Climate factors play critical roles in controlling chemical weathering, while chemically weathered surface material can regulate climate change. To estimate global chemical weathering fluxes and CO2 balance, it is important to identify the characteristics and driving factors of chemical weathering and CO2 consumption on the Tibetan Plateau, especially in glaciated catchments. The analysis of the hydro-geochemical data indicated that silicate weathering in this area was inhibited by low temperatures, while carbonate weathering was promoted by the abundant clastic rocks with fresh surfaces produced by glacial action. Carbonate weathering dominated the riverine solute generation (with a contribution of 58%, 51%, and 43% at the QiangYong Glacier (QYG), the WengGuo Hydrological Station (WGHS), and the lake estuary (LE), respectively). The oxidation of pyrite contributed to 35%, 42%, and 30% of the riverine solutes, while silicate weathering contributed to 5%, 6%, and 26% of the riverine solutes at the QYG, WGHS, and LE, respectively. The alluvial deposit of easily weathering fine silicate minerals, the higher air temperature, plant density, and soil thickness at the downstream LE in comparison to upstream and midstream may lead to longer contact time between pore water and mineral materials, thus enhancing the silicate weathering. Because of the involvement of sulfuric acid produced by the oxidation of pyrite, carbonate weathering in the upstream and midstream did not consume atmospheric CO2, resulting in the high rate of carbonate weathering (73.9 and 75.6 t km−2 yr−1, respectively, in maximum) and potential net release of CO2 (with an upper constraint of 35.6 and 35.2 t km−2 yr−1, respectively) at the QYG and WGHS. The above results indicate the potential of the glaciated area of the Tibetan Plateau with pyrite deposits being a substantial natural carbon source, which deserves further investigation. 相似文献
Dissolved major ions, Sr concentrations and 87Sr/86Sr ratios of 10 coastal lakes from the Larsemann Hills, East Antarctica have been studied to constrain their solute sources, transport and glacial weathering patterns in their catchments. In absence of perennial river/streams, lakes serve as only reliable archive to study land surface processes in these low-temperature regions. The lake water chemistry is mostly Na-Cl type and it does not show any significant depth variations. Sr isotope compositions of these lakes vary from 0.7110 to 0.7211 with an average value of 0.7145, which is higher than modern seawater value. In addition to oceanic sources, major ions and Sr isotopic data show appreciable amount of solute supply from chemical weathering of silicate rocks in lake catchments and dissolution of Ca-Mg rich salts produced during the freezing of seawaters. The role of sulphide oxidation and carbonate weathering are found to be minimal on lake hydro-chemistry in this part of Antarctica. Inverse model calculations using this chemical dataset provide first-order estimates of dissolved cations and Sr; they are mostly derived from oceanic (seawater + snow) sources (cations approximately 76%) and (Sr approximately 92%) with minimal supplies from weathering of silicates (cations approximately 15%); (Sr approximately 2%) and Ca-rich minerals (cations approximately 9%); (Sr approximately 7%). The silicate weathering rate and its corresponding atmospheric CO2 consumption rate estimates for Scandrett lake catchment (3.6 ± 0.3 tons/km2/year and 0.5 × 105 moles/km2/year), are lower than that of reported values for the average global river basins (5.4 tons/km2/year and 0.9 × 105 tons/km2/year) respectively. The present study provides a comprehensive report of chemical weathering intensity and its role in atmospheric CO2 consumption in low-temperature pristine environment of Antarctica. These estimates underscore the importance of Antarctica weathering on atmospheric CO2 budget, particularly during the past warmer periods when the large area was exposed and available for intense chemical weathering. 相似文献
