Beaufort Gyre

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Transpolar Drift and Beaufort Gyre are major ocean currents within the Arctic Ocean. BrnBld ArcticCurrents.svg
Transpolar Drift and Beaufort Gyre are major ocean currents within the Arctic Ocean.

The Beaufort Gyre is one of the two major ocean currents in the Arctic Ocean. It is roughly located north of the Alaskan and Canadian coast. In the past, Arctic sea-ice would circulate in the Beaufort gyre up to several years, leading to the formation of very thick multi-year sea-ice. [1] Due to warming temperatures in the Arctic, the gyre has lost an extensive amount of ice, practically turning what used to be a nursery for sea-ice to mature and grow into the thickest and oldest ice of the Arctic Ocean into a "graveyard" for older ice. [2] [3]

Contents

Dynamical mechanisms

Conditions in the Arctic have favored sea ice loss in recent years during the Northern Hemisphere summers. At the end of the 20th century, analyses of increasing Pacific Surface Water temperatures led to the discovery of a connection between these rising temperatures and the onset of severe loss of Arctic sea ice in the Beaufort Sea. A reason for the existence of this link was proposed: "...delayed winter ice formation allows for more efficient coupling between the ocean and wind forcing." These dynamical mechanisms are observed in the spin-up and circulation of the Beaufort Gyre. [4]

Arctic Sea Ice Age: 1984 - 2019

Housed in the western part of the Arctic Ocean is the Beaufort Gyre, whose growing reservoir of freshwater is shrouded in mystery. In recent years, this increasing freshwater content (FWC) has been the focal point of many studies, particularly those concerning coupled ocean-atmosphere dynamics. The majority of the Arctic’s freshwater content resides in the Beaufort Gyre. Although biased toward the Northern Hemisphere summer months, observations from submarines, ships, and stations on drifting ice suggest that the gyre has been expanding over the past two decades. Researchers have employed coupled sea-ice-ocean general circulation models in order to thoroughly analyze these observations. Model results show that Ekman transport plays an integral role in the variability of freshwater in the gyre, and thus in the Arctic Ocean. The prevailing rotational direction of the Beaufort Gyre is clockwise, following the prevailing wind circulation of the Polar High. Coriolis veers moving objects to the right in the northern hemisphere and "to the right" is inwards in a clockwise rotating system. This is why anything floating, including fresher water, tends to move toward the centre of the system. Indeed, there is a slight bulge in the centre of the Beaufort gyre when it is rotating in its predominant clockwise direction. If, as is speculated, as the Arctic Ocean becomes a heat collector resulting in a low pressure, counter clockwise rotating system, the Beaufort Gyre can be expected to follow suit and send the fresher water outward to be captured by the transpolar current. This could well bring up the saltier, slightly warmer Atlantic water which lies under the floating, fresher Arctic water.

Variations in the Ekman transport change the sea surface height and depth of the halocline, resulting in Ekman pumping. During anticyclonic regimes—where the wind stress curl is negative—freshwater is pumped into the Beaufort Gyre; during cyclonic regimes—where wind stress curl is positive—freshwater is released into the Arctic Ocean, where it can then flow into the North Atlantic. Giles et al. (2012) [5] conclude that the variability in freshwater content varies with wind stress curl. The wind stress curl used by Giles et al. (2012) is from the NCEP/NCAR Reanalysis data at the National Oceanic & Atmospheric Administration, Earth System Research Laboratory, Physical Sciences Division (NOAA/OAR/ESRL PSD) in Boulder, Colorado, USA.

The seasonal cycle of freshwater content does not only concern mechanical (Ekman pumping) processes, but thermal (ice formation) processes as well. The Beaufort Gyre contains a mean volume of 800 km3 of frozen freshwater, or sea ice, based on a mean ice thickness of 2 meters. During the June–July months, the mean seasonal cycle of freshwater content peaks; in this season, sea ice thickness reaches a minimum, implying that the amount of melted sea ice has reached a maximum. The maximum in freshwater content released into the ocean waters coincides with a maximum in wind stress curl (i.e., a minimum in Ekman pumping), allowing for a high volume of freshwater to seep into the Arctic Ocean circulation. This rapid influx of freshwater into the Arctic circulation forces a large volume of freshwater to outflow into the North Atlantic basin, affecting the Atlantic Meridional Overturning Circulation. [6]

