Ice Meltwater Research Articles

The migration law of magnesium ions during freezing and melting processes

To explore the migration law of magnesium ions (Mg2+) during freezing and melting processes, laboratory simulation experiments involving freezing and melting were carried out to investigate the influence of ice thickness, freezing temperature, initial concentration, and initial pH on the distribution of Mg2+ in the ice-water system. The distribution coefficient “K” (the ratio of the Mg2+ concentration in the ice layer to the Mg2+ concentration in the water layer under ice) was used to characterize the migration ability of Mg2+. The results showed that during the freezing process, the concentration distribution of Mg2+ in the ice and water two-phase system was as follows: ice layer < water before freezing < water layer under ice; in other words, it migrated from ice layer to the water layer under ice. “K” decreased with increasing ice thickness, freezing temperature, initial concentration, and initial pH; the higher the ice thickness, freezing temperature, initial concentration, and initial pH were, the higher the migration efficiency of Mg2+ into the water layer under ice was. During the melting process, Mg2+ was released in large amounts (50–60%) at the initial stage (0–25%) and in small amounts (25–100%) uniformly in the middle and later periods. According to the change of Mg2+ concentration in ice melt water, an exponential model was established to predict Mg2+ concentration in ice melt period. The migration law of Mg2+during the freezing and melting process was explained by using first principles.Graphical abstract

Abrupt climate changes in the last two deglaciations simulated with different Northern ice sheet discharge and insolation

There were significant differences between the last two deglaciations, particularly in Atlantic Meridional Overturning Circulation (AMOC) and Antarctic warming in the deglaciations and the following interglacials. Here, we present transient simulations of deglaciation using a coupled atmosphere–ocean general circulation model for the last two deglaciations focusing on the impact of ice sheet discharge on climate changes associated with the AMOC in the first part, and the sensitivity studies using a Northern Hemisphere ice sheet model in the second part. We show that a set of abrupt climate changes of the last deglaciation, including Bolling–Allerod warming, the Younger Dryas, and onset of the Holocene were simulated with gradual changes of both ice sheet discharge and radiative forcing. On the other hand, penultimate deglaciation, with the abrupt climate change only at the beginning of the last interglacial was simulated when the ice sheet discharge was greater than in the last deglaciation by a factor of 1.5. The results, together with Northern Hemisphere ice sheet model experiments suggest the importance of the transient climate and AMOC responses to the different orbital forcing conditions of the last two deglaciations, through the mechanisms of mass loss of the Northern Hemisphere ice sheet and meltwater influx to the ocean.

Sea-Level Fingerprints Due to Present-Day Water Mass Redistribution in Observed Sea-Level Data

Satellite altimetry over the oceans shows that the rate of sea-level rise is far from uniform, with reported regional rates up to two to three times the global mean rate of rise of ~3.3 mm/year during the altimeter era. The mechanisms causing the regional variations in sea-level trends are dominated by ocean temperature and salinity changes, and other processes such as ocean mass redistribution as well as solid Earth’s deformations and gravitational changes in response to past and ongoing mass redistributions caused by land ice melt and terrestrial water storage changes (respectively known as Glacial Isostatic Adjustment (GIA) and sea-level fingerprints). Here, we attempt to detect the spatial trend patterns of the fingerprints associated with present-day land ice melt and terrestrial water mass changes, using satellite altimetry-based sea-level grids corrected for the steric component. Although the signal-to-noise ratio is still very low, a statistically significant correlation between altimetry-based sea-level and modelled fingerprints is detected in some ocean regions. We also examine spatial trend patterns in observed GRACE ocean mass corrected for atmospheric and oceanic loading and find that some oceanic regions are dominated by the fingerprints of present-day water mass redistribution.

