Orbitally and galactic cosmic forced abrupt climate events during the last glacial period

Abstract

Various abrupt climate events have been reported during the last glacial period, but their regional expressions and causes remain complex and not fully understood largely due to lack of high-resolution paleoclimate records. In this study, a high-resolution loess sequence is presented from North China which is significantly influenced by the East Asian Summer Monsoon, and its multiple proxies reveal two strong, abrupt cooling-drying events occurring at 48 ka and ∼42 ka. The 48 ka event corresponds to the fifth Heinrich (H5) event that was characterized by catastrophic iceberg discharges into the subpolar North Atlantic Ocean. Our loess and model results suggest that the 48 ka event could result from the unique and extreme orbital configuration at 48 ka, characterized by the smallest latitudinal summer insolation gradient over the last glacial period. This orbital configuration led to a cooling-drying in the low and mid-latitudes but a warming in high latitudes. The ∼42 ka event corresponds to a catastrophic environmental crisis discovered on the Eurasian and Australian continents. It also corresponds to a major reversal of the Earth's magnetic poles, i.e., the Laschamps Excursion. The cosmic ray increase due to this Excursion could affect the pedogenesis and dust deposition of the loess sequence via cloud increase, regional cooling, aerosol increase and local wind strengthening. This study is a clear demonstration that both extreme orbital conditions and the change of the Earth's magnetic field could cause abrupt climate and environmental changes.