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Despite long‐term analyses of lake ice phenology globally, comparatively little is known about high‐elevation lakes, for which climate shifts are thought to be occurring faster than at lower elevations. Using a 36‐yr dataset (1983–2018) on alpine lakes (> 3000 m ASL) from the Green Lakes Valley, Colorado (GLV), we found that ice‐cover duration decreased by an average of ~ 24 d, due to both earlier ice‐off (9 d) and especially later ice‐on (15 d). Spring ice thickness also decreased by 0.88 cm yr−1. By comparison, ice‐cover duration in the GLV is decreasing ~ 50% faster than for Northern Hemisphere lakes (n = 215), which translates to an increase in open water duration ~ 2.5 times more in the GLV than the average of the Northern Hemisphere. Our analytical comparison demonstrated more rapid trends in this alpine region compared to lakes more broadly, and especially emphasized the influence of elevation on lake ice phenology.

International audience; Zooplankton can spend winter actively under the ice cover of lakes. However, dietary resources under lake ice are both quantitatively and qualitatively limited, and feeding might not be energetically rewarding for most zooplankton species. Many zooplankters are expected to fast throughout the winter, exhausting their previously accumulated fat storage. We hypothesised that only a fraction of the actively overwintering zooplankton contributes to an active food web under lake ice, leading to few trophic linkages within the planktonic community.2. Zooplankton habitats and feeding were investigated under the ice of Lake Onego. Zooplankton habitats and migrations were studied by coupling zooplankton sam-pling around the clock to measurements of particle movement using an acoustic Doppler current profiler. Secondly, fatty acid-specific stable isotope compositions were used to determine whether and which zooplankton fatty acids ultimately came from the assimilation of under-ice seston.3. The algal biomass was low under ice and mostly dominated by large diatoms. Copepods dominated the zooplankton community. Species present as late cope-podite and adult instars were confined to the deeper layers, while nauplii occupied the surface layer. Diel vertical migration by Cyclops was the most tangible ob-servation of persistent feeding under the ice. Previously accumulated fat storage represented most of zooplankton fatty acids, with few, yet detectable, fatty acids recently acquired by feeding under the ice.4. Although some zooplankton taxa maintained feeding activity under the ice of Lake Onego, the food source available beneath the ice was not sufficiently rewarding to leave an isotopic imprint upon the dominant fatty acids of bulk zooplankton. The seston fatty acids that were passed on to zooplankton from feeding under ice were not provided by diatoms, although they made up most of the phytoplank-ton biovolume. Instead, the zooplankton food web was supported by mixotrophic phytoplankton (i.e. cryptophytes and chrysophytes) that represented

The primary drivers of the recent accelerated warming of the Laurentian Great Lakes from 1982 to 2012 are explored through observations, remote sensing, and regional climate model experiments. The study focuses on the abrupt warming from 1997 to 1998 as a proxy for the long-term warming trend. The lake surface warming has been heterogeneous in both space and time, ranging from moderate warming in late spring over the southern lakes and shallow areas of the northern lakes to strong warming in mid-summer over the northern, deep lake areas. The greatest lake warming between 1997 and 1998 occurs over the deepest areas of Lake Superior during mid-summer, primarily arising from enhanced heat accumulation during the mild winter of 1997/1998 and amplified by greater incoming surface solar radiation and air temperature during the spring of 1998, according to model experiments. The mild winter condition, together with the increased solar radiation and air temperature during spring, causes an earlier onset of springtime stratification, resulting in enhanced heat absorption by surface water and thereby contributing to lake surface warming during the subsequent summer in 1998 compared with 1997. In contrast, the modest peak warming over southern lakes and shallow areas of northern lakes from 1997 to 1998 is a rapid response to synchronous increases in solar radiation and air temperature during May between the 2 yr. Changes in antecedent wintertime lake ice cover are found to have played only a minor role in the accelerated warming trend of the Laurentian Great Lakes.