Projection of future sea level rise in the East Asian Seas based on Global Ocean-Sea Ice Coupled Model with SRES A1B Scenario

To project the future sea level rise in the East Asian Seas due to global warming, regional sea level variations are downscaled from three climate system models (GFDL-CM2.1, ECHAM5/MPI-OM, MIROC3.2(hires)) using a global ocean-sea ice coupled model with non-Boussinesq approximation. Based on the SRES A1B Scenario, the projected ensemble mean sea level rise (rate of rise) for the East Sea, Yellow Sea and East China Sea from 1995 to 2050 is 15.60cm (2.84mm/year), 16.49cm (3.0mm/year) and 16.43cm (2.99mm/year), respectively. With the inclusion of the future change of land ice melting and land water storage, the mean sea level rise (rate of rise) increases to 33.55cm (6.10mm/year) for the East Sea, and 34.38~34.44cm (6.25~6.26mm/year) for the Yellow and East China Seas. The present non-Boussinesq ocean model experiment shows that the future sea level rise in the East Sea is mainly due to the steric component changes by heat content increase. On the other hand, the future sea level rise in the Yellow and East China Seas appears to be mainly associated with the non-steric component change by water mass convergence.

Numerical Assessments of Excess Ice Impacts on Permafrost and Greenhouse Gases in a Siberian Tundra Site Under a Warming Climate

Excess ice that exists in forms such as ice lenses and wedges in permafrost soils is vulnerable to climate warming. Here, we incorporated a simple representation of excess ice in a coupled hydrological and biogeochemical model (CHANGE) to assess how excess ice affects permafrost thaw and associated hydrologic responses, and possible impacts on carbon dioxide and methane (CH4) fluxes. The model was used to simulate a moss-covered tundra site in northeastern Siberia with various vertical initializations of excess ice under a future warming climate scenario. Simulations revealed that the warming climate induced deepening of the active layer thickness (ALT) and higher vegetation productivity and heterotrophic respiration from permafrost soil. Meanwhile, excess ice temporarily constrained ALT deepening and thermally stabilized permafrost because of the highest latent heat effect obtained under these conditions. These effects were large under conditions of high excess ice content distributed in deeper soil layers, especially when covered by moss and thinner snow. Once ALT reached to the layer of excess ice, it was abruptly melted, leading to ground surface subsidence over 15–20 years. The excess ice meltwater caused deeper soil to wet and contributed to talik formation. The anaerobic wet condition was effective to high CH4emissions. However, as the excess ice meltwater was connected to the subsurface flow, the resultant lower water table limited the CH4efflux. These results provide insights for interactions between warming climate, permafrost excess ice, and carbon and CH4fluxes in well-drained conditions.

Molecular biomarkers as tool for early warning by chlorpyrifos exposure on Alpine chironomids

Pesticides used in agriculture can be transported at a medium-high distance due to the drift effect, reaching even remote areas as mountain regions, glaciers, and snow cover. With the melting process, pesticides enter freshwater glacier ecosystems, becoming a threat to wildlife fauna, mainly dominated by Diptera Chironomidae. Chlorpyrifos (CPF), as one of the most commonly used pesticides in alpine vineyards and apple orchards, is frequently detected in icemelt waters. We selected as target species, larvae of the cold stenothermal chironomid Diamesa zernyi, collected in two glacier-fed streams (Presena and Amola) in the Italian Alps. Firstly, a de novo transcriptome was obtained, and secondly, a gene array was designed to study the molecular response of a wild population of D. zernyi exposed to three sub-lethal CPF concentrations corresponding to 1/100 LC10 (0.011 μg/L), 1/10 LC10 (0.11 μg/L), and LC10 (1.1 μg/L), for 24 h. The sub-organismal response was evaluated by Real-Time Polymerase Chain Reaction (RT-PCR), employing 40 genes related to essential metabolic routes as future candidates for biomarkers in wildlife chironomids. After 24 h, the endocrine system (E75, E93, EcR, and Met), detoxification response (GSTO3, GSTS1), and stress response (hsp75, hsp83, HYOU1) were altered. CPF seems to act as an endocrine disruptor and could lead to defective larval development, disrupted cellular homeostasis through heat shock proteins (HSPs) alteration (defective protein folding and mitochondrial functions), as well as oxidative damage (confirmed by increased GST expression). For the first time, molecular studies detected early alarm signals in wildlife in glacier environments.Our findings confirm the high environmental risk of CPF affecting aquatic insect metabolism and raise the level of concern about this pesticide in high altitude water bodies, generally considered pristine. Furthermore, this study emphasizes the incipient need to use non-model organisms for the evaluation of natural ecosystems. We also highlight the demand for research into new molecular biomarkers, and the importance of including molecular approaches in toxicology evaluations to detect the early adverse effects of pollutants.

