The occupation history of the longest-dwelling Adélie penguin colony reflects Holocene climatic and environmental changes in the Ross Sea, Antarctica

As a result of climate changes, penguins are predicted to be at risk of losing their breeding habitats. Changes in penguin colony distribution suggest that some colonies have withstood environmental changes better than others, serving as initial post-glacial settlements or refuges in adverse climatic conditions. Here we have synthesized over 200 dates (including 91 new dates) of penguin remains and of guano in 107 ornithogenic profiles from abandoned nests on Inexpressible Island, one of the longest persisting Adelie penguin colonies in Antarctica, to investigate the dynamics of population size and the role of this island in the ecological history of this species. The results indicate that, following the retreat of Ross Ice Shelf, the Adelies first colonized this island at ~8.6 kyr BP, documenting the earliest known breeding site in the Ross Sea since deglaciation. During ~7-3 kyr BP the reconstructed population on Inexpressible Island was generally consistent with the change in pack ice, reaching relative peaks at 5.5 e5.0 and 4.0e3.5 kyr BP. After brief decline at 3.5e3.0 kyr, substantial enlargement of the penguin colony occurred between 3.0 and 1.5 kyr BP, attributed to the immigration from the abandoned colonies along the Scott Coast. During this time, the persistent efficiency of Terra Nova Bay polynya offered conditions favourable to the expansion of the penguin population on Inexpressible Island, which probably represented a refuge area under increased coastal sea-ice. This longest-dwelling penguin colony may provide a valuable refuge for the Adelie penguin if the recurrent Terra Nova Bay polynya persists under future climatic and environmental changes, as occurred in the past.