Potential role of permafrost thaw on increasing Siberian river discharge

Chesnokova A., Baraër M., Bouchard É.

Abstract. The ongoing warming of cold regions is affecting hydrological processes, causing deep changes, such as a ubiquitous increase in river winter discharges. The drivers of this increase are not yet fully identified mainly due to the lack of observations and field measurements in cold and remote environments. In order to provide new insights into the sources generating winter runoff, the present study explores the possibility of extracting information from icings that form over the winter and are often still present early in the summer. Primary sources detection was performed using time-lapse camera images of icings found in both proglacial fields and upper alpine meadows in June 2016 in two subarctic glacierized catchments in the upper part of the Duke watershed in the St. Elias Mountains, Yukon. As images alone are not sufficient to entirely cover a large and hydrologically complex area, we explore the possibility of compensating for that limit by using four supplementary methods based on natural tracers: (a) stable water isotopes, (b) water ionic content, (c) dissolved organic carbon, and (d) cryogenic precipitates. The interpretation of the combined results shows a complex hydrological system where multiple sources contribute to icing growth over the studied winter. Glaciers of all sizes, directly or through the aquifer, represent the major parent water source for icing formation in the studied proglacial areas. Groundwater-fed hillslope tributaries, possibly connected to suprapermafrost layers, make up the other detectable sources in icing remnants. If similar results are confirmed in other cold regions, they would together support a multi-causal hypothesis for a general increase in winter discharge in glacierized catchments. More generally, this study shows the potential of using icing formations as a new, barely explored source of information on cold region winter hydrological processes that can contribute to overcoming the paucity of observations in these regions.

Shi R., Yang H., Yang D.

The source region of the Yangtze River (SRYR), located on the eastern Tibetan Plateau, is an essential part of the Asian Water Tower and plays an important role in the downstream water resources. Significant changes in frozen ground caused by increases in air temperature have been widely reported in the past several decades, which has greatly affected regional runoff. This study evaluated the spatiotemporal variations in frozen ground and hydrological components by utilizing a geomorphology-based eco-hydrological model (GBEHM) and investigated the reasons for runoff changes based on the Budyko framework. The results showed that the area with an elevation range of 4700–4800 m located in the permafrost region was the main source area of runoff generation from 1981 to 2015. Compared with the permafrost region, the seasonally frozen ground (SFG) region had a larger ratio of annual evapotranspiration to annual precipitation, although the aridity indices in the two regions were very similar. From 1981 to 2015, the mean value of the maximum frozen depth of SFG (MFDSFG) decreased by 12.3 cm/10 a and the mean value of the active layer thickness (ALT) of permafrost increased by 4.2 cm/10 a. The annual runoff in the SFG region decreased, while that in the permafrost region increased. Runoff change was more sensitive to precipitation change in the higher altitude regions that were mainly covered by permafrost than in the lower altitude regions that were mainly covered by the SFG, while the evapotranspiration change in the transition zone was more sensitive to climate change. An abrupt change in the annual runoff time series was detected in 1989, 2004, and 2004 in the SFG region, the permafrost region and the entire SRYR, respectively, and the annual runoff change from period 1 (1981 to change point) to period 2 (change point + 1 to 2015) were −25.7 mm, 33.8 mm and 25.8 mm respectively. Frozen ground degradation contributed changes of −15.0 mm, −8.8 mm and −11.6 mm to the annual runoff in the SFG region, the permafrost region and the entire SRYR, respectively. This result implied that frozen ground degradation had a negative impact on regional runoff in the SRYR. These findings deepen our understanding of frozen ground and its hydrological changes and are helpful for water resource management in the SRYR.

Tan X., Liu B., Tan X.

Lamontagne‐Hallé P., McKenzie J.M., Kurylyk B.L., Molson J., Lyon L.N.

Zhao L., Zou D., Hu G., Du E., Pang Q., Xiao Y., Li R., Sheng Y., Wu X., Sun Z., Wang L., Wang C., Ma L., Zhou H., Liu S.

