Melting Of Ice Cover Research Articles

Isotopic signatures of snow, sea ice, and surface seawater in the central Arctic Ocean during the MOSAiC expedition

The Arctic Ocean is an exceptional environment where hydrosphere, cryosphere, and atmosphere are closely interconnected. Changes in sea-ice extent and thickness affect ocean currents, as well as moisture and heat exchange with the atmosphere. Energy and water fluxes impact the formation and melting of sea ice and snow cover. Here, we present a comprehensive statistical analysis of the stable water isotopes of various hydrological components in the central Arctic obtained during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in 2019–2020, including the understudied Arctic winter. Our dataset comprises >2200 water, snow, and ice samples. Snow had the most depleted and variable isotopic composition, with δ18O (–16.3‰) increasing consistently from surface (–22.5‰) to bottom (–9.7‰) of the snowpack, suggesting that snow metamorphism and wind-induced transport may overprint the original precipitation isotope values. In the Arctic Ocean, isotopes also help to distinguish between different sea-ice types, and whether there is a meteoric contribution. The isotopic composition and salinity of surface seawater indicated relative contributions from different freshwater sources: lower δ18O (approximately –3.0‰) and salinities were observed near the eastern Siberian shelves and towards the center of the Transpolar Drift due to river discharge. Higher δ18O (approximately –1.5‰) and salinities were associated with an Atlantic source when the RV Polarstern crossed the Gakkel Ridge into the Nansen Basin. These changes were driven mainly by the shifts within the Transpolar Drift that carried the Polarstern across the Arctic Ocean. Our isotopic analysis highlights the importance of investigating isotope fractionation effects, for example, during sea-ice formation and melting. A systematic full-year sampling for water isotopes from different components strengthens our understanding of the Arctic water cycle and provides crucial insights into the interaction between atmosphere, sea ice, and ocean and their spatio-temporal variations during MOSAiC.

Impacts of Climate Change on Mountaineering Routes in the Écrins Massif (Western Alps, France)

Mountaineering is one of the most affected sports activities due to the current climate crisis and the resulting changes in the physical environment of the high mountain areas. Some routes have disappeared while others are no longer accessible in summer (hazards, technical difficulties, etc.). Research has already been conducted on the impact of climate change on mountaineering and on adaptation. The Mont-Blanc massif and the Valais Alps have been used as study areas to understand the evolution of mountaineering routes over recent decades. A mapping of the geomorphological and glaciological processes affecting mountaineering routes has been conducted for the Valais. This study aims to apply this method to Écrins massif (French Alps), which had so far remained unstudied despite its emblematic character. The famous topo-guide "Le massif des Écrins - Les 100 plus belles courses et randonnées" (1974) was used as a basis for the study with 70 routes being selected according to their notoriety and visitor numbers. All the processes affecting the routes were mapped using GIS, and a statistical analysis was carried out to gain a better understanding of the evolution of the routes, together with semi-directive interviews with experts and practitioners. A new process – the early summer melting of ice and snow cover – was identified. As is the case in the Mont-Blanc massif and the Valais, a route is affected by 9 processes on average, and almost 25% of the routes can no longer be climbed in summer. The mapping method has been successfully applied to Écrins massif, providing new knowledge of the recent evolution of mountaineering routes in the Alps.

CO2 buildup drove global warming, the Marinoan deglaciation, and the genesis of the Ediacaran cap carbonates

