Why Are Scientists Tracking Narwhals in Greenland?
A key purpose of NOAA’s Ocean Exploration Initiative is to investigate the more than 95 percent of Earth’s underwater world that until now has remained virtually unknown and unseen. Such exploration may reveal clues to the origin of life on Earth, cures for human diseases, answers to how to achieve sustainable use of resources, links to our maritime history, and information to help protect endangered species. In addition, exploration of ecosystems in the high Arctic can provide information about how these ecosystems are changing in response to changes in Earth’s climate. Because they are located in the vicinity of oceanographic processes that drive global ocean currents, these explorations can also provide new clues about how climate change may affect many other ecosystems around the world.
Global climate is heavily influenced by Earth’s oceans. One of the most significant climatic influences results from the ‘deep ocean thermohaline circulation’ (THC). This circulation is driven by changes in seawater density, and has a major influence on water movements between the Atlantic, Antarctic, Pacific, and Indian Oceans. The causes and effects of the THC are not fully known. But we do know that it affects almost all of the world’s ocean and plays an important role in transporting dissolved oxygen and nutrients. For this reason, the deep ocean THC is often called the ‘global conveyor belt.’ We also know that the THC is at least partially responsible for the fact that countries in northwestern Europe (Britain and Scandinavia) are about 9ºC warmer than other locations at similar latitudes.
In recent years, changes in the Arctic climate have led to growing concerns about the possible effects of these changes on the deep ocean THC. In the past 30 years, parts of Alaska and Eurasia have warmed by about six degrees Celsius. In the last 20 years, the extent of Arctic sea ice has decreased by at least 5%, and in some areas, sea ice thickness has decreased by 40%. Dense water sinking in the North Atlantic Ocean is one of the principal forces that drives the circulation of the global conveyor belt (see ‘More About the Deep Ocean Thermohaline Circulation,’ below). Since an increase in freshwater inflow (such as from melting ice) or warmer temperatures in these areas would weaken the processes that cause seawater density to increase, these changes could also weaken the global conveyor belt.
Changes are being seen in Arctic regions where dense seawater formation occurs, but the significance of these changes is not yet clear. Although the Arctic as a whole is getting warmer, air and sea surface temperatures near western Greenland show a significant cooling trend, and sea ice concentrations in Baffin Bay have increased significantly since 1953. At the same time, deep (400 m and below) water temperatures in Baffin Bay are slowly increasing. Some of this warmer water flows into the Labrador Sea, which is one of the sources for the cold, dense water that drives the deep ocean THC. Because it is a global process, some scientists wonder whether the THC may be related in some way to other changes being seen in the Earth’s ocean. One such change is an apparent decline in net oceanic primary productivity; more than six percent globally in the last two decades (Gregg, et al., 2003). Nearly 70 percent of the decline occurred in high latitudes (above 30 degrees) in the North Pacific and North Atlantic basins. These observations, coupled with very limited understanding of how the global ocean influences life on Earth, illustrate why many scientists feel that it is critical to learn more about the deep ocean THC and how it is being affected by climate change -- especially in the Arctic.
But the Arctic is not an easy place to do scientific work. Obviously, it is cold. In the winter it can be very cold (-40ºC), as well as dark for six months and covered with sea ice. Not surprisingly, most scientific studies have taken place only in summer months. And since most Arctic regions are not known to contain commercially valuable resources, only limited financial support has been available for exploration and scientific study. Under these conditions, scientists have to be particularly creative; and sometimes find help through unusual partnerships.
One of the species likely to be affected by climate changes in the Arctic is the narwhal, a whale best known for its unicorn-like tusk. Narwhals spend their entire lives in the Arctic, and prefer habitats that are in or near sea ice. Unlike other areas in the Arctic where there has been an average increase in temperature, some parts of the Arctic (e.g., western Greenland and Baffin Bay) have been getting colder in recent decades, and increasing concentrations of sea ice in these regions may be ‘too much of a good thing’ for narwhals, since they need some open water to survive. One of the largest populations of narwhals spends most of the winter in Baffin Bay, where they dive repeatedly to depths that exceed 1,500 m in search of food. The Tracking Narwhals in Greenland Exploration plans to enlist the help of narwhals to learn more about climate change in the Arctic and its impact on ocean ecosystems.
