Palmer LTER

Tracking Global Change on the Antarctic Peninsula

Penguin populations fluctuate with climate warming trends

The Antarctic Peninsula, a relatively long narrow extension of the Antarctic continent (see figure) is defined by a strong climatic gradient between the cold dry continental regime to its south and the warm moist maritime regime to its north. This gradient results in a highly variable environment that is sensitive to climate perturbation. Long-term studies in the western Antarctic Peninsula (WAP) region provide the opportunity to observe how climate-driven variability is related to changes in the marine ecosystem.

Figure 1. Twenty five year trends in Adelie & chinstrap penguin populations at Arthur Harbor (Palmer Station) and for gentoo penguins since founder colonies became established in the early 1990's. Adelie penguins normalized to 100% in 1975 when the record began. Chinstrap and gentoo penguins are normalized to 100% in 1977 and 1995, respectively, one year after founding colonies began.

This is a sea ice-dominated ecosystem where the annual advance and retreat of the sea ice determines spatial and temporal change in its structure and function, from total annual primary production to the breeding success and survival of seabirds (Smith et al. 1999). Ecological responses to this climate variability are evident at all trophic levels, but are most clearly seen in a shift in the population size and distribution of penguin species with different affinities to sea ice (Fraser et al. 1992; Smith et al. 1999).

Long-term research on the WAP region has revealed a significant warming trend during the past half century. In addition, a statistically significant anti-correlation between air temperatures and sea ice extent has been observed. Satellite observations show that sea ice extent in the WAP area has declined during this period, and the sea ice season has shortened (Smith & Stammerjohn 2001).

The basis for understanding the possible causess associated with penguin population trends originated with the hypothesis that a decrease in the number of cold years with heavy winter sea ice due to climate warming produced habitat conditions more suitable for ice-intolerant (Chinstrap & Gentoo), as opposed to ice-dependent (Adelie), penguins. These trends clearly support this "ice reduction" hypothesis and would not have been evident without long-term records.