Contribution Of Meltwater Research Articles

Major tunnel valleys and sedimentation changes document extensive Early Pleistocene glaciations of the Barents Sea

Sedimentary records of Early Pleistocene (~2.6–0.8 Ma) glaciations are sparse on shelves, yet trough mouth fans on adjacent continental slopes provide a continuous record of ice-sheet and climate development throughout the Quaternary. Here, we interpret high-quality 3D seismic reflection data combined with borehole and chronostratigraphic information from a shelf-slope setting in the southwestern Barents Sea to study meltwater and sediment inputs to the deep ocean, focusing on the onset of Pleistocene glaciations. Sandy deposits were brought to the slopes of the high-latitude Bear Island Fan by a preglacial contourite-turbidite system from ⁓2.6–2.4 Ma. Muddy glacigenic debris flows document the first shelf-edge glaciation at ⁓2.4 Ma. From 1.78–0.78 Ma, muddy turbidity-current- and debris-flow-derived sediments were delivered from shelf to slope via six tunnel valleys measuring up to 12 km in width and 200 m in depth. These tunnel valleys and associated downslope deposits formed during the 41-kyr climate cycles of the Early Pleistocene, and evidence abundant channelized, meltwater discharges from these glaciations. Following the mid-Pleistocene transition to 100-kyr cycles, a change in the style of glaciation is suggested by a change in landform and facies associations consistent with a reduced meltwater contribution. This study shows that the Norwegian-Barents shelf was extensively glaciated in the Early Pleistocene, with a first shelf-edge glaciation from ~2.4 Ma.

ТЕСТИРОВАНИЕ ВОЗМОЖНОСТЕЙ МЕТОДИКИ ОПЕРАТИВНОГО МОНИТОРИНГА ГОРНО-ЛЕДНИКОВЫХ СИСТЕМ

The article considers the possibilities of assessing the glaciation area of ​​the Northern Ile and Ile-Kungey glacier systems based on monitoring data from a limited sample of test glaciers. During testing in each of the mentioned glacier systems, based on the data on the area of ​​two samples of 10 glaciers, their total sample (20 glaciers) and their share in the total area of ​​glaciers in each of the named glaciation regions, the area of ​​glaciers of the corresponding glacier system was calculated. According to the testing results, the values ​​of the correlation coefficient of the calculated and actual (based on the results of glacier cataloguing) values ​​of the glaciation area for the three mentioned glacier samples were 0.99, 0.98, and 0.99 for the Northern Ile glacier system and 0.99, 0.97, and 0.99 for the Ilei-Kungey, respectively. The testing results leave no doubt about the possibility of operational monitoring of the glaciation area dynamics of mountain glacier systems based on the data on the area of ​​a limited sample of glaciers of the corresponding glacier system with an error of no more than ±5 %. According to the testing results, the calculated values ​​of the glacier area of ​​the considered glacier systems in 88 % of cases were less than 5% of the actual values, and only in 4 cases out of 33 (12 %) they exceeded this threshold, with an average deviation of the calculated data from the actual values ​​of less than 2 % and the largest calculation errors of 7.8 and -9.6 %. This indicates the high efficiency of the method of operational monitoring of mountain glacier systems. It allows to rapidly (with a repeatability from once every few years to annually) assess the loss of perennial ice in the considered glacier system and the contribution of glacial meltwater to the formation of river flow. Which, in its turn, is a good basis for the corresponding modeling of current and predicted changes.

Rock glacier springs: cool habitats for species on the edge

AbstractUnder climate change, glacier recession and the loss of cold habitats are major threats to aquatic biodiversity. In mountain areas, streams originating from rock glaciers, called “icy seeps”, may represent climate refugia for cold-adapted organisms, given the major persistence of cold waters from these landforms even in unfavourable climates. During late summer 2021, we investigated discharge, turbidity, water chemistry (major ions and trace elements), stable water isotopes (δ18O, δ2H), and macroinvertebrate communities of five rock glacier springs (icy seeps), five glacier springs (glacier springs) and five non-glacial springs (spring brooks) in catchments of the Eastern Italian Alps. In icy seeps, meltwater contribution to runoff (estimated with end-member mixing models) was intermediate between those of the other two spring types. Icy seeps had very cold waters (< 1.5 °C) that were enriched in trace elements, like glacier springs, whereas discharge and turbidity were low, like in spring brooks. Community composition, diversity, and species associations of icy seeps were strongly related to a gradient of chemical harshness (built using trace element concentrations), with less contaminated springs hosting communities like those dwelling in spring brooks. Like glacier springs, those icy seeps with the harshest water chemistry (particularly because of Ni concentrations) and higher meltwater contribution hosted species (e.g., Diamesa steinboecki) that are currently in decline due to glacier loss. This suggests a high conservation value for icy seeps. The protection of these habitats, nowadays overlooked, will be fundamental under the progressive warming and dry-out risk of alpine springs.

