Palmer LTER: Long-Term Ecological Research on the Antarctic Marine Ecosystem: Looking Back in Time Through Marine Ecosystem Space.

The Palmer Station region on the western shore of the Antarctic Peninsula, site of Palmer LTER, is one of the most rapidly warming regions on Earth, especially in winter. Long-term observations (1950-present) at the former UK Faraday Station; now Vernadsky Base, Ukraine) about 40 km south of Palmer Station, as well as more recent Palmer Station records (1975-) indicate a wintertime warming of 1 deg C per decade, about 5 times the global mean. If this warming continues until the mean wintertime temperature exceeds the freezing point of seawater, sea ice will no longer form, triggering fundamental ecosystem regime change. The mean annual temperature at Palmer Station is -2.0 C and the mean annual precipitation is 679 mm.

Sea ice forms each year around the Antarctic continent, extending several 100s of km offshore in winter with a total extent of 19 million km². Sea ice retreat in the Austral spring freshens and stratifies the upper ocean, triggering phytoplankton blooms supporting the marine foodweb. Thus the extent and duration of the annual sea ice cover are major determinants of foodweb dynamics, life histories and biogeochemical cycles in coastal Antarctic ecosystems. In response to warming in the Peninsula region since 1979, sea ice retreats 35 days earlier and advances 48 days later in the year, reducing the period of ice cover by 83 days.

The region is characterized by spring diatom blooms that provide food for the Antarctic krill Euphausia superba, the most abundant metazoan species on Earth, which in turn nourishes abundant large predators including penguins, seals and whales.  In response to reductions in sea ice cover, blooms have declined by 90% in the north while increasing by 60% in the south since 1978. In the south, declining ice cover has opened new, formerly ice-covered areas to light penetration, stimulating new blooms. The species composition of the phytoplankton community is also changing in response to warming and ice loss.

Changes in the number of breeding pairs and distribution of the 3 congeneric species of penguins (Adélie, Gentoo and Chinstrap) dramatically signal the impact of climate change in the PAL region and suggest a major regime shift. Winter sea ice represents critical winter habitat for Adélie penguins, and its regional disappearance has led to a severe decline in the population of this species. Populations of the Subantarctic (ice-avoiding) Gentoo and Chinstrap penguins are migrating south with the warming climate and are now successfully colonizing and breeding in the Palmer region. The combined Gentoo and Chinstrap populations now equal the declining Adélie population. Adélie populations are still growing 400 km to the south.