9632763 Smith This proposal continues, for a second six year period, the Palmer Long-Term Ecological Research program which focuses on the marine ecosystem in the western Antarctic Peninsula region. A central tenet of this research is that the annual advance and retreat of sea ice is a major physical determinant of spatial and temporal changes in the structure and function of the Antarctic marine ecosystem, from total annual primary production to breeding success in seabirds. We are currently evaluating a number of testable hypotheses linking sea ice to: the timing and magnitude of seasonal primary production, the dynamics of the microbial loop and particle sedimentation, krill abundance, distribution, and recruitment, and the breeding success and survival of apex predators. The overall objectives are to: (1) document the interannual variability of annual sea ice and the corresponding physics, chemistry, optics, primary production and the life-history parameters of secondary producers and apex predators within the area, (2) create a legacy of critical data for understanding ecological phenomena and processes within the Antarctic marine ecosystem, (3) identify the processes that cause variation in physical forcing and the subsequent biological response among the representative trophic levels, (4) construct models that link ecosystem processes to environmental variables, which simulate spatial/temporal ecosystem relationships, and employ such models to predict and validate ice-ecosystem dynamics. Since 1991 the program has included spatial sampling during annual and seasonal cruises in portions of our regional grid in the region and temporal sampling from spring through fall (October to March) in the area adjacent to Palmer Station. The program was designed to sample at multiple spatial scales within one regional scale grid, permitting repeated sampling on both seasonal and annual time scales, thus addressing both short and long -term ecological phenomena, as well as providing a basis for specific mechanistic studies. To date, there have been seven regional cruises and two additional cruises emphasizing microbial dynamics (Tables 1 and 2). Core variables routinely sampled and monitored from shipboard during annual cruises. Documentation and data storage are organized through an electronic hub at the Institute for Computational Earth System Science at the University of California at Santa Barbara which also serves as a data archive as needed. There are on-line definitions of core data, datasets and metadata, organized to facilitate rapid information exchange and on-line data documentation. This multidisciplinary project, sited in a climatically sensitive region, has the potential to detect, against a background of natural variability, long term trends in the Antarctic ecosystem.
