Glycerol dialkyl glycerol tetraethers in surficial coastal and open marine sediments around China: Indicators of sea surface temperature and effects of their sources

Accurate reconstruction of past sea surface temperature (SST) is important for the understanding of past climate and its variations. Recently, the TEX86 indicator (TetraEther indeX of tetraethers consisting of 86 carbon atoms), based on glycerol dialkyl glycerol tetraethers (GDGTs) has been developed into a promising proxy for SST reconstruction. In this study, we investigated the distribution of GDGTs in surficial sea bottom sediments from coastal and open marine settings around China between 18 degrees N and 38 degrees N in water depth of either <100 or >1000 m. As the distribution patterns of GDGTs reflect their biological sources and their respective habitats these can be identified from the sediment samples investigated. The distributions of branched GDGTs (brGDGTs) in the Yellow Sea (YS) was found to be similar to that of the lower Yellow River basin indicating that the brGDGTs in the YS originated from terrestrial soil. While the variability of the cyclisation ratio of branched tetraethers (CBT)-derived pH values in the Pearl River estuary (PRE) suggested that brGDGTs might also be produced in situ in coastal sediments or in the water column. In the shallow areas (water depth <100 m, the YS, East China Sea and PRE) TEX(86-)(H)based SST (SST86H) was overestimated or underestimated when compared with mean annual S STsatellite, most likely caused by seasonality or overprint by a cold-biased terrestrial signal. In the South China Sea (SCS), at water depth >1000 m, the SST86H matched well the mean annual SST determined by satellite, indicating the applicability of the TEX86 temperatures for paleodimate investigations in these study areas and, potentially, in similar settings of deep water. These findings provide the basis for application of branched/isoprenoid index (BIT) and TEX86 as indicators for temperature and paleotemperature in coastal and open marine environments around China. (c) 2013 Elsevier B.V. All rights reserved.