Incorporating glacier processes into hydrological simulations in the headwaters of the Yangtze and yellow Rivers

Contemporary hydrological models often oversimplify or neglect the effects of glacier ablation on watershed hydrological processes, leading to inaccurate simulations. To address this issue, we introduce a glacier ablation module that incorporates glacier ablation, sublimation, meltwater refreezing, and snow accumulation, integrated with the fully distributed hydrological model ESSI-3, forming the Glacier-ESSI-3 model. Application of the Glacier-ESSI-3 model in the headwaters of the Yangtze River (HYaR) and Yellow River (HYeR) demonstrates superior accuracy compared to the ESSI-3 model, effectively capturing the impact of glacier ablation on hydrological dynamics. Validation with remotely sensed data of snow cover and glacier dynamics confirms the model's efficacy in reproducing actual conditions in both watersheds. The results indicate that snow meltwater contributes more significantly to runoff than glacier meltwater, and the HYaR exhibiting a larger glacier meltwater contribution than the HYeR. Over time, the contribution rate of snow+glacier meltwater to runoff in the HYaR shows a fluctuating upward trend (10.04 % ± 1.13 % to 25.02 % ± 2.80 %), while it remains relatively stable in the HYeR (6.83 % ± 1.13 % to 10.19 % ± 0.89 %). This study highlights the critical role of glacier ablation in hydrological processes within glacierized watersheds. The Glacier-ESSI-3 model proves to be a robust tool for enhancing hydrological simulations in cold plateau regions, providing valuable insights into the intricate interactions between glaciers and hydrological dynamics.

Spatially heterogeneous discharge of glacial meltwater to drainages surrounding the ablating Coropuna ice cap, Peruvian Andes

ABSTRACT As tropical glaciers recede in response to global warming, glaciated watershed resilience is threatened by the loss of these important water reservoirs. In the Cordillera Occidental, Peru, we investigate the importance of glacial meltwater to mountain groundwater recharge and subsequent discharge to streams surrounding the rapidly retreating Coropuna ice cap. Using stable isotopes, solute concentrations, and radiocarbon activity, our results suggest that in remote ungauged systems, glacial input can be determined via geochemical analysis and a simple mixing model approach. We find that the proportion of glacial meltwater contribution to groundwater and surface waters is spatially heterogeneous. Differences between drainages are attributed to the degree of melting of headwater glaciers and the routing of waters through volcanic strata. These results provide evidence that glacial meltwater recharge is highly variable even within the same mountain block. Furthermore, the effects on streamflow will be disproportionate as the watersheds approach an ice-free state.

Isotope Hydrograph Separation Reveals Rainfall on the Glaciers Will Enhance Ice Meltwater Discharge to the Himalayan Rivers

AbstractThe Indian Summer Monsoon (ISM) and meltwater from the Himalayan are the two most important sources of water in the Indian subcontinent. However, the impact of ISM on Himalayan glaciers and subsequent stream hydrology remains largely unknown. To provide new insight into the impact of rainfall on glacial hydrology, here we present hydro‐meteorological and time‐series observations of meltwater stable water isotope compositions from the snout of the Chorabari glacier in the Upper Ganga Basin, Central Himalayas across the ablation season corresponding to 2019. We observe that rainfall events (>2 mm d−1) on the glacier enhance discharge driven by ice meltwater in River Mandakini. Energy balance calculations reveal that one of the drivers behind enhanced ice meltwater contribution could be rain‐induced melting of the glacier where rainfall on the ice surface melts the glacier producing up to 13% of the total discharge at the glacier snout. Further, rainfall on glacier surface have other control on glacial processes—for example, snow metamorphism, ice flow dynamics such as short‐term acceleration in ice speed flow, and reorganization of the englacial and subglacial drainage network—that are poorly studied and needs further investigation. We conclude rainfall events on the glacier have a complex control on mountain hydrology. This study, therefore, provides an interpretative framework that calls for additional assessments of the direct and indirect impact of rainfall in glacial hydrology.