Studies

The Beaufort Gyre has formed a dome of freshwater that has expanded vertically by about 15 centimetres (5.9 in) since 2002; by 2011 it had swelled to about 8,000 cubic kilometres (1,900 cu mi) in volume. [7] The freshwater within this gyre represents about 10% of all the freshwater in the Arctic Ocean; the majority of the Arctic's freshwater supply originates from Russian rivers as runoff. [7] The clockwise circulation of the Beaufort Gyre is induced by the wind patterns associated with the permanent anticyclonic high pressure system over the western part of the Arctic. In a clockwise-rotating gyre in the Northern Hemisphere, the Coriolis force causes the ocean water to flow inward toward the gyre's center where it accumulates, effectively forming a dome of water. If the wind patterns shift into a cyclonic circulation due to the residence of a low pressure system (rising air induced by warmer ocean temperatures a greater volume of open Arctic Ocean water), this will cause the circulation of the Beaufort Gyre to reverse and flow counter-clockwise. If this occurs, the Coriolis force would bend the flow out and away from the center of the gyre and, instead of the formation of a rising water dome, a depression would form and upwelling of the warmer water from the Atlantic ocean would occur.

Oceanographer Andrey Proshutinsky has theorized that if the winds and the gyre's circulation were to weaken, high volumes of freshwater could leak out of the eastern part of the Arctic Ocean into the Northern Atlantic Ocean, impacting the Thermohaline Circulation and thus climate. [8]

Due to seasonal sea ice formation, the Beaufort Gyre is difficult to access and thus study in the Northern Hemisphere winter months; the lack of sunlight in these months forces the use of artificial light. [9] Studies by Arthur S. Dyke and others show that if the volume of outflow of rivers into the Beaufort Gyre increase, the gyre itself might spatially shift toward the right. [10]

See also

Related Research Articles

Northern Hemisphere Half of Earth that is north of the Equator

The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's North Pole.

Upwelling Replacement by deep water moving upwards of surface water driven offshore by wind

Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. The biomass of phytoplankton and the presence of cool water in those regions allow upwelling zones to be identified by cool sea surface temperatures (SST) and high concentrations of chlorophyll-a.

Ocean current Directional mass flow of oceanic water generated by external or internal forces

An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, shoreline configurations, and interactions with other currents influence a current's direction and strength. Ocean currents are primarily horizontal water movements.

Physical oceanography Study of physical conditions and physical processes within the ocean

Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.

Thermohaline circulation A part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes

Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes. This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. The water in these circuits transport both energy and mass around the globe. As such, the state of the circulation has a large impact on the climate of the Earth.

Ocean gyre Any large system of circulating ocean currents

In oceanography, a gyre is any large system of circulating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity, horizontal friction and vertical friction determine the circulatory patterns from the wind stress curl (torque).

East Greenland Current Current from Fram Strait to Cape Farewell off the eastern coat of Greenland

The East Greenland Current (EGC) is a cold, low-salinity current that extends from Fram Strait (~80N) to Cape Farewell (~60N). The current is located off the eastern coast of Greenland along the Greenland continental margin. The current cuts through the Nordic Seas and through the Denmark Strait. The current is of major importance because it directly connects the Arctic to the Northern Atlantic, it is a major contributor to sea ice export out of the Arctic, and it is a major freshwater sink for the Arctic.

Equatorial Counter Current Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans

The Equatorial Counter Current is an eastward flowing, wind-driven current which extends to depths of 100–150 metres (330–490 ft) in the Atlantic, Indian, and Pacific Oceans. More often called the North Equatorial Countercurrent (NECC), this current flows west-to-east at about 3-10°N in the Atlantic, Indian Ocean and Pacific basins, between the North Equatorial Current (NEC) and the South Equatorial Current (SEC). The NECC is not to be confused with the Equatorial Undercurrent (EUC) that flows eastward along the equator at depths around 200 metres (660 ft) in the western Pacific rising to 100 metres (330 ft) in the eastern Pacific.

The Sverdrup balance, or Sverdrup relation, is a theoretical relationship between the wind stress exerted on the surface of the open ocean and the vertically integrated meridional (north-south) transport of ocean water.

Ice shove

An ice shove is a surge of ice from an ocean or large lake onto the shore. Ice shoves are caused by ocean currents, strong winds, or temperature differences pushing ice onto the shore, creating piles up to 12 metres high. Ice shoves can be caused by temperature fluctuations, wind action, or changing water levels and can cause devastation to coastal Arctic communities. Climate change will also play a role in the formation and frequency of ice shove events; a rise in global temperatures leads to more open water to facilitate ice movement and low pressure systems to destabilize ice sheets and send them shoreward.

