Deep carbon export peaks are driven by different biological pathways during the extended Scotia Sea (Southern Ocean) bloom

Estimating the amount of organic carbon leaving upper water column and becoming sequestered in deep ocean is a major challenge our understanding oceanic C cycle. This study investigate sediment trap material collected at 5 day resolution over 4 month period covering bloom northern Scotia Sea. region characterised by extensive long-lived phytoplankton blooms that collectively take up greatest atmospheric dioxide yet measured Southern Ocean. In particular, resolved multiple peaks POC flux during Sea resulting from distinctly different export processes. work also examine contribution diatoms calcifying species to as well determining FP (faecal pellet) characteristics, including biogeochemical composition sinking velocity. Results showed was concentrated three peak events. The first two were large, similar intensity (24.5 mg m −2 d −1 early November 22.5 December), dominated faecal pellets (FPs, 60–66%). these dominance carbonate (>48%), higher speed (up 347 ) compared with other rest samples. suggest large presence calcium FPs contributed their relatively high velocity which, turn, promoted level bathypelagic depths. Intact single cell important (mainly Fragilariopsis kerguelensis Thalassionema nitzschioides ), while detritus semi-grazed phytodetritus more abundant second peak, suggesting change cycle between peaks. A third, smaller, (12.7 January) diatom resting spores, mainly Chaetoceros Hyalochaete sp. (>70% total contribution), which were, almost exclusively, fully intact cells. Our sampling allowed insights into short time-scale processes influence ultimate magnitude substantial annual this region. Overall findings highlights temporal sequence biological events surface layers has strong on both fluxes. • spring combined 40% flux. dominate December. Biogeochemical Diatoms spore January.