The Southern Ocean (SO) biological carbon pump (BCP) plays a central role in regulating Earth’s climate and global marine biogeochemistry. By controlling the “SO window” – the extent to which the atmosphere is exposed to the large carbon reservoir of the deep ocean – the BCP exerts a first-order influence on atmospheric CO2. Without biological uptake, the upwelling of CO2-rich deep waters would make the SO a major source of CO2 to the atmosphere. Instead, the BCP mitigates this flux by converting much of the upwelled CO2 into organic carbon exported to depth. Despite its importance, the BCP remains poorly constrained due to the region’s remoteness, sparse observations, and strong spatio-temporal variability. It may also be highly sensitive to extreme events such as marine heatwaves and ocean acidity anomalies, whose impacts remain poorly understood. These uncertainties stem from complex interactions linked to Antarctic atmospheric dynamics, sea-ice variability, and the cryosphere.
This complexity is most pronounced in the marginal sea ice zone (MIZ), where spring and summer melt release (micro)nutrients and enhance stratification, promoting nutrient uptake, phytoplankton growth, and carbon export. Phytoplankton composition along with particle aggregation and repackaging exert strong control on export efficiency. In some regions, weak coupling between biogenic silica and particulate organic carbon fluxes indicate low transfer efficiency, underscoring persistent uncertainties in the link between diatom biomass and export.
The Southern Ocean Biogeochemistry research cluster aims to establish a baseline understanding of the BCP by resolving its full seasonal cycle in the MIZ of the South Atlantic sector. The focus is on quantifying net biological carbon fixation and subsequent export to the ocean interior. By integrating these observations with measurements of the (in)organic carbon cycle, RC4 directly links biological processes to the air-sea CO2 balance, providing a robust assessment of BCP efficiency and its contribution to the oceanic carbon sink.
Research Cluster PI
- Samuel Jaccard, Uni Lausanne
Research Cluster Participants
- Thomas Frölicher, Uni Bern
- Nicolas Gruber, ETH Zurich
- Maxi Castrillejo Iridoy, Uni Lausanne
Links with Participants of other Research Clusters
- Franziska Aemisegger, Uni Bern
- Ruzica Dadic, WSL/SLF
- Hendrik Huwald, EPFL, WSL/SLF
- Johannes Sutter, Uni Bern
Swiss and International Partners
- Stefanie Arndt, AWI
- Astrid Bracher, AWI
- Nathan Bindoff, Uni Tasmania
- Hervé Claustre, LOV
- Sarah Fawcett, Uni Cape Town
- Alex Haumann, AWI
- Mario Hoppema, AWI