Atlantic meridional overturning circulation System of currents in the Atlantic Ocean

The Atlantic meridional overturning circulation (AMOC) is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters that are part of the thermohaline circulation. These "limbs" are linked by regions of overturning in the Nordic and Labrador Seas and the Southern Ocean. The AMOC is an important component of the Earth's climate system, and is a result of both atmospheric and thermohaline drivers.

Ekman transport Net transport of surface water perpendicular to wind direction

Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman Transport is a component of wind-driven ocean current. Ekman transport occurs when ocean surface waters are influenced by the friction force acting on them via the wind. As the wind blows it casts a friction force on the ocean surface that drags the upper 10-100m of the water column with it. However, due to the influence of the Coriolis effect, the ocean water moves at a 90° angle from the direction of the surface wind. The direction of transport is dependent on the hemisphere: in the northern hemisphere, transport occurs at 90° clockwise from wind direction, while in the southern hemisphere it occurs at 90° anticlockwise. This phenomenon was first noted by Fridtjof Nansen, who recorded that ice transport appeared to occur at an angle to the wind direction during his Arctic expedition during the 1890s. Ekman transport has significant impacts on the biogeochemical properties of the world's oceans. This is because it leads to upwelling and downwelling in order to obey mass conservation laws. Mass conservation, in reference to Ekman transfer, requires that any water displaced within an area must be replenished. This can be done by either Ekman suction or Ekman pumping depending on wind patterns.

In physical oceanography and fluid dynamics, the wind stress is the shear stress exerted by the wind on the surface of large bodies of water – such as oceans, seas, estuaries and lakes. Stress is the quantity that describes the magnitude of a force that is causing a deformation of an object. Therefore, stress is defined as the force per unit area and its SI unit is the Pascal. When the deforming force acts parallel to the object's surface, this force is called a shear force and the stress it causes is called a shear stress. When wind is blowing over a water surface, the wind applies a wind force on the water surface. The wind stress is the component of this wind force that is parallel to the surface per unit area. Also, the wind stress can be described as the flux of horizontal momentum applied by the wind on the water surface. The wind stress causes a deformation of the water body whereby wind waves are generated. Also, the wind stress drives ocean currents and is therefore an important driver of the large-scale ocean circulation. The wind stress is affected by the wind speed, the shape of the wind waves and the atmospheric stratification. It is one of the components of the air–sea interaction, with others being the atmospheric pressure on the water surface, as well as the exchange of energy and mass between the water and the atmosphere.

Boundary current Ocean current with dynamics determined by the presence of a coastline

Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents.

Weddell Gyre One of two gyres within the Southern Ocean

The Weddell Gyre is one of the two gyres that exist within the Southern Ocean. The gyre is formed by interactions between the Antarctic Circumpolar Current and the Antarctic Continental Shelf. The gyre is located in the Weddell Sea, and rotates clockwise. South of the Antarctic Circumpolar Current (ACC) and spreading northeast from the Antarctic Peninsula, the gyre is an extended large cyclone. Where the northeastern end ends at 30°E, which is marked by the southward turn of the ACC, the northern part of the gyre spreads over the Southern Scotia Sea and goes northward to the South Sandwich Arc. Axis of the gyre is over the southern flanks of the South Scotia, America-Antarctic, and Southwest Indian Ridges. In the southern part of the gyre, the westward return flow is about 66 sverdrup (Sv), while in the northern rim current, there is an eastward flow of 61 Sv.

Indian Monsoon Current Seasonally-varying ocean current regime found in the tropical regions of the northern Indian Ocean

The Indian Monsoon Current refers to the seasonally varying ocean current regime found in the tropical regions of the northern Indian Ocean. During winter, the flow of the upper ocean is directed westward from near the Indonesian Archipelago to the Arabian Sea. During the summer, the direction reverses, with eastward flow extending from Somalia into the Bay of Bengal. These variations are due to changes in the wind stress associated with the Indian monsoon. The seasonally reversing open ocean currents that pass south of India are referred to as the Winter Monsoon Current and the Summer Monsoon Current. The Somali Current, which is strongly linked to the Indian monsoon, is also discussed in this article.