Permafrost on the Qinghai–Tibet Plateau (QTP) has undergone degradation as a result of recent climate change. This may alter the thermo‐hydrological processes and unlock soil organic carbon, and thereby affect local hydrological, ecological, and climatic systems. The relationships between permafrost and climate change have received extensive attention, and in this paper we review climate change for permafrost regions of the QTP over the past 30 years. We summarize the current state and changes in permafrost distribution and thickness, ground temperature, and ground ice conditions. We focus on changes in permafrost thermal state and in active‐layer thickness (ALT). Possible future changes in ground temperature and ALT are also discussed. Finally, we discuss the changes in hydrological processes and to ecosystems caused by permafrost degradation. Air temperature and ground temperature in the permafrost regions of the QTP have increased from 1980 to 2018, and the active layer has been thickening at a rate of 19.5 cm per decade. The response of permafrost to climate change is not as fast as in some reports, and permafrost degradation is slower than projected by models that do not account for conditions deep in permafrost.

Nitzbon J., Westermann S., Langer M., Martin L.C., Strauss J., Laboor S., Boike J.

The ice- and organic-rich permafrost of the northeast Siberian Arctic lowlands (NESAL) has been projected to remain stable beyond 2100, even under pessimistic climate warming scenarios. However, the numerical models used for these projections lack processes which induce widespread landscape change termed thermokarst, precluding realistic simulation of permafrost thaw in such ice-rich terrain. Here, we consider thermokarst-inducing processes in a numerical model and show that substantial permafrost degradation, involving widespread landscape collapse, is projected for the NESAL under strong warming (RCP8.5), while thawing is moderated by stabilizing feedbacks under moderate warming (RCP4.5). We estimate that by 2100 thaw-affected carbon could be up to three-fold (twelve-fold) under RCP4.5 (RCP8.5), of what is projected if thermokarst-inducing processes are ignored. Our study provides progress towards robust assessments of the global permafrost carbon–climate feedback by Earth system models, and underlines the importance of mitigating climate change to limit its impacts on permafrost ecosystems. Siberian Arctic permafrost contains vast stores of carbon, the fate of which is dependent on the climate. Here the authors use models of future scenarios to show that under the direst climate changes up to 2/3 of the stored organic carbon could thaw.

Evans S.G., Yokeley B., Stephens C., Brewer B.

Xu M., Kang S., Wang X., Wu H., Hu D., Yang D.

Changes in the hydrological regimes of Arctic rivers could affect the thermohaline circulation of the Arctic Ocean. In this study, we analysed spatiotemporal variations in temperature and precipitation in the Ob River Basin regions during 1936–2017 based on data from the Global Precipitation Climatology Center. Changes in discharge and response to climate change were examined based on monthly observed data during the same period. It is indicated the Ob River Basin experienced significant overall rapid warming and wetting (increased precipitation) in the study period, with average rates of 0.20°C (10 year⁻¹) and 5.3 mm (10 year⁻¹), respectively. The annual spatial variations of temperature and precipitation showed different scales in different regions. The discharge in spring and winter significantly increased at a rate of 384.1 and 173.1 m³/s (10 year⁻¹), respectively. Hydrograph separation indicated infiltration and supported that deep flow paths increased the contribution of groundwater to base flow. Meanwhile, the variation of the ratio of Qₘₐₓ/Qₘᵢₙ suggested that the basin storage and the mechanism of discharge generation have significantly changed. The hydrological processes were influenced by changes of permafrost in a certain in the Ob River Basin. An increase in the recession coefficient (RC) implies that the permafrost degradation in the basin due to climate warming affected hydrological processes in winter. Permafrost degradation affected the Qₘₐₓ/Qₘᵢₙ more significantly in the warm season than RC due to the enhanced infiltration that converted more surface water into groundwater in the cold season. The impact of precipitation on discharge, including surface flow and base flow, was more significant than temperature at the annual and seasonal scales in the Ob River Basin. The base flow was more obviously influenced by temperature than surface flow. The results of this study are significant for analyses of the basin water budget and freshwater input to the Arctic Ocean.

