McMurdo Dry Valleys: A cold desert ecosystem. W. Berry Lyons, University of Alabama at Tuscaloosa. The McMurdo Dry Valleys, located on the western coast of McMurdo Sound, form the largest ice-free area in Antarctica. In 1993, this area was selected as a study site in the National Science Foundation's Long-Term Ecological Research (LTER) program. The dry valleys are among the most extreme deserts in the world, far colder and drier than any of the other LTER sites. The biological systems in the McMurdo Dry Valleys are composed of only microbial populations, microinvertebrates, mosses, and lichens. Nevertheless, complex trophic interactions and biogeochemical nutrient cycles exist in the lakes, streams, and soils of the dry valleys. Solar energy produces glacial meltwater in the austral summer, and in turn, this meltwater exerts the primary influence on the dry valleys by replenishing water and nutrients to the ecosystems there. All ecosystems are shaped to varying degrees by climate and material transport, but nowhere is this more apparent than in the McMurdo Dry Valleys.

The overall objectives of the McMurdo Dry Valleys LTER are to understand the influence of physical and biological constraints on the structure and function of dry valley ecosystems. These objectives will be accomplished through a program of systematic environmental data collection, long-term experiments, and model development. In addition, LTER researchers will study dry valley lakes as analogs for past Martian environments. The objectives of this aspect of the project are

• to define the biogeochemical processes responsible for controlling the isotopic carbon-13 signature in present-day antarctic lake sediments and use this calibration to infer the environment of paleolakes and
• to determine other environmental markers left in the lake sediments as well as describing the nature of ice/water/sediment interactions in the lakes.

During the 1998–1999 field season, the following studies will be conducted in the McMurdo Dry Valleys as part of the LTER project:

• glacier mass balance, melt, and energy balance (Andrew Fountain, Portland State University);
• chemistry of streams, lakes, and glaciers (W. Berry Lyons, University of Alabama);
• flow, sediment transport, and productivity of streams (Diane McKnight, University of Colorado);
• lake pelagic and benthic productivity and microbial food webs (John Priscu, Montana State University at Bozeman);
• soil productivity (Diana Wall, University of Nevada, Desert Research Institute, and Ross A. Virginia, Dartmouth College);
• aeolian transport processes (Gayle L. Dana, Desert Research Institute); and
• meteorological data collection (Peter T. Doran, Desert Research Institute).

The McMurdo LTER project will emphasize the integration of the biological processes within and material transport between the lakes, streams, and terrestrial ecosystems in the dry valley landscape. This season, several experiments will examine community structure and function within benthic bicrobial mats of the dry valley lakes. In addition, tracer tests will be performed to investigate nutrient transport and uptake in the streams. (BM-042B-O, BM-042-F, BM-042-L, BM-042-M, BM-042-P, BM-042-W, and BM-118-O)

Long-Term Ecological Research on the antarctic marine ecosystem: An ice dominated environment. Maria Vernet, Scripps Institution of Oceanography. The central hypothesis of the Palmer Long-Term Ecological Research (LTER) project 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. Evidence shows that this dynamic variability of sea ice has an important, perhaps major, impact on all levels of the food web, from total annual primary production to breeding success in top predators. For example, variability in sea ice may affect prey and predators directly (e.g., access to open water or preferred habitats) or indirectly (e.g., food availability, which in turn may be affected by the variability in sea ice). We hypothesize that sea ice is a major factor regulating for

• the timing and magnitude of seasonal primary production;
• the dynamics of the microbial loop and particle sedimentation;
• krill abundance, distribution, and recruitment; and
• survivorship and reproductive success of top predators.

The magnitude and timing of sea ice may have different consequences for different key species, and it is still unclear what the ramifications would be for the whole antarctic ecosystem. For example, high levels of survivorship and reproductive success of Adélie penguins appear to depend on high levels of availability of antarctic krill, which in turn appear to be correlated with greater ice coverage. On the other hand, high levels of breeding success of south polar skuas appear to be determined by the availability of antarctic silverfish, which in turn appear to be associated with lesser ice coverage. Thus, the overall objectives of the Palmer LTER project are

• to document not only the interannual variability of annual sea ice and the corresponding physics, chemistry, optics, and primary production within the study area but also the life-history parameters of secondary producers and top predators;
• to quantify the processes that cause variation in physical forcing and the subsequent biological response among the representative trophic levels;
• to construct models that link ecosystem processes to environmental variables and which simulate spatial/temporal ecosystem relationships; and then
• to employ such models to predict and validate ice-ecosystem dynamics.

A key challenge for the Palmer LTER project is to characterize and understand the link between the different spatial and temporal scales of the various physical and biological components of the antarctic ecosystem.

The participants for the 1998–1999 field season will be

• Maria Vernet, Scripps Institution of Oceanography (BP-016-O);
• Douglas Martinson, Columbia University (BP-021-O);
• Langdon Quetin, University of California at Santa Barbara (BP-028-O);
• Raymond Smith, University of California at Santa Barbara (BP-032-O);
• William Fraser, Montana State University (BP-013-O); and
• David Karl, University of Hawaii (BP-046-O).