ESTIMATES OF THE ORIGINS OF ORGANIC MATTER IN THE OLD-HUANGHE ESTUARY USING THE BIT ⅡNDEX

Distinguishing the sources of organic matters in marginal sea sediments is an important aspect of carbon cycle research. The BIT index, as a new proxy for terrestrial organic matter, has been recently used to quantitatively estimate sources of organic matters in estuary and marginal sea sediments. Based on the ratio of crenarchaeol (derived from aquatic crenarchaeota) to Branched GDGTs (produced by soil bacteria), the BIT index has the advantages that the biomarkers have specific origins and they are less affected by diagenesis. So far, the BIT index has not yet been applied to marginal seas of China. We report the contents of microbial biomarkers and the BIT index of 31 surface sediment samples from the western Yellow Sea near the Old-Huanghe River estuary. Our results show higher BIT values (>0.15) for samples close to the Old-Huanghe River, and lower BIT values seaward. The contents of Branched GDGTs range between 5 and 94 ng/g, showing a similar spatial trend with the BIT index. Another biomarker ratio index of terrestrial organic matter, the ATB index (ratio of terrestrial odd-numbered n-alkanes to marine phytoplankton biomarkers), also reveals a similar spatial pattern with higher values near the Old-Huanghe River estuary and decreasing values seaward. However, the absolute values of ATB index are much higher than the BIT values. The differences between ATB and BIT most likely reflect the fact that the ATB index contains both vegetation and soil organic matter input while the BIT index only represents soil organic matter, but they could be caused by different degradation rates of the compounds in the BIT and ATB index.