The ocean plays a central role in regulating Earth’s climate by absorbing, storing, and redistributing carbon. A key process in this system is the biological carbon pump (BCP), which transfers carbon captured by marine organisms at the ocean surface into deeper waters and sediments, where it can be stored for decades to thousands of years. Understanding how this process works, and how it may change in the future, is essential for predicting the resilience of ocean ecosystems under climate change and increasing human pressures.

The biological carbon pump depends on a complex network of interactions between organisms and their environment. Microscopic organisms such as phytoplankton capture carbon near the ocean surface through photosynthesis. As these organisms are consumed, die, or produce waste, carbon is transferred through marine food webs and can sink into deeper waters. This movement of carbon supports deep-sea ecosystems while also contributing to the ocean’s role as a long-term carbon reservoir.

However, many current estimates of the biological carbon pump focus primarily on plankton and do not fully capture the contributions of larger organisms, deep-sea communities, or connections between the seafloor and the open ocean. A more complete understanding requires considering the full range of organisms and processes involved, including carbon transported by migrating animals, sinking organic material, and the exchange of carbon between benthic (seafloor) and pelagic (open ocean) environments.

New observations and advanced modelling approaches will be used to build a more complete picture of carbon flows within ocean food webs. Measurements collected from offshore expeditions will track how carbon moves from surface waters through the mesopelagic zone—the region of the ocean where many organisms migrate between shallow and deep waters—and into deep-sea ecosystems. These observations will include carbon sinking through the water column, carbon reaching the seafloor, and the contribution of different groups of organisms to carbon transfer.

A particular focus will be understanding how bentho-pelagic coupling influences carbon movement. This process describes the exchange of energy, nutrients, organisms, and carbon between the seafloor and the overlying ocean. Seafloor features such as seamounts and areas of strong ocean currents can create hotspots where these connections are enhanced, supporting productive ecosystems and influencing how efficiently carbon is transferred and stored.

The role of larger marine organisms will also be investigated. Deep scattering layers—dense communities of plankton, fish, and other organisms found at mid-depths in the ocean—represent important pathways for moving carbon through daily vertical migrations. As these organisms move between surface and deeper waters, they transport carbon and connect different parts of the ocean food web. Understanding these processes is essential for predicting how changes in biodiversity, fisheries pressures, and emerging activities may affect carbon cycling.

The combined observations will support the development of ecosystem models that represent how carbon moves through ocean food webs. These Linear Inverse Models (LIMs) will be used to explore how carbon pathways may respond to different future scenarios, including climate change, existing human activities, and emerging pressures. By identifying when carbon flows may become disrupted, this approach will help reveal potential limits to the ocean’s ability to maintain ecosystem functions and store carbon.

The knowledge generated will provide a stronger foundation for assessing future ocean risks and developing sustainable management approaches. By improving understanding of the links between biodiversity, food webs, and carbon cycling, this work will support decision-making aimed at protecting ocean ecosystems and the processes that sustain them.

OceanSOS’ work on the biological carbon pump is led by Dr. Emma Cavan at Imperial College London, supported by Dr. Andrew Sweetman at Scottish Association for Marine Science (SAMS) and Dr. Henk-Jan Hoving at Helmholtz-Zentrum Fur Ozeanforschung Kiel (GEOMAR).