The Effects Of Human Activities On Antarctica Seals In The 20^th Century

A sediment core was collected from the Fildes Peninsula of Antarctica, which contained numerous seal hairs. By analyzing its bio-elements,total organic carbon (TOC) and lithologic characteristics, the top 25.5cm is identified as seal excrement deposition, and the section below 25.5cm is littoral deposition. The seal population changes of the past century in this area were also reconstructed, which are primarily controlled by human activities. The sealing industry in the early 20th century caused the dramatic decline of seal populations. The protection of the Antarctic seals since the 1960s and the increased Antarctic krill population due to whaling lead to the recovery of seal populations and make the high level of the seal population sustainable. The fluctuation of seal population in this area indicates the intense effect of human activities on Antarctic ecosystem in the past century, and provides new paleoenvironmental information of past seal population changes in Antarctica using an indirect geochemical method.We picked up the seal hairs in the HN1 sub-examples, analyzed the ratios of carbon and nitrogen stable isotopes in the seal hairs and reconstructed the seal diet and migrating activities in the 20th century. Based on the analysis,δ15N in the seal hairs increased in the first half of the 20th century and kept constant in the second half, which indicates that the proportion of fish rose in Antarctica seals'diet in the 20th century. The valleys ofδ13C in the 1930s and 1970s suggest that seals migrated to the pelagic water in these periods and trended to littoral water in other periods of the 20th century. In consideration of the sealing activity before the 1960s, we think that the valley in the 1930s implies the escape behaviors of Antarctica seals to sealing. And the valley in the 1970s indicates that many seals had to migrate to the pelagic water for food because the seal population increased sharply after 1960s.Combining the results of mice experiment in the lab, we infer that the sealing activity in the last century not only gave huge survival pressure to the seals in the Fildes Peninsula (which forced seals to trend to food of low trophic levels), but also affected the physiological process of Antarctica seals (which induced the fractionation of the nitrogen stable isotope between the seal tissue and food and the decrease ofδ15N in the seal hairs). Thus, we think that the human activity is the main factor inducing the fluctuation of the carbon and nitrogen stable isotopes in the seal hairs in the last century and the changes of seal diet and migrating activities, which has become the main effect on the Antarctica ecosystem.