MAJOR SHIFT IN ADÉLIE PENGUIN EGGSHELL ISOTOPE VALUES IN ANTARCTICA: EVIDENCE FOR DIET CHANGE ~200 YEARS AGO

Abandoned Adélie Penguin (Pygoscelis adeliae) colonies have been identified in numerous coastal, ice-free regions and islands in Antarctica that often contain a well-preserved record of organic remains including penguin bones, feathers, tissue, and eggshell. This record has been used to infer episodes of climate change that have affected the distribution and abundance of penguins in Antarctica for millennia. Dietary remains recovered from the ornithogenic (bird-formed) soil at these sites include otoliths and squid beaks, but no remains of krill (Euphausia spp.) are preserved. Thus, the primary diet of this species in the past has been difficult to infer without additional evidence. Stable isotope analyses eggshell, bone and keratin now provide for an assessment of seabird diets. However, isotope analyses of fossil remains may be compromised by poor preservation. We used modern and well-preserved ancient Adélie Penguin eggshell collected from three major regions in Antarctica to examine variation in nitrogen and carbon isotopes over the last 9000 years. We analyzed eggshell carbonate for carbon and oxygen isotope values and organic components of the shell for carbon and nitrogen isotope values. Our results indicate a major shift in eggshell carbonate and organic matrix isotope values at some time between 265 and 90 years ago. Carbon and nitrogen isotope values both display large shifts. We hypothesize that depletion of whales and seals during the whaling era, beginning in the 1820s, caused an ecological response in penguins and a shift in diet primarily from fish to krill (Euphausia spp.). Additional research on this response and its timing is ongoing.