Alkenone and tetraether lipids reflect different seasonal seawater temperatures in the coastal northern South China Sea

We examined the lipid-based temperature proxies U37K′ and TEX86H in five short sediment cores from the inner shelf of the northern South China Sea and related them to local sea water temperature from the World Ocean Atlas (WOA) database. The U37K′-based temperature values are consistent with euphotic zone temperature in spring and summer, when the southeast monsoon prevails and vertical stratification occurs in the water column, whereas TEX86H-based temperature values reflect sea surface temperature in winter when the northeast monsoon prevails and vertical mixing occurs. The different temperature signals between the TEX86H and U37K′ proxies could be a result of differences in the growing season between the source organisms, with alkenone-producing haptophyte algae blooming in the warmer and nutrient-rich season with higher fluvial influx, and tetraether-producing Thaumarchaeota blooming in the cooler and oligotrophic season.