Sedimentary geochemistry response to climate change on a millennial timescale in the Qiantang River incised-valley system, eastern China

The highly controversial relationship among the chemical weathering of silicate rocks, climatic variability and human activities on various temporal scales has become a hot research topic given the booming interest in global climate change. This study of the Holocene Qiantang River incised-valley fill investigates the variability of weathering intensity and its controlling factors based on geochemical analysis. Results indicate that the variations of chemical weathering indices throughout the studied succession are chiefly climate-controlled, although partly influenced by source-rock lithology, grain-size effects, hydraulic sorting and sediment recycling by tidal bores. Over the last 12 ka, 8 periods with distinct characteristics and weakened weathering intensity are identified. The abruptly weakened weathering intensity documented by chemical weathering indices in the last 2 ka is ascribed to the intensification of human activities and/or EI-Niño activities. Noteworthy, small catchments located near land-ocean boundaries respond more rapidly to climate change and human activities on a millennial (even centennial) timescale. The climatic cooling events (e.g., Younger Dryas, 10.3 ka and 9.3 ka) are better reflected in the study interval as the sediments of units U5, U4 and U3 (before 8.2 ka BP) are sourced from the Qiantang River watershed. Slightly weakened chemical weathering related to climatic events is also documented by the coarser sediments of unit U1, which are primarily derived from the Changjiang (Yangtze River).