Nearly 200 analyses of meltwaters, ice and snow from three alpine glacial sites in carbonate terrain are summarized and discussed in terms of sources of solutes and kinetic controls on the progress of weathering reactions. Most data derive from the Swiss Glacier de Tsanfleuron which is based on Cretaceous and Tertiary pure and impure limestones. Two other sites (Marmolada, Italian Dolomites and the Saskatchewan Glacier, Alberta) are based on a mixed calcitic-dolomitic substrate. Most solutes originate from carbonate dissolution; moreover, where pyrite is present its oxidation supplies significant sulphate and forces more dissolution of carbonate. The ratios Sr2+/Ca2+ and Mg2+/Ca2+ are much higher in Tsanfleuron melt-waters than local bedrock, a phenomenon that can be reproduced in the laboratory at small percentages of dissolution. These anomalous ratios are attributed to incongruent dissolution of traces of the metastable carbonates Mg-calcite and aragonite. These phases also provide Na+ to solution. K+ is argued to originate mainly by ion-exchange on clays with solute Ca2+. Quartz and very minor feldspar dissolution are also inferred. Locally enhanced input from atmospheric sources is recognized by high Cl? and associated Na+. The progress of weathering reactions has been evaluated by the trends in the data, computer modelling and some simple laboratory experiments. The most dilute samples show a trend towards removal of CO2 to low partial pressures (c. 10?5.5 atmospheres), reflecting initially rapid carbonate dissolution and relatively slow dissolution of gaseous CO2. Later addition of atmospheric CO2 or acid from pyrite oxidation allows further carbonate dissolution, but solutions show a wide range of saturations, and CO2 pressures as high as 10?2.2 where pyrite oxidation is important. In a carbonate terrain, measurement of electroconductivity (corrected to 25°C) and alkalinity in the field allows the following preliminary deductions (where meq stands for milliequivalents): where S is the minimum meq(Ca2+ + Mg2+) produced by simple dissolution of carbonate unconnected with pyrite oxidation. As with any proxy method, these deductions do not remove the need for chemical analysis of waters in a given study area. 相似文献
The Nyangqu River, the largest right bank tributary of the Yarlung Zangbo River in the Qinghai–Tibet Plateau, was representative of an alpine riverine carbon cycle experiencing climate change. In this study, dissolved inorganic carbon (DIC) spatial and seasonal variations, as well as their carbon isotopic compositions (δ13CDIC) in river water and groundwater were systematically investigated to provide constraints on DIC sources, recharge and cycling. Significant changes in the δ13CDIC values (from −2.9‰ to −23.4‰) of the water samples were considered to be the result of different contributions of two dominant DIC origins: soil CO2 dissolution and carbonate weathering. Three types of rock weathering (dissolution of carbonate minerals by H2CO3 and H2SO4, and silicate dissolution by H2CO3) were found to control the DIC input into the riverine system. In DIC cycling, groundwater played a significant role in delivering DIC to the surface water, and DIC supply from tributaries to the main stream increased from the dry season to the wet season. Notably, the depleted δ13CDIC ‘peak’ around the 88.9° longitude, especially in the September groundwater samples, indicated the presence of ‘special’ DIC, which was attributed to the oxidation of methane from the Jiangsa wetland located nearby. This wetland could provide large amounts of soil organic matter available for bacterial degradation, producing 13C-depleted methane. Our study provided insights regarding the role of wetlands in riverine carbon cycles and highlighted the contribution of groundwater to alpine riverine DIC cycles. 相似文献
Continental weathering plays a dominant role in regulating the global carbon cycle, soil chemistry and nutrient supply to oceans. The CO2-mediated silicate weathering acts as a major CO2 sink, whereas sulphuric acid-mediated carbonate dissolution releases CO2 to the atmosphere–ocean system. In this study, dissolved major ions and silica concentrations of two tropical (Damodar and Subarnarekha) river systems from India have been measured to constrain the type and rate of chemical weathering for these basins. The total dissolved solids (TDS) of these rivers, a measure of total solute supply from all possible sources, are about 2–3 times higher than that of the global average for rivers. Mass balance calculations involving inverse modelling estimate that 63 ± 11% of total cations are derived from rock weathering, of which 27 ± 7% of cations are supplied through silicate weathering. The sulphide-S concentrations are estimated by comparing the water chemistry of these two rivers with that of a nearby river (Brahmani) with