Multiple proxy estimates of source and spatial variation in organic matter in surface sediments from the southern Yellow Sea

Marginal seas play an important role in the global carbon cycle as organic matter (OM) buried in shelf seas accounts for ca. 80% of marine sedimentary OM. The Yellow Sea (YS) is a significant sink for both terrestrial OM (TOM) and marine OM (MOM), so the source and spatial variation of sedimentary OM in the southern YS were investigated by analyzing several parameters for 54 surface sediment samples. Spatial ranges were 5.4-12.8 for total organic carbon/total organic nitrogen (TOC/TON), −22.8‰ to −19.9‰ for TOC δ13C, 421-4515 ng/g TOC for ∑(C27 + C29 + C31) n-alkanes, 33-152 ng/g TOC for branched glycerol dialkyl glycerol tetraethers, 316-8550 ng/g TOC for total marine biomarkers. TOC/TON displayed no distinct spatial pattern, but the BIT (branched isoprenoid tetratether index) proxy, TMBR [terrestrial and marine biomarker ratio: (C27 + C29 + C31n-alkanes)/(C27 + C29 + C31) n-alkanes + (brassicasterol + dinosterol + alkenones)] and δ13C values revealed similar spatial distribution patterns, indicating higher TOM near coastal regions and especially near the old Huanghe Estuary. Quantitative estimates using a binary model revealed higher %TOM (avg. 34%) from TMBR than from δ13C (avg. 26%) and BIT (avg. 12%). TMBR is a proxy incorporating both soil OM (OMsoil) and plant OM (OMplant) while BIT is a proxy for OMsoil, so quantitative estimates using a three end member model indicated higher OMplant and OMsoil values near the old Huanghe Estuary, but %OMplant (avg. 23%) was higher than %OMsoil (avg. 13%). Our study suggests that these proxies can be used to study the spatial and temporal variation and delivery mechanisms for both OMsoil and OMplant in marginal seas.