Rapid response of silicate weathering rates to climate change in the Himalaya

Abstract

11(<100 yr) to climate change and may act as a key component in the atmospheric CO 2 level short-term regulation (Beaulieu et al., 2012). However, the relative role of climatic parameters on chemical weathering is still debated. Model simulations and geochemical studies of river-born material highlight either a temperature dependence (Walker et al., 1981), where warming promotes chemical weathering, or a predominance of other parameters like mechanical erosion (Raymo and Ruddiman, 1992;Gaillardet et al., 1999;Riebe et al., 2001;Donnadieu et al., 2004) and vegetation (Bayon et al., 2012). To address this question, another possible approach consists in investigating past continental environments through the study of marine or floodplain deposits. However, because in large river systems sediment transport and storage operates over >10 4 yr timescales (Granet et al., 2010), a significant time lag may exist between the time when sediments acquired their geochemical characteristics, reflecting palaeoenvironmental conditions, and their final deposition.Here we use the lithium (Li) isotopic composition of clays from sedimentary records in Himalayan basins to determine how chemical weathering intensity has varied over the past 40 ka and particularly since the Last Glacial Maximum (locally older than 24 ka; Owen et al., 2002). In order to minimise the time lag between source and deposit locations, we have focused on alluvial deposits located in the headwater areas of the Ganges and Yamuna Rivers.While little isotope fractionation occurs during mineral dissolution clay formation induces strong fractionations at low temperature, whereby 6 Li is preferentially incorporated into clays compared to 7 Li, resulting in a strong enrichment of 7 Li in waters (Burton and Vigier, 2011). Thus, it has been shown that the d 7 Li composition of natural waters can be used as a proxy for chemical weathering rates at the catchment scale, since the heaviest d 7 Li compositions in water are associated with the areas characterised by low catchment-wide silicate weathering rates (Fig. 1). Several studies have also shown that the d 7 Li composition of solid weathering products (i.e. soils, river sediments) is sensitive to chemical weathering conditions, where lower d7 Li values reflect more intensive leaching (Burton and Vigier, 2011).To evaluate the reliability of the records studied, we investigated three different regions of the Himalaya and its piedmont in India: the upper Yamuna River basin, the Alaknanda River basin and the Donga Fan (Fig. S-1). Depositional ages for the alluvial deposits reported here were previously constrained by optically-stimulated luminescence (OSL) dating and range from 9 to 41 ka (Singh et al., 2001;Ray and Srivastava, 2010). Both bulk sediments and clay-sized fractions were analysed for Li isotopes. In bulk sediments, mineralogical abundances and Sr isotopes were also measured (see Supplementary Information). et al., 1981;Berner et al., 1983), accounting for nearly half the consumption of atmospheric carbon diox...

Abrupt response of chemical weathering to Late Quaternary hydroclimate changes in northeast Africa

“…Compared to dominant silicate rocks that outcrop in the Nile Basin (see Fig. S4), clays are preferentially enriched in 6 Li, as expected for secondary phases formed on continents7. The particular behavior for Li isotopes during arid versus humid periods is consistent with K/Ti and Mg/Ti variations, reflecting mitigated effects of leaching processes in weathering profiles, which release dissolved Li to the surrounding waters, and clay neoformation, which immobilizes Li (and Mg) in specific soil horizons37.…”

“…In contrast, experimental and field studies have demonstrated significant fractionation of Li isotopes during silicate weathering, with preferential incorporation of 6 Li in neoformed clay minerals25. Recent works illustrate the potential of δ 7 Li (δ 7 Li = ( 7 Li/ 6 Li) sample /( 7 Li/ 6 Li) LSVEC ) − 1) × 1000) as a proxy for determining the intensity or the regime of chemical weathering726. Li in river waters and particles is essentially derived from alteration of silicate lithologies2728.…”

“…In igneous provinces, both river-water and sediment δ 7 Li signatures are usually lower in areas with thick soil sequences (i.e. in transport-limited regimes)726. In contrast, mountainous or glaciated regions (weathering-limited regimes29) are usually characterized by high δ 7 Li signatures, except for regions underlain by shales30.…”

Magma-derived CO 2 emissions in the Tengchong volcanic field, SE Tibet: Implications for deep carbon cycle at intra-continent subduction zone

“…Nevertheless, significant debates still exist on possible links between global climate change and the India-Asia continent collision (Kerrick and Caldeira, 1999;Willenbring et al, 2013), because silicate weathering in response to plateau uplift sequesters carbon (Raymo and Ruddiman, 1992;Dosseto et al, 2015), whereas syn-collisional volcanism (e.g. Mo et al, 2008;Niu et al, 2013;Zhu et al, 2015), post-collisional volcanism (Guo et al, 2006(Guo et al, , 2007(Guo et al, , 2013(Guo et al, , 2014a(Guo et al, , 2015a, subduction zone metamorphism (Kerrick and Connolly, 2001;Cook-Kollars et al, 2014) and modern hydrothermal activities (Guo et al, 2014b;Zhang et al, 2014Zhang et al, , 2016 release carbon.…”

Responses of the East Asian Summer Monsoon in the Low‐Latitude South China Sea to High‐Latitude Millennial‐Scale Climatic Changes During the Last Glaciation: Evidence From a High‐Resolution Clay Mineralogical Record

“…Due to the heavy monsoonal rainfall with strong physical erosion intensity, smectite is washed away from rock surfaces shortly after its formation, preventing it from continuous chemical weathering toward halloysite and kaolinite. In particular, recent studies have demonstrated that chemical weathering rate can respond rapidly to decade-to millennial-scale climate changes with rainfall and temperature variations (e.g., Beaulieu et al, 2012;Dosseto et al, 2015;Gislason et al, 2009). In particular, recent studies have demonstrated that chemical weathering rate can respond rapidly to decade-to millennial-scale climate changes with rainfall and temperature variations (e.g., Beaulieu et al, 2012;Dosseto et al, 2015;Gislason et al, 2009).…”