Golubeva E., Platov G., Iakshina D., Kraineva M.

AbstractContinental runoff is one of the major sources of the Arctic freshwater budget. As is generally known, it influences water column stratification and maintains Arctic halocline, which isolates the sea ice and the cold, fresh upper layer from the warmer, saltier Atlantic waters of the Arctic Ocean. An increase in river runoff was observed in recent years. It is suggested that this will have an impact on Arctic water mass transformations. However, few details are known regarding river freshwater export to the Central Arctic Basin. It is assumed that river water pathways in vast shelf seas and deep basins are closely related to atmospheric variability. In this study, we use three-dimensional coupled regional ocean-ice model simulations forced by atmospheric reanalysis data to investigate the change in Siberian rivers freshwater pathways in the Arctic Ocean due to the variability of atmospheric dynamics. A numerical experiment with an increasing runoff of the largest Siberian rivers is carried out. The consequences of adding freshwater to particular regions of the Arctic Ocean are analysed.

Melnikov V.P., Pikinerov P.V., Gennadinik V.B., Babushkin A.G., Moskovchenko D.V.

A new phenomenon has been investigated - an increase in the winter and early spring streamflow of northern rivers. Assuming that the increased discharge may be due to permafrost degradation in river basins, the thaw rate was estimated by modeling. A mathematical model that takes into account the typification of the four permafrost categories, reflecting the dependence of the runoff on the cryological conditions of the watershed areas, showed a rapid degradation of sporadic permafrost and expansion of discontinuous permafrost at the account of continuous one.

Mu C., Zhang F., Chen X., Ge S., Mu M., Jia L., Wu Q., Zhang T.

Arctic rivers export a large amount of organic carbon (OC) and mercury (Hg) to Arctic oceans. Because there are only a few direct calculations of OC and Hg exports from these large rivers, very little is known about their response to changes in the active layer in northern permafrost-dominated areas. In this study, multiyear data sets from the Arctic Great Rivers Observatory (ArcticGRO) are used to estimate the export of dissolved organic carbon (DOC), particulate organic carbon (POC), total mercury (THg) and methylmercury (MeHg) from the six largest rivers (Yenisey, Lena, Ob, Mackenzie, Yukon and Kolyma) draining to the Arctic Ocean. From 2003 to 2017, annual DOC and POC export to the Arctic Ocean was approximately 21612 Gg and 2728 Gg, and the exports of Hg and MeHg to the Arctic Ocean were approximately 20090 kg and 110 kg (0.002% of the total Hg stored in the northern hemisphere active layer). There were great variations in seasonal OC and Hg concentrations and chemical characteristics, with higher fluxes in spring and lower fluxes in winter (baseline). DOC and Hg concentrations are significantly positively correlated to discharge, as discharge continues to increase in response to a deepening active layer thickness during recent past decades. This study shows that previous results likely underestimated DOC exports from rivers in the circum-Arctic regions, and both OC and Hg exports will increase under predicted climate warming scenarios.

Song C., Wang G., Mao T., Dai J., Yang D.

River runoff in the Arctic and the Tibetan Plateau (TP) change significantly in recent decades. However, the mechanisms of the physical processes of permafrost river runoff change remain uncertain across large scale. This study investigated the mainstreams and tributaries of main Arctic and TP rivers dominated by permafrost and assessed the linkage between hydrological regime change and permafrost. The results show that the effects of permafrost on river runoff are highly dependent on the permafrost coverage of a watershed. For the past decades, the majority of the Arctic and TP basins showed increased discharge, while all of the studied basins showed increased baseflow, with faster increasing speed than total discharge. Both total discharge and baseflow annual change rate (ΔQ and ΔBF) increased with permafrost coverage, indicating the increments of streamflow are enhanced with high permafrost coverage. Meanwhile, the annual change of precipitation showed weak connection with total discharge and baseflow change. The high permafrost coverage basins showed high annual maximum/ minimum discharge ratio (Qmax/Qmin), while the Qmax/Qmin changed slightly in low permafrost cover basins. Our results highlight the importance of permafrost coverage on streamflow regime change for permafrost basins across the northern hemisphere. Due to these linkage between permafrost extent and runoff regime change and the increasing changes of permafrost, more attention should be paid to the change of hydrological processes in permafrost-underlain basins.

