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Lake Hazen, the High Arctic's largest lake, has received an approximately 10-fold increase in glacial meltwater since its catchment glaciers shifted from net mass gain to net mass loss in 2007 common era (CE), concurrent with recent warming. Increased glacial meltwater can alter the ecological functioning of recipient aquatic ecosystems via changes to nutrient budgets, turbidity and thermal regimes. Here, we examine a rare set of five high-resolution sediment cores collected in Lake Hazen between 1990 and 2017 CE to investigate the influence of increased glacial meltwater versus alterations to lake ice phenology on ecological change. Subfossil diatom assemblages in all cores show two major shifts over the past approximately 200 years including: (i) a proliferation of pioneering, benthic taxa at approximately 1900 CE from previously depauperate populations; and (ii) a rise in planktonic taxa beginning at approximately 1980 CE to present-day dominance. The topmost intervals from each sequentially collected core provide exact dates and demonstrate that diatom regime shifts occurred decades prior to accelerated glacial inputs. These data show that diatom assemblages in Lake Hazen are responding primarily to intrinsic lake factors linked to decreasing duration of lake ice and snow cover rather than to limnological impacts associated with increased glacial runoff.

Temperate lakes worldwide are losing ice cover but the implications for under‐ice thermal dynamics are poorly constrained. Using a 92‐year record of ice phenology from a temperate and historically dimictic lake, we examined trends, variability, and drivers of ice phenology and under‐ice temperatures. The onset of ice formation decreased by 23 days century−1, which can be largely attributed to warming air temperatures. Ice‐off date has become substantially more variable with spring air temperatures and cumulative February through April snowfall explaining over 80% of the variation in timing. As a result of changing ice phenology, total ice duration contracted by a month and more than doubled in interannual variability. Using weekly under‐ice temperature profiles for the most recent 36 years, we found that shorter ice duration decreased winter inverse stratification and was associated with an extended spring mixing period. We illustrate the limitations of relying on discrete ice clearance dates in our assumptions around under‐ice thermal dynamics by presenting high‐frequency under‐ice observations in two recent winters: one with intermittent ice cover and a year with slow spring ice clearance. Plain Language Summary: Lakes worldwide are losing ice cover in response to climate change. We used a rare and nearly century‐long data set of ice formation and ice clearance records to examine trends, variability, and drivers. We found that ice cover is getting substantially shorter and more variable with winter ice duration about a month shorter now than it was a century ago. Using under‐ice temperature measurements from the most recent three decades, we found differences in under‐ice temperatures affected by lake ice duration. Key Points: Ice duration and ice formation are getting shorter or occurring later, and both are increasing in interannual variabilityIce break up is not trending earlier, but interannual variability is increasingThis dimictic lake is at risk of transitioning toward monomixis in the near future [ABSTRACT FROM AUTHOR]

The ice phenology of alpine lakes on the Tibetan Plateau (TP) is a rapid and direct responder to climate changes, and the variations in lake ice exhibit high temporal frequency characteristics. MODIS and passive microwave data are widely used to monitor lake ice changes with high temporal resolution. However, the low spatial resolutions make it difficult to effectively quantify the freeze-melt dynamics of lakes. This work used Sentinel-1 synthetic aperture radar (SAR) data to derive highresolution ice maps (about 6 days), then with the aid of Sentinel-2 optical images to quantify freeze-melt processes in three typical lakes on the TP (e.g. Selin Co, Ayakekumu Lake, and Nam Co). The results showed that three lakes had an average annual ice period of 125–157 days and a complete ice cover period of 72–115 days, from 2018 to 2022. They exhibit different ice phenology patterns. Nam Co is characterized by repeated episodes of freezing, melting, and refreezing, resulting in a prolonged freeze-up period. Meanwhile, the break-up period of Nam Co lasts for a longer duration (about 19 days), and the break-up exhibits a smooth process. Similarly, Ayakekumu Lake showed more significant inter-annual fluctuations in the freeze-up period, with deviations of up to 28 days observed among different years. Compared to the other two lakes, Selin Co experienced a relatively short freeze-up and break-up period. In short, Sentinel-1 SAR data can effectively monitor the weekly and seasonal variations in lake ice on the TP. Particularly, this data facilitates quantification of the freeze-melt dynamics. [ABSTRACT FROM AUTHOR]

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Lake ice thickness (LIT) is one of the key climate variables in the lake ice domain, but there are currently large uncertainties in the retrieval of LIT. We present and validate a new LIT retrieval method that utilizes ICESat-2 data to assist CryoSat-2 echo peak selection, aiming to improve the accuracy of LIT retrieval and enable data acquisition without on-site measurements. The method involves screening out similar ICESat-2 and CryoSat-2 tracks based on time and space constraints. It also involves dynamically adjusting the range constraint window of CryoSat-2 waveforms based on the high-precision lake ice surface ellipsoid height obtained from ICESat-2/ATL06 data. Within this range constraint window, the peak selection strategy is used to determine the scattering interfaces between snow-ice and ice-water. By utilizing the distance between the scattering horizons, the thickness of the lake ice can be determined. We performed the ice thickness retrieval experiment for Baker Lake in winter and verified it against the on-site measurement data. The results showed that the accuracy was about 0.143 m. At the same time, we performed the ice thickness retrieval experiment for Great Bear Lake (GBL), which does not have on-site measurement data, and compared it with the climate change trend of GBL. The results showed that the retrieval results were consistent with the climate change trend of GBL, confirming the validity of the proposed method. [ABSTRACT FROM AUTHOR]

The rapid formation of glacial lakes is one of the most conspicuous landscape changes caused by atmospheric warming in glacierised regions. However, relatively little is known about the history and current state of glacial lakes in the High Arctic. This study aims to address this issue by providing the first inventory of glacial lakes in Svalbard, focusing in particular on the post-Little Ice Age evolution of glacial lakes and their typology. To do so, we used aerial photographs and satellite imagery together with archival topographic data from 1936 to 2020. The inventory comprises the development of 566 glacial lakes (146 km2) that were still in direct contact with glaciers during the period 2008–2012. The results show a consistent increase in the total area of glacial lakes from the 1930s to 2020 and suggest an apparent link between climatic and geological factors, and the formation of specific lake dam types: moraine, ice, or bedrock. We also detected 134 glacial lake drainage events that have occurred since the 1930s. This study shows that Svalbard has one of the highest rates of glacial lake development in the world, which is an indicator of the overall dynamics of landscape change in the archipelago in response to climate change.

