Comparison of the U&amp;lt;sub&amp;gt;37&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;K&amp;lt;sup&amp;gt;′&amp;lt;/sup&amp;gt;&amp;lt;/sup&amp;gt;, LDI, TEX&amp;lt;sub&amp;gt;86&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;H&amp;lt;/sup&amp;gt;, and RI-OH temperature proxies in sediments from the northern shelf of the South China Sea

Bingbing Wei,Gesine Mollenhauer,Manyu Kang,Guodong Jia,Eunmi Park,Shizhu Wang,Jens Hefter

doi:10.5194/bg-17-4489-2020

Abstract

Abstract. The temperature proxies U37K′, LDI, TEX86H, 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 U37K′ reflects annual mean SST with a slight bias toward the warm season. Terrestrial inputs appear to have a significant impact on LDI, TEX86H, and RI-OH proxies near the coast, leading to colder LDI- and TEX86H-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 TEX86H- 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.

Highlights

Over the past 3 decades, organic proxies have been successfully applied to reconstruct the Quaternary or even Cenozoic history of sea surface temperature
After excluding samples influenced by terrestrial materials, we find that LDI-derived temperature agrees well with annual sea surface temperature (SST), while TEXH86- and ring index (RI)-OH-derived temperature estimates are close to SSTs in seasons dominated by the East Asian winter monsoon and summer monsoon, respectively
This analysis suggests that UK37 reflects annual mean SST with a slight bias toward the warm season, when the outer shelf is generally oligotrophic and the inner shelf is influenced by the Pearl River input of nutrients characterized by high N : P ratios

Summary

Introduction

Over the past 3 decades, organic proxies have been successfully applied to reconstruct the Quaternary or even Cenozoic history of sea surface temperature. TEX86, as well as its modified versions TEXH86 and TEXL86 (Kim et al, 2010), is based on the relative abundance of isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) containing one to three cyclopentane moieties (iGDGT-1, iGDGT-2, iGDGT-3, respectively) or four cyclopentane moieties with an additional cyclohexane moiety (the crenarchaeol isomer, Cren ). These molecules are produced by marine planktonic Thaumarchaeota (Schouten et al, 2013a)

Methods

Results

Discussion

Conclusion