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Weathering fluxes from four small catchments in the Himalayas, one forested, one agricultural, and two glacial, have been calculated by quantifying stream discharge, deposition, and biomass uptake of major ions. These fluxes were partitioned between silicate and carbonate sources by using a mineral mass-balance model. This approach provides the first well-defined estimates of Himalayan weathering fluxes from small catchments. Silicate weathering rates are highest in the favorable weathering environment of the Middle Hills catchments, despite higher dissolved fluxes in the High Himalayas attributed to high carbonate weathering. The silicate weathering fluxes for High Himalayan small catchments are similar to estimates from the chemistry of large rivers draining the same regions. Much higher silicate weathering intensity for the Ganges basin indicates that the silicate material eroded from the High Himalayas undergoes up to six times as much weathering in the Ganges Plain as in the High Himalayan mountains. Himalayan silicate weathering rates are higher than in equivalent continental settings and, on an area-normalized basis, are comparable to fluxes from weathering of basalts on ocean islands and tropical volcanic provinces. Keywords: catchment, erosion, flux, Himalayas, weathering.

The injected brine solutions had an initial dye concentration of Graph $c 0 = 3.00 \pm 0.05$ g l Graph $^{-1}$ and an initial density Graph $\rho 0 = 1.030$ or 1.070 g cm Graph $^{-3}$, assuming a water temperature of 20 Graph $^{\circ }$ C (Green & Southard 2019). The injected fluid spreads below an impermeable horizontal baffle containing a fault of gap width Graph $d f$, thickness Graph $h f$, permeability Graph $k f$ and porosity Graph $\phi f$ which abuts the boundary. Less dense CO Graph $ 2$ is injected at a constant rate of 0.1 Mt yr Graph $^{-1}$ at the bottom of layer 1, and assumed to have constant density Graph $\rho = 790$ kg m Graph $^{-3}$ and dynamic viscosity Graph $\mu = 6.9 \times 10^{-5}$ Pa s, calculated at typical storage reservoir conditions of 15 MPa and 40 Graph $^{\circ }$ C (Dubacq, Bickle & Evans 2013). Figure 2( I b i ) shows three height profiles at Graph $\tilde {t}=0.5$, Graph $\tilde {t}=5$ and Graph $\tilde {t}=50$ (solid lines), where the extent and height of the profiles have been normalised by the maximum extent Graph $\tilde {x} N$ and the thickness of the current at Graph $\tilde {x}=0$, Graph $\tilde {h} 0$. In diffusion dominated flows, where Graph ${\textit {Pe}} \ll 1$, the transport coefficient Graph $D\simeq D d/\tau$ is constant whereas in advection dominated flows, where Graph ${\textit {Pe}} \gg 1$, Graph $D\simeq d 0U$ is dependent on the flow speed. [Extracted from the article]

Rationale: Li and Mg isotopes are increasingly used as a combined tool within the geosciences. However, established methods require separate sample purification protocols utilising several column separation procedures. This study presents a single‐step cation‐exchange method for quantitative separation of trace levels of Li and Mg from multiple sample matrices. Methods: The column method utilises the macro‐porous AGMP‐50 resin and a high‐aspect ratio column, allowing quantitative separation of Li and Mg from natural waters, sediments, rocks and carbonate matrices following the same elution protocol. High‐precision isotope determination was conducted by multi‐collector inductively coupled plasma mass spectrometry (MC‐ICPMS) on the Thermo Scientific™ NEPTUNE Plus™ fitted with 1013 Ω amplifiers which allow accurate and precise measurements at ion beams ≤0.51 V. Results: Sub‐nanogram Li samples (0.3–0.5 ng) were regularly separated (yielding Mg masses of 1–70 μg) using the presented column method. The total sample consumption during isotopic analysis is <0.5 ng Li and <115 ng Mg with long‐term external 2σ precisions of ±0.39‰ for δ7 Li and ±0.07‰ for δ26Mg. The results for geological reference standards and seawater analysed by our method are in excellent agreement with published values despite the order of magnitude lower sample consumption. Conclusions: The possibility of eluting small sample masses and the low analytical sample consumption make this method ideal for samples of limited mass or low Li concentration, such as foraminifera, mineral separates or dilute river waters. [ABSTRACT FROM AUTHOR]