How and when glacial runoff is important: Tracing dynamics of meltwater and rainfall contribution to river runoff from headwaters to lowland in the Caucasus Mountains

As glacier degradation is intensifying worldwide, understanding how and when glacial runoff is important becomes imperative for economic planning and societal adaptation in response to climate change. This research highlights a probable emergence of new low-flow periods, ranging from one to several weeks, with an anticipated 50–90 % reduction in runoff even in major rivers originating in glacierized mountains by the mid to late 21th century. While the predicted decline in annual and monthly runoff appears moderate for most glaciated regions globally, the emergence of new deglaciation-induced summer low flow periods could create critical “bottle necks” constraining effective water resources management.In this study, a nested catchment approach (7.6–2259 km2) in conjunction with an isotopic tracer method (D, 18O), was employed to quantify the seasonal dynamics of snow and glacial meltwater and rainfall contribution to runoff across various scales of river catchments for the underreported Caucasus Mountains. Although the contribution of meltwater was predictably dominant in the headwaters (75–100 %), it still constituted a substantial 50–60 % of river runoff in the lower reaches most of the time from June to September. While the relative capacity for rainwater storage was found to significantly increase with watershed scale, during weeks devoid of noteworthy rainfall, the runoff in river basins with a mere 7 % glaciation basically entirely consists of what is formed in the glacierized headwaters. The glacial runoff was prevalent in the melt component from late July/early August to mid-September: not less than 30–60 % to the total runoff in the headwaters and 30–40 % in the lower reaches.An approach is proposed to account for the spatial heterogeneity of stable water isotopic content within snow cover and glacier ice. Sources of uncertainties and soundness of assumptions typically used for isotopic hydrograph separation are discussed with particular consideration given to the study objectives.

Ice shelf basal channel shape determines channelized ice-ocean interactions

Growing evidence has confirmed the critical role played by basal channels beneath Antarctic ice shelves in both ice shelf stability and freshwater input to the surrounding ocean. Here we show, using a 3D ice shelf-ocean boundary current model, that deeper basal channels can lead to a significant amplification in channelized basal melting, meltwater channeling, and warming and salinization of the channel flow. All of these channelized quantities are also modulated by channel width, with the level of modulation determined by channel height. The explicit quantification of channelized basal melting and the meltwater transport in terms of channel cross-sectional shape is potentially beneficial for the evaluation of ice shelf mass balance and meltwater contribution to the nearshore oceanography. Complicated topographically controlled circulations are revealed to be responsible for the unique thermohaline structure inside deep channels. Our study emphasizes the need for improvement in observations of evolving basal channels and the hydrography inside them, as well as adjacent to the ice front where channelized meltwater emerges.

The roles of river discharge and sea ice melting in formation of freshened surface layers in the Kara, Laptev, and East Siberian seas

Wide areas of the Siberian Arctic shelf are covered by freshened surface water layers, which are among the largest in the World Ocean. River discharge is the main freshwater source for formation of these layers; therefore, they are commonly referred to as river plumes (the Ob-Yenisei plume in the Kara Sea and the Lena plume in the Laptev and East Siberian seas). The contribution of sea ice meltwater (SIM) to the Ob-Yenisei and Lena plumes is pointed out to be small, albeit its actual volume remains unknown. In this study, we use a novel dataset of satellite-derived sea ice thickness in the Arctic Ocean during the melt period to quantify the annual volume of SIM, which was received by the Ob-Yenisei and Lena plumes during 2012–2020. We reveal that SIM is a significant source for the Lena plume providing, on average, 20% of total annual freshwater content. Moreover, the share of SIM in the Lena plume shows large inter-annual (14%–29%) variability, i.e., during certain years, SIM provides almost one-third of freshwater volume of the Lena plume. This variability is governed by inter-annual variability of ice thickness, as well as seasonal variability of sea ice melting conditions. Conversely, the contribution of SIM to the Ob-Yenisei plume is relatively low (8% on average), and its total annual share varies from 6% to 11% during the study period. This difference is mainly caused by significantly smaller area of the Ob-Yenisei plume as compared with the Lena plume. The forecasted earlier onset of ice melting in the Arctic Ocean in future decades due to climate change could decrease the contribution of SIM to the Ob-Yenisei plume, whereas its influence on the Lena plume remains unclear.