The rapid formation of glacial lakes is one of the most conspicuous landscape changes caused by atmospheric warming in glacierised regions. However, relatively little is known about the history and current state of glacial lakes in the High Arctic. This study aims to address this issue by providing the first inventory of glacial lakes in Svalbard, focusing in particular on the post-Little Ice Age evolution of glacial lakes and their typology. To do so, we used aerial photographs and satellite imagery together with archival topographic data from 1936 to 2020. The inventory comprises the development of 566 glacial lakes (146 km2) that were still in direct contact with glaciers during the period 2008–2012. The results show a consistent increase in the total area of glacial lakes from the 1930s to 2020 and suggest an apparent link between climatic and geological factors, and the formation of specific lake dam types: moraine, ice, or bedrock. We also detected 134 glacial lake drainage events that have occurred since the 1930s. This study shows that Svalbard has one of the highest rates of glacial lake development in the world, which is an indicator of the overall dynamics of landscape change in the archipelago in response to climate change. [ABSTRACT FROM AUTHOR]

Study region: This study analyzed lake surface temperature (LST) trends and spatial distribution across 535 predominantly small to medium lakes across the North Slave Region (NSR) of the Northwest Territories (NWT), Canada. Study focus: The NWT is characterized by a vast number of lakes covering a significant portion of its spatial extent. However, there is limited knowledge of how LST responds to climate warming in this region. To address this, LST was analyzed in four distinct periods: open water season (OW), ice cover season (IC), and the transitional months of May (TM) and October (TO). LSTs from 1984 to 2021 were retrieved from a lake-specific satellite-derived LST dataset (North Slave LST). LST trend distribution and relationships were analyzed using the Mann-Kendall test and a multilinear regression model. New hydrological insights: The analysis revealed an overall increase in LST, with average rates (max) of 0.03 °C/year (0.05 °C/year), 0.03 °C/year (0.06 °C/year), and 0.13 °C/year (0.27 °C/year) for OW, TM, and TO, respectively accross study lakes. A faster rate of change was observed in October compared to other periods. Results indicated significant increases in LST for 411 lakes (77%) during OW, 418 lakes (78%) during TO, and 490 lakes (92%) during TM. The spatial distribution and magnitude of LST change were primarily influenced by geographical than morphometric properties. The analysis demonstrated later freeze-up (0.20 day/year) and earlier break-up (−0.17 day/year) of lake ice across the NSR.

Great Slave Lake (GSL), one of the world's largest and deepest lakes, has undergone an aquatic ecosystem transformation in response to twenty-first-century accelerated Arctic warming that is unparalleled in at least the past two centuries. Algal remains from four high-resolution palaeolimnological records retrieved from the West Basin provide baseline limnological data that we compared with historical phycological surveys undertaken on GSL between the 1940s and 1990s. We document the rapid restructuring of algal community composition ca 2000 CE that is consistent with recent increases in regional air temperature and declines in ice cover and wind speed, that collectively altered habitats for aquatic biota. This new limnological regime initiated the first observation of scaled chrysophytes and favoured the rapid proliferation of small planktonic cyclotelloid diatoms which replaced the long-established dominance of large filamentous Aulacoseira islandica in West Basin sedimentary records. Such abrupt transformations in the primary producers of this socioecologically valuable 'northern Great Lake' may have widespread implications for the entire food web with unknown consequences for aquatic ecosystem functioning and fisheries, which First Nations, Métis and other northern communities depend upon, pointing to the need for new studies. [ABSTRACT FROM AUTHOR]

The occurrence of harmful algal blooms (HABs) in coastal and inland waters has a significant impact on societies. This complex biogeophysical phenomenon becomes further complicated due to the impact of climate change. This review summarizes the research performed in recent years in the direction of climate change on three lake parameters, viz. lake temperature, precipitation, runoff, and lake ice, which impacts the lake ecology and, in turn, impacts the HABs. The present paper also reviews the research work related to the relationship between climate change and HABs. The purpose of this study is to provide the researchers with the opportunity to understand the current research in the direction of climate change and HABs so they can contribute effectively to one of the most important phenomena that will severely impact water quality in the future warmer climate, in coastal as well as inland water bodies. Furthermore, this work aims to discuss how HABs will change in the future warmer climate. [ABSTRACT FROM AUTHOR]

Antarctic lakes with perennial ice covers provide the opportunity to investigate in-lake processes without direct atmospheric interaction, and to study their ice-cover sensitivity to climate conditions. In this study, a numerical model – driven by radiative, atmospheric and turbulent heat fluxes from the water body beneath the ice cover – was implemented to investigate the impact of climate change on the ice covers from two Antarctic lakes: west lobe of Lake Bonney (WLB) and Crooked Lake. Model results agreed well with measured ice thicknesses of both lakes (WLB – RMSE= 0.11 m over 16 years of data; Crooked Lake – RMSE= 0.07 m over 1 year of data), and had acceptable results with measured ablation data at WLB (RMSE= 0.28 m over 6 years). The differences between measured and modeled ablation occurred because the model does not consider interannual variability of the ice optical properties and seasonal changes of the lake's thermal structure. Results indicate that projected summer air temperatures will increase the ice-cover annual melting in WLB by 2050, but that the ice cover will remain perennial through the end of this century. Contrarily, at Crooked Lake the ice cover becomes ephemeral most likely due to the increase in air temperatures.

