Wind-induced upwelling in the Kerguelen Plateau region

[摘要] In contrast to most of the Southern Ocean, the Kerguelen Plateau supports anunusually strong spring chlorophyll (Chl a) bloom, likely because theeuphotic zone in the region is supplied with higher iron concentrations. Thisstudy uses satellite wind, sea surface temperature (SST), and ocean colordata to explore the impact of wind-driven processes on upwelling of cold(presumably iron-rich) water to the euphotic zone. Results show that, in theKerguelen region, cold SSTs correlate with high wind speeds, implying thatwind-mixing leads to enhanced vertical mixing. Cold SSTs also correlate withnegative wind-stress curl, implying that Ekman pumping can further enhanceupwelling. In the moderate to high eddy kinetic energy (EKE) regions surrounding Kerguelen, we findevidence of coupling between winds and SST gradients associated withmesoscale eddies, which can locally modulate the wind-stress curl. Thiscoupling introduces persistent wind-stress curl patterns and Ekman pumpingaround these long-lived eddies, which may modulate the evolution of Chl a inthe downstream plume far offshore. Close to the plateau, this eddy couplingbreaks down. Kerguelen has a significant wind shadow on its downwind side,which changes position depending on the prevailing wind and which generates awind-stress curl dipole that shifts location depending on wind direction.This leads to locally enhanced Ekman pumping for a few hundred kilometersdownstream from the Kerguelen Plateau; Chl a values tend to be more elevated inplaces where wind-stress curl induces Ekman upwelling than in locations ofdownwelling, although the estimated upwelling rates are too small for thisrelationship to derive from direct effects on upward iron supply, and thusother processes, which remain to be determined, must also be involved in theestablishment of these correlations. During the October and November (2011) KErguelen Ocean and Plateau compared Study(KEOPS-2) field program, wind conditions were fairly typical for the region, withenhanced Ekman upwelling expected to the north of the Kerguelen Islands.

[学科分类] 地球化学与岩石