similar lithology but no signatures of sulphide oxidation. The outflows of Damodar and Subarnarekha rivers receive 17% and 55% of SO4 through sulphide oxidation, respectively. The sulphide oxidation fluxes from the ore mining areas, such as upper Damodar (0.52 × 109 mol/yr) and lower Subarnarekha (0.66 × 109 mol/yr) basins, are disproportionally (~9 times) higher compared to their fractional areal coverage to the global drainage area. The corresponding CO2 release rate (2.84 × 104 mol/km2/yr) for the Damodar basin is lower by five times than its CO2 uptake rate (1.38 × 105 mol/km2/yr). The outcomes of this study underscore the dominance of sulphide oxidation in controlling the dissolved chemical (cationic and sulphur) fluxes. 相似文献
Snowmelt‐fed springs and small (0.5 km2) upland catchments in alpine areas of the western United States contribute significantly to the quantity and inorganic chemistry of water delivered to downstream basins but have not been studied extensively. Mineral weathering, transit time, and hydrologic mixing control the solute chemistry of waters that drain the upland zone of Niwot Ridge, Colorado Front Range, and adjacent areas in the granitic core of the Southern Rocky Mountains. Water in 37 springs sampled in this study flows in generally short steep paths (~0.3 km) through shallow regolith with mean transit times (MTT) of weeks to months, producing solutions dominated by Si, Ca2+, Na+, and HCO3?, locally SO42?. Rock type is a significant control on spring, surface, and shallow groundwater chemistry, and plagioclase (oligoclase) is the major source of dissolved Na+ and Si. Concentrations of Ca2+ exceed stoichiometric predictions of oligoclase weathering by ~3.5×; excess Ca2+ likely represents weathering of aeolian material, vein calcite, or trace minerals. Concentrations of base cations and Si increase slowly with estimated MTT of 0.2 years for Niwot Ridge spring waters, and several years for shallow groundwater sampled by wells. Chemical weathering of silicate minerals is slow with estimated rates of ~2.0 and 0.2 pmol·m?2·s?1 for oligoclase and microcline, respectively; the most mineralized spring waters are saturated only with respect to kaolinite and montmorillonite. More than 50% of the dissolved base cations + Si measured in Boulder Creek at Orodell (~25 km downstream) accumulate before water emerges from alpine springs on Niwot Ridge. Warming global temperatures are shifting more high‐elevation precipitation to rain, potentially changing run‐off patterns, transit time, and solute loads. Acquisition of solutes by alpine waters thus has implications far beyond small upland catchments. 相似文献
Long-term climate moderation is commonly attributed to chemical weathering; the higher the temperature and precipitation the faster the weathering rate. Weathering releases divalent cations to the ocean via riverine transport where they promote the drawdown of CO2 from the atmosphere by the precipitation and subsequent burial of carbonate minerals. To test this widely-held hypothesis, we performed a field study determining the weathering rates of 8 nearly pristine north-eastern Iceland river catchments with varying glacial cover over 44 years. The mean annual temperature and annual precipitation of these catchments varied by 3.2 to 4.5 °C and 80 to 530%, respectively during the study period. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all 8 catchments and between mean annual temperature and both mechanical weathering and runoff in 7 of the 8 catchments. For each degree of temperature increase, the runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14% respectively, depending on the catchment. In contrast, annual precipitation is less related to the measured fluxes; statistically significant correlations between annual precipitation and runoff, mechanical weathering, and chemical weathering were found for 3 of the least glaciated catchments. Mechanical and chemical weathering increased with time in all catchments over the 44 year period. These correlations were statistically significant for only 2 of the 8 catchments due to scatter in corresponding annual runoff and average annual temperature versus time plots. Taken together, these results 1) demonstrate a significant feedback between climate and Earth surface weathering, and 2) suggest that weathering rates are currently increasing with time due to global warming. 相似文献
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