Trends in Arctic seasonal and extreme precipitation in recent decades

Daily precipitation data from the European Centre for Medium-Range Weather Forecasts (ERA-Interim) from 1979 to 2016 are analyzed to determine the trends in seasonal and extreme precipitation across the pan-Arctic and estimate the contributions to the trends from the dynamic (e.g., changes in circulation patterns) and thermodynamic processes (e.g., sea ice melt–water vapor feedback) and their interactions. The trends in the seasonal total precipitation are generally consistent with the trends in the occurrence of seasonal extreme precipitation. Although the trends vary considerably in direction and magnitude across the pan-Arctic and the seasons, more regions experience a statistically significant positive trend than negative trend, particularly in autumn and winter seasons and over areas of the Arctic Ocean and the northern North Atlantic. Statistically significant negative trends are mostly found in areas of northern Eurasian and North America. The thermodynamic processes account for more than 85% of the total trends, with the rest of the trends explained by the dynamic processes (e.g., changes in circulation patterns) and the interaction between dynamic and thermodynamic processes.

The value of water isotope data on improving process understanding in a glacierized catchment on the Tibetan Plateau

Abstract. This study integrated a water isotope module into the hydrological model THREW (Tsinghua Representative Elementary Watershed) which has been successfully used in high and cold regions. Signatures of oxygen stable isotope (18O) of different water inputs and stores were simulated coupling with the simulations of runoff generation. Isotope measurements of precipitation water samples and assumed constant isotope signature of ice meltwater were used to force the isotope module. Isotope signatures of water stores such as snowpack and subsurface water were updated by an assumed completely mixing procedure. Fractionation effects of snowmelt and evapotranspiration were modeled in a Rayleigh fractionation approach. The isotope-aided model was subsequently applied for the quantification of runoff components and estimations of mean water travel time (MTT) and mean residence time (MRT) in the glacierized watershed of Karuxung river on the Tibetan Plateau. Model parameters were calibrated by three variants with different combinations of streamflow, snow cover area and isotopic composition of stream water. Modeled MTT and MRT were validated by estimates of a tracer-based sine-wave method. Results indicate that (1) the proposed model performs well on simultaneously reproducing the observations of streamflow, snow cover area and isotopic composition of stream water, despite the fact that only precipitation water samples were available for tracer input; (2) isotope data facilitate more robust estimations on contributions of runoff components (CRCs) to streamflow in the melting season, as well as on MTT and MRT; (3) involving isotope data for the model calibration obviously reduces uncertainties in the quantification of CRCs and estimations of MTT and MRT, through better constraining the competitions among different runoff processes induced by meltwater and rainfall. Our results inform scientists on the high value of water isotope data for improving process understanding in a glacierized basin on the Tibetan Plateau.

Glacial geomorphology of the central sector of the Cordilleran Ice Sheet, Northern British Columbia, Canada

ABSTRACT Northern British Columbia was repeatedly covered by the Cordilleran Ice Sheet (CIS) during the glacial periods. However, its mountainous terrain and remote location have thus far impeded our understanding of the central sector of the ice sheet. The improved resolution of remotely sensed data provides new opportunities to unravel the glacial history of this inaccessible location. Here, we present a comprehensive map of glacial landforms for the central sector of the CIS (55° to 60° N). Seven landform categories were mapped: ice flow parallel lineations, moraines (CIS outlet glacier moraines, Late Glacial moraines and moraines of unknown origin), meltwater channels (lateral and submarginal, subglacial, proglacial, and meltwater channels of unknown origin), kame terraces, eskers (single ridges and esker complexes), perched deltas and subglacial ribs. Collectively, these landforms provide a record of the extent, thickness and behaviour of the CIS, the direction of its movement and pattern of ice retreat.

