Carbon dioxide,methane, and dissolved carbon dynamics in an urbanized river system

Estimates of greenhouse gas evasion from rivers have been refined over the past decades to constrain their role in global carbon cycle processes. However, despite 55% of the human population living in urban areas, urban rivers have had limited attention. We monitored carbon dynamics in an urbanized river (River Kelvin, 331 km², UK) to explore the drivers of dissolved carbon lateral and vertical export. Over a 2-year sampling period, riverine methane (CH₄) and carbon dioxide (CO₂) concentrations were consistently oversaturated with respect to atmospheric equilibria, leading to continual degassing to the atmosphere. Carbon stable isotopic compositions (δ¹³C) indicated that terrestrially derived carbon comprised most of the riverine CH₄ and dissolved CO₂ (CO₂*) load while dissolved inorganic carbon (DIC) from groundwater was the main form of riverine DIC. The dynamics of CH₄, CO₂*, and DIC in the river were primarily hydrology-controlled, that is, [CH₄] and [CO₂*] both increased with elevated discharge, total [DIC] decreased with elevated discharge while the proportion of biologically derived DIC increased with increasing discharge. The concentration of dissolved organic carbon (DOC) showed a weak relationship with river hydrology in summer and autumn and was likely influenced by the combined sewer overflows. Carbon emission to the atmosphere is estimated to be 3.10 ± 0.61 kg C·m⁻²·yr⁻¹ normalized to water surface area, with more than 99% emitted as CO₂. Annual carbon loss to the coastal estuary is approximately 4.69 ± 0.70 Gg C yr⁻¹, with annual DIC export approximately double that of DOC. Per unit area, the River Kelvin was a smaller carbon source to the atmosphere than natural rivers/streams but shows elevated fluxes of DIC and DOC under comparable conditions. This research illustrates the role urban systems may have on riverine carbon dynamics and demonstrates the potential tight link between urbanization and riverine carbon export.     

Dissolved inorganic carbon isotopes of a typical alpine river on the Tibetan Plateau revealing carbon sources,wetland effect and river recharge

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 (δ¹³C_DIC) in river water and groundwater were systematically investigated to provide constraints on DIC sources, recharge and cycling. Significant changes in the δ¹³C_DIC 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 δ¹³C_DIC ‘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.     

Direct evidence of the feedback between climate and weathering

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.     

粤东五华河流域的化学风化与CO2吸收

基于对粤东五华河干流和支流水体的物理、化学组成测试数据,应用质量平衡法和相关分析法探讨湿热山地丘陵地区岩石化学风化过程对大气CO₂的吸收.结果表明:五华河水体的总溶解性固体含量(77.11 mg/L)接近于世界河流的平均值(65 mg/L);离子组成以Ca²⁺、Na⁺和HCO₃^-为主,可溶性Si次之.五华河流域化学径流组成主要源自硅酸盐矿物化学风化过程的贡献,碳酸盐矿物的贡献较少;大气和土壤CO₂是流域内岩石化学风化的主要侵蚀介质.与同一气候带其他河流相比较,五华河流域岩石化学风化过程对大气CO₂的吸收通量(2.14×105mol/(km²·a))较低,这主要是由于流域内缺乏碳酸盐岩所导致.     

Spatial characteristics and controlling factors of chemical weathering of loess in the dry season in the middle Loess Plateau,China

