Palmer Antarctica Long Term Ecological Research (PAL-LTER) Project is one of twenty-five sites in the US LTER Network. The principal goal of LTER is to “…to conduct research on ecological issues that can last decades and span huge geographical areas” (http://www.lternet.edu). Since its inception in 1990 the major scientific objective of our program has been to understand how year to year and decade to decade changes in the marine ecosystem are related to and controlled by changes in the areal extent, seasonality and duration of sea ice in the western Antarctic Peninsula region (WAP). We conduct research annually in the nearshore region at Palmer Station (the area accessed by small boats) and the offshore regions extending 200 km from the coast to the Antarctic Circumpolar Current, and from Palmer Station 700 km south to Charcot Island aboard icebreaker LM GOULD. We also have a very active educational and outreach program. Our aim is to improve understanding of, and literacy in science, technology and mathematics using examples from Antarctic science to engage students and learners at all levels.

Intellectual Merit. By the mid-1990s we recognized and documented that the WAP region is experiencing rapid rates of climate change, including warming ocean and air temperatures, melting and retreating glaciers and declining sea ice cover. The goal of the 2008-14 award has been to document and understand how the marine ecosystem is responding to several decades of climate warming in the WAP region. Previously we had reported on a long term (1980-present) decline in numbers of Adélie penguins in the Palmer region. At the same time, as the region warms and sea ice cover declines, Gentoo and Chinstrap penguins have colonized the region and are successfully breeding. The changes in penguin populations are emblematic of a paradigm that identifies some species of polar plants and animals as ice-obligate (e.g., Adélie penguins and Antarctic krill) and other related species as ice-independent to ice-intolerant (e.g., Gentoo penguins and gelatinous plankton). We hypothesize that we are observing the early stages of an ecosystem transformation from a polar, ice obligate to a subpolar, ice-independent ecosystem (see Figure 1 attached).

Recently our research has been aimed at detecting predicted changes of other organisms in the polar foodweb in our region, and understanding the ecological and physical processes causing the changes. One of the most important PAL discoveries was that phytoplankton stocks (the single-celled plants at the base of the foodweb) had declined by over 50% between 1978 and 2006 in the northern region of the WAP (Figure 2; the area experiencing most climate change). Further, we showed that the phytoplankton decline was linked to sea ice decline. Sea ice decline results in phytoplankton losses by decreasing the vertical stability (resistance to wind mixing) of the water column, and causing phytoplankton to be mixed deeper, and thus experiencing less light, needed for photosynthesis and growth (Figure 3).

Detecting decadal and longer changes in krill populations has been more difficult, even though the Antarctic krill life cycle is intimately tied to the rhythms of sea ice. However, in one of the final papers published during this award, we showed how krill populations vary in response to cycles in phytoplankton growth caused by sea ice changes (Figure 4). At Palmer Station there are cycles with 3 to 5 years of low phytoplankton abundance punctuated by one or two years of high abundance. Krill reproduction responds to the high phytoplankton years. In addition the sea ice/phytoplankton cycle is driven by changes in a large-scale atmospheric pattern, the Southern Annular Mode or SAM (Figure 5). It has been predicted that glo...

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