Evolution of silicate weathering in the Yangtze River Basin since 3.5 Ma as archived in the East China Seas: Controlling factors and global significance

Abstract

The consumption of atmospheric CO₂ as a result of silicate weathering is a very important carbon sink process over geological time scales, serving as a significant mechanism for regulating global carbon cycling and climate. However, whether silicate weathering is a positive driving factor for climate change or a negative feedback to mitigate climate change is still unclear, mainly due to a lack of reliable quantitative estimates of silicate weathering flux. Here, we reconstruct for the first time records of silicate weathering intensity, erosion flux, and silicate weathering flux in the Yangtze River Basin since 3.5 Ma using the sediment cores from the East China Seas (South Yellow Sea and East China Sea), and evaluate their relationship with tectonic and climatic changes. Weathering indices such as Chemical Index of Alteration (CIA) and K/Al ratio indicate that the overall silicate weathering intensity of Yangtze River sediments has been decreasing since about 3.5 Ma, coupled with East Asian paleoclimate indicators and global oxygen isotopes, suggesting that global cooling is the main driving factor for the evolution of weathering intensity. Since the late Pliocene, the silicate weathering flux in the Yangtze River Basin is poorly correlated with weathering efficiency, but shows good consistency with erosion flux, exhibiting a decreasing trend during the late Pliocene to late early Pleistocene followed by an increasing trend since the late early Pleistocene, responding respectively to reduced precipitation caused by cooling climate and increased tectonic activity in the upper Yangtze River Basin. Combined with existing long-term CO₂ consumption flux data in Asia, it is evident that erosion flux is the primary factor controlling silicate weathering flux in large river basins, while the impact of variations in silicate weathering intensity is relatively limited. During tectonically quiescent periods, silicate weathering mainly responds to climate change, acting as a negative feedback; during tectonically active periods, silicate weathering drives global climate change. Therefore, climatic- and tectonic-controlled continental weathering jointly regulate the decrease in atmospheric CO₂ concentration and global cooling at the late Cenozoic.