More than half of the Arctic region is comprised of ocean. Many arctic life forms rely on productivity from the sea, which is highly climate-dependent. Climate variations have profound influences on marine animals. For example, the climate-related collapse of capelin in the Barents Sea in 1987 had a devastating effect on seabirds that breed in the area. And years with little or no ice in the Gulf of St. Lawrence in Canada (1967, 1981, 2000, 2001, 2002) resulted in years with virtually no surviving seal pups, when in other years, these numbered in the hundreds of thousands.

Polar Bears

Polar bears are dependent on sea ice, where they hunt ice-living seals and use ice corridors to move from one area to another. Pregnant females build their winter dens in areas with thick snow cover on land or on sea ice. When the females emerge from their dens with their cubs in spring, the mothers have not eaten for five to seven months. Their seal hunting success, which depends upon good spring ice conditions, is essential for the family's survival. Changes in ice extent and stability are thus of critical importance, and observed and projected declines in sea ice are very likely to have devastating consequences for the polar bear. The earliest impacts of warming would be expected to occur at the southern limits of the bears' distribution, such as James and Hudson Bays in Canada, and such impacts have already been documented in recent years. The condition of adult polar bears has declined during the last two decades in the Hudson Bay area, as have the number of live births and the proportion of first-year cubs in the population. Polar bears in that region suffered 15% declines in both average weight and number of cubs born between 1981 and 1998. Later formation of sea ice in autumn and earlier break-up in spring means a longer period of annual fasting for female polar bears, and their reproductive success is tightly linked to their fat stores. Females in poor condition have smaller litters and smaller cubs that are less likely to survive. Climate change is also likely to increase bear deaths directly. For example, increased frequency and intensity of spring rains is already causing some dens to collapse, resulting in the death of females and cubs. Earlier spring break-up of ice could separate traditional den sites from spring feeding areas, and young cubs cannot swim long distances from dens to feeding areas. Polar bears are unlikely to survive as a species if there is an almost complete loss of summer sea-ice cover, which is projected to occur before the end of this century by some climate models. The only foreseeable option that polar bears would have is to adapt to a land-based summer lifestyle, but competition, risk of hybridization with brown and grizzly bears, and increased human interactions would then present additional threats to their survival as a species. The loss of polar bears is likely to have significant and rapid consequences for the ecosystems that they currently occupy.

Ice-dependent Seals

Ice-dependent seals, including the ringed seal, ribbon seal, and bearded seal, are particularly vulnerable to the observed and projected reductions in arctic sea ice because they give birth to and nurse their pups on the ice and use it as a resting platform. They also forage near the ice edge and under the ice. Ringed seals are likely to be the most highly affected species of seal because all aspects of their lives are tied to sea ice. They require sufficient snow cover to construct lairs and the sea ice must be stable enough in the spring to successfully rear young. Earlier ice break-up could result in premature separation of mothers and pups, leading to higher death rates among newborns.

Adapting to life on land in the absence of summer sea ice seems highly unlikely for the ringed seal as they rarely, if ever, come onto land. Hauling themselves out on land to rest would be a dramatic change to the species' behavior. Giving birth to their pups on land would expose newborns to a much higher risk of being killed by predators. Other ice-dependent seals that are likely to suffer as sea ice declines include the spotted seal, which breeds exclusively at the ice edge in the Bering Sea in spring, and the harp seal, which lives associated with sea ice all year. Unlike these ice-associated seal species, harbour seals and grey seals are more temperate species with sufficiently broad niches that they are likely to expand their ranges in an Arctic that has less ice coverage.

Seabirds

Some seabirds such as ivory gulls and little auks are very likely to be negatively impacted by the decline of sea ice and subsequent changes to the communities in which they live. The ivory gull is intimately associated with sea ice for most of its life, nesting and breeding on rocky cliffs that offer protection from predators, and flying to the nearby sea ice to fish through cracks in the ice and scavenge on top of the ice. As the sea ice edge retreats further and further from suitable coastal nesting sites, serious consequences are very likely to result. Major declines have already been observed in ivory gull populations, including an estimated 90% reduction in Canada over the past 20 years.

The Walrus and the Ice Edge

The ice edge is an extremely productive area and is very sensitive to climate change. The most productive areas are nearest the coasts, over the continental shelves. As sea ice retreats farther from the shorelines, the marine system will lose some of its most productive areas. For walrus in many areas, the ice edge provides the ideal location for resting and feeding because walrus are bottom feeders that eat clams and other shellfish on the continental shelves. As the ice edge retreats away from the shelves to deeper areas, there will be no clams nearby. Walrus also normally travel long distances on floating ice, allowing them to feed over a wide area.

