(PLEASE NOTE: These web pages are for archival purposes only and are no longer maintained. For current information on this topic at the AFSC visit the Ecosystem Monitoring and Assessment program. )

Nutrient distribution has a large impact on phytoplankton growth and taxonomic composition on the eastern Bering Sea shelf, particularly during summer. Primary productivity in turn impacts secondary producers (zooplankton) and higher trophic level consumers (fish, marine mammals, sea birds). Mean concentrations of nitrogenous nutrients (nitrate and ammonium) and chlorophyll a above and below the pycnocline were derived from analysis of discrete water samples collected in the eastern Bering Sea during BASIS surveys in late summer /early fall 2003-2006.

Contact:
Lisa Eisner
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries

Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau AK 99801
(907) 789-6602
Lisa.Eisner@noaa.gov

Collecting water samples.

Filtering water samples.

Various Diatom species collected (Photos by Kristin Cieciel).

Nitrate Above & Below Thermocline			Ammonium Above & Below Thermocline

Chlorophyll a Total & > 10 µm

In 2003,2004, and 2005 (warm years), surface nitrate and ammonium concentrations on the eastern Bering Sea shelf were low with the exception of the southwest region of Bristol Bay. In this region, upwelling through Unimak Pass provides nitrate that subsequently fuels phytoplankton growth. Surface phytoplankton cells were generally small (< 10 µm) except in a few locations nearshore (where diatoms were likely abundant). High nitrate concentrations were seen below the pycnocline in the Outer and Middle Domains in Bristol Bay. Subsurface phytoplankton blooms were observed near the base of the pycnocline in Bristol Bay (mid August to early September) at depths where nitrate was replete. High ammonium concentrations were observed below the pycnocline in low temperature waters in Bristol Bay. These ammonium values may provide a broad indicator of prior production during the growing season (spring and summer).