Melnikov V.P., Pikinerov P.V., Gennadinik V.B., Babushkin A.G., Moskovchenko D.V.

A new phenomenon, an increase in the winter and early spring streamflow of Siberian rivers, has been studied. Based on the assumption that the increased discharge may be due to permafrost degradation in the river basins, the rate of degradation of the different zones of permafrost distribution is estimated by modeling. A mathematical model that takes into account the typification of the permafrost zones and reflects the dependence of the streamflow on the cryological conditions of the drainage basins has shown rapid degradation of sporadic permafrost and expansion of discontinuous permafrost owing to the intense transition of continuous permafrost to this state.

Brown N.J., Nilsson J., Pemberton P.

Simulations from a coupled ice-ocean general circulation model are used to assess the effectson Arctic Ocean freshwater storage of changes in freshwater input through river runoff and precipitation.We employ the climate response function framework to examine responses of freshwater content to abruptchanges in freshwater input. To the lowest order, the response of ocean freshwater content is linear, withan adjustment time scale of approximately 10 years, indicating that anomalies in Arctic Ocean freshwaterexport are proportional to anomalies in freshwater content. However, the details of the transient responseof the ocean depend on the source of freshwater input. An increase in river runoff results in a fairly smoothresponse in freshwater storage consistent with an essentially linear relation between total freshwatercontent and discharge of excess freshwater through the main export straits. However, the response to achange in precipitation is subject to greater complexity, which can be explained by the localized formationand subsequent export of salinity anomalies which introduce additional response time scales. The resultspresented here suggest that future increases in Arctic Ocean freshwater input in the form of precipitationare more likely to be associated with variability in the storage and release of excess freshwater than areincreases in freshwater input from river runoff

Makarieva O., Nesterova N., Post D.A., Sherstyukov A., Lebedeva L.

Abstract. Large Arctic river basins experience substantial variability in climatic, landscape, and permafrost conditions. However, the processes behind the observed changes at the scale of these basins are relatively poorly understood. While most studies have been focused on the “Big 6” Arctic rivers – the Ob', Yenisey, Lena, Mackenzie, Yukon, and Kolyma – few or no assessments exist for small and medium-sized river basins, such as the Yana and Indigirka River basins. Here, we provide a detailed analysis of streamflow data from 22 hydrological gauges in the Yana and Indigirka River basins with a period of observation ranging from 35 to 79 years up to 2015. These river basins are fully located in the zone of continuous permafrost. Our analysis reveals statistically significant (p<0.05) positive trends in the monthly streamflow time series during the autumn–winter period for most of the gauges. The streamflow increases in a stepwise pattern (post-1981) for 17 out of 22 gauges in September (average trend value for the period of record is 58 % or 9.8 mm) and 15 out of 22 gauges in October (61 % or 2.0 mm). The positive trends are seen in 9 out of 19 rivers that do not freeze in November (54 %, 0.4 mm) and 6 out of 17 rivers that do not freeze in December (95 %, 0.15 mm). Precipitation is shown to decrease in late winter by up to 15 mm over the observational period. Additionally, about 10 mm of precipitation that used to fall as snow at the beginning of winter now falls as rain. Despite the decrease in winter precipitation, no decrease in streamflow has been observed during the spring freshet in May and June in the last 50 years (from 1966); moreover, five gauges show an increase of 86 % or 12.2 mm in spring floods via an abrupt change in 1987–1993. The changes in spring freshet start date are identified for 10 gauges; the earlier onset in May varies from 4 to 10 d over the observational period. We conclude that warmer temperatures due to climate change are impacting the hydrological regime of these rivers via changes in precipitation type (rain replacing snow). Other factors, such as the melting of permafrost, glaciers, and aufeis or changes in groundwater conditions, are likely to contribute as well; however, no direct observations of these changes are available. The changes in streamflow can have a significant impact on the ecology of the zone of continuous permafrost, while the increasing freshwater fluxes to the Arctic Ocean can impact the Arctic thermohaline circulation.