Characterization of organic-rich mineral debris revealed by rapid glacier retreat, Indren Glacier, European Alps

In the summer of 2003 and 2004, characterized by a rapid glacier retreat, a stony surface covered by well-structured organic-rich mineral debris was observed very close to the Indren glacier terminus (Monte Rosa Massif, NW Italy, 3100 m ASL), on an area covered by the glacier tongue till the year before. The origin and type of this organic-rich material were investigated, in order to detect their characteristics, potential sources and fate within the foreland system. The deposits were dated using Carbon-14 and analyzed for the chemical characteristics of the organic component, the elemental composition of the mineral fraction and presence of microbial markers. The material, granular and dark in color, had a total organic carbon (TOC) content ranging between 17.4 ± 0.39 and 28.1 ± 0.63 g kg−1 dry weight (dw), significantly higher than the surrounding glacial till (~ 1.4 g kg−1 dw), although only 0.33% of it was in water soluble form. Microbial carbon (C) and nitrogen (N) accounted for 10.6% and 3.13% of TOC and total N, respectively. Dissolved nitrogen (N), mainly present as ammonium, represented 2.40% of the total N. The low aromatic component and large presence of nitrogen (N)-derived compounds suggested that most of the organic carbon (OC) in these organic-rich mineral deposits was derived from microbial cells, although the high average radiocarbon age of about 2900 years may also point to the contribution of aeolian depositions of anthropogenic or natural origin. Elemental composition and the crustal enrichment factor of trace elements in the mineral fraction of the aggregates corroborated the hypothesis that most part of the accumulated material derived from ice meltwater. Some indicators of the colonization of these deposits by microbial communities were also reported, from the abundance of DNA and phylogenetic markers, to the presence of bacterial taxa commonly able to thrive in similar habitats. All these elements suggested that such kind of deposits may have a potential role as energy and nutrient sources in recently deglaciated areas, highlighting the necessity to better understand the processes underlying their formation and their evolution.

Landslide Accumulation Ice-Snow Melting for Thermo-Hydromechanical Coupling and Numerical Simulation

In this paper, we discussed the phase change coupling algorithm of accumulation bank slope under the action of ice-snow melting. We described the effect of temperature gradient on the water migration of soil. We simplified the stress balance, continuity, and energy equation in the coupled model. We discussed the variation law of temperature, seepage, and stress (deformation) field under different conditions of ice-snow melting on the bank slope of the accumulation body. Based on the three-field coupling energy balance equation of ice-snow melting with phase change, the simplified algorithm of three-field coupling is obtained. The simplified algorithm is applied to the coupling model of ice-snow thawing on indoor accumulation bank slope. We established a practical numerical model for the coupling analysis of temperature, seepage, and stress field. We established the coupled control differential equation of three fields. We investigated the three-dimensional numerical simulation of stress, displacement, plastic deformation, and other indicators. The results show that the numerical simulation results are in good agreement with the monitoring results. It is expected that the research results can more truly simulate the actual characteristics of ice and snow melting water on the bank slope of the Three Gorges Reservoir and provide reference for the prevention and prediction of extreme snow and ice disasters in the Three Gorges Reservoir area.

Trophic Dynamics of Calanus hyperboreus in the Pacific Arctic Ocean

AbstractThe zooplankton community composition in the Pacific Arctic Ocean depends heavily on the sea ice and hydrodynamic conditions. The calanoid copepod Calanus hyperboreus is a dominant Arctic zooplankton, but its diet sources in the Pacific Arctic are unclear. C. hyperboreus individuals were collected in the northern Chukchi Sea (NCS) and the northern‐East Siberian Sea (NESS), which display contrasting chlorophyll abundance and sea ice concentration in summer 2018. Nitrogen isotopes of individual amino acid and fatty acid compositions were measured to determine its trophic level (TL) and dominant diet. C. hyperboreus collected in the NCS had higher TL values (3.0 ± 0.2) and a relatively low proportion of C20:5(n‐3). In the NESS, C. hyperboreus had lower TL values (2.7 ± 0.2) and a larger percentage of C20:5(n‐3), suggesting a greater proportion of diatoms in its diet. Spatial TL variations of C. hyperboreus between the NCS and NESS may be caused by variations in phytoplankton composition (micro‐phytoplankton vs. nano‐ and picophytoplankton) as a result of surface seawater stratification triggered by the inflow of sea ice meltwater as well as summer Bering Sea water through the Bering Strait. These results suggest that the filter‐feeding copepod C. hyperboreus could be a useful indicator to understand trophic dynamics in zooplankton food web.

