Regional Assessment of GCM-Simulated Current Climate over Northern Canada

Several international Global Climate Models (GCMs) are evaluated on their ability to simulate the mean values and spatial variability of current (1961–90) temperature and precipitation over four regions across Canada’s North. A number of observed climate data sets for Arctic Canada are also assessed. Results reveal a close correspondence, particularly for temperature, among the four observed climate data sets assessed. However, the various GCM simulations of this observed climate show considerable inter-regional and seasonal variability, with temperature more accurately simulated than precipitation. Temperature findings indicate that the British HadCM3, German ECHAM4, and Japanese CCSR-98 models best replicate annual and seasonal values over all sub-regions. The Canadian CGCM2 and U.S. NCAR-PCM models have intermediate accuracy, and the Australian CSIRO-Mk2b and U.S. GFDL-R30 models are least representative. Temperature simulations from the various GCMs collectively display a similar degree of accuracy over all sub-regions, with no clear evidence of superiority in any given area. Precipitation, conversely, is accurately simulated by the majority of models only over northern Quebec/Labrador. All GCMs substantially overestimate annual and seasonal precipitation amounts in the western and central Canadian Arctic.Plusieurs modèles de climats du globe (MCG) internationaux ont été évalués quant à leur aptitude à simuler les valeurs moyennes et la variabilité spatiale de températures et de précipitations récentes (1961-1990) dans quatre régions du Nord canadien. Certains ensembles de données sur le climat observé dans l’Arctique canadien sont également évalués. Les résultats révèlent une correspondance étroite, surtout pour ce qui est de la température, entre les quatre ensembles de données de climats observés qui font l’objet d’une évaluation. Cependant, les diverses simulations de MCG quant au climat observé affichent une grande variabilité entre les régions et les saisons, les températures faisant l’objet de simulations plus précises que les précipitations. Les constatations en matière de précipitations laissent supposer que les modèles HadCM3 britannique, ECHAM4 allemand et CCSR-98 japonais répliquent mieux les valeurs annuelles et saisonnières dans toutes les sous-régions. Pour leur part, les modèles CGCM2 canadien et NCAR-PCM américain présentent une exactitude intermédiaire, tandis que les modèles CSIRO-Mk2b australien et GFDL-R30 américain sont les modèles les moins représentatifs. Ensemble, les simulations de températures des divers modèles MCG affichent un degré semblable d’exactitude dans toutes les sous-régions, sans qu’il n’y ait de modèle nettement supérieur dans une région donnée. Réciproquement, les précipitations sont simulées avec exactitude par la majorité des modèles dans le nord du Québec et le Labrador seulement. Tous les MCG surestiment, de manière substantielle, les quantités de précipitations annuelles et saisonnières dans l’ouest et dans le centre de l’Arctique canadien

Shifts in Plankton, Nutrient and Light Relationships in Small Tundra Lakes Caused by Localized Permafrost Thaw

Tundra lakes located in the Mackenzie Delta uplands, NWT, Canada, are increasingly being affected by permafrost thaw in the form of shoreline retrogressive thaw slumping. This form of thaw-induced disturbance is used as a surrogate indicator of landscape-related disturbance linked to regional climate warming. We compared 22 lakes, half affected by thaw slumping and half unaffected, to determine whether water column nutrient concentrations, light availability, and plankton biomass differed between these two lake types. Total phosphorus (TP), total dissolved nitrogen (TDN), dissolved organic carbon (DOC), and chlorophyll a concentrations were higher in unaffected lakes than in slump-affected lakes. Absorbance related to water colour of both UV and photosynthetically active radiation in the water column was also higher in unaffected lakes, but bacterioplankton abundance was not different between lake types. UV light absorbance was found to be the best predictor of pelagic chlorophyll a concentrations in unaffected lakes, whereas TDN (and to a lesser extent TP) were the best predictors of pelagic chlorophyll a in slump-affected lakes. These findings indicate that slumping arising from permafrost thaw produces a shift in tundra lake nutrient, light, and phytoplankton relationships. Given the projections of continued warming, this result has significant implications for the future biogeochemical and ecological states of Arctic tundra lakes.Les lacs de toundra situés dans les hautes terres du delta du Mackenzie, dans les Territoires du Nord-Ouest, au Canada, sont de plus en plus touchés par le dégel du pergélisol en ce sens qu’il y a glissement régressif du littoral dû au dégel. Cette forme de perturbation attribuable au dégel sert d’indicateur auxiliaire en matière de perturbation du paysage liée au réchauffement climatique de la région. Nous avons comparé 22 lacs, dont la moitié était touchée par le glissement dû au dégel et l’autre moitié ne l’était pas, afin de déterminer si les concentrations en nutriments des colonnes d’eau, la disponibilité lumineuse et la biomasse du plancton différaient entre ces deux types de lacs. Les concentrations de phosphore total (PT), d’azote dissous total (ADT), de carbone organique dissous (COD) et de chlorophylle a étaient plus élevées dans les lacs non touchés quand dans les lacs où il y avait glissement du littoral. L’absorbance liée à la couleur de l’eau du rayonnement actif photosynthétique et du rayonnement actif ultraviolet dans les colonnes d’eau était également plus élevée dans les lacs non touchés, mais l’abondance du bactérioplancton ne différait pas d’un type de lac à l’autre. On a déterminé que l’absorbance de lumière ultraviolette était le meilleur prédicteur de concentrations de chlorophylle a pélagique dans les lacs non touchés, tandis que l’ADT (et le PT, dans une moindre mesure) constituaient les meilleurs prédicteurs de chlorophylle a pélagique pour ce qui est des lacs faisant l’objet d’un glissement. Ces constatations indiquent que le glissement attribuable au dégel du pergélisol altère les relations qui existent entre les nutriments, la lumière et le phytoplancton des lacs de toundra. Compte tenu des projections à l’égard d’un réchauffement continuel, ce résultat revêt d’importantes incidences sur les états biogéochimiques et écologiques des lacs de la toundra arctique