Wang Z., Shi X., Shu L., Yin X., Zhou K., Xu P.

Hacker C., Kusche J.

Jo N., Kim K., Jang H.K., Park S., Kim J., Whitledge T.E., Stockwell D.A., Lee S.H.

The Laptev Sea (LS) and Western East Siberian Sea (W-ESS) are paradigmatic examples of seas dominated by terrestrial organic matter, attributed to substantial Siberian River discharges and coastal erosion. The influx of terrestrial organic matter significantly alters the biochemical composition of particulate organic matter (POM) in these Arctic coastal regions, potentially reducing the nutritional quality available to higher trophic levels. This study investigated the origin and qualitative characteristics of POM in the LS and W-ESS during the late summer of 2018 by analyzing elemental ratios (C/N ratio), stable carbon isotopes (δ

Lin S., Huang K., Sun X., Song C., Sun J., Sun S., Wang G., Hu Z.

AbstractClarifying the controlling factors of annual variations in evapotranspiration (ET) and its components (transpiration (T) and evaporation (E)) over alpine grasslands of high‐cold regions is vital to understanding the hydrological processes of the terrestrial ecosystem. Therefore, this study investigated the variability of ET and its components over the alpine grasslands of the Tibetan Plateau (TP) and the driving factors underlying these changes during 1961–2013. The results showed that the annual ET over alpine grasslands was 339 mm, of which 59% and 41% were contributed by E and T, respectively. Annual ET, E, and T over the TP grasslands changed insignificantly before 1995, whereas increased dramatically during 1995–2013. Regarding different alpine grassland types, annual ET and its components in seasonal frost regions (SAG) were larger than in permafrost regions (PAG). The increase of ET and its components in PAG was profoundly larger than that in the SAG region during 1995–2013. Water and energy factors controlled the ET of approximately 65% and 31% area of the TP grasslands, respectively. Leaf area index was the major cause of T variability throughout 64% area of TP grasslands, while regions where energy factors were the major force of T change were mainly located in the eastern SAG region. Variability of E on entire TP grasslands (81%) was mainly regulated by available water supply. Our results indicate that as permafrost degradation has the potential to amplify climate warming and precipitation increase, ET over the PAG region was expected to continue increasing faster than the SAG region.

Xue Z., Wang Y., Zhao Y., Li D., Borthwick A.G.

Although permafrost degradation contributes significantly to hydrological change in cold regions, gaps remain in our understanding of streamflow variation induced by degrading permafrost in different river basins. We therefore used a deep learning model to simulate the long-term (⩾30 years) monthly streamflow at 60 hydrological stations along the Lena River, the third longest circum-Arctic river. Analyzing the effects of precipitation, temperature, and thaw depth on streamflow variation throughout the Lena River Basin, we identified two feedback patterns relating streamflow to warming permafrost, observed in areas of continuous and discontinuous permafrost. In northern plain regions with continuous permafrost, 94% of stations presented an increasing trend in annual streamflow from the 1900s to the 2010s due to permafrost degradation. The enhanced streamflow was mainly due to increased meltwater in the flood season. In southern regions covered by both continuous and discontinuous permafrost, approximately 38% of stations exhibited a declining trend in annual streamflow in response to permafrost degradation, with a high proportion (61%) located in mountain regions (elevation ⩾ 500 m). The decline is attributed to the enhanced infiltration capacity of thawing frozen layers within discontinuous permafrost regions. Our study provides new insights into the mechanisms behind permafrost degradation-induced streamflow variation and highlights the importance of formulating tailored strategies for sustainable river management in cold regions experiencing climate change.

