Palmer Long-term Ecological Research on the Antarctic Marine Ecosystem

The Palmer Long-Term Ecological Research (Palmer LTER) program seeks to understand the structure and function of the Antarctic marine ecosystem in the context of physical forcing (atmospheric, oceanic and sea ice) on seasonal to millennial time-scales (http://www.icess. ucsb.edu/lter/lter.html). The western Antarctic Peninsula (WAP) region, the location of the Palmer LTER (Figure 1), is proving to be an exceptional area to study ecological response to climate variability (Smith et al., 1995, 1999; Ross et al., 1996). Mounting evidence (McCarthy et al., 2001) suggests that the Earth is experiencing human-induced climate variability, and air temperatures from the last half-century confirm the rapidity of warming in the WAP area (Sansom, 1989; Weatherly et al., 1991; King, 1994; Stark, 1994; Smith et al., 1996; King and Harangozo, 1998; Marshall and King, 1998; van den Broeke, 1998a, 1998b; Smith and Stammerjohn, 2001). Consistent with this warming, the sea ice season is shorter and the maritime system of the northern WAP is expanding southward and replacing the continental, polar system of the southern WAP. Ecosystem response to this latitudinal climate change is becoming increasingly evident at all trophic levels (Smith et al., 1998; Smith and Stammerjohn, 2001; Quetin et al., 1996). However, this change is most clearly seen in a shift in population size and distribution of penguin species with different affinities to sea ice (Fraser et al., 1992; Fraser and Trivelpiece, 1996; Smith et al., 1999, 2003). The Palmer LTER seeks to understand the full ecological response to and implications of this climate-related change in physical forcing that is presently occurring in the WAP region. There is now widespread recognition of numerous natural and anthropogenic forced phenomena, such as El Nino-Southern Oscillation (ENSO), atmospheric ozone depletion, green-house gas accumulation, global deforestation, and global warming, that can potentially cause significant ecological change, but that require long-term studies to resolve (McCarthy et al., 2001). The NSFfunded LTER program consists of a community of 24 ecological sitesreferred to as the LTER Network (http://lternet.edu)that study ecological systems with a long-term perspective. The LTER Network maintains a comprehensive set of core measurements made across individual sites and project-specific field experiments that test ecosystem-specific hypotheses to climate PALMER LONG-TERM ECOLOGICAL RESEARCH ON THE ANTARCTIC MARINE ECOSYSTEM