Sea-ice impacts inter-annual variability in bloom phenology and carbon export in the Weddell Sea

Abstract

The Antarctic Marginal Ice Zone (MIZ) accounts for 15% of the Southern Ocean's primary production (PP), but limited data has hindered understanding of its variability and connection to carbon export. Using a combination of gliders, biogeochemical Argo floats and satellite observations in the northeast Weddell Sea, we show that years with more sea-ice formation over winter are followed by more intense phytoplankton blooms (~15% greater daily PP) and export to 100 m (~50% higher daily carbon export) the following summer. However, the carbon export beyond the deepest winter mixed layer did not vary in proportion to PP, suggesting different drivers of carbon export at depth compared to surface waters. Furthermore, across the entire MIZ, the response of blooms to sea-ice volume was spatially variable, indicating the need to consider spatial heterogeneity in the response of the biological carbon pump to future sea-ice changes.