wider ocean economy, the implications are significant. Better understanding of carbon cycling supports more credible carbon accounting, more reliable ocean-based climate solutions, and better-informed regulatory frameworks for activities that interact with the deep ocean ecosystem.