Branch Seminar Series: Michael Hiscock

Princeton University
Because of its size, circumpolar circulation, and a large pool of unused surface-layer nutrients, the Southern Ocean is differentially important to understanding the global marine carbon cycle. Here I explore the regulation of primary production in three very different circumpolar regimes of the Southern Ocean: within the Antarctic Circumpolar Current (ACC), poleward of the ACC, and along the continental shelf of Antarctica. Two common threads of this presentation are the influence of iron and Upper Circumpolar Deep Water (UCDW) in these regions. Within the Antarctic Zone and Southern ACC Zone, newly upwelled iron-rich UCDW provides enough iron to support a diatom bloom that annually propagates poleward to the Southern Boundary of the ACC (SBACC). In the zone poleward of the SBACC, the absence of upwelling iron-rich UCDW prevents the bloom's progression. Further poleward, on the Antarctic continental shelf, the varying strength of temporally and spatially heterogeneous intrusions of iron-rich Modified UCDW (MCDW) determines the location and duration of a secondary summer bloom. Modeling, satellite ocean color, field campaign and iron enrichment results reveal the zonal dependence of primary production regulation.