McRoy, C. P. University of Alaska Fairbanks, ffcpm@uaf.edu
Simpson, P. P. University of Alaska Fairbanks, psimpson@ims.uaf.edu
Ward, A. Department of Environmental Protection, alison.ward@state.me.us
Tamburello, K. University of Alaska Fairbanks, ftkrt@uaf.edu

 
INTERANNUAL VARIANCE IN THE SEASONAL CYCLE OF PRIMARY PRODUCTION AND NUTRIENTS IN PRINCE WILLIAM SOUND, ALASKA
 
In early April, a diatom bloom, typically dominated by Skeletonema costatum, begins the seasonal phytoplankton cycle in Prince William Sound. The bloom terminates in mid-May and is succeeded by a period of low biomass of predominately flagellates. A small increase of diatoms develops in June and in some years a bloom of flagellates occurs in late summer. The carbon chlorophyll ratio is a direct consequence of the species composition of the phytoplankton community and varies by a factor of more than 2 fold between years. The timing of the spring increase, as measured by chlorophyll a, based on recent and historical work back to 1971, is remarkably similar with the peak occurring on or about 28 April. The only exceptions to this were in 1993 and 1977. As expected, the spring phytoplankton increase is strongly influenced by light and mixing. While the decline of phytoplankton biomass is a result of nutrient depletion and zooplankton grazing. Estimated primary productivity in 1997 was 46% lower than 1996 and 36% less than 1995. The magnitude of primary production during the bloom is determined by the inventory of nutrients supplied by winter mixing. Recent climate warming events reduce upper layer mixing and hence the nutrient inventory resulting in decreased productivity. Overall, the data indicate a robust, healthy foundation for the pelagic ecosystem in Prince William Sound with no lingering effects of the 1989 oil spill.
 
Day: Thursday, Feb. 4
Time: Poster
Location: Sweeney Center
 
Code: SS39TH1171S