Origin and evolution of the surface desalinated layer of the Kara Sea during the ice-free period

This work focuses on the freshwater contribution (water from the Ob’ and Yenisei rivers and ice meltwater) to the surface layer of the Kara Sea according to 2015–2020 expedition data. Salinity and hydrochemical data (total alkalinity and silicates) were used to calculate the proportion of freshwater in the desalinated layer of the Kara Sea. The ratio of the water fractions with the linear mixing of several sources was considered. Our results showed that riverine sources varied greatly, and the total contributions of the Ob’ and Yenisei runoff ranged from 10 to 60%, while the contribution of ice meltwater did not exceed 25%. The relationship between the period of seasonal ice retreat in the Kara Sea and its proportion in the surface desalinated layer was revealed. The interannual variability in freshwater source composition varied greatly from the southwestern to the eastern part of the sea owing to wind forcing and seasonality in river discharge.

Snow sampling strategy can bias estimation of meltwater fractions in isotope hydrograph separation

The Isotope based Hydrograph Separation (IHS) has been instrumental in understanding the partitioning of streamflow sources and processes. However, uncertainties persist in the accuracy of IHS estimations and the appropriate definition and sampling of endmembers. To address these uncertainties, we used field data of snowpack, snowfall, and snow meltwater isotopes (δ18O) from Pallas, Northern Finland to estimate the total meltwater contribution during the snowmelt period. We investigated the biases resulting from the application of different sampling strategies for event water endmember. The total meltwater contribution to streamflow was 59.6 % (±2% uncertainty) using the time-variant rolling runoff-corrected melt flux-weighted meltwater 18O isotope value. However, replacing it with either snowfall or winter snowpack 18O isotope weighted average values underestimated the meltwater contribution by 17.8 % or 22.6 %, respectively. Conversely, using time-variant instantaneous meltwater 18O isotope values overestimated the meltwater contribution by only 1.5 %. These discrepancies highlight the importance of choosing the appropriate endmember isotopes in IHS. The large differences in meltwater contribution for a 2-week peak discharge period based on different endmembers can lead to different interpretations of hydrological, ecohydrological, and biogeochemical processes. Thus, to better understand streamflow generation processes, we suggest using rolling runoff-corrected meltwater 18O or 2H isotope values in the IHS. In the absence of meltwater samples, the 18O or 2H isotope values of snowpack samples during the peak melt season may provide reasonable estimates of the meltwater contribution, with some minor underestimations. Our study highlights the importance of appropriate event meltwater endmember selection and sampling methodology for the IHS.

Early-Middle Holocene high lake levels of Rinqen Shubtso on the southern Tibetan Plateau and the formation mechanisms

The lake-level highstands on the southern Tibetan Plateau (TP) during the Early-Middle Holocene have traditionally been attributed to increased monsoonal precipitation. However, there has been limited discussion and evaluation regarding how the elevated shoreline indicates the formation of mega-paleolakes and the effects of glacial meltwater on rising lake levels. In this study, we conducted an investigation into the well-preserved paleoshorelines of Rinqen Shubtso, a closed-basin lake system located on the southern TP. By utilizing 14C dating and analyzing shoreline elevations, the Holocene lake-level fluctuation history of Rinqen Shubtso was reconstructed. Through examining strontium (87Sr/86Sr) and oxygen isotopes (δ18O), as well as Rb/Sr ratios in tufa samples from the shoreline, we evaluated the relative contribution of glacial meltwater and East Asian Monsoon precipitation to the lake-level expansion throughout this period. Our findings indicate that prior to 8.5 cal ka BP, the lake level reached its highest elevation before experiencing a rapid drop by approximately 44 m within a short timeframe. Subsequently, maintaining a stable highstand between 8.5 and 5.8 cal ka BP before gradually declining to its present elevation thereafter. We argue that the glacial meltwater induced by rising temperature due to solar insolation likely played a significant role in contributing to these large amplitude high lake levels prior to 8.5 cal ka BP, whereas the maximum East Asian Monsoon precipitation was responsible for sustaining high water levels during 8.5–5.8 cal ka BP when the mean latitudinal position of the summer Intertropical Convergence Zone shifted northward until reached its northernmost point at 8.5 cal ka BP. Following 5.8 cal ka BP, with the weakening of summer monsoon precipitation observed, gradually decreased lake level occurred accordingly. Our results provide valuable insights into understanding past changes in lake level, which are of great importance to predicting future lake variations on the TP.

