1997 SEBSCC Progress Report

Title: Origin and Physical/Biological Dynamics of Nutrients

PI: Terry E. Whitledge
Marine Science Institute
The University of Texas at Austin
750 Channelview Drive
Port Aransas, Texas 78373-5015

phone: (512) 749-6769
fax: (512) 749-6777
e-mail: terry@utmsi.utexas.edu

Objective: To determine the sources and distribution of nutrients in the southeast Bering Sea with respect to physical processes and to determine the utilization and regeneration of nutrients with respect to primary production and recycling biological processes.

Approaches: Nutrient samples for nitrate, nitrite, ammonium, phosphate and silicate were collected during SEBSCC cruises in collaboration with physical and biological sampling. Most nutrient samples were analyzed fresh onboard ship so that analysis results could be used to guide the sampling depths in transects and time series stations. Some nutrient samples collected at the beginning and end of the cruise period during mooring deployment and retrieval were frozen due to funding limitations. Additional analyses for urea and DON were performed on all nutrients from productivity casts. Phytoplankton pigments samples were also collected to obtain profiles of phytoplankton biomass and to calibrate fluorescence sensors on the CTD and underway surface fluorometer.

Accomplishments: Nutrient samples from all SEBSCC cruises were analyzed to provide the basis for determining the origin and rate of supply of nutrients to the southeast Bering Sea study area. Multiple samplings of transects and time series stations will allow estimates of advective and diffusive inputs of nutrients to the shelf areas and an estimate of phytoplankton nutrient uptake in collaboration with isotope uptake studies. Additional nutrient samples were also analyzed in collaboration with deep Bering Sea and inner shelf studies in order to provide a better estimate of the interactions with these areas on the SEBSCC boundaries.

Interpretations: The distributions of nutrients observed indicated that enrichment processes were smaller than previously observed with a probable cause of weaker advective transport and/or stronger stratification. Major biological productivity uptake of nutrients occurred before the May cruise so that nutrient depletion of the water column on the outer shelf and middle was significant. The depletion of nutrients below the pycnocline that occurred later in the summer was interpreted as uptake by deep phytoplankton productivity and nutrients were not replenished by typical physical processes.

Publications:
Vance, T.C., R.D. Brodeur, C. Baier, K. Coyle, M.B. Decker, G. Hunt, J.M. Napp, J.D. Schumacher, P.J. Stabeno, D. Stockwell, C. Tynan, T.E. Whitledge and S. Zeeman. (1998). Ecosystem Anomalies in the Eastern Bering Sea: Including Blooms, Birds and Other Biota. Eos. (In press).

Presentations:
Whitledge, T.E. Origin and Physical/Biological Dynamics of Nutrients. Presented at the annual SEBSCC investigators meeting, Battelle Conference Center, Seattle, 15-16 December 1997.

Napp, J.M., C.T. Baier, R.D. Brodeur, J.J. Cullen, R.F. Davis, M.B. Decker, J.J. Goering, C.E. Mills, J.D. Schumacher, S. Smith, P.J. Stabeno, T.C. Vance, T.E. Whitledge, The 1997 Eastern Bering Sea Shelf-Wide Coccolithophorid Bloom: Ecosystem Observations and Hypotheses. AGU/ASLO Ocean Sciences 98 Meeting, San Diego, 9-13 February 1998.

Hunt, G.L., K.O. Coyle, J.D. Schumacher, P.J. Stabeno, D. Stockwell, T.E. Whitledge and S. Zeeman. Ecosystem Anomolies in the Eastern Bering Sea: Seabird Dieoff and Coccolithophorid Bloom Follow Calm Spring and Strong Stratification. AGU/ASLO Ocean Sciences 98 Meeting, San Diego, 9-13 February 1998.