Albedo products (MOD10A1, MYD10A1, and MCD43A3) from the Moderate Resolution Imaging Spectrometer (MODIS) have the potential to be integrated directly into lake ice models such as the Canadian lake ice model (CLIMo) to improve the simulation of freshwater break-up (ice-off). The high albedo of snow and lake ice has been shown to affect the timing of break-up. Therefore, the surface energy balance parameterization of CLIMo requires accurate estimates of albedo when modelling phenology. MOD10A1, MYD10A1, and MCD43A3 were evaluated against in situ snow and ice albedo observations taken over a partially snow-covered freshwater lake (Malcolm Ramsay Lake) near Churchill, Manitoba, during the ice growth period (15 February 2012 to 25 April 2012). The MODIS albedo products were then compared with the CLIMo's albedo parameterization during the ice break-up period. The MODIS albedo products MOD10A1, MYD10A1, and MCD43A3 retrieved snow and ice albedo with root mean square error values of 0.07, 0.08, and 0.06, respectively, compared with spatially averaged in situ albedo measurements during ice growth. MODIS albedo products compared with CLIMo's melting ice parameterization during the melt season indicate that CLIMo's albedo estimates have a mean difference of at least 0.14 compared with the MODIS retrievals during melt. The quality of the albedo retrievals over lake ice from MODIS and the need for more accurate albedo simulations during the melt season suggest that the assimilation of MODIS albedo products into CLIMo could be beneficial for the determination of break-up (ice-off) dates. Copyright © 2014 John Wiley & Sons, Ltd.

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.

A simple method to automatically measure the date of ice-on, the date of ice-off, and the duration of lake ice cover is described. The presence of ice cover is detected by recording water temperature just below the ice/water interface and just above the lake bottom using moored temperature sensors. The occurrence of ice-on rapidly leads to detectible levels of inverse stratification, defined as existing when the upper sensor records a temperature at least 0.1°C below that of the bottom sensor, whereas the occurrence of ice-off leads to the return of isothermal mixing. Based on data from 10 lakes over a total of 43 winter seasons, we found that the timing and duration of inverse stratification monitored by recording temperature sensors compares well with ice cover statistics based on human observation. The root mean square difference between the observer-based and temperature-based estimates was 7.1 d for ice-on, 6.4 d for ice-off, and 10.0 d for the duration of ice cover. The coefficient of determination between the two types of estimates was 0.93, 0.86, and 0.91, respectively. The availability of inexpensive self-contained temperature loggers should allow expanded monitoring of ice cover in a large and diverse array of lakes. Such monitoring is needed to improve our ability to monitor the progression of global climate change, and to improve our understanding of the relationship between climate and ice cover over a wide range of temporal and spatial scales.

The magnitude and variability in methane (CH4) emissions from lakes are uncertain due to limitations in methods for quantifying the patchiness of ebullition (bubbling). We present a field method to estimate an important and highly uncertain source: ebullition from northern lakes. We defined four classes of CH4 bubble clusters trapped in lake ice representing distinct types of biogenic ebullition seeps that differed in flux rate. Mean annual ebullition determined through long-term (up to 700 d) continuous flux measurements of 31 seeps in three Siberian and one Alaskan lake was (mean ± standard error, 4–10 seeps per class; g CH4 seep−1 y−1): A, 6 ± 4; B, 48 ± 11; C, 354 ± 52; Hotspot, 1167 ± 177. Discrete-seep ebullition comprised up to 87% of total emissions from Siberian lakes when diffusive flux and background and seep ebullition were considered together. Including seep ebullition increased previous estimates of lake CH4 emissions based on traditional methods 5- to 8-fold for Siberian and Alaskan lakes. Linking new ebullition estimates to an established biogeochemical model, the Terrestrial Ecosystem Model, increased previous estimates of regional terrestrial CH4 emissions 3- to 7-fold in Siberia. Assessment of the method revealed that ebullition seeps are an important component of the terrestrial CH4 budget. They are identifiable by seep type by independent observers; they are consistent predictors of flux rate in both Siberia and Alaska; and they allow quantification of what was previously a large source of uncertainty in upscaling CH4 emissions from lakes to regions.