Within Arctic deltas, surficial hydrologic connectivity of lakes to nearby river channels influences physical processes like sediment transport and ice phenology as well as biogeochemical processes such as photochemistry. As the Arctic hydrologic cycle is impacted by climate change, it is important to quantify temporal variability in connectivity. However, current connectivity detection methods are either spatially limited due to data availability constraints or have been applied at only a single time. Additionally, the relationship between connectivity and lake ice is still poorly quantified. In this study, we present a multitemporal classification of functional lake connectivity in the Colville River Delta, Alaska. We introduce a connectivity detection algorithm based on remote sensing of high sediment river water recharge that is expandable to other high sediment Arctic deltas. We compare results to three existing data sets, producing 64.4%, 75.8%, and 85.2% lake classification accuracy. Mismatches between the data sets are often due to inconsistencies in methodology or definition of connectivity. Connectivity varies temporally in about 10% of studied lakes and correlates strongly with discharge and lake elevation, supporting the idea that future changes in discharge will be a driver of changes in connectivity. Highly connected lakes start and end ice break up an average of 26 and 17 days earlier, respectively, compared to lakes that are poorly connected. Because spring and summer ice conditions drive Arctic lake photochemistry processes, our research suggests that surface connectivity is an important parameter to consider when studying biogeochemistry of Arctic delta lakes. Plain Language Summary: Arctic deltas contain a complex tapestry of channels and lakes. Lakes can be isolated from channels or connected to channels—either by feeder channels, other lakes, or by water movement over land during flooding. This connectivity is important because it impacts the movement of sediment, light penetration through water, and when lake ice forms and disappears. While we anticipate future changes in connectivity due to climate change, our ability to monitor connectivity is limited to individual deltas or single instances in time. Additionally, the relationship between lake ice and connectivity is poorly understood. In this study, we used a method based on satellite observations of sediment in water to examine lake connectivity variations within the Colville River Delta, Alaska. We found that most lakes stay connected or disconnected, but that about 10% of lakes have variable connectivity. These lakes are more likely to be connected when river discharge is high. Additionally, lake ice tends to break up earlier and last for a shorter period of time in connected lakes. Because lake ice conditions drive chemical interaction between sunlight and organic compounds in the water, connectivity is important to consider when studying the biology and chemistry of Arctic delta lakes. Key Points: We have developed an algorithm using optical properties of lakes and channels to detect lake‐to‐channel connectivity in an Arctic deltaWe show that this algorithm can be used to detect lakes where functional connectivity varies based on maximum summer dischargeDifferences in functional connectivity drive lake ice phenology, which is likely important for photochemical processes [ABSTRACT FROM AUTHOR]

Long‐term lake ice phenological records from around the Northern Hemisphere provide unique sensitive indicators of climatic variations, even prior to the existence of physical meteorological measurement stations. Here, we updated ice phenology records for 60 lakes with time‐series ranging from 107–204 years to provide the first re‐assessment of Northern Hemispheric ice trends since 2004 by adding 15 additional years of ice phenology records and 40 lakes to our study. We found that, on average, ice‐on was 11.0 days later, ice‐off was 6.8 days earlier, and ice duration was 17.0 days shorter per century over the entire record for each lake. Trends in ice‐on and ice duration were six times faster in the last 25‐year period (1992–2016) than previous quarter centuries. More extreme events in recent decades, including late ice‐on, early ice‐off, shorter periods of ice cover, or no ice cover at all, contribute to the increasing rate of lake ice loss. Reductions in greenhouse gas emissions could limit increases in air temperature and abate losses in lake ice cover that would subsequently limit ecological, cultural, and socioeconomic consequences, such as increased evaporation rates, warmer water temperatures, degraded water quality, and the formation of toxic algal blooms. Plain Language Summary: The timing of lake ice‐on and ice‐off has been observed for decades to centuries because of its importance to refrigeration, transportation, recreation, and cultural traditions. Further, the timing of lake ice is a sensitive indicator of climate as freshwater freezes at 0°C. In our study, we found that ice duration was more than two weeks shorter per century in 60 lakes distributed across the Northern Hemisphere. In the last 25‐year period, trends in ice‐on and duration were over six times faster than in previous quarter centuries. More extremely late ice‐on and early ice‐off years, in addition to years in which a lake did not freeze at all, contributed to this alarming rate of lake ice loss. Mitigation of greenhouse gas emissions is necessary to preserve the existence of annual lake ice cover within this century. Key Points: Lake ice‐on was 11 days later, ice‐off was 7 days earlier, and ice duration was 17 days shorter per century for each lakeTrends in ice‐on and ice duration were six times faster in the last 25‐year period (1992–2016) than previous quarter centuriesIncreased frequency of extreme events, including ice‐free years and short ice durations, were found in larger lakes and warmer regions [ABSTRACT FROM AUTHOR]

More than 50% of global lakes periodically freeze, and their lake ice phenology is sensitive to climate change. However, spatially detailed quantification of the changes in lake ice at the global scale is not available. Here, we map ice cover in >33,000 lakes throughout the North Temperate Zone (23.5°–66.5°N) using 0.55 million Landsat images from 1985 to 2020. Over this period, we found a remarkable reduction in median ice cover occurrence (ICO) (61% to 43%), which was strongly related to warming terrestrial mean surface temperatures (R2 = 0.94, p < 0.05). Lakes in Europe showed the most pronounced ice loss (median ICO decreased from 50% to 24%), and extensive lake ice losses were also detected in the northern US, and central and eastern Asia. An overall increase in ice cover was identified from P2 (1999–2006) to P3 (2007–2014) due to regional decreased temperatures associated with the "global warming hiatus." Thehigh‐resolution mapping of lake ice here provides essentialbaseline information whichcan be used to elucidate ice loss‐induced environmental and societal impacts. Plain Language Summary: Widespread reductions in lake ice have been detected recently worldwide, yet spatially detailed characterization of global lake ice is currently unavailable. Using 0.55 million Landsat satellite images from 1985 to 2020, we provide the first long‐term wall‐to‐wall mapping of lake ice cover over the entire Northern Temperate Zone, comprising >33,000 lakes representing 48% of the global lake area in total. We track spatially detailed changes in lake ice across the entire Northern Temperate Zone, and examine how ice change patterns have differed geographically and temporally in response to climate change. Key Points: We provide the first long‐term wall‐to‐wall mapping of lake ice cover over the entire Northern Temperate ZoneWe found a remarkable reduction in median ice cover occurrence (61‐43%)Extensive lake ice retreats were found in central and southern Europe, the northern US, and central and southeastern Asia [ABSTRACT FROM AUTHOR]

