Bulk Meltwater Research Articles

Patterns in Microbial Assemblages Exported From the Meltwater of Arctic and Sub-Arctic Glaciers.

Meltwater streams connect the glacial cryosphere with downstream ecosystems. Dissolved and particulate matter exported from glacial ecosystems originates from contrasting supraglacial and subglacial environments, and exported microbial cells have the potential to serve as ecological and hydrological indicators for glacial ecosystem processes. Here, we compare exported microbial assemblages from the meltwater of 24 glaciers from six (sub)Arctic regions – the southwestern Greenland Ice Sheet, Qeqertarsuaq (Disko Island) in west Greenland, Iceland, Svalbard, western Norway, and southeast Alaska – differing in their lithology, catchment size, and climatic characteristics, to investigate spatial and environmental factors structuring exported meltwater assemblages. We found that 16S rRNA gene sequences of all samples were dominated by the phyla Proteobacteria, Bacteroidetes, and Actinobacteria, with Verrucomicrobia also common in Greenland localities. Clustered OTUs were largely composed of aerobic and anaerobic heterotrophs capable of degrading a wide variety of carbon substrates. A small number of OTUs dominated all assemblages, with the most abundant being from the genera Polaromonas, Methylophilus, and Nitrotoga. However, 16–32% of a region’s OTUs were unique to that region, and rare taxa revealed unique metabolic potentials and reflected differences between regions, such as the elevated relative abundances of sulfur oxidizers Sulfuricurvum sp. and Thiobacillus sp. at Svalbard sites. Meltwater alpha diversity showed a pronounced decrease with increasing latitude, and multivariate analyses of assemblages revealed significant regional clusters. Distance-based redundancy and correlation analyses further resolved associations between whole assemblages and individual OTUs with variables primarily corresponding with the sampled regions. Interestingly, some OTUs indicating specific metabolic processes were not strongly associated with corresponding meltwater characteristics (e.g., nitrification and inorganic nitrogen concentrations). Thus, while exported assemblage structure appears regionally specific, and probably reflects differences in dominant hydrological flowpaths, OTUs can also serve as indicators for more localized microbially mediated processes not captured by the traditional characterization of bulk meltwater hydrochemistry. These results collectively promote a better understanding of microbial distributions across the Arctic, as well as linkages between the terrestrial cryosphere habitats and downstream ecosystems.

Seasonal progression of uranium series isotopes in subglacial meltwater: Implications for subglacial storage time

The residence time of subglacial meltwater impacts aquifer recharge, nutrient production, and chemical signals that reflect underlying bedrock/substrate, but is inaccessible to direct observation. Here we report the seasonal evolution of subglacial meltwater chemistry from the 2011 melt season at the terminus of the Athabasca Glacier, Canada. We measured major and trace analytes and U-series isotopes for twenty-nine bulk meltwater samples collected over the duration of the melt season. This dataset, which is the longest time-series record of (234U/238U) isotopes in a glacial meltwater system, provides insight into the hydrologic evolution of the subglacial system during active melting. Meltwater samples, measured from the outflow, were analyzed for (238U), (222Rn) and (234U/238U)activity, conductivity, alkalinity, pH and major cations. Subglacial meltwater varied in [238U] and (222Rn) from 23 to 832ppt and 9 to 171 pCi/L, respectively. Activity ratios of (234U/238U) ranged from 1.003 to 1.040, with the highest (238U), (222Rn) and (234U/238U)activity values occurring in early May when delayed-flow basal meltwater composed a significant portion of the bulk melt. From the chemical evolution of the meltwater, we posit that the relative subglacial water residence times decrease over the course of the melt season. This decrease in qualitative residence time during active melt is consistent with prior field studies and model-predicted channel switching from a delayed, distributed network to a fast, channelized network flow. As such, our study provides support for linking U-series isotopes to storage lengths of meltwater beneath glacial systems as subglacial hydrologic networks evolve with increased melting and channel network efficiency.

