Geochemical characteristics of a 107 cm long sediment profile,collected from Ganquan Island,South China Sea,were analyzed.Based on concentrations of bio-elements（Cu,Zn,Cd,Ba,As, Se,P）,^（210）Pb and AMS^（14）C dating,we reconstructed seabird population of Ganquan Island over the past 2200 years.Seabirds inhabited this island more than 2200 years ago,and their population displayed remarkable fluctuations with two peaks around 2100-1850 yr BP and 900-300 yr BP,respectively.The seabird population change profile on Ganquan Island is similar to that on Dongdao Island over the past 1800 years.We examined the relationship between the seabird population and climate,and found it quite complicated.The seabird population did not reach the maximum during the Medical Warm Period（MWP）with relatively high average temperature;however,it remained near the peak value for about 600 years during the climatic transition period and the Little Ice Age（LIA）,indicating that a relatively cool climate is favorable for seabirds on Ganquan Island.
Two ornithogenic sediment cores,which have a time span of 1000 years and are influenced by red-footed booby （Sula sula）,were collected from Dongdao Islands,South China Sea.The determined mercury concentrations of the two cores show similar and substantial fluctuations during the past millennium,and the fluctuations are most likely caused by the changes in mercury level of the ocean environment and in anthropogenic Hg emission.For the past 500 years,the mercury concentration in the red-footed booby excrement has a striking association with global anthropogenic mercury emission.The mercury concentration increased rapidly after AD 1600 in corresponding to beginning of the unparalleled gold and silver mining in South Central America that left a large volume of anthropogenic mercury pollution.Since the Industrial Revolution,the mercury level has increased at a fast pace,very likely caused by modern coal combustion,chlor-alkali and oil refining industries.The comparison of mercury profiles from different places on earth suggested that anthropogenic mercury pollution after the Industrial Revolution is more severe in Northern Hemisphere than in Antarctica.
Compared with traditional chemical analysis methods,reflectance spectroscopy has the advantages of speed,minimal or no sample preparation,non-destruction,and low cost.The present study explored the application of the reflectance spectroscopy within near ultraviolet-visible-near infrared region to predict bio-element compositions in the ornithogenic sediments from the maritime Antarctic.A total of 106 samples were taken from four ornithogenic sediment cores on the Ardley Island of Antarctica,68 samples were used for building calibration equation,and 38 for prediction of nine bio-elements including P,Ca,Cu,Zn,Se, Sr,Ba,F and S.Three multivariate statistical analysis techniques,including stepwise multiple linear regression（Stepwise-MLR）,principal component regression（PCR） and partial least squares regression（PLS） were used to develop mathematical relationships between the spectral data and the chemical reference data.The results showed that the regression models constructed by PCR and PLS models have no significant differences,and obviously supervisor to Stepwise-MLR.The correlations between spectra-predicted and chemically analyzed concentrations of nine bio-elements are statistically significant,and the concentration-versusdepth profiles predicted from reflectance spectra using PLS calibration model are consistent with those from actual chemical analysis.These results demonstrated the feasibility of using reflectance spectroscopy to infer bio-element concentrations in the ornithogenic sediments,and thus it is suggested that the reflectance spectroscopy could provide a rapid and valuable technique to indirectly identify whether the sediments were influenced by penguin droppings in the Antarctic region.
As the topmost predator in Antarctica,the seal is a unique indicator of Antarctic environment and climate changes.In this study,we collected a sediment core from the Fildes Peninsula of West Antarctica,and used cholesterol,cholestanol,epicoprostanol,coprostanol,and seal hair numbers as the proxy indicators of seal population size and phytol as of general vegetation,and we reconstructed the 20th century history of variation of the seal population and vegetation abundance on this island.The sealing industry in the early 20th century caused the dramatic decline of seal population,and the ban of seal hunting since the 1960s led to its recovery of seal population.The seal population during the past century was primarily controlled by human activities and krill density.The reconstructed relation between seal population and vegetation abundance may offer new insights into Antarctic environment and ecology.
Positioned near the top of the food web, the dietary composition of Antarctic penguins and seals can be an excellent indicator of the regional food web and thus the status of the marine ecosystem. The dietary composition of modern penguins and seals has been well investigated; a long-term time series of data on penguin and seal diets,however, are rare. Such data, especially any predating the initiation of human harvesting of fish, whales and seals in Antarctica, are crucial for understanding and predicting responses of regional marine food webs to natural climate changes. Here we review recent progress on research of paleodietary change in Antarctic penguins and seals, specifically the Ade′lie penguin(Pygoscelis adeliae) and Antarctic fur seal(Arctocephalus gazella). These studies indicate that the dietary changes of penguins correspond quite well with fluctuations in climate and sea ice extent during the Holocene. The depleted d15 N ratios found in modern Ade′lie penguins support the ‘‘krill surplus hypothesis' ' in relation to historic human depletion of krilleating fish, seals and whales.
