The Various Responses Of Penguin Ecology To The Variations In Past Climate,in The Vestfold Hills

Penguin is one of the most typical wildlifes of Antarctica,an apex predator in the ecosystem of the Southern Ocean,and also a sensitive indicator of the changes in climate and environment.The subsistence of penguins strongly relies on specific conditions of the atmosphere,land and ocean that they live in.In th is research,Iselected the area of Long Peninsula,on the north of the Vestfold Hills,East Antarctica,as the study field to represent a typical site of maritime Antarctica.Here I analyzed the lacustrine sediment cores,ornithogenic profiles,penguin remains(feathers,bones,eggshells)and carcasses either from the land surface or the guano layers in the strata from the active and abandoned penguin colonies.Applying multi-disciplinary approaches such as sedimentology,paleoclimatology,and elemental/isotopic/organic geochemistry,I reconstructed the ecological history of the local penguin populations,including the changes in population sizes,diets,colony establishment and abandomment,at multiple time-scales during the Holocene.Then I investigated the responses of the penguin ecology to the complex variations in climatic and environmental factors and discussed the diversity in the pattern and mechanism of penguin evolution.1.Penguin colonization following the glacial-interglacial transitionI investigated an ornithogenic core from Long Peninsula,to improve knowledge of postglacial penguin colonization.Local deglaciation occurred around 15.6 kyr BP,based on a coarse-grained detrital layer,a date that is earlier than most of those reported in other studies from the same region.Geochemical analysis of the core suggests penguins started colonizing the northern Vestfold Hills around 14.6 kyr BP,the oldest geological record in East Antarctica on penguin occupation,and their population exhibited a broadly increasing trend thereafter.The population expanded at approximately 6740 yr BP,in the mid-Holocene,which corresponds to a local climatic optimum.Although this inference is based on population changes of local sub-colonies,it corresponds well to reconstructions of regional climate change,and changes in the penguin population based on genetic studies.From a consideration of the results of previous studies of the occupatin history of sea birds following deglaciation in the Arctic,as well as other parts of Antarctica,I propose th at sea birds colonized the emerging ice-free areas shortly after local glacier retreat.Over geological time-scales,the availability of breeding habitat is a key factor controlling the population size and activity range of Antarctic Adelie penguins.2.Centurial to sub-centurial fluctuations in the past-2000-year penguin population and dietIn this section,I analyzed two millennial-scale ornithogenic sediment cores,from Long Peninsula.Using the Al-normalized phosphorus content of the bulk sediment and carbon/nitrogen fractions in penguin remains,we reconstructed relative changes in the penguin population size of each sub-colony and relative krill abundance in the summer Prydz Bay polyn ya.Both records of penguin and krill are correlated to the fluctuations in solar irradiance,over centurial to sub-centurial time-scales:demonstrating a food-chain mechanism that is related to solar activity and light availability at the ocean surface,which influence the intensity of photosynthesis and phytoplankton productivity,and thus the abundance of krill and apex predators such as penguins.The findings highlight the change in food availability is the predominating factor driving the penguin dynamics in the last thousand years.3.Penguin mass mortality and colony abandonment in the last milleniumOn Long Peninsula,I identified numerous mummified Adelie penguin carcasses and phases of rapid sediment deposition at?750 and?200 yr BP,indicating two multi-decadal mass mortality events.Based upon chronological,landscape sedimentary evidence,we propose that the two events were caused by heavy regional precipitation which led to the abandonment of numerous penguin sub-colonies.The anomalous precipitation was likely associated with of the inetnsification of regional meridional air transport under a zonal wave number 3 pattern.Since such atmospheric conditions correspond to present-day observations,and are expected to persist if climate change continues,the mortality events revealed in this study could become an increasing threat to penguins.