Human impact overwhelms long-term climate control of weathering and erosion in southwest China

Abstract

International audienceDuring the Holocene there has been a gradual increase in the influence of humans on Earth systems. High-resolution sedimentary records can help us to assess how erosion and weathering have evolved in response to recent climatic and anthropogenic disturbances. Here we present data from a high-resolution (∼75 cm/k.y.) sedimentary archive from the South China Sea. Provenance data indicate that the sediment was derived from the Red River, and can be used to reconstruct the erosion and/or weathering history in this river basin. Accelerator mass spectrometry 14C dating provides direct age control and reveals coherent variations in clay mineralogy, geochemistry, and terrigenous flux, indicative of strong chemical weathering and physical erosion during the mid-Holocene warm period (6400–4000 cal [calibrated] yr B.P.), followed by weakening from ca. 4000–1800 cal yr B.P., and renewed intensification since 1800 cal yr B.P.. Comparison with climatic records from China indicates that precipitation and temperature controlled both physical erosion and chemical weathering intensity before 1800 cal yr B.P.. However, weathering proxies in the offshore sediment indicate recent increased soil erosion. We suggest that enhanced human activity (deforestation, cultivation, and mining) since the end of the Chinese Han Dynasty (220 CE) has overwhelmed the natural climatic controls on erosion in the Red River

Geochemistry of river‐borne clays entering the East China Sea indicates two contrasting types of weathering and sediment transport processes

“…Such an attempt has been recently made by Wan et al . [] and Lupker et al . [] using the core data from the continental slope of the South China Sea and the Bengal Fan respectively.…”

Magnetic properties of sediments of the Red River: Effect of sorting on the source‐to‐sink pathway and its implications for environmental reconstruction

“…Sediments in the delta region and the margin of the South China Sea have been extensively studied to reconstruct the history of local delta formation, the evolution of the South China Sea, and their relationships with the Asian monsoon and tectonic uplift of the Tibetan Plateau [ Li et al ., ; Wan et al ., ]. In particular, several studies have investigated the magnetic properties of sediments from the South China Sea in order to reconstruct paleoenvironmental changes [ Kissel et al ., ; Ouyang et al ., ; Wang et al ., ].…”

“…The accumulations of these sediments in deltas and continental margins contain valuable information about geological history, climate changes, and human activity in the river catchment and thus they have been extensively studied to reconstruct environmental changes on different time scales [e.g., Colin et al ., ; Kissel et al ., ; Bianchi and Allison , ; Wan et al ., ]. Geochemical and mineralogical methods are conventionally used to characterize sediments derived from these large rivers [e.g., Clift et al ., ; Wan et al ., ]. A number of indicators have been developed [e.g., Clift et al ., , and references therein], such as the conservative Al/Ti ratio for sediment provenance [ Young and Nesbitt , ], and the chemical index of alteration (CIA) [ Nesbitt and Young , ] for climate changes.…”

Influence of Sea Level Change and Centennial East Asian Monsoon Variations on Northern South China Sea Sediments Over the Past 36 kyr

“…Provenance estimation based on REE indicates that both the Red and Pearl Rivers contribute almost equally to Site 38, which is close to PC338 at a water depth of 1,160 m (Liu et al, ). Nd‐Sr isotope results indicate that the Red River is the primary source for core 337PC (Figure a) at a water depth of 516 m (Wan et al, ). REE comparisons demonstrate that the Pearl and southwestern Taiwan Rivers are the main sources for core X2 (Figure a) close to Hainan Island at 77 m water depth (Xu et al, ).…”

“…Cores ODP1144 (Hu et al, ), STD111 (Yang et al, ), MD12–3432 (Chen et al, ), ODP1146 (Kissel et al, ), Qd34 (Yang et al, ), PC24 (Ouyang et al, ), PC83 (Yang et al, ), and PC111 (Yang et al, ) in the northern SCS have also been studied magnetically. Cores STAT22 (Cui et al, ), X2 (Xu et al, ), 337PC (Wan et al, ), and Site 38 (Liu et al, ) were used for provenance studies. Huguangyan Maar Lake (HML; Wang et al, ), Dongge Cave (Dykoski et al, ), Hulu Cave (Wang et al, ), and KNG5 (Huang et al, ) have yielded high‐resolution paleoclimate records and are indicated on the map.…”