The Arctic dipole anomaly is a pressure pattern characterized by high pressure on the arctic regions of North America and low pressure on those of Eurasia. This pattern sometimes replaces the Arctic oscillation and the North Atlantic oscillation. It was observed for the first time in the first decade of 2000s and is perhaps linked to recent climate change. The Arctic dipole lets more southern winds into the Arctic Ocean resulting in more ice melting. The summer 2007 event played an important role in the record low sea ice extent which was recorded in September. The Arctic dipole has also been linked to changes in arctic circulation patterns that cause drier winters in Northern Europe, but much wetter winters in Southern Europe and colder winters in East Asia, Europe and the eastern half of North America.

Transpolar Drift Stream An ocean current of the Arctic Ocean

The Transpolar Drift Stream is a major ocean current of the Arctic Ocean, transporting sea ice from the Laptev Sea and the East Siberian Sea towards Fram Strait. Drift experiments with ships such as the Fram or the Tara expedition showed that the drift takes between two and four years.

A Wind generated current is a flow in a body of water that is generated by wind friction on its surface. Wind can generate surface currents on water bodies of any size. The depth and strength of the current depend on the wind strength and duration, and on friction and viscosity losses, but are limited to about 400 m depth by the mechanism, and to lesser depths where the water is shallower. The direction of flow is influenced by the Coriolis effect, and is offset to the right of the wind direction in the Northern Hemisphere, and to the left in the Southern Hemisphere. A wind current can induce secondary water flow in the form of upwelling and downwelling, geostrophic flow, and western boundary currents.

Eddy pumping is a component of mesoscale eddy-induced vertical motion. It is a physical mechanism through which vertical motion is created from variations in an eddy’s rotational strength. Anticyclonic (cyclonic) eddies lead primarily to upwelling (downwelling) in the Northern Hemisphere and vice-versa in the Southern hemisphere. It is a key mechanism driving biological and biogeochemical processes in the ocean such as algal blooms and the carbon cycle.

References

  1. ↑ "Dynamics: Circulation | National Snow and Ice Data Center". nsidc.org. Retrieved 2020-09-07.
  2. ↑ "Arctic Sea Ice Age 2016". svs.gsfc.nasa.gov. Retrieved 2020-09-07.
  3. ↑ "2019 Arctic Report Card: Old, thick ice barely survives in today's Arctic | NOAA Climate.gov". www.climate.gov. Retrieved 2020-09-07.
  4. ↑ Serreze, M. C.; Holland, M. M.; Stroeve, J. (2007). "Perspectives on the Arctic's Shrinking Sea Ice Cover". Science. 315 (5818): 1533–1536. Bibcode:2007Sci...315.1533S. doi:10.1126/science.1139426. PMID   17363664.
  5. ↑ Giles, Katharine A.; Laxon, Seymour W.; Ridout, Andy L.; Wingham, Duncan J.; Bacon, Sheldon (2012). "Western Arctic Ocean freshwater storage increased by wind-driven spin-up of the Beaufort Gyre". Nature Geoscience. 5 (3): 194–197. Bibcode:2012NatGe...5..194G. doi:10.1038/ngeo1379.
  6. ↑ Proshutinsky, Andrey; Krishfield, Richard; Timmermans, Mary-Louise; Toole, John; Carmack, Eddy; McLaughlin, Fiona; Williams, William J.; Zimmermann, Sarah; Itoh, Motoyo; Shimada, Koji (2009). "Beaufort Gyre freshwater reservoir: State and variability from observations". Journal of Geophysical Research. 114 (C1): C00A10. Bibcode:2009JGRC..114.0A10P. doi:10.1029/2008JC005104. hdl: 1912/3680 .
  7. 1 2 Amos, Jonathan (23 January 2012). "Arctic Ocean freshwater bulge detected". BBC News . Retrieved 23 January 2012.
  8. ↑ "On top of the World". Oceanus. FindArticles. September 2005. Archived from the original on 2012-07-08. Retrieved 19 October 2009.
  9. ↑ Lippsett, Lonny (2005), "The Flywheel of the Arctic Climate Engine: Remote Beaufort Gyre Expeditions Reveal Clues to Climate Change", Oceanus, 44 (3): 28. Expanded Academic ASAP. Web. 13 Oct. 2009.
  10. ↑ Dyke, Arthur S. (1997), "Changes in Driftwood Delivery to the Canadian Arctic Archipelago: the Hypothesis of Postglacial Oscillations of the Transpolar Drift" (PDF), Arctic, 50 (1): 1–16, doi:10.14430/arctic1086 . Expanded Academic ASAP. Web. 13 Oct. 2009.
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