Ice Across Biomes
Key finding overview
KEY FINDING 7. Declining extent and thickness of sea ice, warming and thawing of permafrost, accelerating loss of glacier mass, and shortening of lake-ice seasons are detected across Canada’s biomes. Impacts, apparent now in some areas and likely to spread, include effects on species and food webs.
This key finding is divided into five sections:
Ice is a defining feature of Canada’s ecosystems – permafrost (frozen ground) underlies almost half the country. Arctic sea ice (increasingly seasonal) extends across the North and along parts of the east coast and most Canadian lakes and many rivers are seasonally frozen. Outside of the huge ice sheets of Antarctica and Greenland, Canada has the largest area of glaciers in the world (200,000 km2), of which 75% is in the Arctic Archipelago.1
Ice ecosystems are important because they provide critical habitat for species adapted to living in, under, and on top of ice – from tiny one-celled organisms that live in the network of pores and channels within ice to polar bears. Sea ice helps regulate ocean circulation and air temperatures. Timing and duration of ice cover on rivers, lakes, and the sea are important factors in the types of plant and animal communities that water bodies support. Glaciers store fresh water and feed many of Canada’s largest rivers. Permafrost stores carbon and influences the structure of the landscape and storage and flow of water.
Loss of sea ice has major ecological consequences for biodiversity. Open water has lower refl ectivity than ice and holds more heat, increasing fog cover and reducing sunlight to near-shore plant and animal communities. Reduction of sea ice can expose shorelines to wave action and storms, leading to increased coastal erosion, as observed along the coast of the Beaufort Sea.9, 10 Species such as seals, polar bears,11 Arctic foxes,12 and some caribou herds13 that rely on ice for breeding or feeding habitat, and/or for movement across the landscape are profoundly affected by changes in sea-ice distribution and extent. Some seabirds and gulls – for example, the ivory gull, which has declined dramatically since the 1980s – depend on ice-edge habitat for survival.14, 15 Earlier break-up has been linked to shifts in trophic dynamics in some species assemblages – for example, reduced abundance of Arctic cod along with an increase in capelin.16 Earlier break-up has also been linked to a shift to earlier breeding in seabirds such as thick-billed murres and glaucous gulls.17-19 An emerging issue for Arctic marine biodiversity is the anticipated increase in shipping through an ice-free Arctic, which will expose sensitive marine ecosystems and biota to risk from invasive species released in ballast, increasing noise and contact with ships, and oil spills.11, 20
Changes in sea-ice extent in the northern hemisphere
The average of sea-ice extent for September (the month with the least ice cover) has declined over the Northern Hemisphere by 11.5% per decade since satellite measurements began in 1979.4, 5 Average ice extent declined for all seasons over this period.5 Ice is melting earlier in the year,6 and its age and distribution are changing. Multi-year ice is being lost, meaning that a greater proportion of ice is younger, thinner, and more subject to rapid break-up.7, 8
These changes in sea ice vary regionally. In the Canadian Arctic Archipelago, September ice extent declined by 9% per decade from 1979 to 2008, but the rate of decline varied from about 2% to 25% for different sub-regions.7 In Hudson Bay, summer ice (July through September) declined by almost 20% per decade from 1979 to 2006.5 For the Newfoundland and Labrador Shelves, ice extent declined in all seasons from 1979 to 2006, despite a period of greater ice cover in the 1990s.5 The Gulf of St. Lawrence, with no summertime ice, has experienced less change.5
Deterioration in southern Hudson Bay polar bear body condition
Some 4,000 polar bears, or about 20% of the total world population, range over sea ice of Hudson and James bays in the winter, feeding mainly on seals.22 When ice on these bays melts completely each summer, the bears come ashore where they spend up to five months (eight months for pregnant females) before the sea ice re-forms.23 The annual ice-free period has increased by almost three weeks since the mid-1970s.24 This has reduced the time that polar bears have on the ice to feed on seals and store fat for the summer.
The Southern Hudson Bay subpopulation is showing significant declines in body condition21 as well as declines in survival rates of all age and sex classes.25 Together these observations suggest that this subpopulation, which has been stable from the mid-1980s until at least 2003-2005, may decline in abundance in the future.25 The adjacent Western Hudson Bay subpopulation of polar bears has already declined from about 1,194 bears in 1987 to 935 in 2004, a decline of 22%.26 Coincident with this population decline were indications of declining body condition and reduced survival rates in some age classes.26, 27 The impacts on polar bears documented in Hudson Bay are not yet occurring throughout the polar bear’s range, though they may be a harbinger of changes to come as sea ice declines around the circumpolar Arctic. Currently polar bear trends are variable, with some subpopulations being stable, some increasing, and some not known.28
Mountain glaciers in southwestern Canada (including Peyto, Place, and Helm glaciers) show accelerating losses of ice starting in the mid-1970s, while Arctic glaciers (including Devon Ice Cap) began to show increased ice loss about 20 years later.29 The magnitude of the loss has been much greater for mountain glaciers than for the much colder, more massive Arctic glaciers and ice caps. Glaciers have also shrunk in northwestern Canada, in the Boreal and Taiga Cordillera ecozones+, with 22% loss in the Yukon30 (1958-60 to 2006-08) and 30% in the Nahanni Region31 (1982 to 2008). In both these areas, many smaller glaciers at low elevations have completely melted away.
