FY 2024

Biological production of distinct carbon pools drives particle export efficiency in the Southern Ocean

Huang, Y., and A.J. Fassbender

Geophys. Res. Lett., 51(12), e2023GL107511, doi: 10.1029/2023GL107511, View open access article at AGU/Wiley (external link) (2024)

We use observations from the Southern Ocean (SO) biogeochemical profiling float array to quantify the meridional pattern of particle export efficiency (PE_eff) during the austral productive season. Float estimates reveal a pronounced latitudinal gradient of PE_eff, which is quantitatively supported by a compilation of existing ship-based measurements. Relying on complementary float-based estimates of distinct carbon pools produced through biological activity, we find that PE_eff peaks near the region of maximum particulate inorganic carbon sinking flux in the polar antarctic zone, where net primary production (NPP) is the lowest. Regions characterized by intermediate NPP and low PE_eff, primarily in the subtropical and seasonal ice zones, are generally associated with a higher fraction of dissolved organic carbon production. Our study reveals the critical role of distinct biogenic carbon pool production in driving the latitudinal pattern of PE_eff in the SO.

Plain Language Summary. Microbial organisms in seawater transform carbon dioxide into different types of carbon through photosynthesis and food web cycling. These carbon types include particulate and dissolved phases, with particles being more efficiently transferred out of the sunlit ocean via gravitational sinking. The ratio of sinking particulate organic carbon to total organic carbon production, commonly referred to as the particle export efficiency, is a metric used to describe how efficiently carbon moves from the surface to the deep ocean. Using observations from a large array of robots in the Southern Ocean, we find that the different types of biogenic carbon produced control the latitudinal gradient in particle export efficiency, which is highest in regions where particulate inorganic carbon export is greatest, even when photosynthetically fixed carbon is minimal. In other areas where phytoplankton carbon production is moderate but largely comprised of dissolved organic carbon, the particle export efficiency is lower.