What caused ocean/climate changes that drove Marinoan deglaciation, and the subsequent genesis of Ediacaran cap carbonates remains unclear. To address this issue, we examined the Hg records in Ediacaran cap carbonates from shelf to slope depositional settings in exposures from South China. These cap carbonates show higher total Hg (THg) concentrations (4.9 to 405 ppb), most of which are comparable to that observed in carbonates deposited during non-LIPs periods. The lack of THg/TOC anomalies in these cap carbonates suggests that background volcanic activity, rather than a short-term large igneous province event, drove the Marinoan deglaciation. The cap carbonates show positive Δ199Hg values (0.18 to 0.34 ‰) in slope settings and slightly negative to slightly positive Δ199Hg values (−0.16 to 0.11 ‰) in shelf settings, suggesting a binary mixing of seawater- and terrestrial-derived Hg in early Ediacaran Ocean. We infer that the accumulation of greenhouse gases, due to ongoing volcanic emissions of CO2 and enhanced release of gas hydrates, triggered global warming. This warming led to melting of sea ice cover, enhanced terrestrial inputs of alkalis (e.g., K+, Na+, Ca2+, Mg2+), and large-scale dissolution of atmospheric CO2 into seawater, driving widespread deposition of Ediacaran cap carbonates.

Lake ice phenology variations and influencing factors of Selin Co from 2000 to 2020

湖冰作为湖泊-大气界面能量和物质交换的结果，其物候变化对揭示区域气候变化和湖泊响应过程具有重要意义.本研究基于2000-2020年色林错边界矢量数据、Terra MODIS和Landsat TM/ETM+/OLI遥感影像并结合气象数据及湖泊资料，利用RS和GIS手段综合分析了色林错湖冰物候变化特征及其影响因素.结果表明：①色林错于11月下旬到12月上旬开始冻结，在12月下旬到1月上旬完全冻结，封冻时间约一个月左右.湖冰在每年的3月下旬到4月上旬开始消融，历经半个月左右，至4月下旬完全消融.②近20 a来，色林错开始冻结日期整体呈现逐渐推迟的波动趋势，推迟率约为11.3 d/10 a.湖冰冻结期呈缩短趋势；湖冰存在期整体上呈缩短趋势，缩短率为13.5 d/10 a.③色林错冻结先从北部和东部湖岸处开始逐渐向中部湖心处扩张，解冻时湖冰中心先破裂，向湖岸边逐渐消融.④色林错湖冰物候受气候和湖泊自身理化性质综合影响.冬半年平均气温是影响湖冰消融和封冻期的关键因素；风速和降水对湖冰的冻结和消融亦有一定影响.近20 a来，随着色林错面积扩张、浑浊度上升及透明度下降，湖冰开始冻结时间推迟，湖冰封冻期缩短.全球变暖背景下，包含色林错在内的青藏高原湖泊有加速扩张趋势，本研究结果可为理解变化环境下湖冰物候信息的气候指示意义及湖泊反馈过程提供参考.;As a result of energy and material exchange at the lake-atmosphere interface, the variations of lake ice phenology are of great significance for indicating regional climate change and lake response process. Based on the boundary data of Selin Co, some multi-source remote sensing (RS) datasets including Terra MODIS and Landsat TM/ETM+/OLI product, combined with meteorological records and lake data to analyze spatiotemporal variations of ice phenology of Selin Co and its relationship with climate factors and physical and chemical factors between 2000 and 2020 by applying both RS and GIS technology. The main research conclusions are as follows:(1) Freeze-up start (FUS) and freeze-up end (FUE) of lake ice appears in late November-early December, and late December-early January, respectively. The duration of lake ice freeze-up is about a month. The time of break-up start (BUS) and break-up end (BUE) of lake ice appears in late March-early April, and late April, respectively. The duration of lake ice break-up is about half a month. (2) Data show that FUS dates of lake ice have been delayed at a rate of 11.3 d/10 a from 2000 to 2020. FUD (freeze-up duration) time of lake ice showed an increasingly shortening trend. Ice cover duration had been shortened at a rate of 13.5 d/10 a. (3) Selin Co can be characterized by opposite spatial patterns in both freeze-up and break-up processes. Lake ice freezes from the northern and eastern lakeshore and gradually expands to the center of lake. Instead, lake ice break-up begins in the center of the lake. (4) Ice phenology of Selin Co is influenced by climate and physico-chemical factors of the lake itself. The average temperature of winter half-year (between November and the following April) plays a dominant role in ice phenology variations of Selin Co. Wind speed and precipitation both also some influences on the formation and melting of lake ice cover and also cannot be neglected. In the recent 20 years, with the expansion of Selin Co area, the increase of turbidity and the decrease of water clarity, the freezing dates of lake ice were gradually delayed. Under the background of global warming, the area expansion of lakes on the Tibetan Plateau, including Selin Co, has accelerated. The results of this study can provide a reference for understanding the climate indicator significance of lake ice phenology information and the feedback process of lakes under the changing environment.