The article 'The need for mass balance and feedback in the geochemical carbon cycle' by R.E. Berner and K. Caldeira tackles the issues surrounding long-term controls on atmospheric carbon dioxide levels and the need for and nature of the feedback mechanism between atmospheric carbon dioxide and climate. While their arguments are plausible, the authors have overlooked a significant subtlety in climate control by mountain uplift, which may have essential ramifications for long-term variations in global climate.

We review new and published analyses of river waters, bedloads and their constituent minerals from the Dhauli Ganga and Alaknanda, headwaters of the Ganges in Garhwal, and the Marsyandi in Nepal and their tributaries. These data are used to discriminate between the inputs of major cations and Sr from silicate and carbonate sources. Methods of estimating the proportion of the carbonate and silicate inputs to river waters using mixing arrays in Sr-Ca-Mg-Na-K-87Sr/86Sr space are shown to suffer from systematic correlations between the magnitude of the precipitation of secondary calcite and the fraction of the silicate component. This results in factor-of-two overestimates of the fractions of silicate-derived Ca, Mg and Sr. To correct for this the magnitude of secondary calcite precipitated and relative fractions of silicate and carbonate-derived cations are instead calculated by modeling the displacement of water compositions from the compositions of the carbonate and silicate components of the bedload in subsets of Sr-Ca-Mg-Na-K-87Sr/86Sr space. The compositions of the carbonate and silicate end-members in the bedload are determined by sequential leaching. The results of this modeling are compared with modeling of the modal mineral inputs to waters where mineral compositions are derived from electron-microprobe analyses of the minerals in the bedload. In the upper Marsyandi catchment, which drains low-grade Tethyan Sedimentary Series formations, a set of mainstem samples collected over a two-year period define tight correlations in Sr-Ca-Mg-Na-K-87Sr/86Sr space. Modeling of the magnitude of secondary carbonate precipitation and fractions of silicate-derived Ca, Mg and Sr in Sr-Ca-Mg-87Sr/86Sr space gives self-consistent results that are compatible with both the calculations of mineral modes and published Mg-isotopic compositions, if the ratio of chlorite to biotite weathering is high or if there is another silicate source of Mg. These calculations imply that between 12 and 31 percent of the Sr and 44 and 72 percent of the Mg is derived from silicate minerals where the range reflects the seasonal change in the ratio of silicate-derived to carbonate-derived cations. Modeling in Sr-Ca-Na and/or K space is inconsistent with the Sr-isotopic and Mg-isotopic constraints and we conclude that in this catchment dissolution of Na and K are incongruent relative to Sr-Ca-Mg. Potassium is preferentially retained in micas whereas the controls on Na are unclear. Modeling of the catchments underlain by High Himalayan Crystalline and Lesser Himalayan Series in Garhwal is complicated by the presence of dolomite as well as calcite in the carbonate and the results imply that dolomite dissolves faster in the acetic acid leaches than in nature. Up to 60 percent of the Sr in the catchment on High Himalayan Crystalline Series and 20 to 30 percent of Sr in the catchments on Lesser Himalayan Series are estimated to be derived from silicates. However it should be noted that the element budgets are not all self-consistent and the use of bedrock-element ratios to model the sources of chemical inputs to river waters remains subject to uncertainties. [ABSTRACT FROM AUTHOR]