Transitions in Arctic ecosystems: ecological implications of a changing hydrological regime

Numerous international scientific assessments and related articles have, during the last decade, described the observed and potential impacts of climate change as well as other related environmental stressors on Arctic ecosystems. There is increasing recognition that observed and projected changes in freshwater sources, fluxes, and storage will have profound implications for the physical, biogeochemical, biological and ecological processes and properties of Arctic terrestrial and freshwater ecosystems. However, a significant level of uncertainty remains in relation to forecasting the impacts of an intensified hydrological regime and related cryospheric change on ecosystem structure and function. As the terrestrial and freshwater ecology component of the Arctic Freshwater Synthesis we review these uncertainties and recommend enhanced coordinated circumpolar research and monitoring efforts to improve quantification and prediction of how an altered hydrological regime influences local, regional and circumpolar-level responses in terrestrial and freshwater systems. Specifically, we evaluate i) changes in ecosystem productivity; ii) alterations in ecosystem-level biogeochemical cycling and chemical transport; iii) altered landscapes, successional trajectories and creation of new habitats; iv) altered seasonality and phenological mismatches; and, v) gains or losses of species and associated trophic interactions. We emphasize the need for developing a process-based understanding of inter-ecosystem interactions, along with improved predictive models. We recommend enhanced use of the catchment-scale as an integrated unit of study, thereby more explicitly considering the physical, chemical and ecological processes and fluxes across a full freshwater continuum in a geographic region and spatial range of hydro-ecological units (e.g., stream-pond-lake-river-near shore marine environments)

Arctic system on trajectory to new state

The Arctic system is moving toward a new state that falls outside the envelope of glacial-interglacial fluctuations that prevailed during recent Earth history. This future Arctic is likely to have dramatically less permanent ice than exists at present. At the present rate of change, a summer ice-free Arctic Ocean within a century is a real possibility, a state not witnessed for at least a million years. The change appears to be driven largely by feedback-enhanced global climate warming, and there seem to be few, if any processes or feedbacks within the Arctic system that are capable of altering the trajectory toward this “super interglacial” state

Effects of Ultraviolet Radiation and Contaminant-related Stressors on Arctic Freshwater Ecosystems

Climate change is likely to act as a multiple stressor, leading to cumulative and/or synergistic impacts on aquatic systems. Projected increases in temperature and corresponding alterations in precipitation regimes will enhance contaminant influxes to aquatic systems, and independently increase the susceptibility of aquatic organisms to contaminant exposure and effects. The consequences for the biota will in most cases be additive (cumulative) and multiplicative (synergistic). The overall result will be higher contaminant loads and biomagnifi-cation in aquatic ecosystems. Changes in stratospheric ozone and corresponding ultraviolet radiation regimes are also expected to produce cumulative and/or synergistic effects on aquatic ecosystem structure and function. Reduced ice cover is likely to have a much greater effect on underwater UV radiation exposure than the projected levels of stratospheric ozone depletion. A major increase in UV radiation levels will cause enhanced damage to organisms (biomolecular, cellular, and physiological damage, and alterations in species composition). Alloca-tions of energy and resources by aquatic biota to UV radiation protection will increase, probably decreasing trophic-level productivity. Elemental fluxes will increase via photochemical pathways

Evolution and magnitude of spatial patterns in the winter cover of temperate lakes

The evolution of the winter cover of lakes in Southern Ontario, Canada, is described and explained in great detail with emphasis on spatial patterns. Shore to centre trends of each cover component, snow, white ice, black ice and total ice are identified and the evolution of those trends followed throughout the winter of 1976‑77. Total ice tended to be relatively consistent spatially but snow and white ice consistently decreased in thickness away from lake margins while black ice increased in thickness in the same direction. The implications of the spatial variability including the temporal variation of the spatial variability are discussed notably with respect to the design of lake cover sampling programs. Sampling guidelines were sug­gested which take into account differences between the cover components and changes during a winter