Tibetan Plateau Lakes as Heat Flux Hot Spots

Freshwater lakes on the highest plateau in the world act like lenses that accumulate heat from the intense solar radiation, accelerating ice cover melt and affecting land-atmosphere fluxes.

Ice‐Covered Lakes of Tibetan Plateau as Solar Heat Collectors

AbstractThe Qinghai‐Tibet Plateau possesses the largest alpine lake system, which plays a crucial role in the land‐atmosphere interaction. We report first observations on the thermal and radiation regime under ice of the largest freshwater lake of the Plateau. The results reveal that freshwater lakes on the Tibetan Plateau fully mix under ice. Due to strong solar heating, water temperatures increase above the maximum density value 1–2 months before the ice break, forming stable thermal stratification with subsurface temperatures >6°C. The resulting heat flow from water to ice makes a crucial contribution to ice cover melt. After the ice breakup, the accumulated heat is released into the atmosphere during 1–2 days, increasing lake‐atmosphere heat fluxes up to 500 W m−2. The direct biogeochemical consequences of the deep convective mixing are aeration of the deep lake waters and upward supply of nutrients to the upper photic layer.

Annual survival probabilities of anadromous Arctic Char remain high and stable despite interannual differences in sea ice melt date

Throughout their range, anadromous Arctic Char (Salvelinus alpinus (Linnaeus, 1758)) support commercial, recreational, and subsistence fisheries that are important economically, socially, and culturally. However, drivers of interannual variation in survival in this species remain poorly understood. Here, we aimed to quantify the impact of environmental and biological parameters on the survival probability of anadromous Arctic Char near the community of Cambridge Bay, Nunavut, Canada. To do so, we tracked 183 Arctic Char tagged with acoustic transmitters and used capture–mark–recapture methods to estimate survival probabilities over six years. Annual survival probabilities for individuals was high, varying between 0.79 and 0.88, whereas recapture probabilities varied between 0.64 and 0.90. Interannual variation in survival probability was low and neither the environmental (air temperature and sea ice cover) nor biological (sex) variables influenced survival probability. These estimates suggest that annual survival probability is high for anadromous adult Arctic Char in the Cambridge Bay area, despite clear differences in the ice cover melt date among years. These results further our understanding of the demographic parameters of Arctic Char in the region, which will be important for future assessments of the sustainability of commercial fisheries as well as for predicting population responses to a rapidly changing Arctic.

Global Climate Change: Assessing the Importance of the Roles of Ice Cover and Glacial Changes

Issues of water security are rapidly becoming more widely recognized as impacted. Increased levels of carbon dioxide are clearly evident and long-term temperature increases are clearly evident. These indicators are being used to compile evidence that sea level rise in the future will be between 0.3 and 1.0 m by 2100 and, combined with more severe storms along coastlines, will translate into increasing challenges for coastal cities. The enormous glaciers in Greenland and Antarctica will continue to contribute to sea level rise but fortunately, at modest levels, for thousands of years. On the other hand, land-based glaciers will continue to become depleted and the ramifications to agricultural practices are expected to be profound, with situations of significant percentages of the world’s land-based glaciers being lost by 2100. Further, the disappearance rate of the Arctic Ocean ice cover is already profoundly evident, with losses of ice cover of about 13.1 percent per decade now occurring. Rates of warming in the Arctic are increasing at two to three times the global annual average and warrant further forecasting of the implications. With the reduced ice cover, the water in the Arctic Ocean is now absorbing the energy from the sun, not reflecting the sun’s energy, thereby accelerating further ice cover melting. The result is that the jet stream is weakening and evidence is mounting that there will be increased excursions of the polar vortex causing very cold weather extremes in northern hemisphere areas.

