Weathering-intensity variation in Asia during the Eocene

Continental weathering, by consuming atmospheric carbon dioxide, significantly contributes to long-term climate regulation, particularly in the context of global warming. Research on continental weathering intensity trends during geological warm periods can help predict how continental weathering may evolve under future global warming scenarios. Although several studies have explored continental weathering during the Paleocene-Eocene Thermal Maximum and Middle Eocene Climate Optimum, research on the long-term-scale (e.g., more than 1 Myr) weathering is still relatively scarce. The Eocene Epoch is the warmest period during the Cenozoic Era at long-term scale, which has been commonly regarded as a geological analog for a warming future. Consequently, research on variation in continental weathering intensity during the Eocene and the controlling factors is crucial. In this paper, in addition to global temperature fluctuations and Asian precipitation changes, the secular changes in Eocene continental weathering intensity from various regions of Asia, including Qaidam Basin, Xining Basin, Nangqian Basin, Weihe Basin, Qujing Basin, Fushun Basin, and Nanyang Basin, are compiled. The spatiotemporal variations in weathering intensity across Asia are identified and their controlling factors are analyzed. During the Eocene, most regions of Asia exhibited a long-term decreasing trend in continental weathering intensity, with several basins recording notable declines around 46, 41, and 39 Ma. We argue that both temperature and precipitation played significant roles in controlling continental weathering intensity. Higher temperatures and moderately high humidity promoted intense continental weathering during the early Eocene, whereas temperature falls and precipitation decreases led to declines in continental weathering intensity in mid-latitude basins during the middle and late Eocene. Different from the temperature changes, precipitation showed obvious decreases around 46, 41, and 39 Ma in several basins. The obvious precipitation decreases were generally consistent with the declines in continental weathering intensity. Therefore, compared to temperature falls, precipitation decreases could have had a greater impact on the weathering-intensity declines. In contrast, the Indian monsoon intensified around 41 Ma, rapidly increasing rainfall and humidity. The fast increased rainfall caused a decrease in weathering intensity in the Qujing Basin in the low-latitude zone. Additionally, in the subtropical semi-arid/arid zones, the westerlies carried moisture from the Paratethys to various basins during the Eocene, with those closer to the Paratethys receiving more moisture and exhibiting higher weathering intensity levels. The changes in moisture could be the reason why the continental weathering intensity decreased from Qaidam Basin to Xining Basin, Nangqian Basin, and Nanyang Basin. Different from the aforementioned basins, Fushun Basin was not influenced by the subtropical high pressure, and moisture likely arrived this basin more effectively, which made the environment around the Fushun Basin more humid. This could have favored the stronger weathering intensity recorded in this basin. Despite the records of long-term Eocene continental weathering intensity from the aforementioned basins, more extensive reports from other basins (e.g., Asian marginal sea basins) are still required to reveal more detailed patterns in continental weathering intensity across Asia during the Eocene. Importantly, more quantitative analysis should be emphasized in future studies. More data, including continental weathering intensity, temperature, and precipitation data, can be integrated by using models to explore the spatiotemporal evolution regularity of the continental weathering intensity during the Eocene. Quantitative modelling will provide a better reference, which can help predict future temperature, precipitation, and continental weathering intensity in the context of global warming.