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Insights into the Holocene environmental setting of Terra Nova Bay region (Ross Sea, Antarctica) from oxygen isotope geochemistry of Adélie penguin eggshells

An oxygen isotope record of Adélie penguin (Pygoscelis adeliae) eggshells from Terra Nova Bay (Victoria Land, Antarctica) has been reconstructed in order to provide insights into the palaeoenviroment of this region during the last ~8000 years. The δ18O values measured in eggshell carbonate show a great variability over the course of the studied period, with maximum values consistently around +27.5‰. Adopting a metabolic enrichment relative to water source of ~+28.5‰, eggshell δ18O values can be interpreted in terms of marine water uptake by the penguins. The spread in δ18O of eggshell carbonate at any given time toward more negative values reflects the existence of a low δ18O water end member, most plausibly snow or snowmelt. Samples younger than 2000 years are characterized by a general lack of very negative δ18O values. As also attested by other proxies, this shift toward more positive isotopic values is likely to be related both to a decreasing contribution of snow or meltwater in the seawaters and consequently to an absence or paucity on the boundary of the nesting sites of snow or snowfall and freshwater that could be directly eaten or drunk by penguins.