Lemieux J., Frampton A., Fortier P.

ABSTRACTIncreasing greenhouse gas levels drive extensive changes in Arctic and cold‐dominated environments, leading to a warmer, more humid, and variable climate. Associated permafrost thaw creates new groundwater flow paths in cold regions that are causing unprecedented environmental changes. This review of recent advances in groundwater research in cold environments has revealed that a new paradigm is emerging where groundwater is at the center of these changes. Groundwater flow and associated heat and solute transport are now used as a basis to understand hydrological changes, permafrost dynamics, water quality, integrity of infrastructure along with ecological impacts. Although major advances have been achieved in cold regions' cryohydrogeological research, the remaining knowledge gaps are numerous. For example, groundwater as a drinking water source is poorly documented despite its social importance. Lateral transport processes for carbon and contaminants are still inadequately understood. Numerical models are improving, but the highly complex physical‐ecological changes occurring in the arctic involve coupled thermal, hydrological, hydrogeological, mechanical, and geochemical processes that are difficult to represent and hamper quantitative analysis and limit predictive capacity. Systematic long‐term observatories where measurements involving groundwater are considered central are needed to help resolve these research gaps. Innovative transdisciplinary research will be critical to comprehend and predict these complex transformations.

Shkolnyi D., Magritsky D., Chalov S.

Kim I., Timmermann A., Kim J., Rodgers K.B., Lee S., Lee H., Wieder W.R.

AbstractUnabated 21st-century climate change will accelerate Arctic-Subarctic permafrost thaw which can intensify microbial degradation of carbon-rich soils, methane emissions, and global warming. The impact of permafrost thaw on future Arctic-Subarctic wildfires and the associated release of greenhouse gases and aerosols is less well understood. Here we present a comprehensive analysis of the effect of future permafrost thaw on land surface processes in the Arctic-Subarctic region using the CESM2 large ensemble forced by the SSP3-7.0 greenhouse gas emission scenario. Analyzing 50 greenhouse warming simulations, which capture the coupling between permafrost, hydrology, and atmosphere, we find that projected rapid permafrost thaw leads to massive soil drying, surface warming, and reduction of relative humidity over the Arctic-Subarctic region. These combined processes lead to nonlinear late-21st-century regime shifts in the coupled soil-hydrology system and rapid intensification of wildfires in western Siberia and Canada.

Cao F., Shu W., Liu Q., Wan J., Jiang Z., Liu M., Jiang Y.

The Laptev Sea is a major Marginal Sea in the Western Arctic Ocean. The Arctic amplification brought by global warming influences the hydrological properties of rivers passing through the permafrost zone, which would alter the biological community structure at continental margin. In this study, the structure, assembly, and gene expression of planktonic microbial communities in two estuaries (Protoka Ularovskaya River Estuary, PURE; Lena River Estuary, LRE) of Laptev Sea were examined to investigate the environmental effects of polar rivers. PURE and LRE exhibited distinct environmental characteristics: low temperature and high salinity for PURE, and high temperature and low salinity for LRE, influenced by runoff size. Salinity more closely influenced microbial communities in LRE, with freshwater species playing a significant role in community composition. The findings revealed differences between two estuaries in community composition and diversity. Prokaryotes and microeukaryotes had shown different assembly patterns in response to habitat changes caused by terrestrial freshwater input. Furthermore, compared with the PURE, the co-occurrence and inter-domain network of the LRE, which was more affected by terrestrial input, was more complex and stable. Functional gene prediction revealed a higher gene expression of methane metabolism in LRE than in PURE, particularly those related to methane oxidation, and this conclusion could help better explore the impact of global warming on the methane cycle in the Arctic Marginal Seas. This study explored the increased freshwater runoffs under the background of global warming dramatically affect Arctic microplankton communities from community structure, assembly and gene expression aspects.