Lake ice phenology has been recorded for decades, providing us with long‐term records to investigate the impact of climate change in lakes since the Industrial Revolution. Here, we examine the trends and drivers of 18 lakes across the Northern Hemisphere, with 156–204 years of data, starting in the 1810s. We show that: (a) trends in ice phenology are faster than found by previous studies. Ice‐on is 11 days later per century, ice‐off is 9 days earlier per century, and ice cover duration is 19 days shorter per century; (b) there are significant breakpoints in the 1850s, 1870s, mid‐1890s, and mid‐1990s, after which trends in ice phenology are even faster, and associated with changing weather and climate; and (c) local air temperatures explain the most variation in ice phenology, on average 36.5%, followed by progressive climate change explaining around 17.5% on average, with teleconnection patterns explaining the least variation. Our findings support the assertion that broad‐scale climatic changes have led to more rapid lake ice loss in lakes distributed across the Northern Hemisphere, with potential widespread impacts on critical ecosystem services that lake ice provides. Plain Language Summary: Lake ice cover has been recorded for decades and has been shown to be sensitive to climatic change. Hence, we can use lake ice cover to investigate how climate change has affected lakes over the past ∼200 years. In this study, we explore 18 lakes across the Northern Hemisphere, with ice cover data starting in the 1810s. We find that ice‐on is increasingly later, ice‐off is earlier, and ice duration is shorter, with all these changes occurring at faster rates than previous studies showed. We discovered breakpoints in lake ice cover, after which the trends in lake ice phenology become faster than the trends before the breakpoints, and these breakpoints are related to changing local air temperatures and teleconnection patterns. Finally, we show that local air temperature influences the timing of ice‐on and ice‐off the most, followed by long‐term climate change and teleconnection patterns. Hence, we provide support for the statement that climate change has contributed to faster trends in ice phenology, with likely negative impacts on the important ecosystem services provided by lakes. Key Points: Trends in lake ice phenology are faster than shown in previous studies when including most recent dataSignificant breakpoints in ice phenology are associated with changing weather and climateWarmer air temperature explains most of the variation in later ice‐on and earlier ice‐off dates, in addition to shorter ice duration [ABSTRACT FROM AUTHOR]

Ice‐off dates on lakes are some of the longest phenological records in the field of ecology, and some of the best evidence of long‐term climatic change. However, there has been little investigation as to whether the date of ice‐off on a lake impacts spring and summer ecosystem dynamics. Here, I analyzed 274 years of long‐term data from eight north temperate lakes in two climate zones to address whether lakes have ecological memory of ice‐off in the subsequent summer. Five metrics were investigated: epilimnion temperatures, hypolimnion temperatures, hypolimnetic oxygen drawdown, water clarity, and spring primary productivity. The response of the metrics to ice‐off date were variable across latitude and lake type. The northern set of lakes stratified quickly following ice‐off, and early ice‐off years resulted in significantly warmer hypolimnetic temperatures. Oxygen depletion in the hypolimnion was not impacted by ice‐off date, likely because in late ice‐off years the lakes did not fully mix. In the southern lakes, ice‐off date was not correlated to the onset of stratification, with the latter being a more dominant control on hypolimnetic temperature and oxygen. The implications of these findings is that as ice‐off date trends earlier in many parts of the world, the lakes that will likely experience the largest changes in spring and summer ecosystem properties are the lakes that currently have the longest duration of lake ice. In considering a future with warmer winters, these results provide a starting point for predicting how lake ecosystem properties will change with earlier ice‐off. Plain Language Summary: Lake ice is disappearing around the world. This slow loss of winter is a clear sign of climate change, but does the date of ice‐off impact spring and summer lake processes? Untangling a memory effect of ice‐off from other factors, such as spring and summer weather, requires decades of monitoring data. Here, 274 years of lake records from eight lakes in two climate zones were analyzed to investigate whether lakes have ecological memory of ice‐off. The response of lake temperature, oxygen concentrations, and water clarity to ice‐off date were variable across latitude and lake size and type. It was found that when lakes stratify immediately following ice‐off, bottom water conditions have ecological memory of the timing of ice‐off. However, in lakes with a short duration of lake ice, this memory effect fades. The implication of this finding is that as ice‐off date trends earlier in many parts of the world, the lakes that will likely experience the largest changes in spring and summer lake ecosystem properties are the lakes that currently have the longest duration of lake ice. Key Points: Ice‐off date has variable impacts on ecosystem properties across lake type and climatic zoneLakes with a short duration of ice have little ecological memory of ice‐off dateWhen lakes stratify immediately following ice‐off, ice‐off date impacts summer ecosystem properties [ABSTRACT FROM AUTHOR]

