106 / 2025-03-31 22:04:13

Contrasting Drought Episodes across the Mid-Brunhes Event in northwest China

GDGTs,drought events,Chinese Loess Plateau,the Mid-Brunhes Event

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4e: Microbial Lipid Biomarkers and Their Isotopes in Environment, Biology, and Evolution

Drought events seriously impact our society, yet the occurrence and evolution of extreme drought events, and the underlying mechanism(s) for them, remain largely unknown in ancient times. Here we present a suite of novel microbial lipid records that show the occurrence of two contrasting droughts in the Chinese Loess Plateau (CLP) since 700 thousand years ago (ka). By measuring the relative abundance of archaeal isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) vs. bacterial branched GDGTs (brGDGTs), the R_i/b ratio, and BIT (Branched and Isoprenoid Tetraethers)—all diagnostics of drought events—we find a significant shift in the magnitude of drought episodes across the Mid-Brunhes Event. Droughts identified during the transition from glacial to interglacial climate states were much larger in amplitude after the Mid-Brunhes Event than before, consistent with a transition from generally colder to warmer interglacial conditions reconstructed from bacterial brGDGTs.  This may result from the increased air temperature and atmospheric CO₂ concentrations, vegetation–wildfire feedback, and weakened Pacific Sea surface temperature (SST) gradients. In addition, the Indian summer monsoon intensity and the tropical Pacific SST gradients regulate droughts on the Chinese Loess Plateau before and after the Mid-Brunhes Event, respectively. The shift after the Mid-Brunhes Event to higher temperatures is somewhat analogous to the global warming trends of today, which, in the context of projected hydrological changes in the populous region of Northern China, suggests more droughts are likely to occur in the future.