Salazar J.F., Molina R.D., Zuluaga J.I., Gomez-Velez J.D.

Abstract. Global change is altering hydrologic regimes worldwide, including large basins that play a central role in the sustainability of human societies and ecosystems. The basin water budget is a fundamental framework for understanding these basins' sensitivity and future dynamics under changing forcings. In this budget, studies often treat atmospheric processes as external to the basin and assume that atmosphere-related water storage changes are negligible in the long term. These assumptions are potentially misleading in large basins with strong land–atmosphere feedbacks, including terrestrial moisture recycling, which is critical for global water distribution. Here, we introduce the land–atmosphere reservoir (LAR) concept, which includes atmospheric processes as a critical component of the basin water budget and use it to study long-term changes in the water storage of some of the world's largest basins. Our results show significant LAR water storage trends over the last 4 decades, with a marked latitudinal contrast: while low-latitude basins have accumulated water, high-latitude basins have been drying. If they continue, these trends will disrupt the discharge regime and compromise the sustainability of these basins, resulting in widespread impacts.

Nitzbon J., Schneider von Deimling T., Aliyeva M., Chadburn S.E., Grosse G., Laboor S., Lee H., Lohmann G., Steinert N.J., Stuenzi S.M., Werner M., Westermann S., Langer M.

Arctic permafrost, the largest non-seasonal component of Earth’s cryosphere, contains a substantial climate-sensitive carbon pool. The existence of a global tipping point, a warming threshold beyond which permafrost thaw would accelerate and become self-perpetuating, remains debated. Here we provide an integrative Perspective on this question, suggesting that despite several permafrost-thaw feedbacks driving rapid thaw and irreversible ground-ice loss at local to regional scales, the accumulated response of Arctic permafrost to climate warming remains quasilinear. We argue that in the absence of a global tipping point there is no safety margin within which permafrost loss would be acceptable. Instead, each increment of global warming subjects more land areas underlain by permafrost to thaw, causing detrimental local impacts and global feedbacks. It has been postulated that there is a threshold temperature above which permafrost will reach a global tipping point, causing accelerated thaw and global collapse. Here it is argued that permafrost-thaw feedbacks are dominated by local- to regional-scale processes, but this also means there is no safety margin.

Zhang Y., Qiu Y., Li Y., Leppäranta M., Jia G., Jiang Z., Liang W.

River ice is an essential component of the terrestrial cryosphere, which is sensitive to global and regional climate change. The Yenisei River provides the largest river inflow to the Arctic Ocean, heavily affected by the cold climate. Data on the ice cover in the Arctic great rivers are insufficient due to the absence of a river ice database with high spatiotemporal resolution. In this study, the daily river ice coverage (RIC, defined as the fraction of river ice pixels to river pixels in a grid cell) in the Yenisei River was estimated from 2002 to 2021 in a 12.5 × 12.5 km grid, by utilizing a cloud removal method for Moderate Resolution Imaging Spectroradiometer (MODIS) data. Based on Landsat imagery reference, the RIC correlations (Pearson's R) were 0.77, 0.84, and 0.97 for three separate validation regions. Over the past 20 years, 82.8 % of the grid cells experienced a decreasing ice cover, with 21.9 % significant at the 0.05 level. The mean winter air temperature was the key predictor (R2 = 0.48, P < 0.01), better than the accumulated negative air temperature (R2 = 0.42, P < 0.01). The spatial distribution of winter RIC exhibited a latitudinal gradient (R2 = 0.64, P < 0.01). River ice responded to temperature variation in a non-linear way, depending on latitude, with high sensitivity in the southern part of the watershed. In Lake Baikal in the river basin, the distribution of ice cover was also affected by stream inflows. The results provide a comprehensive insight into the spatial–temporal variations of the Yenisei River and explore the key factor of changes in river ice, enhancing our ability to understand the response of Arctic great rivers to climate change.

Patro E.R., Ghadimi S., Shahrood A.J., Fazel N., Makarieva O., Haghighi A.T.