These perspectives on climate change come largely from two views, i.e. that of a fish and fisheries ecologist with an autecological interest and that of a limnologist interested in long-term dynamics and change. Ideas about the thermal niche evolved from the late F. E. J. Fry's (University of Toronto) paradigm of fish response to environmental factors and the late G. Evelyn Hutchinson's (Yale University) formalization of the niche concept. In contrast, ideas about climatic change and variability have been shaped by long-term observation records from lakes around the northern hemisphere. The history of each set of ideas, i.e. the thermal niche of fishes and learning from nature's long-term dynamics, is briefly reviewed in the context of climatic change.

Paleolimnological approaches were used to assess the ecological and environmental implications of diatom assemblage compositional changes recorded over the last , 200 yr from four sites in the Lake of the Woods (LoW), Ontario, Canada. Comparisons between a reference site (Whitefish Bay) and three disturbed sites (Bigstone Bay, Paleolimnological Project site No. 1, and Forrest Island) provide insights into the effects that multiple stressors (dam construction, total phosphorus [TP] changes, and recent warming) have had on the ecology of this highly complex freshwater system. Overall patterns of diatom compositional changes from highresolution 210Pb-dated sediment cores revealed a strong temporal coherence ca. 1910 and then again over the last few decades among all sites. Hydromanagement activities at the turn of the 19th century and recent warming over the last few decades played key roles in the LoW diatom changes. Diatom compositional changes at all sites were significantly related to trends in nearby air temperature records over the past century and to changes in lake ice phenology over the past , 40 yr from Whitefish Bay. Turn-of-the-century hydromanagement activities do not appear to have had long-term effects on diatom-inferred TP (DI-TP), particularly at the disturbed sites. Clear decreases in DI-TP over the last few decades were evident at all sites, but at the reference site these decreases were well below pre-disturbance levels, which we link in part to recent warming. Substantial changes in climate will amplify the effects of multiple stressors on lake water properties that have major implications on algal communities.

A generalized empirical approach to the problem of the prediction of intermittent lake ice cover for climate- change studies is presented and applied to historical ice data from Muggelsee, a shallow lake in northern Germany that experiences either no ice cover, intermittent ice cover, or continuous ice cover, depending on the severity of the winter. The approach presented allows the total duration of ice cover in any winter to be estimated in terms of an air-temperature probability function. Advantages over traditional empirical methods based on the mean air temperature during a fixed period or on the computed number of negative degree-days are: (1) it is valid for both continuous and intermittent ice cover; (2) it is not necessary to specify a fixed time period for integration in advance; (3) the results emerge in time units, allowing them to be directly compared with the measured duration of ice cover without prior calibration; and (4) it is based on statistical properties of the ambient air temperature that are routinely forecast by climate models, making it easy to apply predictively. Regional climate model forecasts for northern Germany imply that for Muggelsee, the percentage of ice-free winters will increase from ,2% to over 60% by the end of the current century.

Data of ice cover for deep Alpine lakes contain relevant climatological information since ice cover and winter temperature are closely related. For the first time, ice cover data from 11 lakes on the Swiss plateau have been collected and analysed for the period 1901–2006. The ice cover data used stem from systematic registration by individuals or groups (fishermen, an ice club and lake security service) and from several national, regional and local newspapers. It is found that in the past 40 years, and especially during the last two decades, ice cover on Swiss lakes was significantly reduced. This is in good agreement with the observed increase in the winter temperature in this period. The trend of reduced ice cover is more pronounced for lakes that freeze rarely than for the lakes that freeze more frequently. This agrees well with the stronger relative decrease in the probability to exceed the sum of negative degree days (NDD) needed for freezing the lakes that rarely freeze. The ice cover data are related with the temperature measurements such as the sum of NDD of nearby official meteorological stations by means of binomial logistic regression. The derived relationships estimate the probability of a complete ice cover on a lake as function of the sum of NDD. The sums of NDD needed are well related to the average depth of the lake (rNDD–Depth = 0.85). Diagnosing lake ice cover on the basis of the sum of NDD is much better than a prediction on the basis of a climatological freezing frequency. The variance of lake ice cover that cannot be explained by the sum of NDD is important for judging the uncertainty associated with climate reconstruction on the basis of data on lake ice cover. Copyright © 2007 Royal Meteorological Society