Hydrochemistry methods were used to decipher the weathering and geochemical processes controlling solute acquisition of river waters in the dry season in the middle Loess Plateau (MLP), one of the most severely eroded areas and turbid riverine systems in the world. River waters were neutral to slightly alkaline with pH varying from 7.6 to 9.6. The total dissolved solids decreased from northwest to southeast with a mean value of 804 mg/l, much higher than the global average and other large rivers in China. Ternary diagram showed that river waters were dominated by Na⁺, HCO₃^?, and Cl^? with the main water‐type of HCO₃^?–Cl^?–Na⁺. Saturation index values, Mg²⁺, Ca²⁺, and HCO₃^? analyses indicated the preferential Ca²⁺ removal by calcite precipitation. Gibbs plots and stoichiometry plots indicated that the dissolved solutes were mainly derived from rock weathering with minor anthropogenic and atmospheric inputs. Samples in the northwestern basin are also influenced by evaporation. A forward model of mass budget calculation showed that, owing to high soluble characteristics, evaporite dissolution was a major feature of river waters and contributed 41% to the total dissolved cations on average, while carbonate and silicate weathering contributed 28%,and 25% on average, respectively. Besides evaporite dissolution, cation exchange is also responsible for the high concentrations of Na⁺ in river water. Spatial variations showed that evaporite dissolution and silicate weathering were higher in the northern basin, whereas carbonate weathering was higher in the southern basin. Different from most rivers in the world, the physical erosion rates (varying from 117.7 to 4116.6 t/km²y) are much higher than the chemical weathering rates (varying from 3.54 to 6.76 t/km²y) in the MLP because of the loose structure of loess and poor vegetation in the basin. In the future, studies on comparison of water geochemistry in different seasons and on influence of different types of land use and soil salinization on water geochemistry, denudation rates, and water quality should be strengthened in the MLP. These results shed some lights on processes responsible for modern loess weathering and also indicate the importance of time‐series sampling strategy for river water chemistry. Copyright © 2016 John Wiley & Sons, Ltd.     

Major ion chemistry of two cratonic rivers in the tropics: Weathering rates and their controlling factors

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.     

Dissolved major ions,Sr and 87Sr/86Sr of coastal lakes from Larsemann hills,East Antarctica: Solute sources and chemical weathering in a polar environment

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.     

Transport and exchange of U-series nuclides between suspended material,dissolved load and colloids in rivers draining basaltic terrains

This study presents uranium and thorium concentrations and activity ratios for all riverine phases (bedload, suspended load, dissolved load and colloids) from basaltic terrains in Iceland and the Azores. Small basaltic islands, such as these, are thought to account for ~ 25% of CO₂ consumed by global silicate weathering, and for ~ 45% of the flux of suspended material to the oceans. These data indicate that [U] and [Th] in the dissolved and colloidal fractions are strongly controlled by pH, and to a much lesser extent by levels of dissolved organic carbon (which are low in these environments). At high pH, basalt glass dissolution is enhanced, and secondary mineral formation (e.g. Fe-oxyhydroxides and allophane) is suppressed, resulting in high dissolved [U], and low colloidal [U] and [Th], indicating a direct chemical weathering control on elemental abundances. When the dissolved (²³⁴U/²³⁸U) activity ratio is >~1.3 (i.e. when physical weathering, groundwater contribution or soil formation are high), there is little isotope exchange between dissolved and colloidal fractions. At lower activity ratios, the dissolved load and colloids have indistinguishable activity ratios, suggesting that when chemical weathering rates are high, secondary clay formation is also high, and colloids rapidly adsorb dissolved U. Many of the suspended sediment samples have (²³⁴U/²³⁸U) activity ratios of > 1, which suggests that uptake of U onto the suspended load is important. Identical (²³⁰Th/²³²Th) in suspended, dissolved and colloidal samples suggests that Th, like U, is exchanged or sorbed rapidly between all riverine phases. This particle-reactivity, combined with poorly constrained contributions from groundwater and hydrothermal water, and short-term variations in input to soils (volcanic and glacial), suggests that U-series nuclides in riverine material from such basaltic terrains are unlikely to reflect steady state erosion processes.     

Hydrochemistry of carbonate terrains in alpine glacial settings

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.     

