Paleo-temperature inferred from brGDGTs over the past 18 cal ka BP from Lake Barrine, tropical NE Australia

Terrestrial temperature exerts a major influence on vegetation distribution, the hydrologic cycle and many biogeochemical cycles. Yet little research into terrestrial paleo-temperature reconstruction has been conducted covering the last deglaciation in northern Australia, and recent global surface temperature reconstructions include no data from this area. Here, for the first time, we reconstructed the mean annual air temperatures (MAAT) at Lake Barrine in this region from 18.3 to 1.7 cal ka BP at a relatively high resolution (averaged 400 yr). This temperature reconstruction was based on separated 5- and 6-methyl brGDGTs (branched glycerol dialkyl glycerol tetraethers) that are increasingly used to reconstruct terrestrial temperature because of their ubiquity and a preservation window of at least tens of millions of years. A 7.2 m master core from the center of the lake was extracted, along with five surface lake sediment and seven catchment soil samples. The results indicated that the fractional abundances of all the brGDGTs in the catchment soils, surface and downcore sediments in Lake Barrine were closely correlated, with dominant tetramethylated brGDGTs, especially Ia. We applied a global calibration to reconstruct the temperature using the lake sediment samples and a binary mixing model to correct temperature bias caused by soil-derived brGDGT input. The corrected temperature trend estimate compares favorably with the temperature anomaly recorded in the EPICA ice core record, except during the Younger Dryas. The corrected MAAT estimates at Lake Barrine indicated an increase across Heinrich Stadial 1 (HS 1; 18–14.9 cal ka BP) from 19.4 °C to 21.9 °C, a stable temperature during the Antarctic Cold Reversal (ACR; 14.7–13 cal ka BP) of ∼21.6 °C, followed by a slight decrease during the Younger Dryas (YD; 12.8–11.6 cal ka BP). After a further 1.6 °C increase into the early Holocene, the temperature decreased by 1.8 °C through the Holocene until a recent rise by 1.6 °C after 1.7 cal ka BP.