The purpose of the Tracking Narwhals in Greenland Exploration is to improve our understanding of climatic changes occurring in an offshore ecosystem of Baffin Bay, and how these changes may affect narwhal populations that are part of that ecosystem. Expedition activities are directed toward three objectives:
• To employ narwhals as oceanographic sampling platforms to collect temperature data from deep waters in Baffin Bay;
• To identify narwhals’ response to movement of openings in pack ice; and
• To describe relationships between narwhal behavior and properties of the pack ice habitat
Profiles of salinity, temperature, and depth are among the most fundamental pieces of information used by biological and physical oceanographers, and are particularly relevant when studying movements of cold, dense water masses. Yet, these measurements have not been made in Baffin Bay during the winter for reasons described above. Integrating scientific needs and objectives with habitat preferences and diving abilities of narwhals will allow such measurements to be made for the first time. At the same time, data on movements of narwhals and sea ice will provide a completely new picture of how these animals respond to increased sea ice concentration in this region.
The technological foundation of the Tracking Narwhals in Greenland Exploration is an unusual combination of very recent (less than five years old) microprocessor and communications technology combined with very old (around 500,000 years old) natural ‘technology’ in the form of narwhals.
Instrument packages called satellite tags are attached to narwhals by plastic coated wires affixed to two nylon pins (6 mm diameter) inserted through the dorsal ridge on the whales’ back (the whales shed the tags after several months; 14 months is the longest time a tag has stayed on a whale). Narwhals are held in a net between two inflatable boats during the tagging procedure, which lasts about 30 minutes. An alternative method of attaching the tags involves placing the tags into small cylinders that are implanted in the layer of blubber along the whales’ back using hand-held thrown poles similar to harpoons. Tags attached using the latter methods are only expected to provide data for 4-5 weeks. Additional satellite tags will be used to obtain data on sea ice conditions while narwhals are in pack ice.
Each satellite tag includes sensors for temperature and pressure (which corresponds to depth), and a transmitter capable of sending signals to a satellite in polar orbit above Earth. Data collected by the sensors are transmitted to data acquisition equipment attached to NOAA weather satellites. This equipment, part of a system called Argos, records the transmissions and later downloads the data back to Earth where the ground-based part of the Argos system processes the data and determines the location of the satellite tag when the data were collected. For more information on satellite tags and the Argos system visit http://www.wildlifecomputers.com and http://www.argosinc.com .
More About the Deep Ocean Thermohaline Circulation
The deep ocean thermohaline circulation is driven by changes in seawater density. Two factors affect the density of seawater: temperature (the ‘thermo’ part) and salinity (the ‘haline’ part). Major features of the THC include:
• In the Northeastern Atlantic Ocean, atmospheric cooling increases the density of surface waters. Decreased salinity due to freshwater influx partially offsets this increase (since reduced salinity lowers the density of seawater), but temperature has a greater effect, so there is a net increase in seawater density. The formation of sea ice may also play a role as freezing removes water but leaves salt behind causing the density of the unfrozen seawater to increase. The primary locations of dense water formation in the North Atlantic are the Greenland-Iceland-Nordic Seas and the Labrador Sea.
• The dense water sinks into the Atlantic to depths of 1000 m and below, and flows south along the east coasts of North and South America.
• As the dense water sinks, it is replaced by warm water flowing north in the Gulf Stream and its extension, the North Atlantic Drift (note that the Gulf Stream is primarily a wind driven current and is part of a subtropical gyre that is separate from the THC).
• The deep south-flowing current combines with cold, dense waters formed near Antarctica and flows clockwise in the Deep Circumpolar Current. Some of the mass deflects to the north to enter the Indian and Pacific Oceans.
• Some of the cold water mass is warmed as it approaches the equator, causing density to decrease. Upwelling of deep waters is difficult to observe, and is believed to occur in many places, particularly in the Southern Ocean in the region of the Antarctic Circumpolar Current.
• In the Indian Ocean, the water mass gradually warms and turns in a clockwise direction until it forms a west-moving surface current that moves around the southern tip of Africa into the South Atlantic Ocean.
• In the Pacific, the deepwater mass flows to the north on the western side of the Pacific Basin. Some of the mass mixes with warmer water, warms, and dissipates in the North Pacific. The remainder of the mass continues a deep, clockwise circulation. A warm, shallow current also exists in the Pacific, which moves south and west, through the Indonesian archipelago, across the Indian Ocean, around the southern tip of Africa, and into the South Atlantic.
• Evaporation increases the salinity of the current, which flows toward the northwest, joins the Gulf Stream, and flows toward the Arctic regions where it replenishes dense sinking water to begin the cycle again.
The processes outlined above are greatly simplified. In reality, the deep ocean THC is much more complex, and is not fully understood. Our understanding of the connections between the deep ocean THC and Earth’s ecosystems is similarly incomplete, but most scientists agree that:
• The THC affects almost all of the world’s ocean (and for this reason, it is often called the ‘global conveyor belt’);
• The THC plays an important role in transporting dissolved oxygen and nutrients from surface waters to biological communities in deep water; and
• The THC is at least partially responsible for the fact that countries in northwestern Europe (Britain and Scandinavia) are about 9ºC warmer than other locations at similar latitudes.
