Chemical Weathering (U-Series)

Dosseto, Anthony

doi:10.1007/978-94-007-6326-5_246-1

Cited by 5 publications

(4 citation statements)

References 110 publications

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“…95 U-series disequilibria refers to the fractionation between different nuclides within a 96 decay chain resulting in a non-steady state condition (steady state is known as secular 97 equilibrium) (Ivanovich and Harmon, 1992;Bourdon et al, 2003;Dosseto, 2015). When 98 238 U decays to 234 Th in a mineral grain, the alpha decay can result in the physical 99 displacement of the 234 Th nuclide from the original position, which is also known as the 100 α-recoil effect.…”

Section: Comminution Age Theorymentioning

confidence: 99%

The time scale of river sediment source-to-sink processes in East Asia

et al. 2016

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Knowledge of river sediment recycling provides important constraints on continent weathering and earth surface processes. In this study, we estimate the ¿comminution age¿ of sediments from the Changjiang (Yangtze River) and two small mountainous rivers in Taiwan based on their lithogenic (234U/238U) ratio. The (234U/238U) distributions in the Changjiang catchment are overall related to sediment grain size and chemical weathering regime, while (234U/238U) ratios in Taiwan rivers mainly depend on erosion/ denudation processes. The comminution age constrains the time scale of sediment source-to-sink processes in catchments from sediment weathering/denudation to transportation, and finally deposition. Our results indicate that the comminution ages vary from 250 to 600 kyr for the Changjiang sediments and ~ 110 kyr for the Taiwan sediments. Different comminution ages are associated with contrasting erosion and weathering regimes and diverse topography between the large Changjiang catchment and small mountainous Taiwan basins. The longer comminution age of the Changjiang sediment is an interacting effect of a longer erosion/ weathering history and sediment trapping effect (and thus slow transfer rate) created by broad floodplains and lakes in the middle and lower reaches. The shorter comminution age of the Taiwan sediment results from fast sediment denudation and transport associated with strong tectonic uplift, typhoon climate and steep topography. As these two major river systems dominate the sedimentology in East Asia continent margin, the distinct geological and topographical settings between the Changjiang and Taiwan river systems result in different sediment ¿source to sink¿ transport processes. This work presents a systematic and quantitative constraint on the time-scale of river sediment transfer process in East Asia, and also provides new insight into weathering regimes and sediment transport in monsoon climate-dominated continent and Island. Taiwan

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Section: Comminution Age Theorymentioning

confidence: 99%

The time scale of river sediment source-to-sink processes in East Asia

et al. 2016

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“…Land surfaces in the tropics often consist of highly weathered and very old substrates, such as laterites which, on average, contain U close to secular equilibrium (Dequincey et al, 2002). In part, this is the result of the relatively short (246 kyr) half-life of 234 U (e.g., Dosseto, 2014), meaning that 234 U in the residuum of long-lived weathering profiles could return towards secular equilibrium with its parent nuclide ( 238 U) in less than 2 Myr. Furthermore, it is known that the bulk of the mobile elements and their isotopic signals have long been lost from laterites (e.g., Babechuk et al, 2015), and that they typically make a limited contribution to the present dissolved load of rivers.…”

Section: Significance For the Dissolved Riverine U Flux And The Marinmentioning

confidence: 99%

Th/U and U series systematics of saprolite: importance for the oceanic 234U excess

Suhr¹,

Widdowson²,

McDermott³

et al. 2018

Geochem. Persp. Let.

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The presence of excess 234 U in seawater is a compelling argument for active delivery of solutes from the continents to the oceans. Previous studies found, however, that the complementary 234 U deficit on the continents is surprisingly modest, which would require protracted U loss from a large continental weathering pool. Our new compilation and statistical analysis of the published data, coupled with a mass balance calculation demonstrates that the apparent small 234 U deficit in the continental weathering pool implied by previous studies is insufficient to balance the observed oceanic excess. Our new data for a saprolite weathering profile developed on Deccan basalt reveal a very strong overall loss of U (elevated Th/U) with a strong 234 U deficit attributable to chemical weathering. The U and 234 U deficits reported here from a geologically recent saprolite confirm the importance of the early stages of chemical weathering at the weathering front in the supply of nutrients to the oceans. Thus, as much as half the oceanic 234 U inventory is likely sourced from a thin active saprolite zone.

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“…Among the world's 25 largest rivers that carry approximately 42% of the terrestrial dissolved inorganic carbon (DIC), over 60% have high DIC concentrations >1,000 μM (Cai et al., 2008). The high concentrations and fluxes of DIC in large rivers thus represent a major transport pathway of atmospheric CO 2 and play an important role not only in carbon cycling but also in climate variability (Beaulieu et al., 2012; Dosseto, 2015 ; Kump et al., 2000).…”

Section: Introductionmentioning

confidence: 99%

Carbon Isotopic and Lithologic Constraints on the Sources and Cycling of Inorganic Carbon in Four Large Rivers in China: Yangtze, Yellow, Pearl, and Heilongjiang

Shan

Luo

et al. 2021

JGR Biogeosciences

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Transport of terrigenous carbon by rivers has been affected extensively by climate change and anthropogenic activities in China over the last few decades. Here, we present results on carbon isotopes (13C, 14C) of dissolved and particulate inorganic carbon (DIC and PIC) and combined with major lithologic ions measured in the four largest rivers in China, namely, the Yangtze, Yellow, Pearl, and Heilongjiang rivers, to reveal the sources and transport of terrigenous inorganic carbon in the rivers. The DIC concentrations showed large variations in the four rivers and ranged from 253 to 3,122 μM. The Yangtze, Yellow and Pearl rivers transported high DIC contents that had low Δ14C values of millennium‐aged DIC and very old PIC; however, the Heilongjiang River presented a lower DIC concentration with much younger 14C ages than the global average (1,100 μM). The strong correlations between the DIC isotope values and major lithological ions (Ca2+ and Mg2+) suggest that chemical weathering played important but variable roles in controlling the production and fate of DIC in the rivers. Using dual isotopes and the MixSIAR model, we calculated that the chemical weathering of carbonate rocks contributed 95 ± 5% of the riverine DIC to the headwater of the Yangtze River while silicate rock weathering and riverine organic matter respiration contributed 62 ± 25% and 5 ± 5% of the DIC in the middle and lower reaches of the river, respectively. In contrast, chemical weathering of silicate rocks contributed the dominant fraction of DIC in the Yellow (55 ± 17%), Pearl (61 ± 20%) and Heilongjiang (83 ± 29%) rivers.

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Chemical Weathering (U-Series)

Cited by 5 publications

References 110 publications

The time scale of river sediment source-to-sink processes in East Asia

The time scale of river sediment source-to-sink processes in East Asia

Th/U and U series systematics of saprolite: importance for the oceanic 234U excess

Carbon Isotopic and Lithologic Constraints on the Sources and Cycling of Inorganic Carbon in Four Large Rivers in China: Yangtze, Yellow, Pearl, and Heilongjiang

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