Potentially modified hydropower production under climate change in the Italian Alps

AbstractWe present an assessment of the potential impacts of climate change on hydropower production within a paradigmatic, very highly exploited cryospheric area of upper Valtellina valley in the Italian Alps. Based on dependable and unique hydrological measures from our high‐altitude hydrometric network Idrostelvio during 2006–2015, we set up the Poly‐Hydro model to mimic the cryospheric processes driving hydrological flow formation in this high‐altitude area. We then set up an optimization tool, which we call Poly‐Power, to maximize the revenue of the plant manager under given hydrological regimes, namely, by proper operation of the hydroelectric production scheme (reservoirs, pipelines, and power plants) of the area. We then pursue hydrological projections until 2100, feeding Poly‐Hydro with the downscaled outputs of three general circulation models from the Intergovernmental Panel on Climate Change Fifth Assessment Report, under the scenarios Representative Concentration Pathway (RCP) 2.6, RCP 4.5, and RCP 8.5. We assess hydrological flows in two reference decades, that is, at half century (2040–2049), and end of century (2090–2099). We then feed the so obtained hydrological scenarios as inputs to Poly‐Power, and we project future production of hydroelectric power, with and without reoperation of the system. The average annual stream flows for hydropower production decreases along the century under our scenarios (−21 to +7%, on average − 5% at half century; −17 to −2%, average − 8%, end of century), with ice cover melting unable to offset such decrease. Reduction in snowfall and increase in liquid rainfall are the main factors affecting the modified hydrological regime. Energy production (and revenues) at half century may increase under our scenarios (−9 to +15%, +3% on average). At the end of century in spite of a projected increase on average (−7 to +6%, +1% on average), under the warmest scenario RCP 8.5 decrease of energy production is consistently projected (−4% on average). Our results provide an array of potential scenarios of modified hydropower production under future climate change and may be used for brain storming of adaptation strategies.

Spatiotemporal characteristics of Qinghai Lake ice phenology between 2000 and 2016

Lake ice phenology is considered a sensitive indicator of regional climate change. We utilized time series information of this kind extracted from a series of multi-source remote sensing (RS) datasets including the MOD09GQ surface reflectance product, Landsat TM/ETM+ images, and meteorological records to analyze spatiotemporal variations of ice phenology of Qinghai Lake between 2000 and 2016 applying both RS and GIS technology. We also identified the climatic factors that have influenced lake ice phenology over time and draw a number of conclusions. First, data show that freeze-up start (FUS), freeze-up end (FUE), break-up start (BUS), and break-up end (BUE) on Qinghai Lake usually occurred in mid-December, early January, mid-to-late March, and early April, respectively. The average freezing duration (FD, between FUE and BUE), complete freezing duration (CFD, between FUE and BUS), ice coverage duration (ICD, between FUS and BUE), and ablation duration (AD, between BUS and BUE) were 88 days, 77 days, 108 days and 10 days, respectively. Second, while the results of this analysis reveal considerable differences in ice phenology on Qinghai Lake between 2000 and 2016, there has been relatively little variation in FUS times. Data show that FUE dates had also tended to fluctuate over time, initially advancing and then being delayed, while the opposite was the case for BUS dates as these advanced between 2012 and 2016. Overall, there was a shortening trend of Qinghai Lake’s FD in two periods, 2000–2005 and 2010–2016, which was shorter than those seen on other lakes within the hinterland of the Tibetan Plateau. Third, Qinghai Lake can be characterized by similar spatial patterns in both freeze-up (FU) and break-up (BU) processes, as parts of the surface which freeze earlier also start to melt first, distinctly different from some other lakes on the Tibetan Plateau. A further feature of Qinghai Lake ice phenology is that FU duration (between 18 days and 31 days) is about 10 days longer than BU duration (between 7 days and 20 days). Fourth, data show that negative temperature accumulated during the winter half year (between October and the following April) also plays a dominant role in ice phenology variations of Qinghai Lake. Precipitation and wind speed both also exert direct influences on the formation and melting of lake ice cover and also cannot be neglected.