Modelling suspended sediment discharge in a glaciated Arctic catchment–Lake Peters,Northeast Brooks Range,Alaska

Seasonal suspended sediment transfer in glaciated catchments is responsive to meteorological, geomorphological, and glacio-fluvial conditions, and thus is a useful indicator of environmental system dynamics. Knowledge of multifaceted fluvial sediment-transfer processes is limited in the Alaskan Arctic – a region sensitive to contemporary environmental change. For two glaciated sub-catchments at Lake Peters, northeast Brooks Range, Alaska, we conducted a two-year endeavour to monitor the hydrology and meteorology, and used the data to derive multiple-regression models of suspended sediment load. Statistical selection of the best models shows that incorporating meteorological or temporal explanatory variables improves performances of turbidity- and discharge-based sediment models. The resulting modelled specific suspended sediment yields to Lake Peters are: 33 (20–60) t km⁻² yr⁻¹ in 2015, and 79 (50–140) t km⁻² yr⁻¹ in 2016 (95% confidence band estimates). In contrast to previous studies in Arctic Alaska, fluvial suspended sediment transfer to Lake Peters was primarily influenced by rainfall, and secondarily influenced by temperature-driven melt processes associated with clockwise diurnal hysteresis. Despite different sub-catchment glacier coverage, specific yields were the same order of magnitude from the two primary inflows to Lake Peters, which are Carnivore Creek (128 km²; 10% glacier coverage) and Chamberlin Creek (8 km²; 23% glacier coverage). Seasonal to longer-term sediment exhaustion and/or contrasting glacier dynamics may explain the lower than expected relative specific sediment yield from the more heavily glacierized Chamberlin Creek catchment. Absolute suspended sediment yield (t yr⁻¹) from Carnivore Creek to Lake Peters was 27 times greater than from Chamberlin Creek, which we attribute to catchment size and sediment supply differences. Our results provide a foundational understanding of the current sediment transfer regime and are useful for predicting changes in fluvial sediment transport in glaciated Alaskan Arctic catchments.     

Contemporary rates of chemical denudation and atmospheric CO2 sequestration in glacier basins: an Arctic perspective

This paper presents new estimates of solute fluxes from five high Arctic glacier basins in Svalbard. These estimates are combined with data from two other glacier basins to assess the effectiveness of chemical denudation on Svalbard and to estimate rates of temporary (or transient) CO₂ drawdown. We use a solute provenance model to partition solutes into marine, aerosol, atmospheric and crustal components and to estimate their annual fluxes. Crustally derived solute fluxes are equivalent to a mean chemical denudation rate of 350 Σmeq⁺ m⁻² a⁻¹ for Svalbard (range: 160–560 Σmeq⁺ m⁻² a⁻¹), which lies within the global range of 94–4200 Σmeq⁺ m⁻² a⁻¹ for 21 glacier basins in the northern hemisphere, and is close to the continental average of 390 Σmeq⁺ m⁻² a⁻¹. Specific annual discharge is the most significant control upon chemical denudation in the glacierized basins, and basin lithology is an important secondary control, with carbonate‐rich and basaltic lithologies currently showing the greatest chemical denudation rates. Estimates of transient CO₂ drawdown are also directly associated with specific annual discharge and rock type. On Svalbard transient CO₂ drawdown lies in the range 110–3000 kg C km⁻² a⁻¹, whilst the range is 110–13000 kg C km⁻² a⁻¹ for the northern hemisphere glacial data set. Transient CO₂ drawdown is therefore usually low in the Svalbard basins unless carbonate or basalt rocks are abundant. The analysis shows that a large area of uncertainty in the transient CO₂ drawdown estimates exists due to the non‐stoichiometric release of solute during silicate hydrolysis. Silicate hydrolysis is particularly non‐stoichiometric in basins where the extent of glacierization is high, which is most probably an artefact of high flushing rates through ice‐marginal and subglacial environments where K‐feldspars are undergoing mechanical comminution. Copyright © 2000 John Wiley & Sons, Ltd.     

Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef,Australia

Dissolved inorganic carbon (DIC) transport by rivers is an important control on the pH and carbonate chemistry of the coastal ocean. Here, we combine DIC and total alkalinity (TAlk) concentrations from four tropical rivers of the Great Barrier Reef region in Australia with daily river discharge to quantify annual river loads and export rates. DIC in the four rivers ranged from 284 to 2,639 μmol kg⁻¹ and TAlk ranged from 220 to 2,612 μmol kg⁻¹. DIC:TAlk ratios were mostly greater than one suggesting elevated exports of free [CO₂*]. This was pronounced in the Johnstone and Herbert rivers of the tropical wet north. The largest annual loads were transported in the two large river catchments of the southern Great Barrier Reef region, the Fitzroy and Burdekin rivers. The carbon stable isotopic composition of DIC suggests that carbonate weathering was the dominant source of DIC in the southern rivers, and silicate weathering was likely a source of DIC in the northern Wet Tropics rivers. Annual loads and export rates were strongly driven by precipitation and discharge patterns, the occurrence of tropical cyclones, and associated flooding events, as well as distinct seasonal dry and wet periods. As such, short-lived hydrological events and long-term (seasonal and inter-annual) variation of DIC and TAlk that are pronounced in rivers of the tropical and subtropical wet and dry climate zone should be accounted for when assessing inorganic carbon loads to the coastal ocean and the potential to buffer against or accelerate ocean acidification.     

Carbon fluxes in the China Seas: An overview and perspective

This paper aims to provide an overview of regional carbon fluxes and budgets in the marginal seas adjacent to China.The "China Seas" includes primarily the South China Sea, East China Sea, Yellow Sea, and the Bohai Sea. Emphasis is given to CO_2 fluxes across the air-sea interface and their controls. The net flux of CO_2 degassing from the China Seas is estimated to be9.5±53 Tg C yr~(-1). The total riverine carbon flux through estuaries to the China Seas is estimated as 59.6±6.4 Tg C yr~(-1). Chinese estuaries annually emit 0.74±0.02 Tg C as CO_2 to the atmosphere. Additionally, there is a very large net carbon influx from the Western Pacific to the China Seas, amounting to ～2.5 Pg C yr~(-1). As a first-order estimate, the total export flux of particulate organic carbon from the upper ocean of the China Seas is 240±80 Tg C yr~(-1). This review also attempts to examine current knowledge gaps to promote a better understanding of the carbon cycle in this important region.     

Probing deep weathering in the Shale Hills Critical Zone Observatory,Pennsylvania (USA): the hypothesis of nested chemical reaction fronts in the subsurface

Weathering is both an acid‐base and a redox reaction in which rocks are titrated by meteoric carbon dioxide (CO₂) and oxygen (O₂). In general, the depths of these weathering reactions are unknown. To determine such depths, cuttings of Rose Hill shale were investigated from one borehole from the ridge and four boreholes from the valley at the Susquehanna Shale Hills Observatory (SSHO). Pyrite concentrations are insignificant to depths of 23 m under the ridge and 8–9 m under the valley. Likewise, carbonate concentrations are insignificant to 22 and 2 m, respectively. In addition, a 5–6 m‐thick fractured layer directly beneath the land surface shows evidence for loss of illite, chlorite, and feldspar. Under the valley, secondary carbonates may have precipited. The limited number of boreholes and the tight folding make it impossible to prove that depth variations result from weathering instead of chemical heterogeneity within the parent shale. However, carbonate depletion coincides with the winter water table observed at ~20 m (ridge) and ~2 m depth (valley). It would be fortuitous if carbonate‐containing strata are found under ridge and valley only beneath the water table. Furthermore, pyrite and carbonate react quickly and many deep reaction fronts for these minerals are described in the literature. We propose that deep transport of O₂ initiates weathering at SSHO and many other localities because pyrite commonly oxidizes autocatalytically to acidify porewaters and open porosity. According to this hypothesis, the mineral distributions at SSHO are nested reaction fronts that overprint protolith stratigraphy. The fronts are hypothesized to lie subparallel to the land surface because O₂ diffuses to the water table and causes oxidative dissolution of pyrite. Pyrite‐derived sulfuric acid (H₂SO₄) plus CO₂ also dissolve carbonates above the water table. To understand how reaction fronts record long‐term coupling between erosion and weathering will require intensive mapping of the subsurface. Copyright © 2013 John Wiley & Sons, Ltd.     

