Paleoenvironmental changes in the northern South China Sea over the past 28,000 years: A study of TEX86-derived sea surface temperatures and terrestrial biomarkers

We have generated a record of TEX86 (TEX86H)-derived sea surface temperatures (SSTs) over the last 28 ka for core MD97-2146 from the northern South China Sea (SCS). The TEX86H-derived temperature of a core-top sample corresponds to the SSTs in warmer seasons. The SST record shows a drop during the Oldest Dryas period, an abrupt rise at the onset of the Bølling–Allerød period, a plateau across the Younger Dryas period, and an abrupt rise at the beginning of the Holocene. The glacial–interglacial contrast in TEX86H-derived temperature is almost the same as that in foraminiferal Mg/Ca ratio-derived temperature, but it is larger than those in U37K′ and transfer function-derived temperatures. Possible interpretations are: (1) the seasonal shift of glycerol dialkyl glycerol tetraether (GDGT) production, (2) the overestimation of temperature change by TEX86H, and (3) the underestimation of temperature change by U37K′ and transfer function approaches. The similar variation in TEX86H-derived temperature at the study site and Chinese stalagmite δ18O during the last deglaciation suggests that changes in TEX86H-derived temperature in this period reflected atmospheric and oceanic reorganization on a millennial timescale. The long-chain n-alkanes are mainly of higher plant origin before ∼14 ka and a mixture of higher plant and lithic origins after ∼14 ka; the abundance ratio of long-chain to short-chain n-fatty acids decreases at ∼15 ka, suggesting a drastic change in sediment sources at ∼14–15 ka. We attribute the higher content of fresh higher plant n-alkanes and long-chain n-fatty acids before ∼14–15 ka to enhanced aeolian transportation and/or arid environments. Increased precipitation likely due to intensified summer monsoon after ∼14–15 ka enhanced the erosion of sedimentary rocks and increased the contribution of lithic n-alkanes.

Research highlights
► This paper shows the first record of paleotemperatures derived from TEX86H in the South China Sea during the last 28,000 years.
► The glacial–interglacial contrast in TEX86H-derived temperature is almost the same as that in foraminiferal Mg/Ca ratio-derived temperature, but it is larger than those in U37K′ and transfer function-derived temperatures.
► Changes in the distribution of long-chain n-alkanes suggest that the source of terrestrial organic matter changed from higher plants to lithic organic matter at 14–15 ka.