HABs in the Pacific Northwest: emergent findings and new directions from SeaWiFS and other data

Abstract

SeaWiFS RCA-Chl along with sea surface height variations/geostrophic currents, sea surface temperature, wind speed/direction and field observation data, are used to first describe comprehensively the occurrences of various hazardous algal blooms (HABs) and their underlying mechanisms and link to nutrient enrichment during the summer in shelf-slope waters off the Northwest Pacific (NWP). These datasets provide a coherent view of the summertime evolution of HABs and related physical processes in four common dynamic regions: coastal cold/estuary water zones, upwelling zones next to the coast, repeated meanders/eddies, and frontal regimes induced by the Kuroshio and its tributaries. High blooms coincided with the coastal upwelling and cyclonic eddy regimes that followed SST minimum and large negative SSH along with favorable phase of winds. By contrast, relatively low mean RCA were consistent with the fronts and anticyclonic meanders revealing moderate-high SSH fields along with variable winds blown off the NWP coast. These anticyclonic meanders, on some occasions, when nutrient-containing coastal water setoff higher chlorophyll biomass and major currents gained force in August, straddled the continental margin, entraining high chlorophyll water from the coast and from the adjacent cyclonic eddies located nearby into their outer rings that formed a conveyer-belt system of transport to inject coastal blooms into the deep-sea (e.g., East Sea) region of the NWP. The above findings based on satellite data combined with field hydrographic/ bloom observation data evidently illustrated richness of the response of summer HABs to the surface circulation and nutrient enrichment processes in shelf-slope waters off the NWP coast.