Extreme climate events can have significant consequences on ecosystems and by extension human populations. Over 50 million of the world's lakes typically freeze each winter, and the absence of winter ice cover, in lakes where ice has historically been present, can be characterized as an extreme event. We quantified the effects of extreme climate events on lake ice cover using 78‐year ice records from 122 lakes to show that (1) extreme ice‐free years are becoming more frequent and severe, (2) winter air temperature is a significant predictor of ice cover that was driven by large‐scale climate oscillations, (3) extremes in temperature are closely related to extremes in ice cover, and (4) ice‐free years are forecasted to result in significant loss of ice‐cover in the future. Without drastic reductions in carbon emissions, we can expect the widespread loss of lake ice cover could have significant socioeconomic and biological implications. Plain Language Summary: Climate change is expected to have a large impact on humans and our natural systems. Freshwater lakes are an important resource and each year, millions around the world freeze during the winter months. However, climate change is expected to threaten the freezing of some of these lakes. We explored 122 lakes that typically freeze over winter and that had records of freeze/thaw since 1939. We asked, do extremes in winter air temperature affect extremes in lake ice cover and what would that mean for the future? Winter air temperature was found to closely predict ice‐free years for lakes. Years with abnormally hot winters were also years where many lakes remained ice‐free. Projecting into the future, we predicted that lakes will continue to experience more ice‐free years. With a reduction in carbon emissions, there will be a modest increase in ice‐free years, but if carbon emissions continue as they are currently, there could be a large increase in ice‐free lakes. This study highlights lake ice as another victim of climate change. The loss of lake ice will have impacts to natural systems and also socioeconomic implications for human populations that are dependent on it. Key Points: Observed recent increases in ice‐free years for 122 lakes since 1939Extremes in winter air temperature were observed to closely relate to extremes in ice‐free cover for lakesUsing climate change scenarios, ice‐free years for lakes are predicted to increase significantly in the next decades [ABSTRACT FROM AUTHOR]

Lake Hazen, the High Arctic's largest lake, has received an approximately 10-fold increase in glacial meltwater since its catchment glaciers shifted from net mass gain to net mass loss in 2007 common era (CE), concurrent with recent warming. Increased glacial meltwater can alter the ecological functioning of recipient aquatic ecosystems via changes to nutrient budgets, turbidity and thermal regimes. Here, we examine a rare set of five high-resolution sediment cores collected in Lake Hazen between 1990 and 2017 CE to investigate the influence of increased glacial meltwater versus alterations to lake ice phenology on ecological change. Subfossil diatom assemblages in all cores show two major shifts over the past approximately 200 years including: (i) a proliferation of pioneering, benthic taxa at approximately 1900 CE from previously depauperate populations; and (ii) a rise in planktonic taxa beginning at approximately 1980 CE to present-day dominance. The topmost intervals from each sequentially collected core provide exact dates and demonstrate that diatom regime shifts occurred decades prior to accelerated glacial inputs. These data show that diatom assemblages in Lake Hazen are responding primarily to intrinsic lake factors linked to decreasing duration of lake ice and snow cover rather than to limnological impacts associated with increased glacial runoff. [ABSTRACT FROM AUTHOR]

Antarctic lakes with perennial ice covers provide the opportunity to investigate in-lake processes without direct atmospheric interaction, and to study their ice-cover sensitivity to climate conditions. In this study, a numerical model – driven by radiative, atmospheric and turbulent heat fluxes from the water body beneath the ice cover – was implemented to investigate the impact of climate change on the ice covers from two Antarctic lakes: west lobe of Lake Bonney (WLB) and Crooked Lake. Model results agreed well with measured ice thicknesses of both lakes (WLB – RMSE= 0.11 m over 16 years of data; Crooked Lake – RMSE= 0.07 m over 1 year of data), and had acceptable results with measured ablation data at WLB (RMSE= 0.28 m over 6 years). The differences between measured and modeled ablation occurred because the model does not consider interannual variability of the ice optical properties and seasonal changes of the lake's thermal structure. Results indicate that projected summer air temperatures will increase the ice-cover annual melting in WLB by 2050, but that the ice cover will remain perennial through the end of this century. Contrarily, at Crooked Lake the ice cover becomes ephemeral most likely due to the increase in air temperatures. [ABSTRACT FROM AUTHOR]

Lake ice phenology is a climate-sensitive indicator. However, ground-based monitoring suffers from the limitations of human vision and the difficulty of its implementation in harsh environments. Remote sensing provides great potential to detect lake ice phenology. In this study, a new automated method was developed to extract lake ice phenology parameters by capturing the temporal pattern of the transitional water/ice phase using a parameterized time function. The method is based on Moderate-Resolution Imaging Spectroradiometer (MODIS) daily temperature products, which have unique potential for monitoring lake ice cover as a result of providing four observations per day at 1 km spatial resolution from 2002 to 2016. Three seasonally ice-covered lakes with different characteristics in different climate regions were selected to test the method during the period of 2002–2016. The temporal pattern of water/ice transition phase was determined on the basis of unfrozen water cover fraction extracted from the MODIS daily temperature data, and was compared with the MODIS snow and reflectance products and Landsat images. A good agreement with an R2 of above 0.8 was found when compared with the MODIS snow product. The annual variation of extracted ice phenology dates showed good consistency with the MODIS reflectance and AMSR-E/2 products. The approach was then applied to nine seasonally ice-covered lakes in northern China from 2002 to 2016. The strongest tendency towards a later freeze-up start date was revealed in Lake Qinghai (6.31 days/10 yr) among the lakes in Tibetan plateau, and the break-up start and end dates rapidly shifted towards earlier dates in Lake Hulun (−3.73 days/10 yr; −5.02 days/10 yr). The method is suitable for estimating and monitoring ice phenology on different types of lakes over large scales and has a strong potential to provide valuable information on the responses of ice processes to climate change.

