Sea Ice Variability
- Complete Text
- Ecosystem Shifts
- What is Ocean Acidification?
- Sea Ice Variability
- Ocean Climate
- Aquatic Invasive Species
- Cold Water Corals and Sponges
Sea Ice Variability
A dynamic and ever changing component of ocean ecosystems, sea ice is one of the most important climatic variables and a key indicator of climate change. Along with other elements of polar ecosystems, sea ice is part of the global climate system and plays a crucial role in its regulation.
The area covered by sea ice grows in the winter and shrinks in the warmer months. Marine life is closely linked to this seasonal cycle. In addition, ice conditions are characterized by inter-annual variability in extent, duration, thickness, condition (i.e., fragility) and mobility, which are influenced by a range of factors or drivers. A decline in the extent of the ice-covered area will increase the amount of energy entering an ecosystem because sea ice reflects 80 percent of sunlight back into space while a dark ocean surface absorbs 90 percent of sunlight.
As global climate change alters this important component of marine ecosystems, there will be inevitable shifts in the marine food web, putting some species at risk while benefitting others. Changing sea ice can also have impacts on traditional subsistence cultures, coastal communities and other infrastructure, and human activities such as subsistence hunting and fishing, marine shipping, and oil and gas exploration and development. Understanding these changes and their potential impacts is critical toward the development of ecosystem approaches for marine resource management and mitigation and adaptation strategies for northern communities and various social and economic activities.
It is important to note that sea ice trends within a particular Large Ocean Management Area (LOMA) or other ocean region may differ from whole Arctic observations.
Sea Ice Variability in Canada's Oceans
Gulf of St. Lawrence:
Even though the Gulf of St. Lawrence has some of the warmest surface water in Atlantic Canada during the summer, the region also has the most southerly seasonal sea ice during winter.
Winter air temperatures over the Gulf are a key factor that drives the formation of sea ice cover, since cold air combined with strong winds extract heat from the ocean surface. The ice begins forming in early to late December and reaches its greatest extent and volume by early March. Since sea ice is more fragile during its early growth period, storms, thaws and other events can prevent the ice from reaching its full thickness and coverage potential for the season. Storm and thaws can also affect the timing of ice breakup in the spring.
In the winter of 2010, the Gulf of St. Lawrence had the least amount of ice coverage (virtually none) since the Canadian Ice Service began gathering data in 1969. The rare conditions were attributed to the warmest air temperatures on record in the Gulf since 1945. Ice-free winters are likely to occur more regularly due to climate change; however interannual variability will likely ensure there will be sea ice present during many winters over the next few decades.
Placentia Bay-Grand Banks:
Sea ice extent and duration on the Newfoundland and Labrador Shelf was below normal in 2010 for the 15th consecutive year, with the annual average reaching a 48-year record low. The International Ice Patrol of the U.S. Coast Guard reported that only one iceberg drifted south of 48º north latitude onto the Northern Grand Bank during 2010 compared with 1,204 in 2009.
Sea ice is influenced by the North Atlantic Oscillation (NAO), a large-scale variation in atmospheric pressure over the North Atlantic Ocean and a key indicator of climate conditions in the region. Variations in the NAO can directly or indirectly affect ice flow, ocean temperature, the strength of the Labrador Current, and the distribution and biology of marine species. A high NAO index generally indicates colder water temperatures, stronger northwest winds, cooler air temperatures, and heavy ice sea conditions, which was the pattern for the majority of the 1980s and 1990s.
In 2010, the NAO index hit a record low, weakening the outflow of Arctic air to the Northwest Atlantic. This led to broad-scale warming (relative to 2009) throughout the Northwest Atlantic from West Greenland to Baffin Island to Newfoundland.
Since the late 1990s, there has been a dramatic reduction in the extent and age of multi-year sea ice in the Arctic Ocean including the northwestern portion of the Beaufort Sea LOMA. A reduced expanse of multi-year ice implies a greater expanse of ice-free water in August and September. Summertime ice cover is the most important environmental control in the Beaufort marine ecosystem. Moreover, younger pack ice is thinner and weaker and may be more responsive to wind stress.
