This paper was written as part of the 2010 Alaska Oceans Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.
Productivity and Sea Ice Decline in the Arctic Ocean
In recent years, the Arctic Ocean has attained status as the single most studied ecosystem in the world. The reduction in Arctic sea ice and the ramifications from the seemingly unavoidable retreat of ice from the Arctic has scientists scrambling to measure and determine what the effects of this failure might be.
It is accepted throughout the scientific community that the Arctic Ocean is the barometer by which global warming will be monitored. Modern science has not measured an event of this type or magnitude before, so predictions about the future status of the Arctic Ocean are based on hypothetical concepts, historical data, interpretation, and incorporation of current data.
The most commonly accepted ideas about global warming are those involving an extreme negative, almost cataclysmic effect on the earth's biosphere. However, there does appear to be some scenarios in which ecological changes brought on by global warming may bring about positive effects on the Arctic Ocean ecosystem. It remains unknown whether some of these effects will continue over time. We will discuss the effects of a shrinking Arctic ice pack on productivity in the Arctic Ocean, and the subsequent effects the change in productivity may have on the organisms that call the Arctic Ocean home. The Arctic Ocean is covered with ice throughout the year. The role of sea ice in the Arctic ecosystem is the focus of much study, especially as it relates to global warming. Incoming sunlight is reflected by the ice or absorbed by liquid seawater, and the differences between these situations is key. Additionally, we will analyze the changes increased productivity might bring about for the cultures and subsistence practices of people living in the region.
The amount of ice covering the Arctic Ocean is decreasing each year. The average amount of ice in the winter is about 14 million square kilometers, but in the winter these levels drop off to about half that size, to around six to seven million square kilometers in September.
Within the Arctic Ocean, there are three distinct biological communities that constitute the Arctic Ocean ecosystem. The "sea ice realm" includes the plants and animals that live in, on, or just under the ice. Animals living on the ice have obvious challenges. As sea ice recedes, available area for hunting is diminished. Polar bears have less hunting time per year for obtaining high calorie nutrients from the seals they eat. Female polar bears go into hibernation lacking healthy reserves of body fat. Polar bear cubs exhibit a lower survival rate due to malnutrition and instances of cannibalism from larger male bears.
Walruses are also facing difficulties with the prospect of diminished sea ice. Walrus haul out and rest on ice floes, often over their feeding grounds and safe from predators. Loss of ice for them means longer swims to get to haulout locations.
Sea ice itself is riddled with a network of tunnels called "brine channels" that range from a few microns to greater than an inch in diameter. Bacteria and blue-green algae inhabit and photosynthesize within these channels, and are in turn fed upon by worms and other heterotrophs creating a food web of ice-dwelling organisms inhabiting the spaces between ice crystals. Ice melt frees these organisms into the seawater below, providing food for first order consumers and other organisms of the "pelagic" realm. The pelagic realm includes organisms that live below the ice, but above the bottom. Krill are important base food chain organisms in the pelagic realm. Krill consume algae that live on the underside of the ice, and take refuge in its depressions.
Krill populations are being challenged with loss of sea ice habitat and competition from an increasing salp population. It would be logical to assume that bowhead whale populations would show declines as a result of declining krill numbers, but according to the International Whaling Commission, bowhead whale populations appear to be stable if not increasing by about 3% per year.
Ice also acts as an insulator to keep the waters of the Arctic cold by reflecting sunlight. When the sun shines on the white snow and ice, light energy is reflected back into the atmosphere, but when the sun shines on the ocean water it the heat is absorbed. This raises the ambient temperature and melts the surrounding ice. The melting rate per decade in 1979 was 6.5%, but now it has risen to 11.2%. At the rate that the ice is melting, there might not be any summer ice by 2015. Seawater exchange with the Atlantic brings in waters that are slightly warmer than decades ago. The removal of that increased amount of heat contributes to significant ice reduction.