Analysing the elevation-distributed hydro-climatic regime of the snow covered and glacierised Hunza Basin in the upper Indus

In the high altitude Hindukush Karakoram Himalaya (HKH) mountains, the complex weather system, inaccessible terrain and sparse measurements make the elevation-distributed precipitation and temperature among the most significant unknowns. The elevation-distributed snow and glacier dynamics in the HKH region are also little known, leading to serious concerns about the current and future water availability and management. The Hunza Basin in the HKH region is a scarcely monitored, and snow- and glacier-dominated part of the Upper Indus Basin (UIB). The current study investigates the elevation-distributed hydrological regime in the Hunza Basin. The Distance Distribution Dynamics (DDD) model, with a degree day and an energy balance approach for simulating glacial melt, is forced with precipitation derived from two global datasets (ERA5-Land and JRA-55). The mean annual precipitation for 1997–2010 is estimated as 947 and 1,322 mm by ERA5-Land and JRA-55, respectively. The elevation-distributed precipitation estimates showed that the basin receives more precipitation at lower elevations. The daily river flow is well simulated, with KGE ranging between 0.84 and 0.88 and NSE between 0.80 and 0.82. The flow regime in the basin is dominated by glacier melt (45%–48%), followed by snowmelt (30%–34%) and rainfall (21%–23%). The simulated snow cover area (SCA) is in good agreement with the MODIS satellite-derived SCA. The elevation-distributed glacier melt simulation suggested that the glacial melt is highest at the lower elevations, with a maximum in the elevation 3,218–3,755 masl (14%–21% of total melt). The findings improve the understanding of the local hydrology by providing helpful information about the elevation-distributed meltwater contributions, water balance and hydro-climatic regimes. The simulation showed that the DDD model reproduces the hydrological processes satisfactorily for such a data-scarce basin.

Source of soil water in cold regions based on stable isotope tracers

Soil water plays a key role in vegetation growth and ecological stability in cold regions. The soil water sources in the Qilian Mountains of the northeastern Tibetan Plateau have been quantified based on stable isotope data (δ2H and δ18O) of 1913 samples. The results indicated that δ18O of soil water ranged from ˗14.13–11.21‰, with an average of ˗6.78‰, and on a spatial scale, it increased gradually from the southeast to the northwest, where it became more positive. The stable isotopes of soil water are affected by evaporation, leading to a lower slope and interception of the evaporation line: δ2H = 3.23 δ18O–32.51 (R2 = 0.71, p < 0.01). The relationship between soil water and other water bodies showed that the soil water was mainly replenished by precipitation and ground ice meltwater. End-member mixing analysis (EMMA) showed that precipitation and ground ice accounted for approximately 91 % and 9 % of soil water, respectively, during heavy ablation. In the 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm soil layers, the contributions of ground ice meltwater to soil water were 0 %, 3 %, 7 %, 13 %, and 18 %, respectively. Notably, the contribution of ground ice meltwater to soil water gradually increased with elevation, whereas that of precipitation decreased. This study has obtained relevant data for the cold region, where it is typically difficult to conduct observations and sampling. More importantly, it analyzes the source and influencing factors of soil water in cold regions using the stable isotope method, which is of great significance for the study of the water cycle in cold regions.

Quantifying the glacial meltwater contribution to mountainous streams using stable water isotopes: What are the opportunities and limitations?

