Further Insights into the Biogeochemical Cycles of the Ross Sea: A BGC-Argo Analysis

Biogeochemical Argo floats have provided extensive information on the biogeochemical cycles throughout the ocean. Recently, a number of floats were deployed on the Ross Sea continental shelf, which was the first time any ice-covered, shelf region had its annual cycle completely characterized. The floats revealed in great detail the temporal sequence of a complete annual cycle of biological and chemical variables. Changes were greatest in November and March, periods when ice was melting/forming. We quantified the impacts of vertical mixing and brine rejection by using the detailed salinity profiles for one location in conjunction with chlorophyll, particulate organic carbon (POC), dissolved inorganic carbon (DIC), nitrate, and dissolved oxygen vertical distributions to quantify the rates of regeneration during March. Chlorophyll decreased more rapidly than POC, suggesting an additional biological process that was influencing its concentration. A large fraction (ca. 90%) of the chlorophyll disappeared in the first 15 days after ice cover. Mixed layer oxygen decreased along with POC. DIC increased substantially more than POC decreased but was consistent with the oxygen decrease, indicating that the remineralization of dissolved organic carbon was important. The ratios between changed DIC and nitrate exhibited seasonal differences, aligning closely with the Redfield ratio in autumn but increasing in spring. BGC-Argo floats and the detailed analysis of their records provide a unique understanding of the biogeochemical cycles in systems that are impossible to sample for a full annual cycle.