Ice Algae and the Related Food Web

The vast reduction in multiyear ice in the Arctic Ocean is likely to be immensely disruptive to microscopic life forms associated with the ice, as they will lack a permanent habitat. Research in the Beaufort Sea suggests that ice algae at the base of the marine food web may have already been profoundly affected by warming over the last few decades. Results indicate that most of the larger marine algae under the ice at this site died out between the 1970s and the late 1990s, and were replaced by less-productive species of algae usually associated with freshwater. Researchers say that this is likely to be related to the fact that melting has formed a 30-meter thick layer of relatively fresh water below the remaining ice, one third deeper than it was 20 years before. Among the areas likely to be most severely affected by such changes will be the Bering Sea and Hudson Bay, in the lower Arctic, where sea ice is already disappearing earlier in spring and forming later in the autumn. As the Arctic continues to warm, sea ice will melt rapidly in the spring over continental shelf areas and withdraw toward the deep ocean of the central Arctic.

Additional Climate-Related Threats to Marine Species

Climate change poses risks to arctic marine mammals and some seabirds beyond the loss of habitat and forage bases. These include increased risk of disease due to a warmer climate, increased pollution impacts as rising precipitation brings more atmospheric and river-borne pollution northward, increased competition as temperate species expand their ranges northward, and impacts due to increased human traffic and development in previously inaccessible, ice-covered areas.

Chemicals and Climate Interact to Impact Polar Bears

The increase in environmental stress on polar bears caused by climate change interacts with the stresses caused by chemical contaminants. Polar bears, at the top of the marine food chain, accumulate contaminants in their fat by eating ringed seals and other marine mammals who have absorbed the chemicals by eating contaminated species lower on the food chain. High levels of chlorinated compounds and heavy metals have been found in polar bears. In some cases, contaminants may be stored in fat, keeping the chemicals from affecting the bears' health when fat reserves are high. But during a poor feeding season, when the fat reserves must be used, the chemicals are released into the body. Polar bears in some areas of the Arctic have been observed to have less fat reserves in recent decades as sea ice breakup occurs progressively earlier, forcing them ashore where they are required to fast for increasingly longer periods.

Climate and Social Changes Interact to Impact Marine Hunters

Many arctic communities depend on hunting polar bear, walrus, seals, whales, seabirds, and other marine animals. Changes in the species' ranges and availability, and the decreased ability to travel safely in changing and unpredictable ice conditions are making people feel like strangers in their own land. Some societal changes have increased vulnerability to climate-induced changes. For example, over recent decades, many Inuit hunters have switched from dog sleds to snowmobiles, and while dogs could sense dangerous ice conditions, snowmobiles cannot. (On the other hand, snowmobiles allow people to hunt over larger areas and to transport bigger loads.) In addition, people are no longer nomadic, following animals' seasonal movements. Because people now live in permanent settlements, their ability to adapt to changing climatic conditions and/or animal availability by moving has been greatly reduced.
 

More than half of the Arctic region is comprised of ocean. Many arctic life forms rely on productivity from the sea, which is highly climate-dependent. Climate variations have profound influences on marine animals. For example, the climate-related collapse of capelin in the Barents Sea in 1987 had a devastating effect on seabirds that breed in the area. And years with little or no ice in the Gulf of St. Lawrence in Canada (1967, 1981, 2000, 2001, 2002) resulted in years with virtually no surviving seal pups, when in other years, these numbered in the hundreds of thousands.

Polar Bears

Polar bears are dependent on sea ice, where they hunt ice-living seals and use ice corridors to move from one area to another. Pregnant females build their winter dens in areas with thick snow cover on land or on sea ice. When the females emerge from their dens with their cubs in spring, the mothers have not eaten for five to seven months. Their seal hunting success, which depends upon good spring ice conditions, is essential for the family's survival. Changes in ice extent and stability are thus of critical importance, and observed and projected declines in sea ice are very likely to have devastating consequences for the polar bear. The earliest impacts of warming would be expected to occur at the southern limits of the bears' distribution, such as James and Hudson Bays in Canada, and such impacts have already been documented in recent years. The condition of adult polar bears has declined during the last two decades in the Hudson Bay area, as have the number of live births and the proportion of first-year cubs in the population. Polar bears in that region suffered 15% declines in both average weight and number of cubs born between 1981 and 1998. Later formation of sea ice in autumn and earlier break-up in spring means a longer period of annual fasting for female polar bears, and their reproductive success is tightly linked to their fat stores. Females in poor condition have smaller litters and smaller cubs that are less likely to survive. Climate change is also likely to increase bear deaths directly. For example, increased frequency and intensity of spring rains is already causing some dens to collapse, resulting in the death of females and cubs. Earlier spring break-up of ice could separate traditional den sites from spring feeding areas, and young cubs cannot swim long distances from dens to feeding areas. Polar bears are unlikely to survive as a species if there is an almost complete loss of summer sea-ice cover, which is projected to occur before the end of this century by some climate models. The only foreseeable option that polar bears would have is to adapt to a land-based summer lifestyle, but competition, risk of hybridization with brown and grizzly bears, and increased human interactions would then present additional threats to their survival as a species. The loss of polar bears is likely to have significant and rapid consequences for the ecosystems that they currently occupy.