Western Canadian mountain glaciers drain into river systems,32 regulating summer river flow and influencing ecosystem characteristics, such as water temperature and chemistry, that affect aquatic life. The influence of glaciers is especially important for cold-adapted species like salmonids.33-35
Lake and river ice
Greater variability from year to year, as well as overall trends toward shorter duration of lake and river ice, are closely linked to increasing spring and fall air temperatures.41-43 Ice is an important part of aquatic habitat and changes in ice cover alter a range of conditions, including length of the growing season for algae, water temperature, and levels of sediment and dissolved oxygen.44 Ice conditions also affect land animals by controlling access to the shoreline and to routes across lakes and rivers.45
Trends in the timing of spring ice break-up on large lakes
Lake-ice break-up is generally occurring earlier in the spring (1.8 days earlier per decade, on average). Ice freeze-up for the same set of large lakes (over 100 km2) shows a trend to later in the year (1.2 days per decade on average) for the majority of lakes – but less confidence is given to these fall measurements. The northern lakes showed the strongest rate of change, both in spring and in fall. This analysis is based on a combination of ground-based and remote-sensing data. Trends for the six most northerly lakes are based only on remote-sensing data from 1984 to 2004.49
Change in Great Lakes ice cover
Ice cover forms in near-shore areas of the Great Lakes in December and January and in deeper offshore waters in February and March.47 It affects the temperature of the lakes and the timing of spring overturn (the mixing of the top water layer to the bottom).47 This in turn has an impact on the availability of coldwater habitat for coldwater species such as lake trout.48 Less ice cover leads to earlier spring overturn, earlier warming of deep water, and less coldwater habitat.
Permafrost (rock or soil that remains below 0°C throughout the year) is warming across the northern half of Canada.50 Since the 1980s, shallow permafrost has warmed at a rate of 0.3 to 0.6°C per decade in the central and northern Mackenzie Valley in response to an increase in air temperature.51 In the Eastern and High Arctic, shallow permafrost has also warmed, by about 1°C per decade, mainly since the late 1990s.52 In southern parts of the permafrost zone, the area of frozen ground and frozen peatlands has shrunk or disappeared in several ecozones+ – for example, along the Alaska Highway in the Boreal Cordillera,53 in the northern peatlands of the Boreal Plains, and Boreal Shield54, 55 and in the peatlands of the eastern Taiga Shield56, 57 and the peatlands of Nunavik in the Arctic.58
Ecological consequences of changes in permafrost conditions are evident now, especially along the southern edges of its distribution in Canada. In colder regions of the country, it is likely that widespread impacts will occur in coming decades as frozen ground and the ice within it continue to warm. In subarctic and boreal regions, thawing permafrost and collapse of frozen peatlands may flood the land, replacing forest ecosystems with wet sedge meadows, bogs, ponds, and fens59, 60 – as is happening now in northern Quebec.57, 61, 62 In colder areas, on the other hand, deepening of the ground layer that thaws in the summer (the active layer) or melting of ground ice can lead to collapse and drainage of channels and wetlands63 or lower the water table and dry out the land,64, 65 altering plant species and affecting wildlife.64 There are signs of these ecological impacts now, especially in the Western Arctic.66-68
Permafrost temperatures in the central Mackenzie Valley
Permafrost in the south-central Mackenzie Valley (Fort Simpson and Northern Alberta) is likely being preserved by an insulating layer of peat.70 Frozen peatlands are, however, decreasing in the southern part of the Mackenzie Valley, with an estimated loss of 22% at four study sites over the latter half of the 20th century. Permafrost further north (in the Mackenzie Delta) has warmed at a rate of 0.1 to 0.2°C per decade at a depth of 15 m since the 1960s.71, 72 While these changes are consistent with changes in air temperature over the past few decades, changes in snow cover73, 74 and in wildfires75 are also affecting rates and locations of warming and thawing of permafrost.
Lichen and shrub-covered palsas surrounded by a pond resulting from thawing permafrost in a bog near the village of Radisson, Quebec
Permafrost temperatures at Alert, Nunavut
Trends at Alert are characteristic of the High Arctic – although air temperatures have been increasing since the 1980s, distinct warming of permafrost has only been observed since the mid-1990s. In the eastern Arctic51 and Nunavik (northern Quebec),76-78 shallow permafrost cooled up to the early 1990s in response to a period of cooler air temperatures, then it started to warm as air temperatures increased.
Changes in land cover with loss of permafrost, northern Quebec
Permafrost has thawed at a rapid rate over the past 50 years in northern Quebec and the southern permafrost limit has retreated about 130 km north.62 As a result, the landscape is changing from frozen peat plateaus and palsas (mounds of peat and soil containing ice lenses) which support dry, lichen-heath ecosystems and black spruce trees, to wetter landscapes characterized by ponds, fens, and bogs. The changes are widespread – from east of the southern part of James Bay north to the southern boundary of the “continuous” permafrost zone on the Ungava Peninsula, where, in a study area along the Boniface River, palsas decreased by 23% in area and permafrost-thaw ponds increased by 76% between 1957 and 2001.57 Lichen, an important forage for caribou, is expected to decrease in abundance along with this transition.
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