Although perennially ice‐covered Antarctic lakes have experienced variable ice thicknesses over the past several decades, future ice thickness trends and associated aquatic biological responses under projected global warming remain unknown. Heat stored in the water column in chemically stratified Antarctic lakes that have middepth temperature maxima can significantly influence the ice thickness trends via upward heat flux to the ice/water interface. We modeled the ice thickness of the west lobe of Lake Bonney, Antarctica, based on possible future climate scenarios utilizing a 1D thermodynamic model that accounts for surface radiative fluxes as well as the heat flux associated with the temperature evolution of the water column. Model results predict that the ice cover of Lake Bonney will shift from perennial to seasonal within one to four decades, a change that will drastically influence ecosystem processes within the lake. Key Point: Future loss of permanent ice cover is predicted [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) lakes are sensitive to climate change due to ice-albedo feedback, but almost no study has paid attention to the ice albedo of TP lakes and its potential impacts. Here we present a recent field experiment for observing the lake ice albedo in the TP, and evaluate the applicability of the Moderate Resolution Imaging Spectroradiometer (MODIS) products as well as ice-albedo parameterizations. Most of the observed lake ice albedos on TP are <0.12, and the clear blue ice albedo is only 0.075, much lower than reported in the previous studies. Even that of ice covered with snow patches is only 0.212. MOD10A1 albedo product has the best agreement with observations, followed by those of MYD10A1. MCD43A3 product is consistently higher than the observations. Due to an error of snow flag and inconsistent time windows in MCD43A2 and MCD43A3, at certain times, the albedo of the ice without snow is even higher than that covered with snow. When the solar zenith angle is not considered, there is no significant correlation between the albedo and the ice surface temperature. None of the existing ice-albedo parameterizations can reproduce well the observed relationship of the albedo and surface temperature. [ABSTRACT FROM AUTHOR]

Monitoring and analyzing the (decreasing) trends in lake freezing provides important information for climate research. Multi-temporal satellite images are a natural data source to survey ice on lakes. In this paper, we describe a method for lake ice monitoring, which uses low spatial resolution (250m -1000m) satellite images to determine whether a lake is frozen or not. We report results on four selected lakes in Switzerland: Sihl, Sils, Silvaplana and St. Moritz. These lakes have different properties regarding area, altitude, surrounding topography and freezing frequency, describing cases of medium to high difficulty. Digitized Open Street Map (OSM) lake outlines are back-projected on to the image space after generalization. As a pre-processing step, the absolute geolocation error of the lake outlines is corrected by matching the projected outlines to the images. We define the lake ice detection as a two-class (frozen, non-frozen) semantic segmentation problem. Several spectral channels of the multi-spectral satellite data are used, both reflective and emissive (thermal). Only the cloud-free (clean) pixels which lie completely inside the lake are analyzed. The most useful channels to solve the problem are selected with xgboost and visual analysis of histograms of reference data, while the classification is done with non-linear support vector machine (SVM). We show experimentally that this straight-forward approach works well with both MODIS and VIIRS satellite imagery. Moreover, we show that the algorithm produces consistent results when tested on data from multiple winters. [ABSTRACT FROM AUTHOR]

Lakes are a prominent geographic feature in northern landscapes and play an important role in understanding regional climate systems. In order to better model changes within climate systems, it is important to study lake ice processes. Although the availability of records for lake ice through ground measurements has declined in recent years, the increased use of remote sensing provides an alternative to this. Using a preclassified snow and ice remote sensing product with a 500-m resolution, based on images from the Moderate Resolution Imaging Spectroradiometer (MODIS/MOD10A1), and the use of measured and reanalysis temperature data, this study evaluated lake ice phenology dates in connection to recent trends in temperature and 0 °C isotherms within Ontario and Manitoba between 2001 and 2014. Temperature trends indicated both regional warming and cooling, with significant cooling observed in Southern Ontario ( p < .05) and significant warming in Southern Manitoba ( p < .1) during the fall. Spatial analysis of the trends in the lake ice data showed significant clustering of significant trends in ice on dates ( p < .01). When analysing the trends in ice phenology in connection to the trends in temperature, it was found that 70% of lakes experienced a change in the ice on date with the expected change in temperature and 85% of lakes for ice off date. When shifting ice on and ice off dates are investigated in relation to 0 °C isotherms, it was seen that 80% of ice on dates and 100% of ice off dates shifted in sync with the isotherm dates. This demonstrates that the ice phenology of lakes in Ontario and Manitoba, Canada, is responding to short-term variability in temperature. The MODIS product could be used to investigate ice phenology on a large scale and contribute towards expanding existing records of ice phenology. Establishing long-term ice records could be a valuable asset for other research ranging from water balance studies to the response of lake biota under changing climate. [ABSTRACT FROM AUTHOR]

Several lake ice phenology studies from satellite data have been undertaken. However, the availability of long-term lake freeze-thaw-cycles, required to understand this proxy for climate variability and change, is scarce for European lakes. Long time series from space observations are limited to few satellite sensors. Data of the Advanced Very High Resolution Radiometer (AVHRR) are used in account of their unique potential as they offer each day global coverage from the early 1980s expectedly until 2022. An automatic two-step extraction was developed, which makes use of near-infrared reflectance values and thermal infrared derived lake surface water temperatures to extract lake ice phenology dates. In contrast to other studies utilizing thermal infrared, the thresholds are derived from the data itself, making it unnecessary to define arbitrary or lake specific thresholds. Two lakes in the Baltic region and a steppe lake on the Austrian–Hungarian border were selected. The later one was used to test the applicability of the approach to another climatic region for the time period 1990 to 2012. A comparison of the extracted event dates with in situ data provided good agreements of about 10 d mean absolute error. The two-step extraction was found to be applicable for European lakes in different climate regions and could fill existing data gaps in future applications. The extension of the time series to the full AVHRR record length (early 1980 until today) with adequate length for trend estimations would be of interest to assess climate variability and change. Furthermore, the two-step extraction itself is not sensor-specific and could be applied to other sensors with equivalent near- and thermal infrared spectral bands. [ABSTRACT FROM AUTHOR]

