BGC-Argo profiling floats are capable of collecting data throughout the full seasonal cycle in ice-covered waters of the Southern Ocean, allowing a greater understanding of the processes occurring that have significant impacts on biogeochemistry. While observations of the growth of phytoplankton and its relationship to ice and vertical mixing have been completed, less attention has been given to the processes that occur when ice forms, vertical mixing increases, and production largely stops due to irradiance limitation.  We compiled data from south of 60°S during the 3 week period prior to ice formation and 3 weeks following ice formation from 39 floats, most which had multiple years of data collection. After ice formation, chlorophyll and particulate organic carbon decreased rapidly due to both dilution from low particulate matter waters at depth and vertical mixing, as well as oxidation and removal by biological processes. In general over 90% of the biologically produced organic matter had been removed within three weeks of ice formation. Variations among floats were largely dependent on the extent of vertical mixing, which was the dominant feature controlling organic matter removal. The results suggest that the mixed layer pump as part of the biological carbon pump may not be a significant process in sequestering organic matter at depth.
BGC-Argo profiling floats are capable of collecting data throughout the full seasonal cycle in ice-covered waters of the Southern Ocean, allowing a greater understanding of the processes occurring that have significant impacts on biogeochemistry. While observations of the growth of phytoplankton and its relationship to ice and vertical mixing have been completed, less attention has been given to the processes that occur when ice forms, vertical mixing increases, and production largely stops due to irradiance limitation.  We compiled data from south of 60°S during the 3 week period prior to ice formation and 3 weeks following ice formation from 39 floats, most which had multiple years of data collection. After ice formation, chlorophyll and particulate organic carbon decreased rapidly due to both dilution from low particulate matter waters at depth and vertical mixing, as well as oxidation and removal by biological processes. In general over 90% of the biologically produced organic matter had been removed within three weeks of ice formation. Variations among floats were largely dependent on the extent of vertical mixing, which was the dominant feature controlling organic matter removal. The results suggest that the mixed layer pump as part of the biological carbon pump may not be a significant process in sequestering organic matter at depth.
 

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