Utility of 222Rn as a passive tracer of subglacial distributed system drainage

Water flow beneath the Greenland Ice Sheet (GrIS) has been shown to include slow-inefficient (distributed) and fast-efficient (channelized) drainage systems, in response to meltwater delivery to the bed via both moulins and surface lake drainage. This partitioning between channelized and distributed drainage systems is difficult to quantify yet it plays an important role in bulk meltwater chemistry and glacial velocity, and thus subglacial erosion. Radon-222, which is continuously produced via the decay of 226Ra, accumulates in meltwater that has interacted with rock and sediment. Hence, elevated concentrations of 222Rn should be indicative of meltwater that has flowed through a distributed drainage system network. In the spring and summer of 2011 and 2012, we made hourly 222Rn measurements in the proglacial river of a large outlet glacier of the GrIS (Leverett Glacier, SW Greenland). Radon-222 activities were highest in the early melt season (10–15 dpm L−1), decreasing by a factor of 2–5 (3–5 dpm L−1) following the onset of widespread surface melt. Using a 222Rn mass balance model, we estimate that, on average, greater than 90% of the river 222Rn was sourced from distributed system meltwater. The distributed system 222Rn flux varied on diurnal, weekly, and seasonal time scales with highest fluxes generally occurring on the falling limb of the hydrograph and during expansion of the channelized drainage system. Using laboratory based estimates of distributed system 222Rn, the distributed system water flux generally ranged between 1–5% of the total proglacial river discharge for both seasons. This study provides a promising new method for hydrograph separation in glacial watersheds and for estimating the timing and magnitude of distributed system fluxes expelled at ice sheet margins.

Stable oxygen isotope variability in two contrasting glacier river catchments in Greenland

Abstract. Analysis of stable oxygen isotope (δ18O) characteristics is a useful tool to investigate water provenance in glacier river systems. In order to attain knowledge on the diversity of δ18O variations in Greenlandic rivers, we examined two contrasting glacierised catchments disconnected from the Greenland Ice Sheet (GrIS). At the Mittivakkat Gletscher river, a small river draining a local temperate glacier in southeast Greenland, diurnal oscillations in δ18O occurred with a 3 h time lag to the diurnal oscillations in run-off. The mean annual δ18O was −14.68 ± 0.18 ‰ during the peak flow period. A hydrograph separation analysis revealed that the ice melt component constituted 82 ± 5 % of the total run-off and dominated the observed variations during peak flow in August 2004. The snowmelt component peaked between 10:00 and 13:00 local time, reflecting the long travel time and an inefficient distributed subglacial drainage network in the upper part of the glacier. At the Kuannersuit Glacier river on the island Qeqertarsuaq in west Greenland, the δ18O characteristics were examined after the major 1995–1998 glacier surge event. The mean annual δ18O was −19.47 ± 0.55 ‰. Despite large spatial variations in the δ18O values of glacier ice on the newly formed glacier tongue, there were no diurnal oscillations in the bulk meltwater emanating from the glacier in the post-surge years. This is likely a consequence of a tortuous subglacial drainage system consisting of linked cavities, which formed during the surge event. Overall, a comparison of the δ18O compositions from glacial river water in Greenland shows distinct differences between water draining local glaciers and ice caps (between −23.0 and −13.7 ‰) and the GrIS (between −29.9 and −23.2 ‰). This study demonstrates that water isotope analyses can be used to obtain important information on water sources and the subglacial drainage system structure that is highly desired for understanding glacier hydrology.

Bulk meltwater flow and liquid water content of snowpacks mapped using the electrical self-potential (SP) method

Abstract. Our ability to measure, quantify and assimilate hydrological properties and processes of snow in operational models is disproportionally poor compared to the significance of seasonal snowmelt as a global water resource and major risk factor in flood and avalanche forecasting. We show here that strong electrical self-potential fields are generated in melting in situ snowpacks at Rhone Glacier and Jungfraujoch Glacier, Switzerland. In agreement with theory, the diurnal evolution of self-potential magnitudes ( ∼ 60–250 mV) relates to those of bulk meltwater fluxes (0–1.2 × 10−6 m3 s−1) principally through the permeability and the content, electrical conductivity and pH of liquid water. Previous work revealed that when fresh snow melts, ions are eluted in sequence and electrical conductivity, pH and self-potential data change diagnostically. Our snowpacks had experienced earlier stages of melt, and complementary snow pit measurements revealed that electrical conductivity ( ∼ 1–5 × 10−6 S m−1) and pH ( ∼ 6.5–6.7) as well as permeabilities (respectively ∼ 9.7 × 10−5 and ∼ 4.3 × 10−5 m2 at Rhone Glacier and Jungfraujoch Glacier) were invariant. This implies, first, that preferential elution of ions was complete and, second, that our self-potential measurements reflect daily changes in liquid water contents. These were calculated to increase within the pendular regime from ∼ 1 to 5 and ∼ 3 to 5.5 % respectively at Rhone Glacier and Jungfraujoch Glacier, as confirmed by ground truth measurements. We conclude that the electrical self-potential method is a promising snow and firn hydrology sensor owing to its suitability for (1) sensing lateral and vertical liquid water flows directly and minimally invasively, (2) complementing established observational programs through multidimensional spatial mapping of meltwater fluxes or liquid water content and (3) monitoring autonomously at a low cost. Future work should focus on the development of self-potential sensor arrays compatible with existing weather and snow monitoring technology and observational programs, and the integration of self-potential data into analytical frameworks.

