Holocene mean annual air temperature (MAAT) reconstruction based on branched glycerol dialkyl glycerol tetraethers from Lake Ximenglongtan, southwestern China

Abstract

Here we investigate the sources of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in Lake Ximenglongtan from southwestern China and present a brGDGTs-based Holocene (∼9.4 cal kyr BP) temperature reconstruction. The similarities in the distributions of brGDGTs between surface sediments and catchment soils indicate that soil is the dominant source of brGDGTs. This contrasts with the recent emphasis on lacustrine GDGTs in other regional studies. Holocene temperature evolution is characterized by an early cool phase (with a mean annual air temperature (MAAT) of 12.5 °C) prior to 7.6 cal kyr BP, followed by a rapid warming towards the local thermal maximum (MAAT = 13.8 °C) from 7.6 to 5.5 cal kyr BP and a subsequent long-term cooling that ended at 1.5 cal kyr BP. Temperature changes after 1.5 cal kyr BP show high variability and low correspondence to global climate events such as the Medieval Warm Period. Overall Holocene temperature variation has been primarily controlled by boreal summer insolation changes. The larger amplitude (1.5–4.0 °C) in annual cooling during the early Holocene in MAAT contrasts with summer temperature records from this region (range of cooling 0.3–1.0 °C) and indicates the likely influence of lower winter temperature on MAAT variation. We suggest that substantial remnants of the Northern Hemisphere ice-sheets during the early Holocene enhanced the winter westerlies and East Asian winter monsoon (EAWM), and decreased the winter temperature in southwestern China, leading to a cold early Holocene climate.