Perennial ice is ice that is built up and lasts more the one summer season, while seasonal ice is thinner, and has a greater salinity, and lasts only one winter. The seasonal ice coverage is about 5-6 million km2, and perennial ice currently covers an area of about 7 million km2. The amount of perennial ice is decreasing. Ice area used to decrease by 6% per year, but that rate has recently increased to 15%. During the 2004-2005 season, the perennial ice shrank 14%, about 750,000 km,2, or the approximate size of Turkey. The extent of perennial ice is decreasing, along with the thickness of the ice. The average ice thickness in the Arctic Ocean is about eight feet. Sea ice thickness is declining rapidly, and was up to 19% thinner last winter than the ice thickness of the five previous winters, according to the European Space Agency's Envisat satellite. The top layer of the water acts as a thermocline and is typically the warmest layer. Due to higher temperatures the water doesn't refreeze and therefore doesn't restore the thickness to the ice. The thickness of the ice is also connected to light penetration. Scientists E. M. Little, M. B. Allen, and F. F. Wright measured light penetration through sea ice and found that light attenuation is greatest at the ice-air interface. Values just below the ice surface were 3 to 20% of the initial value. Another 70 to 100 cm of ice was required to affect a further 50% decrease in illumination. Light penetration is critical to the phytoplankton that use sunlight to photosynthesize. If the plankton do not receive adequate sunlight, they cannot photosynthesize, making sunlight a limiting factor. Currently, several organizations, including NOAA and NASA, are working in partnership with international institutions to monitor ocean temperatures in the Arctic. For example, Woods Hole Oceanographic Institute, in cooperation with the National Science Foundation, conducted a workshop in 2004 to plan and setup a system of ice-tethered buoys to monitor ocean conditions such as temperature and ice thickness. Additionally, the National Science Foundation sponsored the creation of the North Pole Environmental Observatory in 2000 in order to track Arctic climate changes through the use of floating buoys, aerial surveys, and ocean moorings.
The third realm is the Benthic realm, consisting of organisms that live on the bottom. These organisms rely on the settling of organic compounds from the surface for their energy requirements.
Currently, the main limiting factor in the Arctic Ocean is sunlight, as vertical stratification caused by fluctuating water temperatures creates continuous overturn of water providing ample nutrients throughout the water column. Productivity, then, is most affected by sunlight availability and will be limited substantially in the winter months when the sun does not come above the horizon. Additionally, sunlight availability is affected by sea ice, which reflects large amounts of solar energy. According to the National Snow and Ice Data Center, sea ice reflects up to 80% of the sunlight that strikes it, while the ocean absorbs up to 90% of the sunlight that hits its surface.
With less sea ice and more exposed open water, photosynthesis will increase. According to calculations by oceanographers from Stanford University based on images from NASA's GeoEye satellite and SeaWiFS instrument, approximately 30% of the observed increase of phytoplankton in 2006 and 2007 was a direct effect of increased sunlight exposure due to melting sea ice.
With more available sunlight, the growing season in the Arctic Ocean is expanding, and photosynthetic organisms such as phytoplankton and various algae will be limited by the availability of nutrients rather than sunlight. The logistic growth equation, where N represents population size, t represents time, r represents maximum rate of increase, K represents carrying capacity, and d represents the Greek symbol delta, explains a population's logistic growth curve. As N approaches K, the population's growth rate will slowly decline. The carrying capacity is much like an asymptote in that a population will approach the maximum carrying capacity, but suffer a dramatic decline in growth rate before the carrying capacity is reached. As sunlight becomes nonlimiting, the Arctic Ocean's carrying capacity will increase, meaning the ecosystem can support more organisms. (See Figure 1.)
There are some 50 dominant species of phytoplankton in the Arctic Ocean. These small photosynthetic organisms are primary producers that support the entire Arctic ecosystem. With sunlight becoming more readily available for photosynthesis, the phytoplankton biomass will greatly increase. The Marine Research Initiative in Southern Florida conducted a study in 1997-1999 and observed a 6.2% increase in planktonic standing crop in the Arctic region. Today it is expected that this fluctuation in plankton abundance could be much greater, but these studies are yet to be conducted.
6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2
Stated above is the chemical formula for photosynthesis. Photosynthesis is the process of converting light energy to chemical energy and then storing it in an organism as bonds of glucose. Photosynthesis is the main source of oxygen in marine ecosystems, occurring most frequently inside photosynthetic plankton. Phytoplankton produce about 50% of all the oceans' oxygen. Plankton photosynthesize by using light energy and turning it into chemical energy, which is then stored in chemical bonds as sugar. The byproduct of photosynthesis for plankton is O2. This oxygen is then released into the body of water and used during respiration. With an increase of open seawater in the Arctic region, due to the fact that the Arctic ice pack is receding, there is a greater amount of sunlight that reaches the Arctic Ocean's surface. Because of this, there has been an increase of plankton in the Arctic region. Both of these factors, along with increased sunlight and increased water surface, attribute to the fact that there have been grander plankton blooms in the Arctic region. With an increase of plankton, there has also been an increase in photosynthesis by these organisms, which ultimately leads to an increase in the water's oxygen levels.