A comparative overview of weathering intensity and HCO3 flux in the world's major rivers with emphasis on the Changjiang,Huanghe, Zhujiang (Pearl) and Mississippi Rivers

In this paper, general relationships of riverine bicarbonate concentrations and fluxes as a function of drainage basin mineral content and runoff are examined using a database of the 25 largest rivers in the world. Specific HCO₃⁻ flux normalized to unit basin area, which peaks in the mid latitudes, was found to be strongly correlated with the carbonate mineral content of river basins, while river HCO₃⁻ concentration was related to the balance of precipitation and evaporation. Within this global context, the weathering patterns of CO₂ in a few large rivers (Changjiang, Huanghe, Pearl, and Mississippi rivers) were examined in further detail. The Zhujiang (Pearl River), especially its largest branch (Xijiang), was characterized by the highest specific weathering rate among all the world's large rivers due to an exceptionally high carbonate mineral content (over 80%) in its drainage basin and its warm and wet environment. It has a moderate level of HCO₃⁻ concentration, however, due to dilution by relatively high precipitation in the watershed. In stark contrast, the Huanghe (Yellow River) has one of the lowest specific weathering rates because of low carbonate mineral content and a dry climate. However, it has a high HCO₃⁻ concentration due largely to the concentrating effects of high evaporative water loss, as a result of arid weather and the agricultural use of water through irrigation systems, as well as carbonate-containing surficial deposits (i.e., loess). The strong correlation between specific HCO₃⁻ fluxes and discharge in all four rivers with different discharge seasonality suggests that higher precipitation in drainage basins promotes higher weathering rates.     

Geochemical weathering at the bed of Haut Glacier d'Arolla,Switzerland—a new model

Waters were sampled from 17 boreholes at Haut Glacier d'Arolla during the 1993 and 1994 ablation seasons. Three types of concentrated subglacial water were identified, based on the relative proportions of Ca²⁺, HCO₃^? and SO₄^2? to Si. Type A waters are the most solute rich and have the lowest relative proportion of Si. They are believed to form in hydrologically inefficient areas of a distributed drainage system. Most solute is obtained from coupled sulphide oxidation and carbonate dissolution (SO–CD). It is possible that there is a subglacial source of O₂, perhaps from gas bubbles released during regelation, because the high SO₄^2? levels found (up to 1200 µeq/L) are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 °C (c.414 µeq/L). A more likely alternative is that sulphide is oxidized by Fe³⁺ in anoxic environments. If this is the case, exchange reactions involving Fe^III and Fe^II from silicates are possible. These have the potential to generate relatively high concentrations of HCO₃^? with respect to SO₄^2?. Formation of secondary weathering products, such as clays, may explain the low Si concentrations of Type A waters. Type B waters were the most frequently sampled subglacial water. They are believed to be representative of waters flowing in more efficient parts of a distributed drainage system. Residence time and reaction kinetics help determine the solute composition of these waters. The initial water–rock reactions are carbonate and silicate hydrolysis, and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites. Hydrolysis is followed by SO–CD. The SO₄^2? concentrations usually are <414 µeq/L, although some range up to 580 µeq/L, which suggests that elements of the distributed drainage system may become anoxic. Type C waters were the most dilute, yet they were very turbid. Their chemical composition is characterized by low SO₄^2? : HCO₃^? ratios and high pH. Type C waters were usually artefacts of the borehole chemical weathering environment. True Type C waters are believed to flow through sulphide‐poor basal debris, particularly in the channel marginal zone. The composition of bulk runoff was most similar to diluted Type B waters at high discharge, and was similar to a mixture of Type B and C waters at lower discharge. These observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow. Little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric CO₂. The progression of reactions is from carbonate and silicate hydrolysis, through sulphide oxidation by first oxygen and then Fe^III, which drives further carbonate and silicate weathering. A crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 : 1. We speculate that microbial oxidation of organic carbon also may occur. Both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions. Hence, we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric CO₂ and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity, which catalyses the reduction of Fe^III and the oxidation of FeS₂. Copyright © 2002 John Wiley & Sons, Ltd.     

