Zonal asymmetries in Southern Ocean primary productivity and carbon uptake

The distribution of phytoplankton biomass in the Southern Ocean has important implications for the biological pump and thus the global carbon cycle. Satellite chlorophyll-based studies have found that primary productivity in the Southern Ocean is patchy and zonally asymmetric. Satellite data coverage, however, is limited by cloud cover and sea ice. Furthermore, phytoplankton biomass has a complex vertical structure that is not captured by surface chlorophyll values from satellites. Here, we use subsurface data from an array of more than 150 autonomous biogeochemical profiling floats in the Southern Ocean to investigate zonal asymmetries in primary productivity and air-sea carbon fluxes. We find significant differences between the Atlantic and Indo-Pacific sectors, suggesting a possible role of biogenic carbon uptake in driving the basin asymmetries in carbon fluxes. For example, carbon uptake in the Polar Frontal Zone of the Atlantic coincides with a region of high biological productivity in the Argentine Basin. We then investigate patterns in float-based estimates of annual net community production to examine biogenic carbon uptake more directly. Finally, we consider other possible drivers of basin asymmetries in air-sea carbon fluxes, including spatial variability in upwelling of Circumpolar Deep Water.