An Observational‐Data‐Based Theoretical Assessment of the Impact of Intact Polar Lipids on Peat brGDGT‐Based Paleotemperature Reconstruction

Abstract Branched glycerol dialkyl glycerol tetraethers (brGDGTs), which consist of intact polar lipids (IPLs, with head group, from living microorganisms and recently deceased cells) and core lipids (CLs, without head group, normally from the degradation of IPLs), are proposed as proxies for temperature reconstruction in peat deposits. To date, most brGDGT‐based temperature reconstructions have focused on core‐brGDGTs, which are thought to be degraded from IPL brGDGTs. For peat brGDGT‐based paleotemperature reconstructions, the fundamental assumption is that core‐brGDGTs in surface peats can record the environmental temperature in real‐time and are then well preserved after burial. However, whether newly synthesized IPL brGDGTs might mask geological core‐brGDGTs signals—crucial for paleotemperature reconstruction—needs further investigation. Here, we analyzed both core‐ and IPL brGDGTs from a peat core in the Sahara Sand peatland (Northwest China) to investigate this issue. Our theoretical results indicate that, for any sample in the Holocene, more than 87.2% of core‐brGDGTs were produced in the acrotelm. Consequently, less than 12.8% of core‐brGDGTs—derived from IPL brGDGTs—originated from the catotelm, suggesting that IPL brGDGTs in the catotelm made a limited contribution to the overall composition of core‐brGDGTs. Thus, we suggest that peat core‐brGDGTs are suitable for temperature estimation, while their signals are possibly time‐smoothed due to peat accumulation in the acrotelm. Our results support the fundamental assumption for peat brGDGT‐based paleotemperature reconstructions.