Southern Ocean Phytoplankton Blooms Observed by Biogeochemical Floats

The spring bloom in the Southern Ocean is the rapid-growth phase of the seasonal cycle in phytoplankton. Many previous studies have characterized the spring bloom using chlorophyll estimates from satellite ocean color observations. Assumptions regarding the chlorophyll-to-carbon ratio within phytoplankton and vertical structure of biogeochemical variables lead to uncertainty in satellite-based estimates of phytoplankton carbon biomass. Here, we revisit the characterizations of the bloom using optical backscatter from biogeochemical floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling and Southern Ocean and Climate Field Studies with Innovative Tools projects. In particular, by providing a three-dimensional view of the seasonal cycle, we are able to identify basin-wide bloom characteristics corresponding to physical features; biomass is low in Ekman downwelling regions north of the Antarctic Circumpolar Current region and high within and south of the Antarctic Circumpolar Current.