A 35,000 year record of terrigenous and marine lipids in Amazon Fan sediments

Elemental and lipid analyses were carried out on sediments recovered from Ocean Drilling Program (ODP) Site 942 to provide a 35 kyr record of organic matter input to Amazon Fan sediments. Total organic carbon (TOC) and higher plant biomarker mass accumulation rates were an order of magnitude greater during the last glacial period compared to the current interglacial due to sea-level controlled variations in Amazon River sediment supply. Large maxima were also seen at 12 ka, which are most likely due to discharge events. Higher plant n-alkane average chain lengths did not change throughout the record, suggesting consistency in the source vegetation type. The abundance of taraxerol relative to other plant biomarkers increased at 12 ka, indicating increased mangrove input due to either higher mangrove productivity or increased erosion of mangrove deposits. The mass accumulation rates (MARs) of some bacterial and eustigmatophyte biomarkers varied closely with those of higher plant biomarkers and so seem to have a non-marine source. Long chain alkenones were present in some of the sediments, generally in very low concentration, indicating dilution of the marine signal with terrestrial organic matter.