Sources of long chain fatty acids in deep sea sediments from the Bering Sea and the North Pacific Ocean

The distributions and compound specific carbon isotope ratios of long chain n-fatty acids and long chain n-alkanes in two sedimentary cores collected from the North Pacific Ocean and the Bering Sea have been examined. Long chain fatty acids were further fractionated into three sub-fractions (esterified, free and polar) to investigate their sources. The δ13C values of these fractions clarified the sources of different fatty acids. The esterified fraction had lighter δ13C values (∼−30.1‰, σ = 0.70), similar to those of the long chain n-alkanes (−30.2, σ = 1.08), consistent with a mainly terrestrial plant origin. In contrast, the long chain fatty acids (except >C28) from the polar and free fractions had heavier isotopic values (∼−27.5‰, σ = 1.06), suggesting a mixed origin from terrestrial and marine organisms. The esterified fatty acids from the North Pacific Ocean and the Bering Sea can be used as terrestrial biomarkers.