AbstractThis study aims to determine the opportunities and limitations of using stable water isotopes to quantify the glacial meltwater contribution to mountainous streams. For this purpose, three partially glaciated catchments in the Swiss Alps were selected as the study area. In the three catchments, stable isotope analysis (δ18O and δ2H) was conducted of the streams and the end‐members that contribute to the stream discharge (glacial meltwater, rain, snow). The investigations revealed that the contribution of glacial meltwater to mountainous streams can be quantified using stable water isotopes if three criteria are met: (A) The snow meltwater contribution to mountainous streams must be negligible due to its highly variable stable isotope signature; (B) the groundwater input needs to be either insignificant during this snow‐free period or the groundwater residence time must be short such that groundwater contribution does not delay the end‐member signal arriving in the streams; and (C) the isotope signal of the glacial melt end‐member needs to be distinct from the other end‐members. One of the three investigated catchments fulfilled these criteria in August and September, and the glacial meltwater contribution to the mountainous streams could be estimated based on stable water isotopes. During this time period, the glacial meltwater contribution to the stream discharge corresponded to up to 85% ± 2% and to 28.7% ± 10% of the total annual discharge, respectively. This high glacial meltwater contribution demonstrates that the mountainous stream discharges in August and September will probably strongly decrease in the future due to global warming‐induced deglaciation. Overall, this study demonstrates that many hydrogeological conditions need to be met so that stable water isotopes can be used to quantify the glacial meltwater contribution to mountainous streams. This highlights the challenges when using stable water isotopes for hydrograph separation and serves as a guide for future stable water isotope studies in mountainous regions.

ПРОСТРАНСТВЕННОЕ РАСПРЕДЕЛЕНИЕ АТМОСФЕРНЫХ ОСАДКОВ И ИХ ВКЛАД В ФОРМИРОВАНИЕ СТОКА ТРАНСГРАНИЧНОЙ РЕКИ ЗЕРАВШАН (ТАДЖИКИСТАН)

The spatial distribution of atmospheric precipitation in the basin of the transboundary Zeravshan River and the contribution of precipitation and glacial meltwater to the formation of the river runoff within the Republic of Tajikistan are considered. It has been found that the average integral change in the amount of precipitation in the Zeravshan River basin for the period of 1940-2020 was 20 mm/10 years. The maximum volume of the glacial meltwater in the Zeravshan River fell on the third quarter (June-August) and was equal to 3.11 km3 or 60% of the average annual river runoff, and 0.39, 0.70, and 0.96 km3 of the runoff was formed in the first, second, and fourth quarters, respectively.

Coupling of river discharges and alpine glaciers in arid Central Asia

Water resource is the primary factor impacting socio-economic development and security in arid Central Asia where high water stress occurs. Therefore, understanding the mechanism of water resource, particularly its associations with global warming, has unique importance for regional sustainable development. However, the dynamics of water resource is far from constrained in arid Central Asia indicated by the observed heterogenous trends of both alpine glaciers in high mountains (water tower) and river runoffs (dominant freshwater sources). Both meltwater and precipitations have been assumed to be the major contribution to the river runoff. Here, we make a systematic analysis on the 10Be exposure ages of the moraines in the high mountains and river terraces across Central Asia (n = 1057) to characterize the past changes of alpine glaciers and river discharges. The results show that the high river discharges are coupled with the alpine glacier expansions on both orbital and millennial scales, indicating a dominant contribution of meltwater to the freshwater supply. Both high river discharges and alpine glacier expansions occurred during the cold periods of the past 130 ka in Central Asia, indicating relatively low water stress under low-temperature conditions. This characteristic suggests that the water stress would increase with the decrease in both water reservoir and river discharges, and thus the environment would become drying with global warming in Central Asia.

