A novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids

We propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high-performance liquid chromatography/mass spectrometry (HPLC/MS). Analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol, the characteristic membrane lipid of non-thermophilic crenarchaeota, which is especially abundant in the marine and lacustrine environment. Based on these findings, an index was developed, the so- called Branched and Isoprenoid Tetraether (BIT) index, based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol. This BIT index was applied to surface sediments from the Angola Basin, where it was shown to trace the outflow of the Congo River. Furthermore, analyses of particulate organic matter from the North Sea showed relatively higher BIT indices in water column particulate organic matter near large river inputs. A survey of globally distributed marine and lacustrine surface sediments shows that the BIT index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable. The new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 Ma old.