Lake ice phenology, i.e. the timing of freeze-up and break-up and the duration of the ice cover, is regarded as an important indicator of changes in regional climate. Based on the boundary data of lakes, some moderate-high resolution remote sensing datasets including MODIS and Landsat TM/ETM+ images and the meteorological data, the spatial-temporal variations of lake ice phenology in the Hoh Xil region during the period 2000-2011 were analyzed by using RS and GIS technology. And the factors affecting the lake ice phenology were also identified. Some conclusions can be drawn as follows. (1) The time of freeze-up start (FUS) and freeze-up end (FUE) of lake ice appeared in the late October-early November, mid-November-early December, respectively. The duration of lake ice freeze-up was about half a month. The time of break-up start (BUS) and break-up end (BUE) of lake ice were relatively dispersed, and appeared in the early February-early June, early May-early June, respectively. The average ice duration (ID) and the complete ice duration (CID) of lakes were 196 days and 181 days, respectively. (2) The phenology of lake ice in the Hoh Xil region changed dramatically in the last 10 years. Specifically, the FUS and FUE time of lake ice showed an increasingly delaying trend. In contrast, the BUS and BUE time of lake ice presented an advance. This led to the reduction of the ID and CID of lake. The average rates of ID and CID were-2.21 d/a and-1.91 d/a, respectively. (3) The variations of phenology and evolution of lake ice were a result of local and climatic factors. The temperature, lake area, salinity and shape of the shoreline were the main factors affecting the phenology of lake ice. However, the other factors such as the thermal capacity and the geological structure of lake should not be ignored as well. (4) The spatial process of lake ice freeze-up was contrary to its break-up process. The type of lake ice extending from one side of lakeshore to the opposite side was the most in the Hoh Xil region. [ABSTRACT FROM AUTHOR]

The physical dynamics of lake temperature and ice phenology are important in the modelling and management of temperate aquatic ecosystems. One-dimensional hydrothermal lake models have not been well evaluated in terms of how they simulate ice dynamics in particular. We chose four models (Hostetler, Minlake, Simple Ice Model or SIM and General Lake Model) to test and compare their performance modelling water temperature and ice dynamics using 16 years of field data from Harp Lake, an extensively studied inland lake in south-central Ontario. Each model produced satisfactory water temperature profiles over the simulated period, with small differences in the model performance. Model fits for ice phenology and ice thickness were, however, considerably lower than those for water temperature, with Minlake generating the best agreement with observed ice-on and ice-off dates as well as ice thickness, followed by SIM. The responses of lake ice dynamics to future climate scenarios were simulated by running each of the four models for 91 years, from 2010 to 2100. The predicted decrease in ice season length was significantly different among models, varying between 30 and 81 days, with an average of 48 days. Corresponding decreases in ice thickness varied between 0.11 and 0.20 m, averaging 0.17 m. This study demonstrates that uncertainty due to model performance and selection is considerable, and further testing and refinement of hydrothermal lake dynamic models are needed to improve predictive abilities for ice dynamics. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The study examined the formation, break-up, and duration of ice phenomena and ice cover on Lake Morskie Oko (1,395.4 metres above sea level (masl)), which is a representative of high mountain lakes in the Tatra Mountains located in the western Carpathian Mountains with a maximum elevation of 2,655 masl in the period 1971-2010. The maximum thickness was analyzed additionally. The lake covers an area of nearly 32 hectares and its greatest depth is 51.8 m. Its water is very clear with transparency reaching 12.5 m in depth. The trend towards a delayed freeze-up reaches 4.1 days per decade (d decade-1) (p < 0.01) and the ablation of ice on Lake Morskie Oko tends to take place earlier at a rate of 4.5 d decade (p < 0,05). The time period with ice cover on the lake has been getting shorter at a rate of 10 d decade-1 during the time frame of interest. Results of ice cover research on Lake Morskie Oko are consistent with recent studies which have shown that ice duration on lakes throughout the Northern Hemisphere has decreased over the last few decades and they serve as new evidence which confirms a warming of the climate in this section of Europe. [ABSTRACT FROM AUTHOR]

The Arctic cryosphere is a critically important component of the earth system, affecting the energy balance, atmospheric and ocean circulation, freshwater storage, sea level, the storage, and release of large quantities of greenhouse gases, economy, infrastructure, health, and indigenous and non-indigenous livelihoods, culture and identity. Currently, components of the Arctic cryosphere are subjected to dramatic change due to global warming. The need to document, understand, project, and respond to changes in the cryosphere and their consequences stimulated a comprehensive international assessment called 'SWIPA': Snow, Water, Ice, Permafrost in the Arctic. Some of the extensive key SWIPA chapters have been summarized and made more widely available to a global audience with multi-disciplinary interests in this Special Report of Ambio. In this article, an overview is provided of this Special Report in the context of the more detailed and wider scope of the SWIPA Report. Accelerated changes in major components of the Arctic cryosphere are documented. Evidence of feedback mechanisms between the cryosphere and other parts of the climate system are identified as contributing factors to enhanced Arctic warming while the growing importance of Arctic land-based ice as a contributor to global sea-level rise is quantified. Cryospheric changes will result in multifaceted and cascading effects for people within and beyond the Arctic presenting both challenges and opportunities. [ABSTRACT FROM AUTHOR]

Climatic changes to freshwater ice in the Arctic are projected to produce a variety of effects on hydrologic, ecological, and socio-economic systems. Key hydrologic impacts include changes to low flows, lake evaporation regimes and water levels, and river-ice break-up severity and timing. The latter are of particular concern because of their effect on river geomorphology, vegetation, sediment and nutrient fluxes, and sustainment of riparian aquatic habitats. Changes in ice phenology will affect a wide range of related biological aspects of seasonality. Some changes are likely to be gradual, but others could be more abrupt as systems cross critical ecological thresholds. Transportation and hydroelectric production are two of the socio-economic sectors most vulnerable to change in freshwater-ice regimes. Ice roads will require expensive on-land replacements while hydroelectric operations will both benefit and be challenged. The ability to undertake some traditional harvesting methods will also be affected. [ABSTRACT FROM AUTHOR]