Tracing the isotopic signatures of cryospheric water and establishing the altitude effect in Central Himalayas: A tool for cryospheric water partitioning

This study focuses on the isotopic characterization of cryospheric water and quantification of different components contributing to Alaknanda River (major tributary of the Ganges River system) at its place of origin near snout of the Satopanth Glacier. A detailed understanding of various sources/flow components contributing to the river is useful for water resource management under changing climate scenario and helpful in risk assessment due to natural hazards in the headwater catchments, Extensive fieldwork was conducted, and water samples were collected from the river, snow, glacial ice, rain, lakes, and supraglacial channels of Satopanth Glacier Basin during the ablation period of 2017 and analysed for δ18O, δ2H, and 3H along with electrical conductivity. The results helped to establish the spatio-temporal and altitudinal variability in isotopic signatures of rain, snow, and ice in Satopanth Glacier Basin. The altitudinal effect in δ18O of pre-monsoon and monsoon rainfall is −0.13‰ and −0.41‰ per 100 m rise in elevation, respectively. Snow samples show depleting isotopic trend with an altitude effect of −0.43‰ in δ18O per 100 m rise in altitude. However, snowpack samples show an enrichment with time indicating post-depositional isotopic fractionation. The contrasting isotopic gradient in debris covered and non-debris covered ice are −0.9‰ and +3.4‰ per 100 m rise in elevation, respectively. These results divulge the spatial as well as temporal variation in cryospheric waters and these variations are used to derive the isotopic signatures of snow melt, glacier melt, and rain water. The results of hydrograph separation show that the snow melt, ice melt and rain water contribute about 33%, 49% and 18% respectively, to the discharge of Alaknanda River during the ablation period. Tracer based hydrograph separation indicates that the snow melt contribution dominates in river discharge during the initial ablation period. River discharge is a mixture of snow melt, glacier melt and rain water during July and August, while there is a dominance of glacier melt during end of the ablation period. The results of the present study highlight the importance of accounting the spatial and temporal variability in tracer signatures of cryospheric water for quantifying the contributions of snow and ice melt in a river originating from glacerised area.

First High-Frequency Underway Observation of DMS Distribution in the Southern Ocean during Austral Autumn

We investigate the distribution of dimethyl sulfide (DMS) in the Southern Ocean’s (50° W to 170° W) surface water, including the Antarctic Peninsula and the marginal sea ice zone (MIZ) in the Ross and Amundsen Seas. This is the first high-frequency observation conducted in the austral autumn (in April) in the Southern Ocean. The mean DMS concentration was 2.7 ± 2.5 nM (1 σ) for the entire study area. Noticeably enhanced DMS (5 to 28 nM) concentrations were observed in the MIZ around the Ross and Amundsen Seas and the coastal regions in the Antarctic Peninsula; this could be attributed to biological production of local ice algae, which appears to be supplied with nutrients from glacial or sea ice melt water. These observed DMS inventories were significantly higher (an order of magnitude) than current climatological DMS inventories. The local DMS sources being transported outward from the polynyas, where strong bloom occurs during summer, could result in larger discrepancies between observed DMS and climatological DMS in the MIZ area (in the Amundsen Sea). Overall, this study is the first to highlight the significance of the underestimation of current DMS fluxes in the austral autumn, which consequently results in significant errors in the climate models.

