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Abstract: Carbon and nitrogen stable isotope analyses were performed on modern and Holocene Adélie penguin guano samples collected from ornithogenic soils along the Scott Coast (Southern Victoria Land, Antarctica), from Cape Irizar to Dunlop Island, and at Cape Bird (Ross Island). Guano samples also were sieved and sorted under stereomicroscope in order to select penguin dietary remains, such as fish bones and otoliths. Carbon and nitrogen stable isotope composition, coupled with the taxonomic identification of fish otoliths from Scott Coast Holocene samples, indicated a mainly fish-based diet for this area, with Pleuragramma antarcticum as the most eaten prey throughout the investigated period (from 390cal BP to ca 7300cal BP). The isotopic values of Ross Island samples (from modern to 3850cal BP) showed a krill consumption increase in the samples younger than 2000cal BP, with the maximum in modern samples. Scott Coast and Ross Island Holocene samples showed δ13C and δ15N trends similar to those previously published from Terra Nova Bay (northern Victoria Land), whereas modern samples from Ross Island have similar δ15N composition but different δ13C values. This δ13C divergence started at ca 2000 BP and follows the abandonment of the Scott Coast colonies. The δ13C trend observed in Ross Island and Terra Nova Bay samples and the abandonment of the Scott Coast colonies could suggest the stability and the persistence of the previous oceanographic conditions (i.e. polynya) for the Terra Nova Bay area and the establishment of new conditions for water circulation in the Southern Ross Sea since ~2000 BP when persistent sea-ice sealed the Scott Coast. [Copyright &y& Elsevier]

délie penguin ( Pygoscelis adeliae) modern and fossil eggshells and guano samples collected from ornithogenic soils in Terra Nova Bay (Victoria Land, Ross Sea) were processed for carbon and nitrogen isotopic ratios with the aim of detecting past penguin dietary changes. A detailed and greatly expanded Adélie penguin dietary record dated back to 7,200 years BP has been reconstructed for the investigated area. Our data indicate a significant dietary shift between fish and krill, with a gradual decrease from past to present time in the proportion of fish compared to krill in Adélie penguin diet. From 7,200 to 2,000 years BP, δC and δN values indicate fish as the most eaten prey. The dietary contribution of lower-trophic prey in penguin diet started becoming evident not earlier than 2,000 years BP, when the δC values reveal a change in the penguin feeding behavior. Modern eggshell and guano samples reveal a major dietary contribution of krill but not a krill-dominated diet, since δC values remain much too high if krill prevail in the diet. According to the Holocene environmental background attested for Victoria Land, Adélie penguin dietary shifts between fish and krill seem to reflect penguin paleoecological responses to different paleoenvironmental settings with different conditions of sea-ice extension and persistence. Furthermore, Adélie penguin diet appears to be particularly affected by environmental changes in a very specific period within the breeding season, namely the egg-laying period when penguin dietary and feeding habit shifts are clearly documented by the δC of eggshell carbonate. [ABSTRACT FROM AUTHOR]