Therefore, a thinner arctic ice pack can influence ocean circulation and the distribution of surface salinity, with consequences for the marine food web. Although multi-year ice is clearly less common in the Arctic Ocean than two decades ago, observations reveal no trend in the thickness of first-year ice.
Other characteristics of sea ice conditions in the Beaufort LOMA during the last five years include:
- large inter-annual variations in the mean thickness of first-year ice;
- large inter-annual variations in summer ice concentration (the fraction of the sea surface covered by sea ice of any thickness);
- the duration of summertime ice clearance from the shelf varied by more than two months.
There are 30-year trends towards a reduced presence of sea ice over the Mackenzie Shelf, in Amundsen Gulf and in the Canadian sector of the Canada Basin. However, these trends are small relative to the magnitude of inter-annual variations.
Inter-annual variability makes it more challenging to identify the drivers of change in sea ice (i.e., natural variation versus climate change.)
Impacts of Sea Ice Variability
Gulf of St. Lawrence:
Variations in sea ice can have far-reaching impacts on marine ecosystems, including ocean characteristics (i.e., water layers and mixing), food webs, and the distribution, habitat and survival of marine life. For example, ice could have direct and indirect impacts on the survival of the 16 species of whales (cetaceans) and seven species of seals that inhabit the St. Lawrence Estuary and Gulf either seasonally or throughout the year. Changes in ice cover, freeze-up and melt patterns may affect the availability of zooplankton and other food resources for fish. Ice may limit access to the surface or reduce the available foraging habitat for some marine mammals while providing other species with a platform for breeding and resting. Ice movement could also lead to the entrapment of whales.
It is difficult to predict how marine mammals will respond to changing ice conditions. In the St. Lawrence Estuary and Gulf, a reduction in total ice cover and stability has the potential to:
- open up foraging areas that were previously not accessible;
- cause marine mammals to become more widely dispersed or alter their north-south distribution;
- cause seasonally resident cetaceans to spend more time in the Estuary and Gulf, increasing the potential for competition between Harp Seals, Beluga Whales and other cetaceans for zooplankton and fish species such as Capelin, Herring and cod;
- increase exposure to potential predation from Killer Whales, which generally try to avoid sea ice because it can entrap them or injure their large dorsal fin;
- likely cause the breeding population of Harp Seals to shift more towards the northern Gulf or even outside of the Gulf;
- favour an expansion in distribution and abundance of Grey Seals throughout the Gulf, and increase interactions with fisheries and the transmission of parasites to commercially important fish species;
- increase shipping opportunities or cause a shift in shipping patterns. Higher ship traffic would increase potential for vessels to strike marine mammals and increase ambient noise levels, which may have an impact on marine mammal communication, particularly among cetaceans.
Since 2002, the Joint Ocean Ice Studies (JOIS) has carried out an annual expedition to the Beaufort Gyre, a clockwise circulation (looking from above the North Pole) in the Beaufort Sea north of Alaska. This circulation is the result of a strong high-pressure system that creates winds over the region.
Since 2003, the surface waters of the Beaufort Gyre have been freshening (becoming less saline), a trend that has been linked to wind-induced convergence of low salinity water at the surface and to the melting of thick, multi-year ice. Reduced ice cover over the gyre means there is more open water. The darker open water surface absorbs more energy from the sun, causing the surface water to warm and reducing sea ice.
Since warmer water is less dense (lighter) than cold water, and fresher water is lighter than salty water, the ocean here is becoming increasingly stratified. Increased stratification reduces water column mixing and the movement of nutrients into the surface layer. It is in this sun-lit, near-surface zone that the foundation of the marine food web, phytoplankton, grows. Greater stratification has led to an increase in the smallest algae (picoplankton) in the Canada Basin, both in total amount and as a percentage of total phytoplankton and a decrease in larger nanoplankton, which has the potential to alter other parts of the food web.
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