Spectacular celestine geodes occur in a Jurassic peri-evaporitic sequence (Ardon Formation) exposed in Makhtesh Ramon, southern Israel. The geodes are found only in one specific location: adjacent to an intrusive contact with a Lower Cretaceous basaltic dyke. Celestine, well known in sedimentary associations worldwide and considered as a low temperature mineral, may therefore be associated with magmatic-induced hydrothermal activity. Abundant fluid inclusions in celestine provide valuable information on its origin: gas-rich inclusions in celestine interiors homogenized at T≥200°C whereas smaller liquid-rich inclusions record the growth of celestine rims at T≤200°C. Near 0°C melting temperatures of some fluid inclusions and the occurrence of hydrous Ca-sulphate solid crystals in other inclusions indicate that celestine precipitated from variably concentrated Ca-sulphate aqueous solutions of meteoric origin. Celestine crystallized from meteoric water heated by the cooling basaltic dyke at shallow levels (c. 160 m) during a Lower Cretaceous thermal perturbation recorded by regional uplift and magmatism. The 87Sr/86Sr ratio of geode celestine, 0.7074, is similar to that measured in the dolostones of the host Jurassic sequence, but differs markedly from the non-radiogenic ratio of the dyke. Strontium in celestine was derived from dolostones preserving the 87Sr/86Sr of Lower Jurassic seawater, while sulphur (δ34S = 19.9‰) was provided by in situ dissolution of precursor marine gypsum (δ34S = 16.8‰) indicated by relict anhydrite inclusions in celestine. Low-temperature meteoric fluid flow during the Campanian caused alteration of the dyke into secondary clays and alteration of geodal celestine into quartz, calcite and iron oxides. [ABSTRACT FROM AUTHOR]

Abstract: We present a semi-empirical thermodynamic model with uncertainties that encompasses the full range of compositions in H2O–CO2–NaCl mixtures in the range of 10–380°C and 1–3500bars. For binary H2O–CO2 mixtures, the activity–composition model is built from solubility experiments. The parameters describing interactions between H2O and CO2 are independent of the absolute thermodynamic properties of the end-members and vary strongly non-linearly with pressure and temperature. The activity of water remains higher than 0.88 in CO2-saturated solutions across the entire pressure–temperature range. In the H2O–NaCl system, it is shown that the speciation of aqueous components can be accounted for by a thermodynamic formalism where activities are described by interaction parameters varying with intensive properties such as pressure and temperature but not with concentration or ionic strength, ensuring consistency with the Gibbs–Duhem relation. The thermodynamic model reproduces solubility experiments of halite up to 650°C and 10kbar, and accounts for ion pairing of aqueous sodium and chloride ions with the use of associated and dissociated aqueous sodium chloride end-members whose relative proportions vary with salinity. In the H2O–CO2–NaCl system, an activity–composition model reproduces the salting-out effect with interactions parameters between aqueous CO2 and the aqueous species created by halite dissolution. The proposed thermodynamic properties are compatible with the THERMOCALC database (Holland and Powell, 2011) and the equations used to retrieve the activity model in H2O–CO2 can be readily applied to other systems, including minerals. [Copyright &y& Elsevier]

Abstract: Secure storage of anthropogenic carbon dioxide (CO2) in geological reservoirs requires predicting gas–water–rock interactions over millennial timescales. Noble gases and carbon isotope measurements can be used to shed light on the nature of competing dissolution—precipitation processes over different timescales, from the fast dissolution of gaseous CO2 in groundwater to more sluggish reactions involving dissolution and precipitation of newly formed minerals in the reservoir. Here we study a compilation of gas analyses including noble gases and δ13C of CO2 from nine different natural CO2 reservoirs. Amongst these reservoirs, the Bravo Dome CO2 field (New Mexico, USA) shows distinct geochemical trends which are explained by degassing of noble gases from groundwater altering the composition of the gas phase. This groundwater degassing is synchronous with the dissolution of CO2 in groundwater. Progressive creation of alkalinity via CO2-promoted mineral dissolution is required to explain the observed positive correlation between CO2/3He and δ13C of the gas phase, a unique feature of Bravo Dome. The differences between Bravo Dome and other natural CO2 reservoirs are likely explained by the more recent filling of Bravo Dome, reflecting CO2–water–rock interactions over thousands of years rather than over millions of years in older reservoirs. [Copyright &y& Elsevier]

