Mid-latitude precipitation in East Asia influenced by a fluctuating greenhouse climate during the latest Cretaceous through the earliest Paleogene

Deep-time records from greenhouse climate periods (e.g., the Late Cretaceous) provide a reference point for understanding how high atmospheric CO2 concentrations influence precipitation in the mid-latitude Northern Hemisphere (e.g., East Asia). In this study, we quantitatively reconstruct mean annual precipitation (MAP) in East Asia during the latest Cretaceous through the earliest Paleogene (similar to 76-65.5 Ma), based on a well-studied paleosol sequence from the Sifangtai and Mingshui Formations from the SK-ln scientific borehole in the Songliao Basin, northeastern China. We use several proxies, including sedimentary-based observational proxies (e.g., depth to the calcic horizon, DTC) and elemental geochemistry proxies in the paleosol B horizon (e.g., the chemical index of alteration minus potassium, CIA-K; the calcium-magnesium weathering index, CALMAG), which show the consistency with weathering proxies and previously published isotopic records. Changes in the MAP are associated with warming and cooling events. In the warciaming period (e.g., at similar to 69.5-68.5 Ma), an increase in the land-sea thermal contrast led to an expanded, enhanced, poleward-shifted thermal low-pressure system over the East Asian continent, which triggered an enhanced hydrological cycle and increasing MAP in the Songliao Basin. During the cooling period (e.g., at similar to 72.5-69.5 Ma and similar to 68.5-66.5 Ma), weakened East Asian monsoon and strengthened equatorward-shifted westerlies allowed for colder and arid air masses to encroach upon the Songliao Basin, which led to decreased MAP. Changes in MAP across the K-Pg boundary coincide with climate fluctuations and catastrophic geological events. Furthermore, our work compares three warming intervals in deep-time (middle Maastrichtian, late Maastrichtian and earliest Paleogene) with Shared Socioeconomic Pathway scenarios used by the IPCC for the end of the 21st century, and indicates MAP increases in East Asia with ongoing anthropogenic CO2 emissions.

Automated summary

This study quantitatively reconstructs mean annual precipitation in East Asia during the late Cretaceous to the early Paleogene period using paleosol sequences and proxies. The results show that changes in precipitation are associated with climate warming and cooling events, and also coincide with climate fluctuations and geological events. The study also suggests that ongoing anthropogenic CO2 emissions may lead to increased precipitation in East Asia.