Abstract
High-resolution records of grain size, major and trace elements, and Sr-Nd isotopes of Core K17 from the western Sunda Shelf were investigated to evaluate the response of weathering and terrigenous input to climatic changes and human activities over the past 7400 years. Sr-Nd isotopic results indicate that the Kelantan River is the main source of sedimentary material in the study core since the mid-Holocene. Chemical weathering levels are represented by the chemical index of alteration (CIA), αAlNa, and K2O/Al2O3 ratios; and geochemical and grain size proxies (including TiO2/CaO, Rb/Sr ratios, and grain size end-member) were used to establish variations of terrigenous input into the study core since 7400 cal yr BP. Based on these records, the evolution of weathering and terrigenous input processes in the western Sunda Shelf can be divided into four stages. During stage 1 (7400–3700 cal yr BP), increasing precipitation and decreasing temperature jointly balanced the relatively stable weathering and terrigenous sediment supply. Dramatically decreasing weathering rates were consistent with less rainfall and lower temperatures during stage 2 (3700–2600 cal yr BP). Heavy rainfall played a more important role than low temperature in controlling weathering and erosion, leading to increasing terrigenous input in stage 3 (2700–1600 cal yr BP). Because of the decoupling between weathering, erosion, and climate in the late Holocene (stage 4, since 1600 cal yr BP), increasing agriculture and related human activities likely dominated weathering and erosion relative to climate changes. Furthermore, the initial time at which human activity overwhelmed natural processes in the southern South China Sea (SCS) is similar to that in the northern SCS. Our results highlight that human activities during the past 1600 years have gradually overwhelmed natural climatic controls on weathering and erosion processes in the western Sunda Shelf.
Highlights
Continental weathering and erosion are critical processes controlling the delivery of sediments and solutes from the land to the ocean, shaping the terrestrial landscape, and regulating atmospheric CO2 (Raymo and Ruddiman, 1992; Bi et al, 2015; Wan et al, 2015; Hu et al, 2020)
Repeated analyses of the NBS987 standard yielded 87Sr/86Sr = 0.71031 ± 0.00000777 (1σ), and the JNdi-1 standard yielded 143Nd/144Nd = 0.512115 ± 0.00000556 (1σ), which is well within the recommended range. The ages of this downcore were calculated by linear interpolation among five dated sediment layers, and the basal age was 7400 cal years before present (yr BP) (Figure 2), which was calculated by linear extension after 6298 cal yr BP based on the same sedimentary rate with upper section under similar sedimentary environment
The sedimentation rates of the Middle Holocene were relatively higher than those during the Late Holocene, and the highest sedimentation rate occurred during 3700–4200 cal yr BP, with a value of 39 cm/ka
Summary
Continental weathering and erosion are critical processes controlling the delivery of sediments and solutes from the land to the ocean, shaping the terrestrial landscape, and regulating atmospheric CO2 (Raymo and Ruddiman, 1992; Bi et al, 2015; Wan et al, 2015; Hu et al, 2020). Anthropogenic processes can alter landscapes and result in weathering and erosion pattern changes (Hu et al, 2013; Huang et al, 2018). Some studies on the interaction between climate change, human activities, and weathering and erosion have been performed in different locations in the northern South China Sea (SCS) regions and around the world (Corella et al, 2013; Hu et al, 2013; Wan et al, 2015; Huang et al, 2018). For the southern SCS, anthropogenic impacts have not been distinguished from natural variability in tropical Southeast Asia (Tan et al, 2019)
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