A new Scandinavian reference 10Be production rate

An important constraint on the reliability of cosmogenic nuclide exposure dating is the rigorous determination of production rates. We present a new dataset for ¹⁰Be production rate calibration from Mount Billingen, southern Sweden, the site of the final drainage of the Baltic Ice Lake, an event dated to 11,620 ± 100 cal yr BP. Five samples of flood-scoured bedrock surfaces (58.5°N, 13.7°E, 105–120 m a.s.l.) unambiguously connected to the drainage event yield a reference ¹⁰Be production rate of 4.19 ± 0.20 atoms g⁻¹ yr⁻¹ for the CRONUS-Earth online calculator Lm scaling and 4.02 ± 0.18 atoms g⁻¹ yr⁻¹ for the nuclide specific LSD_n scaling. We also recalibrate the reference ¹⁰Be production rates for four sites in Norway and combine three of these with the Billingen results to derive a tightly clustered Scandinavian reference ¹⁰Be production rate of 4.13 ± 0.11 atoms g⁻¹ yr⁻¹ for the CRONUS Lm scaling and 3.95 ± 0.10 atoms g⁻¹ yr⁻¹ for the LSD_n scaling scheme.     

Sedimentary phosphorus species and sedimentation flux in the East China Sea

Core sediment samples were collected from the middle shelf of the East China Sea (ECS) to study the phosphorus forms, P accumulation rate (PAR), P burial efficiency and the burial flux in the ECS. The sediment samples were sequentially extracted and directly extracted to analyze different forms of sedimentary P: lossely sorbed P and iron-bound P (P_CDB); inorganic P associated with francolite (carbonate fluorapatite, CFA), biogenic hydroxyapatite, smecite, and CaCO₃ (P_CFA); detrital P (P_Detrital); organic P (P_Organic); and total P. In addition, the Fe contents in the citrate-dithionite-bicarbonate (CDB) extracted solution were also measured.The total concentrations of P in the surface sediments in the study area ranged from 13.5 to 22.3 μmol g⁻¹. Inorganic P was the major form and accounted for 72–93% of the total P pool. The average percentage of each fraction of P followed the sequence: P_Detrital (70%)>P_Organic (15.5%)>P_CDB (8.4%)>P_CFA (5.8%). The distribution pattern of total P in the surface sediment was similar to that of P_Detrital and P_Organic, but different from that of P_CDB and P_CFA. The profile variation of P_Organic was the most significant among the phosphorus forms at the study stations. The concentrations of P_CDB and P_CFA showed minor variation with depth. These results may suggest that transformations of P_Organic, P_CFA and P_CDB occurred at the study stations during sedimentary P burial.Based on the concentrations of total P, P_CDB and Fe_CDB obtained in the present study and the mass accumulation rate (MAR) reported in the literature, the values of the PAR, the P diffusion flux (J_PFe) supplied by reducible iron hydroxides and the P burial efficiency were calculated. The calculated results for PAR and J_PFe in the study area ranged from 1.02 to 24.23 μmol cm⁻² yr⁻¹ and from 0.1 to 2.11 μmol cm⁻² yr⁻¹, respectively. The phosphorus burial efficiency (PBE) was approximately 90%. The ECS is a phosphorus sink, and the average annual P burial flux has been reasonably estimated to be in the range of 20–25×10⁹ mol yr⁻¹.     