The Influence of the Duration of Wind Impact on the Formation of Currents and a Thermal Bar in a Freshwater Reservoir over the Period of Melting of the Ice Cover

The impact of wind of different strengths, directions, and durations on the development of a thermal bar and accompanying currents in reservoirs over the period of ice cover melting was studied using mathematical modeling. It is shown that as the duration of the wind impact on the reservoir increases, the role of energy exchange at the water-air interface in the formation of currents in the reservoir increases. The passage of surface waters through the temperature of maximum density (4°C) leads to the formation of a thermal bar and convective structures to the right and to the left of it. In this case, the increase in the energy exchange as the duration of the wind grows occurs with different degrees of intensity on different sides of the thermal bar. In certain hydrometeorological situations (when the wind is directed offshore) this can increase the intensity of the convective vortex in the deep part of the reservoir and weaken it in the shore part, which will slow the propagation of the thermal bar towards the center of the reservoir.

Lake‐Atmosphere Heat Flux Dynamics of a Thermokarst Lake in Arctic Siberia

AbstractWe conducted eddy covariance measurements from April to August 2014 on a Siberian thermokarst lake. The study site is located in the Lena River Delta and characterized as a floating ice lake. Heat fluxes differed in magnitudes, directions and temporal patterns depending on the lake surface conditions (“frozen” ice cover, ice cover melt, and open water). Significant heat release during frozen ice cover conditions highlighted the importance of lakes for the landscape heat budget and water balance. The energy balance was nearly closed during the open water period and highlighted the impact of melting energy on its closure during the ice cover period. Sensible and latent heat dynamics were driven by temperature and water vapor gradients scaled by wind speed, respectively. We calculated bulk aerodynamics transfer coefficients and evaluated the performance of the derived in situ and three independent heat flux parameterization schemes. We found that bulk transfer models perform moderately to poorly for the different lake surface conditions. During the open water period small‐scale temporal variability could not be represented by the models, particularly in case of latent heat flux. The model results were less sensitive to the specific model type than to the accuracy of the surface water temperature measurement, which is dependent on a well‐thought‐out measurement design. Our study stresses considerations that are crucial for similar campaigns in the future, in order to face the measurement challenges encountered on arctic lakes especially during the ice cover period.

POSSIBILITIES OF THE JOINT USE OF OPTICAL AND RADAR DATA IN FLOOD SPACE MONITORING

Abstract. The article gives a brief description of the system of space monitoring of high water and floods. Its main tasks are the operational dynamics of snow and ice cover melting and the passage of flood waters. The solution of these tasks is carried out in three levels corresponding to the low, medium and high resolution of remote sensing data. An important role in monitoring is given to radar data. This is due to the features of the radar survey: independence from weather conditions and time of day, regularity, good spatial resolution, the possibility of using polarimetric properties (including phase information). The use of radar data also provides additional information, including the allocation of wet soils, flooded vegetation and infrastructure. The presence of large time periods of repeated survey, interference (cloudiness, haze, noise, etc.), different spatial resolution necessitates a complex analysis of optical and radar data in flood space monitoring. Such analysis makes it possible to better observe the flood dynamics, more precisely identify of flooding zones and determine their structure. Features of radar survey (transparency of dry snow and change of reflected signal during snowmelt) allow using them to determine the beginning of snow melt and determine the degree of water content in it. Optical data are also used to determine the area and structure of the snow cover. Method of detecting the beginning of the snowmelt period consists in the comparison of the current radar image with a base image created as an average image from the winter images with dry snow.

