2024-11-292024-11-292024Williams, J.R., Giering, S., Baker, C.A., Pabortsava, K., Briggs, ‪., East, H.,...,Martin, A.P. (2024). Inefficient transfer of diatoms through the subpolar Southern Ocean twilight zone. Nature Geoscience, 11, 1-14. https://doi.org/10.1038/s41561-024-01602-2.1752-08941752-0908https://hdl.handle.net/11441/165149The Southern Ocean, a region highly vulnerable to climate change, plays a vital role in regulating global nutrient cycles and atmospheric CO2 via the biological carbon pump. Diatoms, photosynthetically active plankton with dense opal skeletons, are key to this process as their exoskeletons are thought to enhance the transfer of particulate organic carbon to depth, positioning them as major vectors of carbon storage. Yet conficting observations obscure the mechanistic link between diatoms, opal and particulate organic carbon fuxes, especially in the twilight zone where greatest fux losses occur. Here we present direct springtime fux measurements from diferent sectors of the subpolar Southern Ocean, demonstrating that across large areas of the subpolar twilight zone, carbon is efciently transferred to depth, albeit not by diatoms. Rather, opal is retained near the surface ocean, indicating that processes such as diatom buoyancy regulation and grazer repackaging can negate ballast efects of diatoms’ skeletons. Our results highlight that the presence of diatoms in surface waters of the Southern Ocean’s largest biome does not guarantee their importance as vectors for efcient carbon transfer through the subpolar twilight zone. Climate change-driven shifts in phytoplankton community composition may afect biologically sequestered carbon pools less than currently predicted.application/pdf14 p.engAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/info:eu-repo/semantics/articleinfo:eu-repo/semantics/openAccess10.1038/s41561-024-01602-2