Lipid biomarker fluxes in the Arabian Sea, with a comparison to the equatorial Pacific Ocean

Fluxes and distributions of organic carbon (OC) and lipid biomarkers were measured in the western Arabian Sea as a function of season, depth, and distance from the coast of Oman during the US JGOFS Arabian Sea Process Study in 1994–1995. A strong seasonal pattern in OC and lipid flux is related to the annual monsoon cycle in the western Arabian Sea, with the highest fluxes measured during the Southwest Monsoon. Fluxes were greatly attenuated with depth in the water column and in surface sediments as remineralization effectively consumed particulate organic matter. A comparison of water-column fluxes with OC and lipid accumulation rates in sediments confirms that the water–sediment interface is a “hot-spot” for organic matter degradation. Biomarker compositions also varied seasonally and with distance offshore, reflecting seasonal and spatial succession of their biological sources and their subsequent export through the water column. Degradation of OC and biomarkers was extremely efficient, with only a tiny fraction (<1%) of their water-column flux preserved in sediments, although a range of compound-specific degradation efficiencies was apparent. This intense degradation has strong implications for contemporary carbon cycling and for interpreting sediment records for paleoceanographic reconstructions.