Lithium isotope behaviour during weathering in the Ganges Alluvial Plain

Abstract

17The Ganges river system is responsible for the transportation of a large flux of 18 dissolved materials derived from Himalayan weathering to the oceans. Silicate 19 weathering-driven cooling resulting from uplift of the Himalayas has been 20 proposed to be a key player in Cenozoic climate variation. This study has 21analysed Li isotope (δ 7 Li) ratios from over 50 Ganges river waters and 22 sediments, in order to trace silicate weathering processes. Sediments have δ 7 Li of 23 ~0‰, identical to bulk continental crust, however suspended sediment depth 24 profiles do not display variations associated with grain size that have been 25

Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes

“…The Li isotopic composition of the Lena River main channel is relatively uniform throughout the catchment (~19 ± 2‰; 1σ), and is several permil lower than the global riverine mean of ~23‰ (Huh et al, 1998a), with the exception of one atypical sample with high [Li] and δ 7 Li (LR2013-41; δ 7 Li = 29.0‰, 396 nM). The ranges of δ 7 Li and [Li] measured in this study are similar to those of data from other large global rivers systems elsewhere (e.g., the Mackenzie River, Millot et al, 2010; the Ganges-Brahmaputra, Kısakűrek et al, 2005, Bagard et al, 2015, Pogge von Strandmann et al, 2017 and the Amazon, Dellinger et al, 2015).…”

“…Thus, the δ 7 Li data have not been corrected for these inputs, consistent with the approaches of other riverine studies (e.g. Millot et al, 2010;Bagard et al, 2015;Liu et al, 2015;Pogge von Strandmann et al, 2017).…”

“…2), which broadly overlaps with average continental silicate rock values (UCC, ~ 0.6 ± 0.6‰, Teng et al, 2004;Sauzéat et al, 2015;andbasalts ~3 to 5‰, Elliott et al, 2006, Tomascak et al, 2008). The suspended sediments are isotopically heavier than the global mean suspended sediment Li isotopic composition for large global rivers of -1.5 ± 1‰ (1σ; Dellinger et al, 2014) but comparable to δ 7 Lisusp values for other rivers (e.g., the Mackenzie River, Millot et al 2010; the Ganges-Brahmaputra; Kısakűrek et al 2005, Bagard et al 2015, Pogge von Strandmann et al 2017the Dongqu, Weynell et al, 2017); and the Amazon, Dellinger et al, 2014). Variations in d 7 Li have been reported for suspended sediments related to variations in Si/Al (a proxy for grain size) in depth profiles in the Amazon, Mackenzie and Ganges-Brahmaputra Rivers that are the result mineral sorting within the water column (Bouchez et al 2011, Dellinger et al 2014, Dellinger et al 2017).…”

“…High riverine d 7 Li values have been interpreted as reflecting less complete weathering, greater secondary mineral formation and thus greater 'weathering intensity' (i.e., the ratio of chemical to physical denudation; Bouchez et al, 2013;Dellinger et al, 2015). There have been a number of large global rivers in tropical and temperate environments where the behaviour of Li isotopes has been studied: e.g., the Amazon River (Chan et al, 1992;Huh et al, 1998a;Dellinger et al, 2014Dellinger et al, , 2015; the Orinoco River (Huh et al, 1998a;Huh et al, 2001); rivers in the high Himalayas and the Ganges-Brahmaputra (Huh et al, 1998a;Kısakűrek et al, 2005;Bagard et al, 2015;Manaka et al, 2017;Pogge von Strandmann et al, 2017) the Changjiang (Yangtzee)…”

The Response of Magnesium, Silicon, and Calcium Isotopes to Rapidly Uplifting and Weathering Terrains: South Island, New Zealand

“…This is expected, given that both plant (or algal) growth and clay formation are significantly greater on the east coast. In other words, the enhanced dissolution of primary silicates in mountainous regions causes a correlation of Li and Si isotopes (also observed in the Himalayan foothills; Pogge von Strandmann et al, 2017). This co-relationship between the two systems can be modeled using a Rayleigh relationship (Vigier et al, 2009;Pogge von Strandmann et al, 2012, 2014b, 2017Murphy et al, 2019), and by assuming a continental crust starting composition (Savage et al, 2010;Sauzéat et al, 2015).…”