Contrasting responses of North American and Asian climates to orbital forcing during the Late Cretaceous

Stratigraphic records from Asia and North America indicate that Late Cretaceous climates on both continents were modulated by orbital forcing. To improve the integration and correlation of their climatic and stratigraphic signals at orbital time scales, we simulated regional climate responses to orbital variations using a coupled climate system model. The results show that both obliquity and precession exerted substantial influences on the East Asian climate, with precipitation increasing or decreasing in accordance with enhanced or reduced Northern Hemisphere (NH) summer insolation driven by orbital cycles. In contrast, the North American climate exhibited a weak and opposite response to precessional forcing, characterized by reduced (enhanced) precipitation under strong (weak) NH summer insolation. Obliquity forcing had negligible impact on North American hydroclimate. These contrasting continental-scale responses to precessional forcing may be due to the fact that East Asia was situated within a pronounced monsoon regime, whereas North America was not. It underscores an important caveat for orbital-scale stratigraphic correlation: intervals interpreted as wetting phases in East Asian sequences correspond to drying ones in North American records, and vice versa. 亚洲和北美洲的地层记录表明, 晚白垩世两个大陆的降水都受到轨道强迫的影响.数值模拟显示, 亚洲降水会随着轨道周期驱动的北半球夏季日照增强 (减弱) 而增加 (减少) .北美洲气候对岁差强迫的响应较弱且相反, 即夏季日照增强 (减弱) 时, 降水减少 (增加) ;而倾角对其影响微乎其微.这种大陆尺度上对岁差强迫的截然不同的响应可能归因于东亚处于季风区, 而北美洲则不然.这暗示, 在 轨道时间尺度上 东 亚地层中的湿润层位对应着北美洲地层中的干旱层位, 反之亦然.