An Experimental Fuzzy Inference System for Global Grid Electricity Peak Power Load Forecasting Third Core Module of First Console on G2P3S

Our World gives several symptoms of climate change. Devastating draughts increase (negative for World (-)), global mean temperature increase (-), lightning strikes increase (-), sea ice cover melt (-), tree mortality increase (-), and forest degradation increase (-) have been observed for decades. They are all negative measures for continuity of life. Diversity of species has been decreasing, so that life on Earth is dying. Only responsible specie for this situation is humankind. This study presents a small footstep to prevent this situation. Modeling of a 100% renewable power grid on World (Global Grid) is eminent. Annual peak power load (Gigawatt: GW, Kilowatt: kW) (peak demand or load) forecasting in power demand side is crucial for global grid modeling. This study presents an experimental fuzzy inference system for the third core module (100 years’ power demand forecasting) of the first console (long term prediction) of Global Grid Peak Power Prediction System (G2P3S). The inputs (world population, global annual temperature anomalies °C) and the output (annual peak power load demand of Global Grid in GW) are modeled with seven triangular fuzzy input membership functions and seven constant output membership functions. The constant Sugeno-Type fuzzy inference system is used in the current experimental model. The maximum absolute percentage error (MAP) is calculated as 45%, and the mean absolute percentage error (MAPE) is found as 39% in this experimental study. The MAP and MAPE of the first core module model (Type 1) were 0,46 and 0,36. The MAP and MAPE of the second core module model (Interval Type 2) were 0,46 and 0,36. As a result, this study is a good start for the third core module of the first console on Global Grid Peak Power Prediction System research, development, demonstration, & deployment (RD3) project. This experimental study also warns humankind in this subject. Hopefully, the most polluting societies on our World such as China, United States, India, Russia, Japan, Germany, South Korea, and Canada take urgent actions to start to build the foundations of 100% renewable power global grid by organizing a global grid consortium.

Understanding and Predicting the Fate of Semivolatile Organic Pesticides in a Glacier-Fed Lake Using a Multimedia Chemical Fate Model

Melting glaciers release previously ice-entrapped chemicals to the surrounding environment. As glacier melting accelerates under future climate warming, chemical release may also increase. This study investigated the behavior of semivolatile pesticides over the course of one year and predicted their behavior under two future climate change scenarios. Pesticides were quantified in air, lake water, glacial meltwater, and streamwater in the catchment of Lake Brewster, an alpine glacier-fed lake located in the Southern Alps of New Zealand. Two historic-use pesticides (endosulfan I and hexachlorobenzene) and three current-use pesticides (dacthal, triallate, and chlorpyrifos) were frequently found in both air and water samples from the catchment. Regression analysis indicated that the pesticide concentrations in glacial meltwater and lake water were strongly correlated. A multimedia environmental fate model was developed for these five chemicals in Brewster Lake. Modeling results indicated that seasonal lake ice cover melt, and varying contributions of input from glacial melt and streamwater, created pulses in pesticide concentrations in lake water. Under future climate scenarios, the concentration pulse was altered and glacial melt made a greater contribution (as mass flux) to pesticide input in the lake water.

Features of thermal bar and current development in a deep lake in spring

Features of thermal bar development in a fresh water reservoir during ice cover melting are investigated by means of mathematical modeling. It is shown that the presence of water with the temperature of maximum density (4°C) leads to two opposite effects. On the one hand, a thermal bar forms near the shore and moves to the center of the water basin; on the other hand, an eddy arises near the ice edge, which slows down the process.

Inter-annual variability and forecast of the spring ice phenomena on Lake Baikal and reservoirs of the Angara cascade

The study of interannual variability of ice phenomena on large inland waters, as well as the ice forecasts for them are of great practical importance for navigation because any ice on water interferes with navigation. This article presents a description of the developed approach to mapping the stages of melting and destruction of ice cover on Lake Baikal, and the Bratsk and Ust-Ilimsk reservoirs using data from AVHRR (Advanced Very High Resolution Radiometer) and shows examples of the ice condition maps in the spring. The AVHRR data, obtained for the period 1998–2015, made possible to analyze processes of the ice disappearance on aquatories of the South, Central and North parts of Lake Baikal, and the Bratsk and Ust'-Ilimsk reservoirs including determination of dates of the total ice disappearance (the first ice-free dates) on the reservoirs under investigation: the average, earliest and latest dates, and a range. It has been found that the interannual changes of these dates are the opposite to the inter-annual fluctuations of values of the Arctic Oscillation (AO) index, that allows using the AO index as a predictor in regional predictive dependencies. Using results of analysis of the AO index values, averaged over different time intervals, and the data series of the first dates of the ice-free situations we constructed regional equations allowing to foresee a character of the ice situation with the average earliness from 21 to 33 days. Tests of effectiveness of the proposed predictive dependencies demonstrated a good quality of forecasts of the dates when Southern, Central and Northern parts of Lake Baikal,as well the Bratsk and Ust-Ilimsk reservoirs become totally free of ice.