Identifying weathering sources and processes in an outlet glacier of the Greenland Ice Sheet using Ca and Sr isotope ratios

Chemical and isotope data (ε40Ca, δ44/42Ca, 87Sr/86Sr, δ18O) of river water samples were collected twice daily for 28 days in 2009 from the outlet river of Leverett Glacier, West Greenland. The water chemistry data was combined with detailed geochemical analysis and petrography of bulk rock, mineral separates and sediment samples in order to constrain the mineral weathering sources to the river. The average isotopic compositions measured in the river, with 2SD of all the values measured, were ε40Ca=+4.0±1.4, δ44/42Ca=+0.60±0.10‰ and 87Sr/86Sr=0.74243±0.00327. Based on changes in bulk meltwater discharge, the hydrochemical data was divided into three hydrological periods. The first period was marked by the tail-end of an outburst event and was characterised by water with decreasing suspended sediment concentrations (SSC), ion concentrations and pH. During the second hydrological period, discharge increased whilst 87Sr/86Sr decreased from 0.74550 to 0.74164. Based on binary mixing diagrams using 87Sr/86Sr with Na/Sr, Ca/Sr and ε40Ca, this is interpreted to reflect an increase in reactive mineral weathering, in particular epidote, as the water residence time decreases. The decrease in water residence time is a result of the evolution from a distributed (long water residence time) to a channelised (short water residence time) subglacial drainage network. The third hydrological period was defined as the period when overall discharge was decreasing. This hydrological period was marked by prominent diurnal cycles in discharge. During this period, significant correlations between δ44/42Ca and SSC and δ18O were observed which are suggestive of fractionation during adsorption. This study demonstrates the potential of radiogenic Ca to both identify temporally changing mineral sources in conjunction with 87Sr/86Sr values and to separate source and fractionation effects in δ44/42Ca values.

A decade (2002–2012) of supraglacial lake volume estimates across Russell Glacier, West Greenland

Abstract. Supraglacial lakes represent an ephemeral storage buffer for meltwater runoff and lead to significant, yet short-lived, episodes of ice-flow acceleration by decanting large meltwater and energy fluxes into the ice sheet's hydrological system. Here, a methodology for calculating lake volume is used to quantify storage and drainage across Russell Glacier, West Greenland, between 2002 and 2012. Using 502 MODIS scenes, water volume at ~200 seasonally occurring lakes was derived using a depth–reflectance relationship, which was independently calibrated and field validated against lake bathymetry. The inland expansion of lakes is strongly correlated with air temperature: during the record melt years of 2010 and 2012, lakes formed and drained earlier, attaining their maximum volume 38 and 20 days earlier than the 11 yr mean, as well as occupying a greater area and forming at higher elevations (> 1800 m) than previously. Despite occupying under 2% of the study area, lakes delay the transmission of up to 7–13% of the bulk meltwater discharged. Although the results are subject to an observational bias caused by periods of cloud cover, we estimate that across Russell Glacier, 28% of supraglacial lakes drain rapidly (< 4 days). Clustering of such events in space and time suggests a synoptic trigger mechanism. Further, we find no evidence to support a unifying critical size or depth-dependent drainage threshold.