Arctic rivers and water resources currently experience significant hydrological changes due to climate change and global warming. The flow regime alteration in Arctic rivers strongly influences the conservation and sustainability of the native biodiversity of the riverine ecosystem. The change in major characteristics of the daily and monthly flow regime of seven arctic rivers has been assessed in this study. The daily flow (40–120 years) at the outlet of Lena River, Yenisey River, Kolyma River, and Ob' River in Russia; Yukon River in the USA; Mackenzie River in Canada; and Tana River, Norway was used. Except for the Tana River, the rest of these rivers have been regulated. In addition, monthly flow alteration in the headwater of these rivers and below sixteen dams was assessed. In this research, we applied 'Indicator of Hydrologic Alteration' (IHA) and 'River Impact' (RI) methods to estimate daily monthly flow change in the river. Based on the daily analysis, the most significant change was observed for Yenisey and Ob rivers. The Kolyma hydropower shows the lowest impact, while the Shushenskaya Dam on Yenisey shows the highest impact on the flow regime.

Stringer C.D., Boyle J.F., Hrbáček F., Láska K., Nedělčev O., Kavan J., Kňažková M., Carrivick J.L., Quincey D.J., Nývlt D.

Proglacial regions are enlarging across the Antarctic Peninsula as glaciers recede in a warming climate. However, despite the increasing importance of proglacial regions as sedi ment sources within cold environments, very few studies have considered fluvial sediment dynamics in polar settings and spatio-temporal variability in sediment delivery to the oceans has yet to be unravelled. In this study, we show how air temperature, precipitation, and ground conditions combine to control sediment loads in two catchments on James Ross Island, Antarctica. We estimate that the sediment load for the Bohemian Stream and Algal Stream over the 50 day study period, the average sediment load was 1.18 ± 0.63 t km-2 d-1 and 1.73 ± 1.02 t km-2 d-1 , respectively. Both catchments show some sensitivity to changes in precipitation and air temperature, but the Algal catchment also shows some sensitivity to active layer thaw. The downstream changes in sediment provenance are controlled by underlying lithology, while differences in sediment load peaks between the two catchments appear to be primarily due to differing glacier and snowfield coverage. This identification of the controls on sediment load in this sub-polar environment provides insight into how other fluvial systems across the Antarctic Peninsula could respond as glaciers recede in a warming climate.

Kim S.H., Son W., Yoo J., Cho K., Park T., Yang E.J., Kang S., La H.S.

A multidisciplinary survey was carried out in the Pacific Arctic and sub-Arctic regions of the North Pacific Ocean on the Korean icebreaking research vessel Araon. During this survey, ichthyoplankton fishes in the Pacific Arctic and sub-Arctic region ranged from the Bering Sea to the northern Chukchi Shelf in summer. The most dominant species was Gadus chalcogrammus, followed by Pleuronectes quadrituberculatus and Boreogadus saida. Gadus chalcogrammus and P. quadrituberculatus were particularly abundant near the Bering Sea and Bering Strait, whereas B. saida was dominant in the Chukchi Sea. Hierarchical cluster analysis revealed four distinct ichthyoplankton communities in Pacific Arctic and sub-Arctic regions based on geographical regions. However, Eleginus gracilis, which was previously known to be seen between latitudes 66.5°N and 69.5°N, was found above 70°N, suggesting that its distribution extends further north. Furthermore, we noticed that Benthosema glaciale, which is usually found in the Atlantic sector of Arctic Ocean, was observed in the northern Chukchi Sea. In addition to these unusual species distributions, several species that are mainly observed in coastal areas are observed in the Chukchi Sea region. The observed influx of various uncommon fish species into the Chukchi Sea can be attributed to multiple factors, including freshwater inflow from the East Siberian Sea and the intrusion of warm Atlantic and Pacific waters, which are strongly affected by global warming. Consequently, it is imperative to conduct rigorous monitoring of the Pacific Arctic region, with a particular focus on the Chukchi Sea, to better understand the implications of global warming.