ABSTRACT

The Palmer, Antarctica, Long-Term Ecological Research Project (PAL) seeks to understand the structure and function of the Western Antarctic Peninsula's marine and terrestrial ecosystems in the context of seasonal-to-interannual atmospheric and sea ice dynamics, as well as long-term climate change. The PAL measurement system (or grid) is designed to study marine and terrestrial food webs consisting principally of diatom primary producers, the dominant herbivore Antarctic krill, and the apex predator Adelie penguin. An attenuated microbial food web is also a focus. PAL studies these ecosystems annually over a regional scale grid of oceanographic stations and seasonally at Palmer Station. Sea ice extent and variability affects ecosystem changes at all trophic levels. In recent years, sea ice extent has diminished in response to a general warming in the region. Long-term population trends of ice-dependent Adelie penguins in the region provide a clear example of impact of the climate warming trend in the in the region. Adelie populations at the five major colonies studied near Palmer Station have all shown a gradual decrease in numbers over thirty years. The Peninsula runs perpendicular to a strong climatic gradient between the cold, dry continental regime to the south, characteristic of the Antarctic interior, and the warm, moist, maritime regime to the north. North-south shifts in the gradient give rise to large environmental variability to climate change. Currently more maritime conditions appear to be replacing the original polar ecosystem in the northern part of the peninsula as the climatic gradient shifts southward. To date, this shift appears matched by an ecosystem shift along the peninsula, as evidenced by declines in Adelie populations that require longer snow-cover seasons for successful recruitment. The main hypothesis is that ecosystem migration is most clearly manifested by changes in upper level predators (penguins) and certain polar fishes in predator foraging environments. This is because these longer lived species integrate recent climate trends and because individual species are more sensitive indicators than aggregated functional groups. Analogous modifications are expected to be manifested at lower trophic levels in the marine parts of the system in the years ahead. However, these lower level changes are likely to be observed only through long-term observations consistent with the concept of expansion and contraction of ecosystem boundaries along the Peninsula. The PAL-LTER will continue to investigate ecosystem changes at lower trophic levels along the Peninsula, in response to the continued, dramatic climate warming and pole ward shifts in the climatic gradient. In addition to the long-term research activities, graduate student training, the involvement of K-12 teachers and web-based education are an integral part of the PAL-LTER.

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