Groundwater age of spring discharges under changing permafrost conditions: the Khangai Mountains in central Mongolia

Obtaining a better understanding of groundwater dynamics in permafrost zones is a critical issue in permafrost hydrology. This includes assessing the impacts of climate change on permafrost thaw and ground ice-melt. Both permafrost thaw and ground ice-melt can be related to groundwater discharges (i.e. spring discharges), and spring water is an important local water resource; accordingly, changes in these processes can have large impacts on local people and their subsistence activities. To detect permafrost thaw and ground ice-melt in the permafrost zone of Mongolia, groundwater ages of several spring discharges were determined using two transient tracers: tritium (3H) and chlorofluorocarbons (CFCs). Spring water samples were collected seasonally from 2015 to 2019 at seven spring sites around the Khangai Mountains in central Mongolia. The sites included two thermokarst landscapes on the northern and southern sides of the mountains. The 3H and CFC concentrations in the spring water in the thermokarst landscapes were very low, especially on the southern side of the mountains, and the estimated mean groundwater age for these sites was older than that for the other sampled springs. Consequently, the young water ratios of the thermokarst sites were lower than those for the other springs. This ratio, however, showed a gradual increase with time, which indicates that recently recharged rainwater began to contribute to the spring discharge at the thermokarst sites. An atmospheric water budget analysis indicated that net recharge from modern and recent precipitation to shallow groundwater in the summer season was almost zero on the southern side of the mountains. Thus, we inferred that the spring water at the thermokarst sites on the southern side of the mountains contained large amounts of ground ice-melt water.

Novel dc flashover model for predicting flashover voltage of the iced insulators

This work first proposes a novel flashover model based on the deduced residual resistance of the ice layer. The most important finding of the field icing tests is that the double-layer ice-melting water film exists on the inner and outer surfaces of the ice layer. The conductivity of melting water on the inner and outer surface of the ice layer has been measured, and the corresponding surface conductivity has been calculated. According to the proposed flashover model, the ratio η of the resistance of the ice layer to that of the pollution layer gradually increases with the increase of the ratio k of the resistance of the outer surfaces to that of inner surfaces, and eventually approaches saturation. Furthermore, the icing flashover criterion has been modified, and the voltage gradient of the inner surface is less than that of the outer surface. Test results show that the ice flashover voltage is lower than the pollution flashover voltage between 2.18–9.69% and 14.75–20.32% under light ice and semi-cylindrical ice, respectively. The simulation results based on the proposed model and the classic model are compared with the field test data. Results show that the proposed model could attain a high accuracy of dc flashover voltage and demonstrate the effectiveness of the proposed model.

Glacial Drivers of Marine Biogeochemistry Indicate a Future Shift to More Corrosive Conditions in an Arctic Fjord

AbstractA detailed survey of a high Arctic glacier fjord (Kongsfjorden, Svalbard) was carried out in summer 2016, close to the peak of the meltwater season, in order to identify the effects of glacier runoff on nutrient distributions and the carbonate system. Short‐term weather patterns were found to exert a strong influence on freshwater content within the fjord. Freshwater inputs from glacier runoff and ice meltwater averaged (±SD) low nitrate (1.85 ± 0.47 μM; 0.41 ± 0.99 μM), orthophosphate (0.07 ± 0.27 μM; 0.02 ± 0.03 μM), dissolved organic carbon (27 ± 14 μM in glacier runoff), total alkalinity (708 ± 251 μmol kg−1; 173 ± 121 μmol kg−1), and dissolved inorganic carbon (622 ± 108 μmol kg−1; 41 ± 88 μmol kg−1), as well as a modest silicate concentration (3.71 ± 0.02 μM; 3.16 ± 5.41 μM). pCO2 showed a nonconservative behavior across the estuarine salinity gradient with a pronounced undersaturation in the inner‐fjord, leading to strong CO2 uptake from the atmosphere. The combined effect of freshwater dilution and atmospheric CO2 absorption was the lowering of aragonite saturation state to values that are known to negatively affect marine calcifiers (ΩAr, 1.07). Glacier discharge was therefore a strong local amplifier of ocean acidification. Future increases in discharge volume and the loss of marine productivity following the retreat of marine‐terminating glaciers inland are both anticipated to further lower ΩAr within inner‐fjord surface waters. This shift may be partially buffered by an increase in the mean freshwater total alkalinity as the fractional importance of iceberg melt to freshwater fjord inputs declines and runoff increases.