Recent studies have shown that ice duration in lakes and rivers over the Northern Hemisphere has decreased over the 19th and 20th centuries in response to global warming. However, lake ice trends have not been well documented in Canada. Because of its size, considerable variability may exist in both freeze-up and break-up dates across the country. In this paper, results of the analysis of recent trends (1951–2000) in freeze-up and break-up dates across Canada are presented. Trends toward earlier break-up dates are observed for most lakes during the time periods of analysis which encompass the 1990s. Freeze-up dates, on the other hand, show few significant trends and a low degree of temporal coherence when compared with break-up dates. These results are compared with trends in autumn and spring 0 °C isotherm dates over the time period 1966–95. Similar spatial and temporal patterns are observed, with generally significant trends toward earlier springs/break-up dates over most of western Canada and little change in isotherm and freeze-up dates over the majority of the country in autumn. Strong correlations ( r> 0Ð5) between 0 °C isotherm dates and freeze-up/break-up dates at many locations across the country reveal the high synchrony of these variables. These results are also consistent with more recent observations of other cryospheric and atmospheric variables that indicate, in particular, a general trend toward earlier springs in the latter part of the 20th century. The results of this study provide further evidence of the robustness of lake ice as a proxy indicator of climate variability and change. Copyright  2006 John Wiley & Sons, Ltd.

The instantaneous daytime conductive heat flow through the snow on lake ice was derived from snow depth, temperature and density measurements made during the course of six winters at MST Pond in central Alaska. The MST Pond data for winter 2003-04 are compared with results for the same period at six other sites (Barrow, Nome, Amos Lakes, Fairbanks, Wasilla, Seward) in Alaska. The maximum heat flow at MST Pond has varied between -19-5 and -8·8 W m -2 . Each winter, the heat flow decreases as the total thickness of snow and ice increases with time. Superimposed on this trend are variations due to fluctuating air temperatures. The comparison of the MST Pond data with the other locations in Alaska reveals heat flow differences that reflect different weather conditions, particularly air temperature and wind, and the latter's effect on snow depth and density. Notwithstanding the regional differences, the heat flow values are of the same order of magnitude as those obtained for sea ice in the Arctic and Antarctica. The implications for the total winter conductive heat loss at large lakes and for regions where many small lakes cover a large proportion of the land are discussed.

Among the perennially frozen lakes of the Dry Valleys of South Victoria Land (Antarctica), some are dry-based, i.e. frozen to the bottom. One of these is studied here by a multiparametric investigation (isotopic composition in υ Da nd υ 18 O, ions, gas and ice texture analyses). A sediment layer about 10 cm thick appearing at a depth of 3Ð 5m is also studied by grain size, X-ray diffraction and scanning electron microscope analyses. The information retrieved indicates that this ice-block lake results from a build-up in two steps and explains how aeolian sediments were included as a layer into the ice. Copyright  2002 John Wiley & Sons, Ltd.

