Abstract

Archaea have unique glycerol dialkyl glycerol tetraether (GDGT) lipids that can be used to develop paleotemperature proxies such as TEX86. This research is to validate proposed GDGT-proxies for paleotemperature determination in the South China Sea (SCS). Samples were collected from core-top sediments (0–5 cm) in the northern SCS. Total lipids were extracted to obtain core GDGTs, which were identified and quantified using liquid chromatography-mass spectrometry (LC-MS). The abundance of isoprenoidal GDGTs (iGDGTs) ranged from 271.5 ng/g dry sediment to 1266.3 ng/g dry sediment, whereas the branched GDGTs (bGDGTs), supposedly derived from terrestrial sources, ranged from 22.2 ng/g dry sediment to 56.7 ng/g dry sediment. The TEX86-derived sea surface temperatures ranged from 20.9 °C in the coast (water depth < 160 m) to 27.9 °C offshore (water depth > 1000 m). TEX86-derived temperatures near shore (<160 m water depth) averaged 23.1 ± 2.5 °C (n = 4), which were close to the satellite-derived winter mean sea surface temperature (average 22.6 ± 1.0 °C, n = 4); whereas the TEX86-derived temperatures offshore averaged 27.4 ± 0.3 °C (n = 7) and were consistent with the satellite mean annual sea surface temperature (average 26.8 ± 0.4 °C, n = 7). These results suggest that TEX86 may record the sea surface mean annual temperature in the open ocean, while it likely records winter sea surface temperature in the shallower water.

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