Although all phytoplankton depend on and incorporate carbon dioxide in photosynthesis, some can incorporate and utilize their supplies more efficiently; typically, these are the phytoplankton of larger size, and currently they are suffering.
When seawater freezes, the sodium chloride ions are driven down through the ice, creating less saline ice formation and an increased level of salinity in the water beneath the ice. The high levels of salinity and cold water temperatures create a dense layer of water high in the water column optimal for phytoplankton that depend on density to enhance their buoyancy but need to be high in the photic zone to proceed with photosynthesis. With the increased ice melt, the underlying water is decreasing in salinity and increasing in temperature. These two factors affect density; the density of the photic zone in the Arctic Ocean is decreasing. The decline in water density has caused many of the larger plankton to sink much lower in the photic zone, where there is less available light. As this positive feedback loop continues, there may be a point where light penetration would no longer support large phytoplankton. With density becoming a limiting factor for large phytoplankton, smaller plankton, called picoplankton, could thrive.
Picoplankton are small planktonic organisms ranging from 0.2-2.0 micrometers, and they mainly consist of bacteria and cyanobacteria. These small plankton are less density dependent, and sink more slowly because they have a greater surface area to volume ratio. Therefore, in the increasingly less dense waters of the Arctic Ocean, ice reduction may be the picoplankton's chance to become the dominant members of the phytoplankton population. If smaller plankton begin to dominate the ecosystem, a loss of biological energy supply and transfer would result. This would affect organisms at higher trophic levels that require a high caloric intake to survive.
If phytoplankton of larger sizes were to decline, the species populations could react to current conditions and either become smaller or adapt. In order to survive in a less dense environment larger phytoplankton must evolve to increase their surface area to volume ratio. A plausible method in which large phytoplankton could increase their buoyancy would either be to increase their central vacuoles or incorporate gas vesicles into their cell. The idea of incorporating gas vesicles into a phytoplankton's cellular design was studied by The Marine Science laboratories in 1975, they conducted a study of the effects of gas vesicles. The results showed that phytoplankton with cells that had larger gas vesicles correlated with a larger size, and with larger gas vesicles the overall buoyancy of the organism would increase. Another possible strategy would be enlarging the central vacuole; the plankton cells will increase their surface area to volume ratio, thus enhancing buoyancy. Keep in mind, these are not current but plausible effects of what could happen if the population of larger phytoplankton were to drastically reduce as a result of decreasing density.
Assuming that photosynthesis is increasing, causing larger phytoplankton blooms, it is reasonable to assume that the general Arctic ecosystem will be affected.
Undersea ridges make the Arctic Ocean unique compared to the other oceans; these ridges create stagnant pools of seawater deep in the water column, while surface currents circulate above. For example, due to the Lomonosov Ridge, deep ocean waters have a difficult time traveling from the Amerasian Basin to the Eurasian Basin. As depicted in Figure 2 below, several large surface currents exist to move nutrients through the Arctic Ocean. The Arctic surface waters extend to a depth of about 46 meters, and are far less salty than the waters below. The most powerful of these currents is the Beaufort Gyre. The Beaufort Gyre is a large circular current that rotates the surface waters of the Arctic basin clockwise while rotating the polar ice cap once every four years. It rotates right over the northern coasts of Canada and Alaska as well as Russia and then up around the North Pole. The Barents Gyre is similar to the Beaufort Gyre, but is smaller and less powerful. The Barents Gyre rotates counter clockwise over Europe pulling warmer Atlantic waters up into the colder polar regions. Both of these major gyres feed into the Transpolar current, which runs in between the two gyres and flows right into the Labrador current and the West Greenland current, which then flow down the east coast of North America and into the North Atlantic Current.
Due to the isolation of the deep ocean waters, towards the bottom of both of these gyres the water is much colder and has a higher salinity than the surface waters, which are routinely flushed out. These deep ocean waters are rich in nutrients that are brought up to the Arctic through the Bering Strait and the North Atlantic Current; the Bering Strait and the North Atlantic Current bring waters from the Bering Sea and the North Atlantic, which are some of the most productive oceanic regions in the world. Another source of nutrients for the Arctic Ocean is through rivers in Northern Russia that empty into the Arctic Ocean.
