Polar Oceanography: Arctic and Southern Ocean Dynamics and Global Connections
Polar Oceanography: Arctic and Southern Ocean Dynamics and Global Connections
Polar oceanography examines the unique oceanographic processes of the Arctic and Southern Oceans, regions that play an outsized role in the global climate system despite their remote locations. The polar oceans are characterized by extreme seasonal variations in light and temperature, the presence of sea ice, and unique physical processes including deep water formation that drives global ocean circulation. The polar oceans are also experiencing some of the most rapid environmental changes on Earth due to climate change, with the Arctic warming at two to three times the global average. Understanding polar oceanography is essential for predicting global climate, sea level rise, and the future of polar ecosystems. This guide explores the physical and biological oceanography of the polar regions and their connections to the global ocean.
The Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the world’s oceans, covering about fourteen million square kilometers. It is surrounded by the landmasses of North America, Europe, and Asia and is connected to the global ocean primarily through the Fram Strait and the Bering Strait. The Arctic Ocean is characterized by a strong stratification, with a low-salinity surface layer maintained by river input and sea ice melt overlying warmer, saltier Atlantic water.
The Arctic Ocean is unique in being largely ice-covered for most of the year. The sea ice cover has declined dramatically over the past four decades, with summer sea ice extent decreasing by about forty percent since satellite records began in 1979. The loss of sea ice is one of the most visible indicators of climate change and has profound implications for Arctic ecosystems, indigenous communities, and global climate.
The Southern Ocean
The Southern Ocean surrounds Antarctica and is defined by the Antarctic Circumpolar Current, the largest ocean current on Earth. The Southern Ocean connects the Atlantic, Pacific, and Indian Oceans and plays a critical role in global ocean circulation. The ACC transports about one hundred thirty million cubic meters of water per second, more than one hundred times the flow of all the world’s rivers combined.
The Southern Ocean is a region of intense air-sea interaction and deep water formation. Cold, dense water forms in the Weddell and Ross Seas, sinking to form Antarctic Bottom Water that spreads throughout the global ocean. The Southern Ocean is also the primary region where deep water from the Atlantic, Pacific, and Indian Oceans returns to the surface, closing the global overturning circulation.
Sea Ice Dynamics
Sea ice is a defining feature of polar oceans, covering about seven percent of the global ocean surface at its maximum extent. Sea ice forms when seawater freezes, expelling salt and creating ice that is less dense than the surrounding water. The growth and melt of sea ice follow a seasonal cycle, with maximum extent in late winter and minimum in late summer.
Sea ice plays multiple roles in the climate system. It reflects solar radiation, with its high albedo reducing the amount of heat absorbed by the ocean. It insulates the ocean from the atmosphere, reducing heat exchange. It influences ocean circulation through the rejection of salt during ice formation, which increases surface water density and can drive deep convection.
Deep Water Formation
The polar oceans are the source of the deep water masses that drive global ocean circulation. In the North Atlantic, cooling and sea ice formation in the Greenland and Norwegian Seas create North Atlantic Deep Water, which flows southward through the Atlantic Basin. In the Southern Ocean, Antarctic Bottom Water forms in the Weddell and Ross Seas and spreads northward into the global ocean.
Deep water formation is a key process in the global carbon cycle. When surface waters sink, they carry dissolved carbon dioxide into the deep ocean, where it can be stored for centuries to millennia. Changes in deep water formation, which are projected under climate change, could alter the efficiency of the ocean carbon sink.
Polar Marine Ecosystems
Polar marine ecosystems are adapted to extreme seasonal conditions, with intense productivity during the summer months when twenty-four-hour sunlight supports phytoplankton blooms. Krill, small shrimp-like crustaceans, are a key component of Southern Ocean food webs, serving as the primary food source for whales, seals, penguins, and fish. The Antarctic krill fishery is the largest in the Southern Ocean.
Arctic marine ecosystems are changing rapidly as sea ice declines. Ice-associated algae, which grow on the underside of sea ice and form the base of the food web in spring, are declining with the loss of sea ice. The opening of Arctic waters is allowing subarctic species to move northward while challenging ice-dependent species including polar bears and walruses.
Climate Change in the Polar Regions
The polar regions are experiencing some of the most rapid environmental changes on Earth. Arctic amplification, where the Arctic warms faster than the global average, is caused by feedbacks including the loss of sea ice, which reduces albedo and increases heat absorption. The warming of the Arctic has implications for global weather patterns, including potential effects on the jet stream and mid-latitude weather.
Antarctica is also experiencing rapid change, particularly in West Antarctica and the Antarctic Peninsula. The melting of Antarctic ice sheets is accelerating, contributing to sea level rise. The warming of the Southern Ocean is affecting krill populations and the marine food web. The changes in polar regions have global implications through sea level rise, changes in ocean circulation, and feedbacks in the climate system.
Frequently Asked Questions
Why are the polar oceans important for global climate? The polar oceans drive global ocean circulation through deep water formation, store vast amounts of carbon, and reflect solar radiation through sea ice. Changes in polar oceans affect the entire global climate system.
How much sea ice is lost each year? Arctic sea ice extent has declined by about thirteen percent per decade since satellite records began. The summer minimum extent has declined by about forty percent. Antarctic sea ice has shown more variable trends.
What lives in the waters under the ice? The waters under polar sea ice support diverse ecosystems including algae that grow on the underside of ice, krill, fish, and the predators that feed on them. The ice provides habitat and shelter for many organisms.
How do scientists study polar oceans? Polar oceanography uses icebreakers, autonomous underwater vehicles, moored instruments, satellite remote sensing, and drifting buoys. The harsh conditions and logistical challenges make polar research expensive and difficult.
Conclusion
Polar oceanography reveals the critical role of the Arctic and Southern Oceans in the global climate system. From deep water formation that drives ocean circulation to sea ice that reflects solar radiation and provides habitat, the polar oceans are integral to Earth’s functioning. The rapid changes occurring in polar regions, driven by climate change, have profound implications for global climate, sea level, and marine ecosystems. Understanding polar oceanography is essential for predicting and responding to these changes.