Numerous studies utilizing remote sensing imagery and other methods have documented that thermokarst lakes are undergoing varied hydrological transitions in response to recent climate changes, from surface area expansion to drainage and evaporative desiccation. Here, we provide a synthesis of hydrological conditions for 376 lakes of mainly thermokarst origin across high-latitude North America. We assemble surface water isotope compositions measured during the past decade at five lake-rich landscapes including Arctic Coastal Plain (Alaska), Yukon Flats (Alaska), Old Crow Flats (Yukon), northwestern Hudson Bay Lowlands (Manitoba), and Nunavik (Quebec). These landscapes represent the broad range of thermokarst environments by spanning gradients in meteorological, permafrost, and vegetation conditions. An isotope framework was established based on flux-weighted long-term averages of meteorological conditions for each lake to quantify water balance metrics. The isotope composition of source water and evaporation-to-inflow ratio for each lake were determined, and the results demonstrated a substantial array of regional and subregional diversity of lake hydrological conditions. Controls on lake water balance and how these vary among the five landscapes and with differing environmental drivers are assessed. Findings reveal that lakes in the Hudson Bay Lowlands are most vulnerable to evaporative desiccation, whereas those in Nunavik are most resilient. However, we also identify the complexity in predicting hydrological responses of these thermokarst landscapes to future climate change.
Lake-rich northern permafrost landscapes are sensitive to changing climate conditions, but ability to track real-time and potentially multiple hydrological responses (e.g. lake expansion, drawdown, drainage) is challenging due to absence of long-term, sustainable monitoring programs in these remote locations. Old Crow Flats (OCF), Yukon, is a Ramsar Wetland of International Importance where concerns about low water levels and their consequences for wildlife habitat and traditional ways of life prompted multidisciplinary studies during the International Polar Year (2007–2008) and led to the establishment of an aquatic ecosystem monitoring program. Here, we report water isotope data from 14 representative thermokarst lakes in OCF, the foundation of the monitoring program, and time-series of derived metrics including the isotope composition of input waters and evaporation-to-inflow ratios for a 13 year period (2007–2019). Although the lakes spanned multiple hydrological categories (i.e. rainfall-, snowmelt- and evaporation-dominated) based on initial surveys, well-defined trends from application of generalized additive models and meteorological records reveal that lakes have become increasingly influenced by rainfall, and potentially waters from thawing permafrost. These sources of input have led to more positive lake water balances. Given the documented role of rainfall in causing thermokarst lake drainage events in OCF and elsewhere, we anticipate increased vulnerability of lateral water export from OCF. This study demonstrates the value of long-term isotope-based monitoring programs for identifying hydrological consequences of climate change in lake-rich permafrost landscapes.
Old Crow Flats is a 5600 km 2 glaciolacustrine plain that straddles the forest-tundra ecotone in northern Yukon. Continuous taiga corridors occur in the entrenched river valleys, where annual mean ground temperatures (T g ) at the depth of zero annual amplitude at two locations were À3.1 and À4.0ºC in 2013. On the Flats, the vegetation cover is patchy, and T g varied between À5.1 and À2.6ºC. Annual mean near-surface permafrost temperatures (T ps ) measured on the Flats between 2008 and 2011 in patches of taiga, tall shrubs and low shrubs were correlated with local snow depth. Snow depth was controlled by vegetation height if the snow supply was not limited, for example, where low shrubs and large lakes dominate the landscape. In this setting, snow depths and, hence, T ps in taiga patches were higher (À2.6 to À2.9ºC) than in the surrounding shrub vegetation (À3.5 to À5.5ºC). Where taiga patches were more extensive, redistributed snow was trapped at the patch edge and T ps in taiga was lower (À4.1 to À4.3ºC) than in the surrounding shrub patches (À3.2 to À3.6ºC). The permafrost temperature field is heterogeneous under patchy vegetation in the forest-tundra ecotone. Our data suggest that it is governed by both the snow-holding capacity of local vegetation patches and the spatial configuration of vegetation in the surrounding landscape, which controls snow supply.
Evidence from remote sensing studies suggests that the frequency of thermokarst lake drainage events is increasing in response to climate change, but the consequences of these changes on the limnology of remaining waterbodies remain unknown. Here, we utilize a multiparameter paleolimnological record and post-drainage water isotope and chemistry monitoring to characterize the limnological evolution of Zelma Lake in Old Crow Flats, Yukon. During the early part of the record (~1678 to 1900 CE), analysis of geochemical variables and algal pigments indicate relatively stable limnological conditions. Abruptly beginning at~1900, Zelma Lake experienced a 40 year phase of reduced production, likely resulting from thermokarst shoreline expansion and associated increases in turbidity and low light availability. This was followed by~70 years of increasing production, likely from the stabilization of shorelines combined with a warming climate. Zelma Lake catastrophically drained in June 2007. Post-drainage conditions were characterized by intense eutrophication marked by increases in nutrient and major ion concentrations and the unprecedented occurrence of okenone and diatoxanthin pigments. Comparison to the post-drainage paleolimnological record from another thermokarst lake in Old Crow Flats indicates that a sharp increase of production is likely a common outcome of thermokarst lake drainage, yet intensity differs owing to site-specific catchment characteristics.Key words: climate change, thermokarst lakes, paleolimnology, limnology, lake drainage.Résumé : La preuve obtenue des études de télédétection suggère que la fréquence des évé-nements de drainage de lacs thermokastiques augmente en réponse au changement climatique, mais les conséquences de ce changement sur la limnologie des plans d'eau restant ne sont pas connues. Ici, nous utilisons un rapport paléolimnologique à multiples paramètres et la surveillance isotopique et chimique de l'eau postdrainage afin de caractériser l'évolu-tion limnologique du lac Zelma, à Old Crow Flats au Yukon. Pendant la première période faisant l'objet du rapport (~1678 à 1900 notre ère), l'analyse des variables géochimiques et des pigments algaires indiquent des conditions limnologiques relativement stables. Brusquement débutant~1900, le lac Zelma a subi une phase de 40 ans de production réduite, probablement en raison de l'expansion du rivage thermokarstique et des augmentations de la turbidité et de la faible luminosité disponible qui y sont associées. Il s'en suivit~70 ans de production accrue, probablement en raison de la stabilisation du rivage combinée avec le réchauffement du climat. Le lac Zelma s'est vidé de façon catastrophique en juin 2007.
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