Holocene warming trend based on peat brGDGTs records from southeastern humid to northwestern arid China

Recent syntheses of marine paleoclimate records have revealed an overall long-term Holocene warming trend, especially in mean annual temperature (MAT), which is inconsistent with most terrestrial records on continental and global scales. We present a record of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from the Shiwangutian (SWGT) peatland in central-southern China. Comparative results from surface peat samples from the SWGT peatland and the surrounding surface soils demonstrate that the brGDGTs are primarily of in-situ origin, demonstrating their potential as a record of local environmental changes. Monthly observational results show no seasonal variations in the methylation index of 5-methyl brGDGTs (MBT'5MEwhich has been proposed as an indicator of local environmental temperature in peatlands) in the surface peat samples, suggesting that it is an indicator of MAT. Thus, we conclude that the long-term increasing trend in the brGDGTs-based MBT'5ME records of two parallel independently-dated peat cores from the SWGT peatland clearly demonstrate a long-term warming trend during the Holocene. Additionally, we found that the brGDGTs-based records from five peatlands along an environmental gradient from southeastern (SE) humid to northwestern (NW) arid China also show a long-term Holocene warming trend. However, this trend is the opposite to the long-term Holocene cooling trend indicated by brGDGTs records from two peatlands in northeastern (NE) China, highlighting the complexity of peat brGDGTs as a climatic indicator. We therefore appeal for more peat brGDGTs studies, which are important for understanding the climate history of the Holocene and its potential relationship with human activities.