Hydrochemical characteristics and solute dynamics of meltwater runoff of Urumqi Glacier No.1, eastern Tianshan, northwest China

Hydrochemical characteristics and solute dynamics of bulk meltwater draining from Urumqi Glacier No.1 were investigated in years 2006 and 2007. The glacial meltwater was slightly alkaline with the mean pH of 7.64 and 7.61 in 2006 and 2007, respectively. In the meltwater, the dominant anions were the bicarbonate and sulphate, and the dominant cation was calcium. The concentration of major cations were varied as c(Ca2+) > c(Mg2+) > c(K+) > c(Na+), while the order for the cations was c(HCO3−) > c(SO42−) > c(NO3−) > c(Cl−). The total dissolved solids (TDS) in meltwater had inverse relationships with the diurnal discharge. The major ion composition of meltwater was mainly controlled by rock weathering as inferred from the Gibbs model. Furthermore, the ion ratios and Piper diagram indicated that the main processes controlling the meltwater chemistry were carbonate weathering, pyrite weathering and feldspar weathering in rocks, and Ca2+ and HCO3− were the dominant ions during the carbonate weathering process. Solute flux calculation at Glacier No.1 station suggested that chemical denudation rates were 11.46 and 13.90 ton·km−2·yr−1 in 2006 and 2007, respectively.

Seasonal evolution of water contributions to discharge from a Greenland outlet glacier: insight from a new isotope-mixing model

AbstractThe Greenland ice sheet (GrIS) subglacial hydrological system may undergo a seasonal evolution, with significant geophysical and biogeochemical implications. We present results from a new isotope-mixing model to quantify the relative contributions of surface snow, glacial ice and delayed flow to the bulk meltwater discharge from a small (∼5 km2) land-terminating GrIS outlet glacier during melt onset (May) and at peak melt (July). We use radioactive (222Rn) and stable isotopes (18O, deuterium) to differentiate the water source contributions. Atmospherically derived 7Be further constrains meltwater transit time from the glacier surface to the ice margin. We show that (1) 222Rn is a promising tracer for glacial waters stored at the bed and (2) a quantitative chemical mixing model can be constructed by combining 222Rn and the stable water isotopes. Applying this model to the bulk subglacial outflow from our study area, we find a constant delayed-flow (stored) component from melt onset through peak melt. This component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses. Results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land-terminating sections of the GrIS undergoes a seasonal evolution from a distributed to a channelized system.

Modeling Geochemical and Biogeochemical Reactions in Subglacial Environments

ABSTRACTThis study examines current subglacial biogeochemical weathering models using PHREEQCi, a computer-based speciation mass-balance (SMB) model, parameterized using hydrochemical and mineralogical field data from Haut Glacier d’Arolla, Switzerland. The aim is to investigate the utility of SMB models for quantifying subglacial biogeochemical mechanisms, and the mathematical and thermodynamic robustness of current subglacial weathering models in a temporally variable, spatially heterogeneous hydrological and geochemical subglacial environment.The chemical evolution of meltwaters between their source in the supraglacial environment and their output from the hydroglacial system as bulk meltwaters are modeled, and compared with in situ meltwaters collected from the base of boreholes drilled to the glacier bed. SMB modeling produced a broad range of weathering outcomes, but delivered no unique weathering scenario which could account for the observed changes in water chemistry between input and output waters over the ablation season. Organic carbon oxidation and sulfide oxidation by dissolved O2, coupled to carbonate dissolution and incongruent silicate dissolution, could account for seasonal changes in meltwater chemistry, supporting current subglacial biogeochemical weathering models. Atmospheric CO2 was not required under any weathering scenario, and organic carbon and atmospheric CO2 dissolution was only possible in one weathering scenario, at a mass ratio of 10:1, further suggesting that CO2-driven dissolution is unimportant in subglacial environments. This investigation indicates the utility of SMB models applied to subglacial hydrological systems for determining geochemical and biogeochemical processes and interpreting water quality.

Hydrochemical characteristics of bulk meltwater from an entire ablation season, Longyearbreen, Svalbard

AbstractThe ionic and isotopic characteristics of bulk waters emanating from the cold-based Longyearbreen, central Svalbard, in 2004 are examined to determine lithological, hydrological and glaciological controls on water composition, solute provenance and chemical denudation. The geology consisted of reactive coal seams and associated sedimentary rocks. Acidity caused by microbial-mediated oxidation of sulfides and, to a lesser extent, nitrogen-bearing minerals was neutralized by congruent dissolution of dolomite and incongruent weathering of silicates in open-system subglacial drainage channels. The ablation season was divided into an early melt season, a peak-flow period and a late melt season. The runoff distribution during these periods was 1.7%, 89.7% and 8.6%, respectively, whereas the solute flux distribution was 1.9%, 82.1% and 16.0%, respectively. Comparisons between different annual solute flux estimation methods indicated that extrapolation of peak-flow period data significantly underestimated both the early- and late-melt-season solute fluxes. About 3.8% of the solutes derived from sea-salt spray, 0.7% from acid aerosol deposition and 95.5% from crustal/organic sources. The physical and chemical conditions resulted in diffusion of CO2 rather than atmospheric drawdown. The cation-equivalent weathering rate and the crustal solute yield were 322 ΣmEq+m−2 a−1 and 22 t km−2 a−1, respectively, which are within the regional range of Svalbard. However, the chemical weathering intensity was as high as 940 ΣmEq+ m−3 owing to the relatively low specific discharge of 0.34 m a−1.

