Comparison of the U 37 K ′ , LDI, TEX 86 H , and RI-OH temperature proxies in sediments from the northern shelf of the South China Sea
2020
Abstract. The temperature proxies
U 37 K ′ , LDI,
TEX 86 H , and RI-OH are derived from
lipid biomarkers, namely long-chain alkenones from coccolithophorids and
long-chain diols ascribed tentatively to eustigmatophytes, as well as
glycerol dialkyl glycerol tetraethers (GDGTs) and OH-GDGTs produced by
Archaea. The applicability of these proxies in the South China
Sea (SCS) has been investigated previously. However, in each study only one
or two of the proxies were compared, and the recently updated
calibrations or new calibrating methods such as BAYSPAR and BAYSPLINE were
not applied. Here, we investigate four proxies in parallel in a set of
surface sediment samples from the northern SCS shelf and relate them to
local sea surface temperature (SST), which allows for us to compare and assess
similarities and differences between them and also help improve regional
multiproxy seawater temperature reconstructions. Our results indicate that
U 37 K ′ reflects annual mean SST with a
slight bias toward the warm season. Terrestrial inputs appear to have a
significant impact on LDI, TEX 86 H , and
RI-OH proxies near the coast, leading to colder LDI- and
TEX 86 H -derived temperatures but a
warmer RI-OH temperature estimate. After excluding samples influenced by
terrestrial materials, we find that LDI-derived temperature agrees well with
annual SST, while TEX 86 H - and RI-OH-derived temperature estimates are close to SSTs in seasons dominated by the
East Asian winter monsoon and summer monsoon, respectively. The different
seasonal biases of these temperature proxies provide valuable tools to
reconstruct regional SSTs under different monsoonal conditions.
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