Sinking Particles and Pelagic Food Webs in the SE Bering Sea : 1997 - 2002

Sinking Particles and Pelagic Food Webs in the SE Bering Sea: 1997-2002 Susan M. Henrichs and Stacy Smith, School of Fisheries and Ocean Sciences, UAF The southeastern Bering Sea shelf is an economically and ecologically important system that is subject to substantial natural and human-induced change (National Research Council, 1996). Despite this, long term observations are limited and fragmentary in time and space, which severely restricts our ability to identify the effects on the ecosystem due to climatic variability. During recent years, marked changes in the physical and biological environment of Bering Sea have occurred. The most comprehensive characterization ofthe changes in the physical environment has been based upon observations collected from biophysical moorings (Stabeno et aI., 1998~ 1999~ 2001). Since 1995 Stabeno and collaborators have been monitoring site M2, over the Bering Sea middle shelfnear 56°N, with funds provided by NOAA's Southeast Bering Sea Carrying Capacity (SEBSCC, Phases I, II, and III) and Fisheries Oceanography Coordinated Investigations (FOCI), measuring temperature, salinity, chlorophyll, current speed, and meteorological conditions. A time-series sediment trap has been deployed near that mooring since 1997. The composition of sinking organic material collected by the trap, along with a parallel time-series of zooplankton stable isotopic composition, has reflected changes in the pelagic food web during that period. The biophysical mooring deployment will continue through 2002 if support is provided through the Pollock Conservation Cooperative (Whitledge and Stabeno proposal)~ unfortunately .~. NOAA support for the mooring (except for some logistical support) will end in 2001, making their funding request to the PCCRI necessary to continue this very valuable series of observations. This proposal requests funds for two additional deployments ofa time-series sediment trap, at the same time and location as the biophysical mooring, for analysis ofthe sediment traps samples, and for collection and analysis of zooplankton samples. The specific hypothesis to be addressed by the research proposed here is that the temporal variation ofthe quantity and composition of sinking particles depends on changes in the pelagic food web, which in tum are largely dependent on interactions among weather and climate. The research aims to improve understanding ofbiophysical controls on primary production and ofthe transfer ofwater column production to the benthos. The carbon and nitrogen stable isotope composition and selected biomarkers, including wax esters and sterols, will be measured in the trapped material, as has been done for Phases I and II ofthe SEBSCC program and for 2001 with support from the Pollock Conservation Cooperative Research Center. Together with the research being conducted by Stabeno, this proposed research will provide measurements to identify and characterize spatial and temporal variability ofthe physical environment and the biological response to changing conditions. Such monitoring is essential to address the influence of climate change on this ecosystem. Sinking Particles and Pelagic Food Webs in the SE Bering Sea: 1997·2002. Susan M. Henrichs and Stacy Smith, School ofFisheries and Ocean Sciences, University ofAlaska, P. O. Box 757220, Fairbanks, AK 99775.