Northern Mediterranean precipitation variation and orbital forcing on westerlies over the past 250-400 thousand years ago

The behavior of westerlies plays an important role in European hydrological change. However, the mechanism of westerlies variation and its influence on paleoclimate is still in dispute. Here we combine speleothem δ¹⁸O and trace element records from Basura Cave, northern Italy. Holocene records show that Mg/Ca ratio is primarily controlled by rainfall amount and the time series can preserve past rainfall history. Absolute and precise ²³⁰Th-dated flowstone carbonate Mg/Ca record reveals that paleo-precipitation at 250-400 thousand years ago matches summer insolation curve. The results suggest that the orbital-scale westerlies are strongly governed by precession-dominated northern hemisphere summer insolation and accordingly induce precipitation variability in northern Mediterranean.