Although these surface currents remain present throughout the year, the region undergoes drastic changes between the summer and winter months. The amount of ice in the summer months, which decreases more and more each year, is far less than the amount of ice that is present in the cold winter months. This Arctic ice cap holds large amounts of nutrients that are trapped during the freezing months and are released back into the water in the spring and summer months when the climate warms.
Global warming is a very pressing issue for the Arctic region. Every year, the amount of winter ice continues to be less than the previous year. Higher global temperatures cause the polar ice caps to melt more rapidly, which increases the amount of freshwater being dispersed into the ocean. Another question is how continued climate change will affect the currents in the polar region. Currents are driven by wind on the surface and the Coriolis Effect, as well as differences in temperature and salinity. If ocean temperatures in the polar regions increase, causing more ice to melt, the overall effect could potentially change the flow of the currents in the Arctic, or even possibly cause them to shut down. If this were to happen, it could starve the region of nutrients, which are predicted to become the main limiting factor in the Arctic after diminished sea ice allows for increased sunlight exposure. These nutrients are the necessary building blocks of the food chain; their depletion could result in significant changes to the Arctic ecosystem.
The melting of Arctic Sea ice is hypothesized to have profound effects on the surrounding ecosystem. Just as important, however, are the consequent effects on Arctic communities. Rural villages in the Arctic often rely on subsistence hunting techniques to support their communities, and with the projected changes to the Arctic ecosystem, a subsequent shift in the social structure of these villages is inevitable.
The native peoples of the Arctic, namely the Inuit, Yupik, and Inupiaq, rely heavily on a subsistence lifestyle to sustain community life. While some modern amenities are available, hunts for walrus and bowhead whale are still important means of supporting the community and the culture.
Arctic subsistence hunters from northern Alaska, Russia, Greenland, and Canada have harvested walruses for centuries. The native peoples find uses for their ivory tusks, their meat, the thick pelts, and other body parts, including the inner organs. To hunt for walrus, Alaska natives north of Bristol Bay must wait for the sea ice surrounding their communities to recede, so that they can move their boats out to sea. Then, walrus hunters must find the walrus and wait for them to haul up on thick sheets of floating sea ice to harvest them. The walrus, which are benthic feeders, will periodically dive to the bottom to feed on bottom-dwelling crustaceans and mollusks and return to rest on the ice several times a day.
The melting of sea ice could disrupt the walrus hunting practice in several ways. Firstly, an early ice melt causes the walrus population to move out to sea, away from the coastal villages, at an earlier time of year. The walrus follow the receding ice northward during the spring. This is problematic because of the remaining ice near the coast. Once the coastal ice has melted, the walruses may already be much farther away than the hunters have energy or time to hunt for. In essence, quickly receding Arctic sea ice tends to reduce the amount of time that subsistence hunters have available to hunt for walrus each year. Secondly, the walrus population itself could be put at risk because of loss of habitat. As walruses dive to feed on crustaceans and mollusks at the bottom, they intermittently resurface to rest on thick ice sheets. With the Arctic ice thinning and receding much further than in previous years, walrus are forced to crowd themselves in much denser groups on land. Reports have shown that overcrowding of walrus populations has resulted in younger individuals being trampled to death by larger individuals when the group is startled. Additionally, in some areas, the ice has retreated to an area where it is too deep for walruses to dive to the bottom to feed.
As shown figures 3 and 4, walrus distribution in the Arctic north of Alaska corresponds to the bathymetry of the Arctic region. Because walrus dive to the bottom for food, the water must be shallow enough for them to reach the bottom and have enough time to come up for air. The continental shelf in the Bering Sea and the Arctic north of Alaska is limited in depth to about 150 meters, which is ideal for walrus feeding patterns. The deepest walrus dive on record extended to 113 meters for 25 minutes, which is within the range for continental shelf depth in the Arctic. Thus, if the sea ice extent ever fails to surpass the continental shelf break, walrus feeding patterns would be disrupted due to lack of resting ice floes within waters shallow enough for feeding. According to Woods Hole Oceanographic Institute, this has resulted in several walrus calves being abandoned by their mothers. For example, in 2004, researchers aboard the Healy reported seeing nine stranded walrus pups in the Canada Basin. The researchers attributed their abandonment to the fact that mothers had no place to leave their pups while feeding in shallow waters. Consequently, the pairs become separated and pups are left to fend for themselves with little knowledge of how to defend or support themselves.
