Reconstructing millennial scale temperature and precipitation variability in monsoonal East Asia during MIS3 using branched tetraether membrane lipids

Abstract

Monsoons are seasonal changes in wind direction and associated precipitation driven by land-sea temperature contrasts. The East Asian monsoon is among the largest systems on Earth, and its history is mainly derived from oxygen isotope (δ18O) records of cave stalagmites and loess-paleosol sequences from the Chinese Loess Plateau (CLP). However, these records represent a mixed signal of both temperature and precipitation, which hampers assessing the response of monsoon precipitation to ongoing global warming. To create independent records for temperature and precipitation for East Asia, we here use branched glycerol dialkyl glycerol tetraethers (brGDGTs), a suite of membrane-spanning lipids synthesized by soil bacteria that record changes in temperature and (precipitation-induced) soil pH in their molecular structure stored in the Yuanbao section located on the western edge of the CLP. The high sedimentation rate in this section allows us to focus on millennial scale climate variations that occurred during Marine Isotope Stage – 3 (MIS3, spanning from 27 to 55 ka BP). Our high-resolution temperature record indeed shows millennial scale variability, although decoupled in timing from the magnetic susceptibility and grain size records for this same section that instead follow the global-scale variations that characterize MIS3. This decoupling suggests that the brGDGT-derived temperatures likely reflect a more local signal. This was attributed to glaciation trends on Tibetan plateau which maximize during the early MIS3. In addition, the strong influence of the westerlies at Yuanbao makes it prone to changes in the Atlantic Ocean circulation. Creating similar multi-proxy records across the CLP should reveal the extend of local temperature conditions on the CLP and its influence on East Asian monsoon dynamics.