Paleolimnological evidence from some Arctic lakes suggests that longer ice-free seasons have been experienced since the beginning of the nineteenth century. It has been inferred from some additional records that many Arctic lakes may have crossed an important ecological threshold as a result of recent warming. In the instrumental record, long-term trends exhibit increasingly later freeze-ups and earlier break-ups, closely corresponding to increasing air temperature trends, but with greater sensitivity at the more temperate latitudes. Broad spatial patterns in these trends are also related to major atmospheric circulation patterns. Future projections of lake ice indicate increasingly later freeze-ups and earlier break-ups, decreasing ice thickness, and changes in cover composition, particularly white-ice. For rivers, projected future decreases in south to north air-temperature gradients suggest that the severity of ice-jam flooding may be reduced but this could be mitigated by changes in the magnitude of spring snowmelt. [ABSTRACT FROM AUTHOR]

Abstract: Formation of lake ice is common in lakes located in mid and high latitudes. Lake ice plays a vital role in heat storage, controlling lake water temperature, survival of aquatic ecosystems, and maintaining the bio diversity of lakes. Significant warming in air temperature during the cold season (October–May) may lead to reduced ice cover of lakes and eventually disturb the lake''s seasonal dynamics. We examined the role of climate variability on lake ice phenology for small inland lakes in the Great Lakes region. The Variable Infiltration Capacity (VIC) model with a physically based lake algorithm was implemented to simulate long term (i.e. 1916–2007) changes in lake ice phenology, as described by the date of ice break-up, date of ice freeze-up, and number of ice-free days. Model performance was evaluated against observed lake ice phenology. A statistically significant increase (0.08–0.21°C) in air temperature resulted in a significant change (0.2–2.0days/decade) in lake ice freeze-up and break-up dates. While lake ice freeze-up was strongly associated (correlation>0.60) with air temperature of the early (October–December) cold season, lake ice break-up was highly associated (correlation=−0.80) with air temperature during the late (March–May) cold season. The number of ice-free days was affected by the temperature changes during the entire cold season. Lakes located in the southern part of the study domain experienced stronger trends in ice phenology than those located in the northern part. Inter-decadal to decadal scale variability in the number of ice-free days not associated with long-term trends in air temperature were largely driven by the Atlantic Multi-decadal Oscillation (AMO), El-Niño Southern Oscillation (ENSO), and Pacific Decadal Oscillation (PDO). [Copyright &y& Elsevier]

Summary: Ice duration has shortened and the ice-off date has become earlier for Lake Mendota from 1905 to 2000 as air temperatures have warmed and snowfall has increased. In addition, the ice record has cyclic components at inter-annual and inter-decadal scales. We examined the frequency domain relations between ice, local climate and the teleconnections, Southern Ocean Oscillation (SOI), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and Northern Pacific Index (NP), through a three-tiered analysis of coherence. The coherence results provide evidence of linear relations between the three levels at inter-annual and inter-decadal frequencies. Of the three local climate variables analyzed, namely temperature, snowfall and snow depth, temperature is the variable that most significantly affects ice duration and ice-off date, at both inter-annual and inter-decadal frequencies. The most significant effect of teleconnections on local climate are the effects of PDO on snowfall and snow depth, and SOI on temperature, at inter-annual frequencies, and the effect of NAO on snowfall at inter-decadal frequencies. The teleconnections that most significantly affect ice-cover duration and ice-off date, particularly at inter-decadal frequencies, are the PDO and the NAO. The influence of PDO on ice-cover appears to be transmitted through temperature, while the influence of the NAO appears to be transmitted through temperature and snowfall. A cascading set of links between teleconnections, local climate, and lake ice explain some, but not all, of the dynamics in these time series. [Copyright &y& Elsevier]

The Qinghai Lake is the largest inland lake in China. The significant difference of dielectric properties between water and ice suggests that a simple method of monitoring the Qinghai lake freeze-up and break-up dates using satellite passive microwave remote sensing data could be used. The freeze-up and break-up dates from the Qinghai Lake hydrological station and the MODIS L1B reflectance data were used to validate the passive microwave remote sensing results. The validation shows that passive microwave remote sensing data can accurately monitor the lake ice. Some uncertainty comes mainly from the revisit frequency of satellite overpass. The data from 1978 to 2006 show that lake ice duration is reduced by about 14-15 days. The freeze-up dates are about 4 days later and break-up dates about 10 days earlier. The regression analyses show that, at the 0.05 significance level, the correlations are 0.83, 0.66 and 0.89 between monthly mean air temperature (MMAT) and lake ice duration days, freeze-up dates, break-up dates, respectively. Therefore, inter-annual variations of the Qinghai Lake ice duration days can significantly reflect the regional climate variation. [ABSTRACT FROM AUTHOR]

Lakes are dominant landforms in the National Petroleum Reserve Alaska (NPRA) as well as important social and ecological resources. Of recent importance is the management of these freshwater ecosystems because lakes deeper than maximum ice thickness provide an important and often sole source of liquid water for aquatic biota, villages, and industry during winter. To better understand seasonal and annual hydrodynamics in the context of lake morphometry, we analyzed lakes in two adjacent areas where winter water use is expected to increase in the near future because of industrial expansion. Landsat Thematic Mapper and Enhanced Thematic Mapper Plus imagery acquired between 1985 and 2007 were analyzed and compared with climate data to understand interannual variability. Measured changes in lake area extent varied by 0.6% and were significantly correlated to total precipitation in the preceding 12 months ( p < 0.05). Using this relation, the modeled lake area extent from 1985 to 2007 showed no long-term trends. In addition, high-resolution aerial photography, bathymetric surveys, water-level monitoring, and lake-ice thickness measurements and growth models were used to better understand seasonal hydrodynamics, surface area-to-volume relations, winter water availability, and more permanent changes related to geomorphic change. Together, these results describe how lakes vary seasonally and annually in two critical areas of the NPRA and provide simple models to help better predict variation in lake-water supply. Our findings suggest that both overestimation and underestimation of actual available winter water volume may occur regularly, and this understanding may help better inform management strategies as future resource use expands in the NPRA. [ABSTRACT FROM AUTHOR]