Ice-dependent Seals

Ice-dependent seals, including the ringed seal, ribbon seal, and bearded seal, are particularly vulnerable to the observed and projected reductions in arctic sea ice because they give birth to and nurse their pups on the ice and use it as a resting platform. They also forage near the ice edge and under the ice. Ringed seals are likely to be the most highly affected species of seal because all aspects of their lives are tied to sea ice. They require sufficient snow cover to construct lairs and the sea ice must be stable enough in the spring to successfully rear young. Earlier ice break-up could result in premature separation of mothers and pups, leading to higher death rates among newborns.

Adapting to life on land in the absence of summer sea ice seems highly unlikely for the ringed seal as they rarely, if ever, come onto land. Hauling themselves out on land to rest would be a dramatic change to the species' behavior. Giving birth to their pups on land would expose newborns to a much higher risk of being killed by predators. Other ice-dependent seals that are likely to suffer as sea ice declines include the spotted seal, which breeds exclusively at the ice edge in the Bering Sea in spring, and the harp seal, which lives associated with sea ice all year. Unlike these ice-associated seal species, harbour seals and grey seals are more temperate species with sufficiently broad niches that they are likely to expand their ranges in an Arctic that has less ice coverage.

Seabirds

Some seabirds such as ivory gulls and little auks are very likely to be negatively impacted by the decline of sea ice and subsequent changes to the communities in which they live. The ivory gull is intimately associated with sea ice for most of its life, nesting and breeding on rocky cliffs that offer protection from predators, and flying to the nearby sea ice to fish through cracks in the ice and scavenge on top of the ice. As the sea ice edge retreats further and further from suitable coastal nesting sites, serious consequences are very likely to result. Major declines have already been observed in ivory gull populations, including an estimated 90% reduction in Canada over the past 20 years.

The Walrus and the Ice Edge

The ice edge is an extremely productive area and is very sensitive to climate change. The most productive areas are nearest the coasts, over the continental shelves. As sea ice retreats farther from the shorelines, the marine system will lose some of its most productive areas. For walrus in many areas, the ice edge provides the ideal location for resting and feeding because walrus are bottom feeders that eat clams and other shellfish on the continental shelves. As the ice edge retreats away from the shelves to deeper areas, there will be no clams nearby. Walrus also normally travel long distances on floating ice, allowing them to feed over a wide area.

Ice Algae and the Related Food Web

The vast reduction in multiyear ice in the Arctic Ocean is likely to be immensely disruptive to microscopic life forms associated with the ice, as they will lack a permanent habitat. Research in the Beaufort Sea suggests that ice algae at the base of the marine food web may have already been profoundly affected by warming over the last few decades. Results indicate that most of the larger marine algae under the ice at this site died out between the 1970s and the late 1990s, and were replaced by less-productive species of algae usually associated with freshwater. Researchers say that this is likely to be related to the fact that melting has formed a 30-meter thick layer of relatively fresh water below the remaining ice, one third deeper than it was 20 years before. Among the areas likely to be most severely affected by such changes will be the Bering Sea and Hudson Bay, in the lower Arctic, where sea ice is already disappearing earlier in spring and forming later in the autumn. As the Arctic continues to warm, sea ice will melt rapidly in the spring over continental shelf areas and withdraw toward the deep ocean of the central Arctic.

Additional Climate-Related Threats to Marine Species

Climate change poses risks to arctic marine mammals and some seabirds beyond the loss of habitat and forage bases. These include increased risk of disease due to a warmer climate, increased pollution impacts as rising precipitation brings more atmospheric and river-borne pollution northward, increased competition as temperate species expand their ranges northward, and impacts due to increased human traffic and development in previously inaccessible, ice-covered areas.

Chemicals and Climate Interact to Impact Polar Bears

The increase in environmental stress on polar bears caused by climate change interacts with the stresses caused by chemical contaminants. Polar bears, at the top of the marine food chain, accumulate contaminants in their fat by eating ringed seals and other marine mammals who have absorbed the chemicals by eating contaminated species lower on the food chain. High levels of chlorinated compounds and heavy metals have been found in polar bears. In some cases, contaminants may be stored in fat, keeping the chemicals from affecting the bears' health when fat reserves are high. But during a poor feeding season, when the fat reserves must be used, the chemicals are released into the body. Polar bears in some areas of the Arctic have been observed to have less fat reserves in recent decades as sea ice breakup occurs progressively earlier, forcing them ashore where they are required to fast for increasingly longer periods.

Climate and Social Changes Interact to Impact Marine Hunters

Many arctic communities depend on hunting polar bear, walrus, seals, whales, seabirds, and other marine animals. Changes in the species' ranges and availability, and the decreased ability to travel safely in changing and unpredictable ice conditions are making people feel like strangers in their own land. Some societal changes have increased vulnerability to climate-induced changes. For example, over recent decades, many Inuit hunters have switched from dog sleds to snowmobiles, and while dogs could sense dangerous ice conditions, snowmobiles cannot. (On the other hand, snowmobiles allow people to hunt over larger areas and to transport bigger loads.) In addition, people are no longer nomadic, following animals' seasonal movements. Because people now live in permanent settlements, their ability to adapt to changing climatic conditions and/or animal availability by moving has been greatly reduced.