Evolution of a Subducted Carbon-Rich Filament on the Edge of the North Atlantic Gyre

The oceanic biological carbon pump encompasses a variety of mechanisms by which CO2, fixed into organic form by phytoplankton, is transported from the sunlit surface layers to the interior ocean. Here, we investigate submesoscale and mixed layer subduction, estimated to represent ∼20% of global particulate organic carbon (POC) export. Seven Biogeochemical (BGC) Argo profiling floats were analyzed for evidence of subduction of POC in the North Atlantic Ocean, revealing a pattern in the seasonality. Although vertical processes that give rise to subduction are enhanced during late winter and spring, the bio-optical evidence for intrusions—namely a deep local maxima in POC, co-located with a temperature and salinity anomaly—were more commonly observed in the summer. We hypothesize that these deep intrusions can be long-lived, having been subducted months earlier and persisting at depth throughout the warm season. We present a case study of a notable anomaly, observed in 10 consecutive BGC Argo profiles on the northeastern edge of the subtropical gyre. Analysis of the profiles, complemented by remote sensing and HYCOM model output, provides insight into the history and subsequent fate of the subducted water