In recent years, changes in the Arctic climate have led to growing concerns about the possible effects of these changes on the deep ocean THC. In the past 30 years, parts of Alaska and Eurasia have warmed by about six degrees Celsius. In the last 20 years, the extent of Arctic sea ice has decreased by 5%, and in some areas, sea ice thickness has decreased by 40%. Overall, the Arctic climate is warming more rapidly than elsewhere on Earth. Reasons for this include:
- When snow and ice are present, as much as 80% of solar energy that reaches Earth’s surface is reflected back into space. As snow and ice melt, surface reflectivity (called ‘albedo’) is reduced, so more solar energy is absorbed by Earth’s surface;
- Less heat is required to warm the atmosphere over the Arctic because the Arctic atmosphere is thinner than elsewhere;
- With less sea ice, the heat absorbed by the ocean in summer is more easily transferred to the atmosphere in winter.
Dense water sinking in the North Atlantic Ocean is one of the principal forces that drives the circulation of the global conveyor belt. Since an increase in freshwater inflow (such as from melting ice) or warmer temperatures in these areas would weaken the processes that cause seawater density to increase, these changes could also weaken the global conveyor belt.
More About Narwhals
Narwhals (Monodon monoceros) are classified as members of the order Cetacea, which includes whales, dolphins, and porpoises. Because they have teeth, they are members of the suborder Odontoceti, or toothed whales. Actually, they only have two teeth, in the upper jaw. In most female narwhals, the teeth never erupt through the gum. In males, however, the left tooth not only emerges from the gum but continues to grow out of the jaw to form a tusk that may be nine feet long. Seen through the narwhal’s eyes, the tusk grows in a counterclockwise spiral. Rarely, the right tooth may also develop into a tusk. There have also been reports of one or two tusks in female narwhals. The narwhal’s tusk may have been the source for myths about unicorns, and many ideas have been suggested for its actual function. Since most female narwhals do not have tusks, the most widely accepted hypothesis is that it is a secondary sexual characteristic, possibly involved with mating behavior (e.g., as a display feature analogous to a peacock’s feathers), or as a weapon in battles over possession of females. Male narwhals reach a length of about 4.7 m (15 ft) and weigh an average of 1,600 kg (about 3,500 lb), while females are somewhat smaller with an average length of 4.0 m (13 ft), and average weight of 900 kg (about 2,000 lb).
Narwhals spend their entire lives in the Arctic, and range from the Canadian Arctic to central Russia. They feed on fish (including polar cod, Greenland halibut, flounder, salmon, and herring), cephalopods (squids and octopuses), and shrimp. Since they are mammals, narwhals must surface periodically to breathe air, but are also capable of deep dives. Researchers have documented as many as 20 dives per day to depths of 1,500 m (4,900 ft) or more.
Narwhals seem to prefer deep water near loose pack ice. In the summer, they occupy deep bays and fjords in the Canadian High Arctic and Greenland. As winter approaches, narwhals migrate into the pack ice of Baffin Bay, the northern Davis Strait, and adjacent waters. Migrating narwhals may form groups that contain thousands of individuals, but at other times are found in pods of 6 to 30 animals. During months when ice is forming, narwhals are in danger of being trapped beneath the ice. Such entrapments are known to have killed hundreds of narwhals.
Data on narwhal reproduction are limited, but suggest that
• Males reach sexual maturity at eight to nine years;
• Females become sexually mature at four to seven years;
• Mating usually occurs in mid-April;
• The gestation period is 15 months;
• Calves weigh about (180 lb) at birth;
• A mature female produces one calf every three years; and
• A calf remains with its mother for up to 20 months.
Narwhals live 50 years or more. Their natural enemies include orcas, and (rarely) walruses and polar bears. Narwhals have been traditionally hunted by indigenous Arctic peoples who value them as a staple food (the skin is rich in vitamin C), as well as for their tusks (though international efforts to control the global ivory trade may have reduced tusk sales in recent years). About 50,000 narwhals are estimated to live in Greenland and Canada, but recent research suggests that the numbers have declined by about 6% since the 1980’s. Three possible causes have been suggested:
• Increased competition for food, due to the development of an inshore fishery for Greenland halibut; and
• Climate change (in contrast to the overall trend in the Arctic, sea ice in Baffin Bay has been increasing over the last several decades, increasing the risk of entrapment)