Suspended sediment transport in glacial meltwater during the initial quiescent phase after a major surge event at Kuannersuit Glacier, Greenland

This paper describes a rough estimate of the suspended sediment transport in the bulk meltwater evacuated from Kuannersuit Glacier during the summers of 2000 and 2001. In 1995–98, an 11 km terrestrial surge of Kuannersuit Glacier, an outlet glacier of the largest ice cap on Disko Island, West Greenland, affected the catchment dramatically. The results show that in 2000, the daily sediment discharge was about 32,500 t day−1, corresponding to a specific sediment load of 19,000 t km-2 year−1. In 2001 the diurnal suspended sediment load was about 26,000 t day−1, corresponding to a specific sediment load of 15,000 t km−2 year−1. There was only a poor relation between meltwater discharge and suspended sediment transport, indicating that the drainage system was highly unstable. In 2001 the discharge and the sediment transport on several occasions was affected by collapse within the glacial drainage system and at the glacier margin. Assuming that suspended sediment transport and bedload is equal, the effective mechanical erosion is about 15 mm year−1. Compared to the sediment transport from other parts of Greenland and High Arctic regions the transport during the surge event and in the early quiescent phase is significantly higher. This indicates the importance of glacier surge in initiating sediment transport pulses in cold regions.

Isotopic exchange between snow and atmospheric water vapor: Estimation of the snowmelt component of groundwater recharge in the southwestern United States

The contribution of snowmelt to groundwater recharge at four sites in the southwestern United States was evaluated using stable isotopes of O and H. Paired precipitation collectors were installed at the study sites; data show that (1) there is often a significant difference between the stable isotope composition of fresh snow and the bulk meltwater derived from it (this suggests that using the isotope composition of high‐elevation springs as a proxy for precipitation may not be sound if snow is a recharge source) and (2) collector design can significantly influence the stable isotope composition of collected snow. Because the isotope composition of snow from a given location becomes heavier (i.e., more rain‐like) with increased exposure, using bulk snowmelt compositions to calculate input to groundwater recharge results in significantly increased estimates of snowmelt contributions to recharge (compared to estimates derived from fresh snow signatures). Snowmelt provides at least 40–70% of groundwater recharge at the study sites, although only 25–50% of average annual precipitation falls as snow. On the basis of these results and presently accepted scenarios for alterations in precipitation in the western United States over the next 50 years (significantly decreased snowpack due to increased atmospheric CO2), investigations of how climate change may affect groundwater resources are needed. We also investigated the potential for snow/atmospheric water vapor isotope exchange to influence the isotope signature of snow (which has been a subject of debate); the results of a laboratory experiment suggest that it can drive significant shifts in the isotope signature of snow, even at temperatures below 0°C.

Minor and trace elements as indicators of solute provenance and flow routing in a subglacial hydrological system

AbstractThe utility of minor and trace elements for subglacial solute‐provenance and hydrological flow‐routing studies is investigated at Haut Glacier d'Arolla (HGA), Switzerland. Principal component analysis (PCA) applied to the bulk meltwater chemistry indicates the concentration of most major ions, and some minor and trace elements (Sr, Mo, Ti) are inversely related to bulk meltwater discharge and have a clear hydrological control. Conversely, many other minor and trace elements have no clear relationship with meltwater discharge. This suggests that such solutes are affected by physico‐chemical controls such as sorption, (oxy)hydroxide formation and co‐precipitation reactions, in addition to any simple hydrological influence. PCA applied to rock digests and water‐rock interaction experiments indicates the complexity of determining the lithogenic source of minor and trace elements from subglacial chemical weathering processes. This reflects the complex aqueous mobility of many minor and trace elements and the heterogeneous geology of the HGA catchment. However, the study suggests that there is potential in minor and trace elements for solute‐provenance and flow‐routing studies in glacierized catchments underlain by a more homogeneous geology. Copyright © 2006 John Wiley & Sons, Ltd.