Particularity of hydrological processes under heavy ablation based on environmental isotopes in transition zones between endorheic and exorheic basins

Drastic changes in the cryosphere have a significant impact on the quantity and formation process of water resources in the Qilian Mountains. The present study focused on quantitative evaluation of runoff components and runoff formation processes during strong ablation periods (August), in 2018, 2020, and 2021, in the transition zone between endorheic and exorheic basins in China, based on 1906 stable isotope samples. The results revealed that as the altitude decreased, the contribution of glacier and snow meltwater and permafrost water to runoff decreased, whereas that of the precipitation increased. Precipitation is a major source of river runoff in the Qilian Mountains. Notably, the runoff yield and concentration of rivers that were greatly affected by the cryosphere exhibited the following characteristics: (1) The altitude effect of stable isotopes was not significant and even showed a reverse trend in some rivers. (2) The processes of runoff yield and composition were relatively slow; as such, precipitation, glacier and snow meltwater, and supra-permafrost water were first transformed into groundwater and then supplied runoff to upstream mountainous region. (3) Finally, stable isotope composition in such rivers were similar to those in glaciers and snow meltwater, with small fluctuations. Therefore, the water sources of rivers affected by the cryosphere are more uncertain than those of rivers unaffected by the cryosphere. In future study, a prediction model of extreme precipitation and hydrological events will be developed, and a prediction technology for runoff formation and evolution in glacier snow and permafrost will be developed to integrate short-and long-term forecasts.

Isotopic evidence for an intensified hydrological cycle in the Indian sector of the Southern Ocean

The hydrological cycle is expected to intensify in a warming climate. However, observational evidence of such changes in the Southern Ocean is difficult to obtain due to sparse measurements and a complex superposition of changes in precipitation, sea ice, and glacial meltwater. Here we disentangle these signals using a dataset of salinity and seawater oxygen isotope observations collected in the Indian sector of the Southern Ocean. Our results show that the atmospheric water cycle has intensified in this region between 1993 and 2021, increasing the salinity in subtropical surface waters by 0.06 ± 0.07 g kg−1 per decade, and decreasing the salinity in subpolar surface waters by -0.02 ± 0.01 g kg−1 per decade. The oxygen isotope data allow to discriminate the different freshwater processes showing that in the subpolar region, the freshening is largely driven by the increase in net precipitation (by a factor two) while the decrease in sea ice melt is largely balanced by the contribution of glacial meltwater at these latitudes. These changes extend the growing evidence for an acceleration of the hydrological cycle and a melting cryosphere that can be expected from global warming.

Projected Impacts of Antarctic Meltwater Anomalies over the Twenty-First Century

Abstract Antarctic margin and Southern Ocean surface freshening has been observed in recent decades and is projected to continue over the twenty-first century. Surface freshening due to precipitation and sea ice changes is represented in coupled climate models; however, Antarctic ice sheet/shelf meltwater contributions are not. Because Antarctic melting is projected to accelerate over the twenty-first century, this constitutes a fundamental shortcoming in present-day projections of high-latitude climate. Southern Ocean surface freshening has been shown to cause surface cooling by reducing both ocean convection and the entrainment of warm subsurface waters to the surface. Over the twenty-first century, Antarctic meltwater is expected to alter the pattern of projected surface warming as well as having other climatic effects. However, there remains considerable uncertainty in projected Antarctic meltwater amounts, and previous findings could be model dependent. Here, we use the ACCESS-ESM1.5 coupled model to investigate global climate responses to low and high Antarctic meltwater additions over the twenty-first century under a high-emissions climate scenario. Our high-meltwater simulations produce anomalous surface cooling, increased Antarctic sea ice, subsurface ocean warming, and hemispheric differences in precipitation. Our low-meltwater simulations suggest that the magnitude of surface temperature and Antarctic sea ice responses is strongly dependent on the applied meltwater amount. Taken together, these findings highlight the importance of constraining projections of Antarctic ice sheet/shelf melt to better project global surface climate changes over the twenty-first century. Significance Statement Antarctic ice sheets and shelves are melting, adding meltwater to the Southern Ocean and changing the ocean circulation. Antarctic meltwater stratifies the upper ocean, resulting in cooling of the surface Southern Ocean but warming at depth that could accelerate ice shelf melting. Coupled climate models used to project twenty-first-century climate do not represent ice sheets or shelves, neglecting important climate impacts. Here we conduct meltwater simulations with a coupled climate model and find that the magnitude of climate responses is strongly dependent on the applied meltwater amount. This highlights 1) the importance of constraining Antarctic meltwater projections to better project global climate over the twenty-first century and 2) that it is important that Antarctic meltwater be represented in future-generation coupled climate models.