Carbon isotopes of n-alkanoic acids in Antarctic ornithogenic sediments as indicators of sedimentary lipid sources and paleocological change

Abstract

Sedimentary n-alkanoic acids are ubiquitous in the environment and their carbon isotopic composition is increasingly used to identify the source of organic matter and to reconstruct past climatic and ecological changes. Here we investigate the distribution and carbon isotope ratios of n-alkanoic acids in two sediment profiles influenced by animal excrement in Antarctica. We found that organic matter input from animal excrement is the predominate source of short- and mid-chain n-alkanoic acids in the ornithogenic sediments. Decreased δ¹³C values are closely related to increased excrement input of penguins and seals that occupied the study site, especially in C₁₆n-alkanoic acid. Long-chain (>C₂₄) n-alkanoic acids likely originate from moss and heterotrophic microbes, and the δ¹³C values of C₂₆n-alkanoic acid were consistent with organic biomarkers and bio-elements from animal excrement. Two possible processes are suggested to explain the close relationship between C₂₆n-alkanoic acid δ¹³C values and animal excrement input. All the results indicate that the carbon isotopes of n-alkanoic acids in ornithogenic sediments can be used to indicate historical population change of penguins or seals in Antarctica.

Keywords: Antarctica; Carbon isotope ratios; Ornithogenic sediments; Penguin population change; n-alkanoic acids.