Comparison of Microbial Community Compositions of Two Subglacial Environments Reveals a Possible Role for Microbes in Chemical Weathering Processes

Viable microbes have been detected beneath several geographically distant glaciers underlain by different lithologies, but comparisons of their microbial communities have not previously been made. This study compared the microbial community compositions of samples from two glaciers overlying differing bedrock. Bulk meltwater chemistry indicates that sulfide oxidation and carbonate dissolution account for 90% of the solute flux from Bench Glacier, Alaska, whereas gypsum/anhydrite and carbonate dissolution accounts for the majority of the flux from John Evans Glacier, Ellesmere Island, Nunavut, Canada. The microbial communities were examined using two techniques: clone libraries and dot blot hybridization of 16S rRNA genes. Two hundred twenty-seven clones containing amplified 16S rRNA genes were prepared from subglacial samples, and the gene sequences were analyzed phylogenetically. Although some phylogenetic groups, including the Betaproteobacteria, were abundant in clone libraries from both glaciers, other well-represented groups were found at only one glacier. Group-specific oligonucleotide probes were developed for two phylogenetic clusters that were of particular interest because of their abundance or inferred biochemical capabilities. These probes were used in quantitative dot blot hybridization assays with a range of samples from the two glaciers. In addition to shared phyla at both glaciers, each glacier also harbored a subglacial microbial population that correlated with the observed aqueous geochemistry. These results are consistent with the hypothesis that microbial activity is an important contributor to the solute flux from glaciers.

The presence of thrust-block naled after a major surge event: Kuannersuit Glacier, West Greenland

AbstractThrust-block naled in front of Kuannersuit Glacier, West Greenland, appears to have formed during the termination of a terrestrial surge event by a combination of enhanced winter runoff, rapid advance of the glacier terminus, and proglacial stress release by thrusting and stacking of naled blocks. This process is equivalent to the formation of thrust-block moraines. The thrust-block naled consists of at least seven thrust sheets, which are characterized by stratified ice with beds composed of a lower debris-rich lamina, an intermediate dispersed lamina and a top clean-ice lamina, and underlain by frozen outwash deposits. The thrust-block naled differs from basal stratified ice in the absence of internal deformation structures, a relatively low debris concentration, a clay-rich particle-size distribution and a preferential sorting of lighter minerals. The oxygen isotope composition of the thrust-block naled is indistinguishable from δ18O values from meteoric glacier ice and bulk meltwater, but different from basal stratified ice facies. The d–δD relationship indicates that thrust-block naled has been formed by freezing of successive thin layers of bulk waters with variable isotopic composition, whereas basal stratified ice has developed in a subglacial environment with regelation. This work shows that the association between proglacial naled and rapidly advancing glaciers may have significant consequences for the proglacial geomorphology and the interpretation of basal ice layers.

Glacier hydrochemistry, solute provenance, and chemical denudation at a surge-type glacier in Kuannersuit Kuussuat, Disko Island, West Greenland

In 1995–1998, Han 11 km terrestrial surge of Kuannersuit Glacier, an outlet glacier of the largest ice cap on Disko Island, West Greenland, affected the catchment dramatically. In order to estimate solute fluxes and provenances, bulk meltwaters were sampled at the main subglacial outlet during the initial part of the quiescent phase. The hydrochemistry is significantly influenced by a subglacial basaltic weathering regime with absence of carbonate minerals. The results show that marine and aerosol derived solutes have minimal contribution to the total ion content, whereas sequestration of atmospheric CO 2 associated with carbonation of Ca-rich feldspar and reactive volcanic glass is more dominant than previously reported from glacierized catchments. Application of a sampling strategy dividing water samples into four groups to determine the content of dissolved HCO 3 − and CO 3 2− shows that the cationic equivalent weathering rate range is 683–860 Σmeq + m −2 a −1 and solute flux ranges between 76 and 98 t km −2 a −1. The crustal denudation rate is estimated to 26 t km −2 a −1, and the transient CO 2 drawdown amounts to 8500–13700 kg C km −2 a −1.

