Nutrients and primary production along the eastern Aleutian Island Archipelago

The distribution of nutrients (nitrate, phosphate, and silicic acid), chlorophyll and primary productivity were examined in the central and eastern Aleutian Archipelago. The data were collected from moorings (temperature, salinity, nitrate, and currents) and two hydrographic research cruises (June 2001 and May-June 2002). During the hydrographic cruises salinity, temperature, nutrients, chlorophyll and primary production were measured in and around the eastern and central Aleutian Passes. The net nutrient transport through the passes was northward, and it was relatively low in the eastern passes compared to the central passes. In the shallow eastern passes the source water from the Pacific was the nutrient-poor Alaska Coastal Current, while in the deeper central passes it was the nutrient-rich Alaskan Stream. Within the passes, vigorous tidal mixing resulted in enriched surface concentrations, especially in the central passes. Chlorophyll sections and satellite composites from summer indicate high chlorophyll east of Samalga Pass and very low chlorophyll between Samalga and Seguam Passes. Production was relatively low across the study area, except at the northern end of Seguam Pass and in the vicinity of the shelf edge in the southeastern Bering Sea. Production and chlorophyll concentrations were lowest in the deep passes. These results suggest that, within the passes, deep mixing inhibits new production, but substantial blooms may occur downstream of the passes subsequent to stratification.