Year‐round observations of carbon biomass and flux variability in the Southern Ocean

Abstract

Three Carbon Explorer (CE) floats profiling to kilometer depths in the Southern Ocean tracked dawn‐dusk variations of mixing and stratification, particulate organic carbon, and light scattering and sedimentation at 100, 250, and 800 m continuously from January 2002 to April 2003. Data were analyzed in conjunction with contemporaneous satellite winds and chlorophyll and derived subsurface light fields. The CE deployed at 66°S, 172°W operated in the ice edge zone in absence of light. Two CEs deployed at 55°S, 172°W recorded wintertime mixing to ∼400 m yet observed very different bloom dynamics and sedimentation the following spring. Four hypotheses are explored. The strongest hypothesis is that shallow transient stratification of the deep winter mixed layer to shallower than photosynthetic critical depth occurred more frequently in the nonbloom, higher‐sedimentation case. The lower particle export to 800 m under the bloom was hypothesized to be due to higher interception of sinking carbon by a relatively starved overwintering zooplankton population. In the Southern Ocean, surface phytoplankton biomass may counterindicate particle flux at kilometer depths.