δ13C and δ15N in the ornithogenic sediments from the Antarctic maritime as palaeoecological proxies during the past 2000 yr

In this paper, we have examined carbon and nitrogen isotopic compositions in two ornithogenic sediment profiles from the Ardley Island and Barton Peninsula of Antarctica for palaeoecological changes during the past 2000 yr. The δ13C values of the two sediment profiles range from − 22.26‰ to − 19.15‰ (PDB) in Core G and from − 24.01‰ to − 19.87‰ in profile A, showing that the predominant carbon source in the sediments plausibly comes from terrestrial and aquatic plants in Antarctic such as mosses, lichens, and algae in lakes. As these δ13C values are also close to those in the fresh lake sediments that are not influenced by penguin guano, one may not use the δ13C values as evidence for the influence of guano on the sediments. The δ15N values of the two profiles range from 4.75‰ to 18.34‰ (air) and from 5.17‰ to 10.38‰ for Core G and Core A, respectively. The δ15N variations have positive correlations with the trends of the bio-element contents in the sediments. As the levels of these bio-elements in ornithogenic sediments had been used to reconstruct the changes of historical penguin population and tundra vegetation abundance and diversity, we then suggest that the δ15N records can be utilized to study palaeoecological processes of penguin. Our results show that penguin population and activity has generally decreased over the past 2000 yr. From 1300 to 900 yr BP and from 1790 to 1860 AD, penguin population and activity experienced two strong decreases. It will be interesting to understand the cause of these decreases.