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Creators/Authors contains: "Emslie, Steven D."

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  1. Abstract

    Studies of Antarctic paleo‐archives have produced conflicting hypotheses on the relative impact of long‐term climate change and historic exploitation of marine mammals on Southern Ocean krill predator foraging ecology. We disentangle these hypotheses using amino acid stable isotope analysis on a 7000‐yr Holocene archive of Adélie penguin (Pygoscelis adeliae) eggshells to differentiate variation in diet and trophic dynamics from baseline biogeochemical cycling as drivers of the rapid decline in krill predator bulk tissue δ15N values in recent centuries. Contrary to previous hypotheses suggesting solely trophic dynamic mechanisms as drivers of this decline, we identified an abrupt decline in source amino acid δ15N values, indicative of major changes in biogeochemical cycling at the base of the Southern Ocean food web that mirrored the decline in penguin bulk tissue δ15N values. These abrupt shifts in penguin δ15N values and associated biogeochemical cycling aligned with climatic events during the Little Ice Age that decreased surface δ15NNO3−, likely connected to a proposed increase in Ekman upwelling via a southward migration of the Westerlies. This baseline shift was in addition to a long‐term, gradual decline in penguin trophic position over the Holocene that began prior to both recent anthropogenic climate change and a proposed “krill‐surplus” following historic marine mammal exploitation in the 19thand 20thcenturies. In resolving these outstanding hypotheses about drivers of Southern Ocean food web dynamics, this study emphasizes the fundamental importance of climate‐induced variability in biogeochemical cycling on ecological processes and improves the ability of paleo‐archives to inform the ecological consequences of future environmental change in the Southern Ocean.

     
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  2. Abstract The Ross Sea (Antarctica) is one of the most productive marine ecosystems in the Southern Ocean and supports nearly one million breeding pairs of Adélie penguins (Pygoscelis adeliae) annually. There also is a well-preserved record of abandoned penguin colonies that date from before the Last Glacial Maximum (>45,000 14C yr B.P.) through the Holocene. Cape Irizar is a rocky cape located just south of the Drygalski Ice Tongue on the Scott Coast. In January 2016, several abandoned Adélie penguin sites and abundant surface remains of penguin bones, feathers, and carcasses that appeared to be fresh were being exposed by melting snow and were sampled for radiocarbon analysis. The results indicate the “fresh” remains are actually ancient and that three periods of occupation by Adélie penguins are represented beginning ca. 5000 calibrated calendar (cal.) yr B.P., with the last occupation ending by ca. 800 cal. yr B.P. The presence of fresh-appearing remains on the surface that are actually ancient in age suggests that only recently has snowmelt exposed previously frozen carcasses and other remains for the first time in ∼800 yr, allowing them to decay and appear fresh. Recent warming trends and historical satellite imagery (Landsat) showing decreasing snow cover on the cape since 2013 support this hypothesis. Increased δ13C values of penguin bone collagen further indicate a period of enhanced marine productivity during the penguin “optimum”, a warm period at 4000–2000 cal. yr B.P., perhaps related to an expansion of the Terra Nova Bay polynya with calving events of the Drygalski Ice Tongue. 
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