Disruption of the time window in which natives are able to hunt walrus as well as a potentially declining walrus population could have disastrous effects on native communities because of their reliance on subsistence hunting. Already, the number of walruses being harvested per year in Alaskan waters has decreased; from the year 1996 to 2000, the average yearly walrus harvest amounted to about 5,789 individuals, while today the harvest averages about 4,869 individuals. Some native subsistence hunters, in addition to distributing the nutritious meat among members of the community, use walrus products as their only source of income. Ivory carving provides some of the only revenue for natives in rural villages, and without a successful walrus harvest, these natives could be left without work. Unemployment poses a threat to natives due to the high costs of living in Arctic communities. Prices of gasoline and food are already very high in most rural villages. In some Alaska villages, gasoline is already spiked in price to about $5 to $8 per gallon, and food is more expensive because everything has to be shipped in by plane. A single gallon of milk, for example, can cost up to $14. In order to support themselves, ivory carvers will have to find new mediums for their craft, such as wood or stone, or find completely new lines of work. Thus, the walrus has the potential to disappear from the culture of the Arctic peoples who used to rely on them so heavily. A future without subsistence hunting for walruses has been predicted, though the cultural implications of such a future are unknown. However, it can be expected that a society whose traditions have been in place for thousands of years must now prepare for drastic change, should ice melting in the Arctic continue to affect walrus populations.
A similar prediction can be made about the same cultures regarding the bowhead whale. Like the walrus, the bowhead whale is a major resource for subsistence hunters in the Arctic. Bowhead whales are completely adapted to life in the Arctic, especially with regard to Arctic sea ice. The whales have reinforced bone structures in their heads to enable them to punch through sea ice up to two feet thick; the whales' survival depends on their ability to find open water. For this reason, the bowhead whale migration pattern tends to follow the movement of sea ice. During the winter, Alaskan whales survive by staying near polynyas, which are areas of open water within the Bering Sea pack ice. Then, as the ice begins to melt in spring, the whales swim north through the Bering Strait. From here, they tend to follow cracks in the retreating ice until they pass by Point Barrow. After spending the summer on the coast of Canada, they follow the same route back in the fall to the Bering Sea to prepare for another winter. Hence, the hunting seasons for Arctic subsistence hunters in Alaska correspond to the whales' migration. During spring and fall, while the whales are passing near Point Barrow, Arctic peoples such as the Inupiaq and the Yupik make use of handheld harpoons as well as motorized and traditional skin boats for the whale harvest.
Because the whale migration trails the northward retreat of sea ice, it follows that a change in the melting patterns of the ice will have consequent effects on the whales' annual migration. A thinner ice pack could be beneficial for the whales; with thinner ice, the threat of suffocation due to lack of available breathing holes is significantly lessened. If the ice is thin enough, polynyas and ice cracks are no longer necessary. With the ice becoming thinner, bowhead whales will have the opportunity of gaining access to a greater range during all four seasons. Additionally, if the ice pack continues to retreat farther north and at a faster rate, this new range will become available earlier in the year. Thus, the migration patterns of the bowhead whale have the potential to be considerably altered. This change is an impending threat to whaling communities in the Arctic. If the whales begin their migration earlier in the year, they may be able to make it farther north before the ice has cleared from the coast. By the time the whalers are able to move their boats out to sea, the whales may already be farther north than the hunters are willing to go for their harvest. While this is bad news for subsistence hunters, the whale population may benefit. Indeed, the recent trend of the Alaskan bowhead whale population is that of increased numbers; the current estimate for net population increase according to the International Whaling Commission is about 3.2% per year. Increased numbers for subsistence hunters is a good thing, but the potential problem lies in the harvest. Should sea ice continue to melt at such a rate, hunters' ability to harvest the whales could be dramatically affected by the whales' changing migration patterns.
