Transport of organic carbon from the California coast to the slope region: A study of Delta C-14 and delta C-13 signatures of organic compound classes

Abstract

[1] Surface sediments along a transect from an abyssal site in the northeastern Pacific ( Station M, 34 degrees 50'N, 123 degrees 00'W) to a small mountainous river on the California coast ( Santa Clara River) were studied to investigate the sources and cycling of organic matter on the continental margin. Sediment samples were separated into organic compound fractions ( extractable lipids, amino acids (THAA), carbohydrates (TCHO), and the acid-insoluble fraction), and their carbon isotope ratios were measured. The Delta C-14 values of all the THAA and TCHO fractions were greater than - 100 parts per thousand, indicating relatively modern organic carbon (OC) source(s), and rapid cycling of these fractions. In contrast, the Delta C-14 values of extractable lipids and the acid-insoluble fraction were distinctly lower than those of the THAA and TCHO fractions. The Delta(14) C values of source OC to the sediments were estimated using a simple mixed layer model. These values were lower than the Delta C-14 signatures of pre-industrial plankton suggesting input of both old OC and contemporary plankton to the margin sediments. The source of old OC at the 2000-m site was likely from laterally transported coastal sediment. The estimated low Delta(14) C value of the transported OC suggests that old lipids and acid-insoluble material were selectively transported to the 2000-m site. The contribution of riverine POC to the margin sediments were estimated from Delta C-14 and delta C-13 values and indicate that relict OC exported by rivers was an important source of old lipids and acid-insoluble material to sedimentary OC on the shelf.