Tracking Dissolved Trace and Heavy Metals in the Ganga River From Source to Sink: A Baseline to Judge Future Changes

AbstractUnderstanding how dissolved trace elements chemically evolve in the Ganga River from source to sink is important to understand subcatchment contributions and chemical variability across space and time but remains poorly constrained. What exists is site‐specific data sets that are focused on capturing contamination “hotspots.” Here, we present riverine trace element concentrations of 38 targeted locations in the Ganga Basin. Samples in the headwater and the upstream segments of the river were collected during the premonsoon, monsoon, and postmonsoon seasons of 2014, 2015, and 2016, and the downstream samples were collected in 2016. In addition, monthly time‐series samples were collected at a downstream site to capture the geochemical variability at a higher temporal‐resolution. To evaluate the geogenic contributions, groundwater, rainwater, snow, glacier‐ice, and sediment samples were also analyzed. We find that the river chemistry displays a wide spatio‐temporal variability. Headwater samples are characterized by high concentrations of trace elements that are primarily controlled by ice meltwater, intense weathering, and interactions with glacial flour and are therefore geogenic in nature. Moreover, high concentrations of trace metals were also observed in a few localized downstream sites. However, such enriched signals are not persistent further downstream as they get diluted by the joining of large tributaries. We show that the dissolved trace element concentrations in the Ganga River are low compared to existing datasets and are comparable to the global average river water composition. We additionally quantified the present‐day “baseline” concentration ranges to facilitate future water quality assessment in the Ganga Basin.

Sources of particulate organic matter in the Chukchi and Siberian shelves: clues from carbon and nitrogen isotopes

The stable isotopic composition (δ13C and δ15N) and carbon/nitrogen ratio (C/N) of particulate organic matter (POM) in the Chukchi and East Siberian shelves from July to September, 2016 were measured to evaluate the spatial variability and origin of POM. The δ13CPOC values were in the range of −29.5‰to −17.5‰ with an average of −25.9‰±2.09‰, and the δ15NPN values ranged from 3.9‰ to 13.1‰ with an average of 8.0‰±1.6‰. The C/N ratios in the East Siberian shelf were generally higher than those in the Chukchi shelf, while the δ13C and δ15N values were just the opposite. Abnormally low C/N ratios ( 10‰) values were observed in the Wrangel Island polynya, which was attributed to the early bloom of small phytoplankton. The contributions of terrestrial POM, bloom-produced POM and non-bloom marine POM were estimated using a three end-member mixing model. The spatial distribution of terrestrial POM showed a high fraction in the East Siberian shelf and decreased eastward, indicating the influence of Russian rivers. The distribution of non-bloom marine POM showed a high fraction in the Chukchi shelf with the highest fraction occurring in the Bering Strait and decreased westward, suggesting the stimulation of biological production by the Pacific inflow in the Chukchi shelf. The fractions of bloom-produced POM were highest in the winter polynya and gradually decreased toward the periphery. A negative relationship between the bloom-produced POM and the sea ice meltwater inventory was observed, indicating that the net sea ice loss promotes early bloom in the polynya. Given the high fraction of bloom-produced POM, the early bloom of phytoplankton in the polynyas may play an important role on marine production and POM export in the Arctic shelves.

Dissolved Inorganic Carbon ([DIC], δ13С(DIC)) in Waters of the Eastern East Siberian Sea

Concentrations and carbon isotope composition of dissolved inorganic carbon (DIC) and isotope composition (δD, δ18O) of waters were studied in the eastern East Siberian Sea, along two submeridional sections extending from the Indigirka and Kolyma mouths to the edge of perennial ice. Estimated contents of river waters, sea ice meltwater, and modified waters showed that the eastern part of the shelf of the East Siberian Sea in summer, 2017 was globally freshened by riverine waters (6–57%). A slight contribution of sea ice meltwater (2–3%) was found only in the surface waters of the Kolyma section. The waters of the Indigirka section experienced intense modification, which is related to the ice formation and reaches 20% ice extraction from water. The concentration and δ13C values of DIC are controlled by mixing between sea water and river runoff. Their shift relative to the values determined by conservative mixing suggests that shelf waters contain an excess of DIC with an isotopically light carbon. Main processes leading to these shifts are the decomposition of organic matter and water modification. The rate of the latter is 3–4 times higher than that of organic matter oxidation. The isotope composition and concentrations of DIC could partially reflect the influence of Pacific seawaters coming through the Bering Strait and the Chukchi Sea.