Carbon pools and fluxes in the China Seas and adjacent oceans

The China Seas include the South China Sea, East China Sea, Yellow Sea, and Bohai Sea. Located off the Northwestern Pacific margin, covering 4700000 km~2 from tropical to northern temperate zones, and including a variety of continental margins/basins and depths, the China Seas provide typical cases for carbon budget studies. The South China Sea being a deep basin and part of the Western Pacific Warm Pool is characterized by oceanic features; the East China Sea with a wide continental shelf, enormous terrestrial discharges and open margins to the West Pacific, is featured by strong cross-shelf materials transport; the Yellow Sea is featured by the confluence of cold and warm waters; and the Bohai Sea is a shallow semiclosed gulf with strong impacts of human activities. Three large rivers, the Yangtze River, Yellow River, and Pearl River, flow into the East China Sea, the Bohai Sea, and the South China Sea, respectively. The Kuroshio Current at the outer margin of the Chinese continental shelf is one of the two major western boundary currents of the world oceans and its strength and position directly affect the regional climate of China. These characteristics make the China Seas a typical case of marginal seas to study carbon storage and fluxes. This paper systematically analyzes the literature data on the carbon pools and fluxes of the Bohai Sea,Yellow Sea, East China Sea, and South China Sea, including different interfaces(land-sea, sea-air, sediment-water, and marginal sea-open ocean) and different ecosystems(mangroves, wetland, seagrass beds, macroalgae mariculture, coral reefs, euphotic zones, and water column). Among the four seas, the Bohai Sea and South China Sea are acting as CO_2 sources, releasing about0.22 and 13.86–33.60 Tg C yr~(-1) into the atmosphere, respectively, whereas the Yellow Sea and East China Sea are acting as carbon sinks, absorbing about 1.15 and 6.92–23.30 Tg C yr~(-1) of atmospheric CO_2, respectively. Overall, if only the CO_2 exchange at the sea-air interface is considered, the Chinese marginal seas appear to be a source of atmospheric CO_2, with a net release of 6.01–9.33 Tg C yr~(-1), mainly from the inputs of rivers and adjacent oceans. The riverine dissolved inorganic carbon (DIC) input into the Bohai Sea and Yellow Sea, East China Sea, and South China Sea are 5.04, 14.60, and 40.14 Tg C yr~(-1),respectively. The DIC input from adjacent oceans is as high as 144.81 Tg C yr~(-1), significantly exceeding the carbon released from the seas to the atmosphere. In terms of output, the depositional fluxes of organic carbon in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea are 2.00, 3.60, 7.40, and 5.92 Tg C yr~(-1), respectively. The fluxes of organic carbon from the East China Sea and South China Sea to the adjacent oceans are 15.25–36.70 and 43.93 Tg C yr~(-1), respectively. The annual carbon storage of mangroves, wetlands, and seagrass in Chinese coastal waters is 0.36–1.75 Tg C yr~(-1), with a dissolved organic carbon(DOC) output from seagrass beds of up to 0.59 Tg C yr~(-1). Removable organic carbon flux by Chinese macroalgae mariculture account for 0.68 Tg C yr~(-1) and the associated POC depositional and DOC releasing fluxes are 0.14 and 0.82 Tg C yr~(-1), respectively. Thus, in total, the annual output of organic carbon, which is mainly DOC, in the China Seas is 81.72–104.56 Tg C yr~(-1). The DOC efflux from the East China Sea to the adjacent oceans is 15.00–35.00 Tg C yr~(-1). The DOC efflux from the South China Sea is 31.39 Tg C yr~(-1). Although the marginal China Seas seem to be a source of atmospheric CO_2 based on the CO_2 flux at the sea-air interface, the combined effects of the riverine input in the area, oceanic input, depositional export,and microbial carbon pump(DOC conversion and output) indicate that the China Seas represent an important carbon storage area.     

Himalayan metamorphic CO2 fluxes: Quantitative constraints from hydrothermal springs

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 δ¹³C 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.