The importance of oxygen isotope provenance in relation to solute content of bulk meltwaters at Imersuaq Glacier, West Greenland

AbstractStable oxygen isotope analysis and measurement of several dissolved cations and anions of bulk meltwater samples have provided information about the hydrochemical environment of the glacial hydrological system at Imersuaq Glacier, an outlet tongue from the Greenland ice‐sheet, West Greenland. The samples were collected at frequent intervals during the period 20–28 July 2000 in a small (<20 L s−1) englacial meltwater outlet at the glacier margin. The results document the following findings: (i) a marked diurnal variation of δ18O is related to the composition of oxygen isotope provenances, mainly near‐marginal local superimposed ice and basal up‐sheared ice further up‐glacier; (ii) a relationship is seen between all base cations (Na+, K+, Ca2+, Mg2+), SO42− and δ18O, indicating that solute acquisition is provided by solid–solution contact with the up‐sheared ice—as the relationship with Cl− is weak the influence of seasalt‐derived solutes is small in the area; (iii) when the melt rate is high, two diurnal maxima of δ18O values and solute concentrations are measured, and it is suggested that a snow meltwater component is responsible for the second maximum of δ18O—a short residence time leads to a delayed decrease in ion concentrations. Copyright © 2003 John Wiley & Sons, Ltd.

Groundwater hydrochemistry in the active layer of the proglacial zone, Finsterwalderbreen, Svalbard

Glacial bulk meltwaters and active-layer groundwaters were sampled from the proglacial zone of Finsterwalderbreen during a single melt season in 1999, in order to determine the geochemical processes that maintain high chemical weathering rates in the proglacial zone of this glacier. Results demonstrate that the principle means of solute acquisition is the weathering of highly reactive moraine and fluvial active-layer sediments by supra-permafrost groundwaters. Active-layer groundwater derives from the thaw of the proglacial snowpack, buried ice and glacial bulk meltwaters. Groundwater evolves by sulphide oxidation and carbonate dissolution. Evaporation- and freeze-concentration of groundwater in summer and winter, respectively produce Mg–Ca-sulphate salts on the proglacial surface. Re-dissolution of these salts in early summer produces groundwaters that are supersaturated with respect to calcite.There is a pronounced spatial pattern to the geochemical evolution of groundwater. Close to the main proglacial channel, active layer sediments are flushed diurnally by bulk meltwaters. Here, Mg–Ca-sulphate deposits become exhausted in the early season and geochemical evolution proceeds by a combination of sulphide oxidation and carbonate dissolution. At greater distances from the channel, the dissolution of Mg–Ca-sulphate salts is a major influence and dilution by the bulk meltwaters is relatively minor. The influence of sulphate salt dissolution decreases during the sampling season, as these salts are exhausted and waters become increasingly routed by subsurface flowpaths.

Minor and trace element export from a glacierized Alpine headwater catchment (Haut Glacier d'Arolla, Switzerland)

AbstractMajor ion concentrations in meltwaters draining glacial environments have been widely reported. However, concentrations of minor and trace elements have received scant attention. This study presents trace and minor element variations in bulk meltwaters draining Haut Glacier d'Arolla (Switzerland) based on twice‐daily sampling throughout the 1999 ablation season, which represents the most detailed meltwater quality dataset to date. In order to assess the mode of export from the catchment, these elements are partitioned into (i) ‘dissolved’ and (ii) ‘particulate‐associated’ minor and trace element components.A computer‐based speciation model (PHREEQCi) was applied to the bulk meltwater data, suggesting that Ba, Be, Cd, Cu, Li, Rb and Sr exist primarily as mobile monovalent or divalent dissolved cations, which may be involved in interactions with suspended sediment surfaces. Conversely, the model predicts the precipitation of Fe, Al, Mn and Cr (oxi)hydroxides, suggesting these species may be predominantly transported as colloids, which may remove other minor and trace elements from solution by co‐precipitation reactions.Laboratory leaching experiments on suspended sediments and fresh rock powder suggests that minor and trace element concentrations may also be influenced by (oxy)hydroxide precipitation and adsorption–desorption reactions with suspended sediment surfaces. The quantity and transport mode of trace and minor elements may influence their bioavailability downstream of glacierized headwater catchments. Further, the enrichment of many dissolved minor and trace elements in meltwaters compared with world stream‐waters, coupled with the timing of water and sediment delivery during the summer months, may have implications for downstream aquatic environments. Copyright © 2001 John Wiley & Sons, Ltd.