Evidence for Poleward Migration of the Asian Monsoon During the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma), was a transient episode of global warming, and caused profound changes in biology and climate. The evolution of the hydroclimate during the PETM in East Asia, which currently is influenced by the Asian Monsoon and hosts ∼20% of the world's population, is crucial to understand the future monsoon and climate changes. However, PETM records in Asia are relatively rare and it remains poorly understood how the hydroclimate responded to climate forcing under extreme atmosphere pCO₂. Here we present stable carbon isotope records of bulk carbonate and total organic carbon (δ¹³C_carb and δ¹³C_TOC) from lacustrine deposits in the Jianghan Basin, Central China that both record the global carbon isotope excursion (CIE) that marks the PETM. The magnitude of both the CIEs in δ¹³C_carb and δ¹³C_TOC are larger than that presumed in the global exogenic carbon pool, as is common for terrestrial and marginal marine records. The particularly large amplitude (∼11.4‰) and unique shape of CIE in δ¹³C_carb, which represents authigenic lacustrine carbonates and therefore lake dissolved inorganic carbon δ¹³C values. Although our evidence against diagenesis is not fully conclusive, this signal implies the local addition of ¹³C-depleted carbon in excess of the global input. We consider increased transport rates of organic matter-derived carbon from the catchment to the lake the most likely source. Combined with the disappearance of evaporitic deposits during the PETM, we attribute this to an increase in precipitation and erosion, possibly linked to a northward extension of the Asian summer monsoon.