Jin, Z. D., Bickle, M. J., Chapman, H. J., Yu, J., An, Z., Wang, S. & Greaves, M. J. 2010: Ostracod Mg/Sr/Ca and Sr/Sr geochemistry from Tibetan lake sediments: Implications for early to mid-Pleistocene Indian monsoon and catchment weathering. Boreas, 10.1111/j.1502-3885.2010.00184.x. ISSN 0300-9483 Lacustrine sediment serves as a valuable archive for tracing catchment weathering processes associated with past climatic and/or tectonic changes. High-resolution records of fossil ostracod Mg/Ca, Sr/Ca and Sr/Sr ratios from a lake sediment core from the central Tibetan Plateau reveal a temporal link between lake-water chemistry and catchment weathering and distinct monsoonal oscillations over the early to mid-Pleistocene. Between 2.01 and 0.95 Ma, lake-water chemistry was dominated by a high proportion of carbonate weathering related to variations in the Indian monsoon, resulting in relatively low and constant ostracod Sr/Sr but obvious fluctuations in Mg/Ca, Sr/Ca and δO. Across the mid-Pleistocene transition (MPT), a significant increase in Sr/Sr and frequently fluctuating ratios of ostracod Mg/Ca, Sr/Ca and δO are coincident with increases in both Chinese loess grain size and Arabian Sea lithogenic flux. This correlation indicates an increased glaciation and a strong monsoon seasonal contrast over the plateau. The increase in lake-water Sr/Sr across the MPT highlights a change in catchment weathering patterns, rather than one in climate-enhanced weathering intensity, with an increased weathering of Sr-rich minerals potentially induced by marked extensive glaciation and strong seasonality in the central plateau. [ABSTRACT FROM AUTHOR]

Abstract: As one of the pioneering projects of the Chinese Environmental Scientific Drilling (CESD) Program, a 206.5m long sediment core (CE) was retrieved from Co Ngoin (Co = lake) Basin in the central Tibetan Plateau. Limnic records of the abundance of ostracod shells and their oxygen and carbon isotope measurements, together with the geochemical and the sedimentological investigations, were carried out on the interval between 143 and 52m core depths, corresponding to ca. 2.01–0.84Myr. Distinct oscillations of the abundance and the chemical compositions of ostracod shells have yielded the original information about variations in lakewater chemistry in association with the change in the Indian monsoon over the period of 2.01 to 0.84Myr. The climate conditions during the Early Pleistocene were characterized by frequent oscillations and the ostracod records had expressed its synchronous response to these oscillations. A major climate change occurred in the Co Ngoin area at about 0.93Myr. A pronounced fluctuation in ostracod δ 18O and δ 13C during the Mid-Pleistocene transition (MPT) is possibly associated with an increase in continental ice sheets. The compositional and the sedimentological characters of the immediately overlying sediments imply a shallow aquatic environment and also a harsh (salinity?) condition beyond the tolerance limits for ostracod survival, resulting in the disappearance of the Qinghaicypris crassa Huang 1979 around 0.84Myr. [Copyright &y& Elsevier]

Abstract: Hot springs in the Marsyandi Valley, Nepal, vent CO2 sourced from metamorphic fluids that mix with shallow groundwaters before degassing near the Earth''s surface. The δ 13C of spring waters ranges up to +13‰, while that of the coexisting free gas phase is close to −4‰. Empirical and thermodynamic modelling of this isotopic fractionation suggests >97±1% CO2 degassing. The calculated minimum total CO2 degassing in the Marsyandi catchment is 5.4×109 mol/yr from a Cl-based estimate of the spring water discharge to the Marsyandi River and the fraction of CO2 degassed. Extrapolated to the whole of the Himalayas, this implies a probable minimum metamorphic CO2 flux of 0.9×1012 mol/yr, or ∼13% of solid Earth CO2 degassing. The calculated flux is a factor of three greater than the estimated CO2 drawdown by silicate weathering in the Himalayas. Himalayan metamorphic degassing contributes a significant fraction of the global solid Earth CO2 flux and implies that metamorphism may cause changes in long-term climate that oppose those resulting from the orogenic forcing of chemical weatherability. [Copyright &y& Elsevier]