Various studies have shown that changes over time in spring ice-out dates can be used as indicators of climate change. Ice-out dates from 29 lakes in New England (USA) with 64 to 163 years of record were assembled and analysed for this study. Ice-out dates have become significantly earlier in New England since the 1800s. Changes in ice-out dates between 1850 and 2000 were 9 days and 16 days in the northern/mountainous and southern regions of New England respectively. The changes in the ice-out data over time were very consistent within each of the two regions of New England, and more consistent than four air-temperature records in each region. The ice-out dates of the two regions had a different response to changes in air temperature. The inferred late winter–early spring air-temperature warming in both regions of New England since 1850, based on linear regression analysis, was about 1.5°C. Published in 2002 by John Wiley & Sons, Ltd.

Records of freezeup and breakup dates for Grand Traverse Bay, Michigan, and Lake Mendota, Wisconsin, are among the longest ice records available near the Great Lakes, beginning in 185 1 and 1855, respectively. The timing of freezeup and breakup results from an integration of meteorological conditions (primarily air temperature) that occur before these events. Changes in the average timing of these ice-events are translated into changes in air temperature by the use of empirical and process-driven models. The timing of freezeup and breakup at the two locations represents an integration of air temperatures over slightly different seasons (months). Records from both locations indicate that the early winter period before about 1890 was - 15°C cooler than the early winter period after that time; the mean temperature has, however, remained relatively constant since about 1890. Changes in breakup dates demonstrate a similar 1.0-l .5”C increase in late winter and early spring air temperatures about 1890. More recent average breakup dates at both locations have been earlier than during 1890-l 940, indicating an additional warming of 1.2”C in March since about 1940 and a warming of 1 . 1°C in January-March since about 1980. Ice records at these sites will continue to provide an early indication of the anticipated climatic warming, not only because of the large response of ice cover to small changes in air temperature but also because these records integrate climatic conditions during the seasons (winter-spring) when most warming is forecast to occur. Future reductions in ice cover may strongly affect the winter ecology of the Great Lakes by reducing the stable environment required by various levels of the food chain.

Most adult sockeye salmon returning to Redfish Lake had spent two years in the ocean. Survival from smolt to returning adult at the lake ranged from 0.14 to 1.83%. The sex-ratio was nearly even. Survival of sockeye in the lake from potential egg deposition to smolt migration was usually less than 6%. In at least one year, smolts originating from kokanee and/or residual sockeye may have comprised a large proportion of the migration. There was little relationship between egg deposition and smolts produced. Sockeye salmon smolts migrated from Redfish Lake primarily from 1800 to 2400 hr. There was no consistent relationship between seasonal timing of the migration, lake ice cover, temperatures or flow of the outlet stream. The role of photoperiod in timing of the migration and the parr-smolt transformation is unclear. Growth of juvenile sockeye in the lake was inversely related to population density and age at migration was dependent upon first year growth in the lake. More than half the fish of a ye...

Top (Top et al. 1983, 1985) has found that in laboratory-grown ice and in Arctic ice floes 50% of the gas is retained in the ice upon freezing. As Top points out in his comment, Bari and Hallett (1974), whom we cite in Wharton et al. (1986), actually discussed how and when the ice-rejected dissolved gas gets back into the ice. We did not misquote this reference. Careful examination of the Bari and Hallett paper will reveal that in their experiments “bubbles cease abruptly” at freezing rates below about 3 pm sl. The freezing rate of the ice in the Antarctic lakes is estimated to be 30 cm yrl which corresponds to 0.009 pm s-l, well below the limit of bubble formation. The rate of freezing is an important variable in the exclusion of gas when water freezes. Hence, we do not expect a significant amount of gas to be retained in the Antarctic lake ice. This is consistent with observations of the ice cover. The results from laboratory experiments and Arctic floes reported by Top are not relevant since much higher freezing rates occur in these relatively thin ice environments. Indeed, the thick, stable, perennial ice cover of an Antarctic lake is unique in nature. Therefore, it is not too surprising that Arctic experience led Top to an incorrect conclusion. In conclusion, we feel that our original assumption of 100% exclusion is indeed representative of the conditions in the Antarctic lake. Top’s other comments are based on his incorrect estimate of the gas retention and hence do not apply.