Like the walrus, the disappearance of bowhead whales from Arctic subsistence diets could have disastrous effects on the native cultures. This is predominantly due to the prominence of whale meat in local diets. The meat and blubber is very nutritious, and is distributed throughout the community after the whale is brought in by hunters. It takes several people to bring in a whale, and afterwards to butcher it and distribute it. The harvesting of a whale is an extremely community-minded activity, and the loss of the ability to hunt for bowhead whales has the potential to diminish this long-standing cultural practice. For some communities, harvesting whales serves as a rite of passage and as a symbol of cultural significance and teamwork. Additionally, natives whose income consists of the sale of handicrafts from whale products, including, for example, carved whalebones or baleen products, may have to find new ways of making money. Closely-knit native communities that have survived for thousands of years by using whaling practices can be predicted to undergo vast social changes, should the Arctic ice melting trend continue at the present rate.
Subsistence hunting for walrus and bowhead whales is important to maintaining a way of life for Arctic communities. Just as important is the practice of subsistence fishing. In the Arctic, several species of fish are harvested for subsistence; these species include Arctic Cisco, Arctic cod, Arctic char, shee fish, and turbot, among others. Using nets placed under the ice, subsistence fishers harvest several Arctic fish species for consumption. Arctic ice melting has the potential to change the practice of subsistence fishing in the future, based on predictions made about the northward movement of foreign fish species to the Arctic.
According to scientists and leaders who attended the October 2009 International Arctic Fisheries Symposium, climate change and Arctic ice melting is to be held responsible for a shift in Arctic fish species. As the earth warms and Arctic ice continues to recede northward, some fish species such as salmon will migrate north in search of colder waters. Already, foreign species of salmon have been reported north of the Bering Strait. The northward migration of fish into the Arctic will obviously affect the diet of subsistence fishers, but more importantly it opens the possibility for Arctic commercial fisheries in the future. Already, a small-scale fishery for Arctic Cisco, a fish native to the Arctic region, operated by the Helmericks family exists at the mouth of the Colville River, but as more open water becomes exposed, the way becomes paved for larger-scale fisheries to begin their own operations. The likelihood of this increases as more commercially harvested species of fish begin to migrate northward. This could lead to a more industrialized Arctic, in terms of the annual fish harvest.
As of yet, there has been much debate over whether opening a large fishery in the Arctic would be detrimental to the ecosystem. With climate change and ice melting playing such an important role in the Arctic ecosystem, it is difficult to predict the future for fish species in Arctic waters. Some scientists and environmentalists, as well as some representatives of the fishing industry, have proposed to close all commercial fishing north of the Bering Strait. The North Pacific Fishery Management Council has already submitted a plan regarding the closing of the Arctic to commercial fishing for review. The plan aims to hold off the instatement of commercial fisheries until scientists can properly assess the state of the Arctic ecosystem and the potential risks for present and future fish species. This assessment should allow for better management of fisheries, if fisheries are instated in the Arctic. As of today, the Arctic is closed to all commercial fishing operations. If commercial fishing is ever officially opened in Arctic waters, subsistence communities can expect drastic changes in their communities. In essence, the melting of Arctic sea ice has opened up the possibility of an industrialized Arctic fish harvest in an area where oil has supplied the majority of industrial activity.
For native communities, sea ice melting affects subsistence activities in more ways than one. The possibility of Arctic fisheries, in addition to the effects of receding ice on subsistence harvests of walrus and bowhead whales, have the potential for drastic shifts in the local social structure.
With an increase in the water's surface that is exposed to sunlight, there is a greater expanse of water that plankton can thrive and photosynthesize in. In this larger space, increased sunlight allows for more plankton, causing a condition of increased productivity. Consequently, there can also be an increase of animals that feed upon plankton, and an increase in the animals that feed upon these first order consumers, and so on through all the Arctic trophic levels. It would seem that with this domino effect there would be an ever greater number of animals sustained by the Arctic ecosystem, yet there is a limiting factor still in place that will keep these numbers from rising enormously. With an increased amount of the ocean surface being exposed to sunlight, nutrients will become the limiting factor in the Arctic, assuming that the current circulation of nutrients remains unchanged; the transportation of these nutrients throughout the Arctic is dependent on the system of Arctic currents. Although the recent trend in ocean productivity is upward, the diminished amount of sea ice poses a threat to several species, such as seals, bowhead whales, and walrus. Several of the affected species are important subsistence food sources for Arctic communities, and the loss of these species from Arctic communities could have significant effects on social structure.
- With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change—Fred Pearce (Book)