Ice berg cracking events as identified from underwater ambient noise measurements in the shallow waters of Ny-Alesund, Arctic

This paper presents the work carried out on the analysis of preliminary underwater ambient noise measurements in the shallow waters of Kongsfjorden fjord, Arctic in the summer season, in which the ice berg cracking noise is identified. In the summer period, the melting of ice cover is fast and hence the ice bergs are free to move and float in the ocean. Underwater ambient noise has been acquired in the Kongsfjorden fjord, Arctic sea on 19th July 2015 at 5 m water depth, where the ocean depth is 50 m. Due to the tensile cracks at the surface of the sea ice by thermal expansion, ice berg calving and bobbing occurred near the experiment site. Analysis of power spectra shows that ice berg calving noise falls in the frequency band 100 Hz–500 Hz and the ice berg bobbing noise falls in the frequency band 200 Hz–400 Hz.

Physico-chemical changes in two northern headwater lakes in the Northwest Territories, Canada, during winter to spring seasonal transitions

Abstract This note describes extended monitoring of two small headwater lakes in the Lockhart River in the Northwest Territories (Canada) during consecutive late winter and spring transitions. During these transitions, the lakes changed from isolated ice-bound water bodies to interconnected lakes, throughout which they exhibited similar modifications to their physico-chemical characteristics. Lake temperature changes were linked to ambient conditions, with warming after May 1 initiating snow- and ice melt inflows. Lake temperatures of 3 °C to 4 °C were measured in both lakes at the start of monitoring, which were maintained until a steady increase commenced in early June 1 as ice cover started to recede. This period was also associated with peak water levels and lake discharges. Conductivity decreases (~ 26 to ~ 12 μS/cm in the larger, shallower lake, Area 8, to 16 to 11 μS/cm in the smaller, deeper lake, Lake I1) commenced around mid-May, in advance of lake temperatures increases, and stabilized after approximately 3 weeks once lake ice had melted. The extent of lake dilution based on conductivity decreases (54–56% in Area 8, and 31% in Lake I1) was attributed primarily to the ice cover melt volume on each lake at the start of monitoring. DO concentrations were mostly undersaturated at the start of the monitoring period, with values below aquatic life guidelines; Area 8 reached saturation once lake conductivity stabilized, but Lake I1 was saturated once conductivity started to decrease. pH transitioned from slightly acidic (~ 5.8; below aquatic life guidelines) to circumneutral, with the transition slightly different between lakes depending on the lake conductivity transition.

The influence of wind on the development of a thermal bar and currents in reservoirs of different depths during ice cover melting

The influence of wind on the development of a thermal bar and currents in reservoirs of different depths during ice cover melting was studied using mathematical modeling. It is shown that the reservoir depth, as well as the wind velocity and direction, determine the behavior and lifetime of vortex structures in a reservoir that form on both sides of a thermal bar, as well as the location of their convergence zone and the 4°C isotherm. The dominant mechanisms of the instability of water masses in reservoirs of different depths under wind action on their surface are identified. It is shown that the higher wind speed is, the deeper the reservoir should be in order to get the zone of divergence of water masses close to 4°C isotherm. In this situation it is justified to use a classical interpretation of a thermal bar as a region of water convergence near 4°C, unlike shallow reservoirs where even slight winds lead to the significant divergence of these zones.