Labrador Sea Water is an intermediate water mass characterized by cold water, relatively low salinity compared to other intermediate water masses, and high concentrations of both oxygen and anthropogenic tracers.
[Pickart, Robert S., et al. "Is Labrador Sea Water formed in the Irminger basin?" Deep-Sea Research Part I: Oceanographic Research Papers 50.1 (2003): 23-52] It is formed by convective processes in the
Labrador Sea
The Labrador Sea (French: ''mer du Labrador'', Danish: ''Labradorhavet'') is an arm of the North Atlantic Ocean between the Labrador Peninsula and Greenland. The sea is flanked by continental shelves to the southwest, northwest, and northeast. It ...
[Yashayaev, I.M., et al. "Recent Decline of the Labrador Sea Water." Bedford Institute of Oceanography, 2000] located between
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...
and the northeast coast of the
Labrador Peninsula
The Labrador Peninsula, or Quebec-Labrador Peninsula, is a large peninsula in eastern Canada. It is bounded by the Hudson Bay to the west, the Hudson Strait to the north, the Labrador Sea to the east, and the Gulf of Saint Lawrence to the sout ...
. Deep convection in the Labrador Sea allows colder water to sink forming this water mass, which is a contributor to the upper layer of
North Atlantic Deep Water
North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the ...
. North Atlantic Deep Water flowing southward is integral to the Atlantic Meridional Overturning Circulation. The Labrador Sea experiences a net heat loss to the atmosphere annually.
Formation
Convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the conve ...
in the Labrador Sea is the result of a combination of cyclonic oceanographic circulation of the sea currents and cyclonic atmospheric forcing. At the southern tip of Greenland, water enters the
West Greenland Current
The West Greenland Current is a weak cold water current that flows to the north along the west coast of Greenland. The current results from the movement of water flowing around the southernmost point of Greenland caused by the East Greenland Curr ...
from the
East Greenland Current
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 t ...
, continues to flow northwest around the Baffin Bay, and then southeast into the Baffin Island Current continuing in the same direction in the
Labrador Current
The Labrador Current is a cold current in the North Atlantic Ocean which flows from the Arctic Ocean south along the coast of Labrador and passes around Newfoundland, continuing south along the east coast of Canada near Nova Scotia. Near Nova Scot ...
.
Sea ice in the winter months inhibits surface flow into Baffin Bay. The Labrador Current and the Western Greenland Current flow in opposite directions resulting in a cyclonic
eddy
Eddie or Eddy may refer to:
Science and technology
*Eddy (fluid dynamics), the swirling of a fluid and the reverse current created when the fluid flows past an obstacle
* Eddie (text editor), a text editor originally for BeOS and now ported to Lin ...
. During winter months low pressure dominates in this region, and in years with a positive
North Atlantic Oscillation
The North Atlantic Oscillation (NAO) is a weather phenomenon over the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the ...
deeper convection is observed.
Spreading
Labrador Sea Water spreads through the North Atlantic Ocean by three routes: northeast directly into the Irminger Sea, into the eastern North Atlantic by means of the deep North Atlantic current, and meridionally via the Deep Western Boundary Current.
Oceanographer Robert Pickart, in a paper published in 2002, presented data that suggest that the Labrador Sea is not the only formation site for Labrador Sea Water. They observed similar convective processes in the Irminger Sea and noted that transit times for Labrador Sea Water into Irminger Sea were unusually fast, suggesting that there is another source in the Irminger Sea.
Variability
Labrador Sea Water properties experience seasonal and interannual variations. In late spring and summer, large amounts of cold freshwater accumulate from melting ice and are mixed downward during convection. The source for heat in the Labrador Sea is modified North Atlantic Current water after circulating the
subpolar gyre
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 determ ...
.
[Straneo, F. "Heat and Freshwater Transport through the Central Labrador Sea." Journal of Physical Oceanography 36 (2005)] In winter the sea becomes more saline as freshwater freezes to form sea ice. The greatest seasonal variability is largely confined to the surface waters, however an annual cycle of convective mixing and re-stratification is observed throughout the water column. Warming and increased salinity in the lower level and freshening at the surface is associated with re-stratification (May–December), whereas a convective mixing period (January–April) leads to cooling and a decrease in salt content in intermediate and deep waters and an increase in salt content at the surface.
Interannual variations in the intermediate Labrador Sea Water are due largely to changes in convection throughout these periods. Weak convective periods are associated with more heat in the water column and deep convective periods are characterized by cold water. In the early 1990s, several consecutive severe winters contributed towards deep convection in the Labrador Sea. These winters were also associated with strong positive fluctuations in the North Atlantic Oscillation. Labrador Sea Water became very cold, fresh, and dense during this period, and the layer extended to depths of 2300m in the spring of 1994.
Due to weakened convection, Labrador Sea Water began warming significantly and increased in salinity over the following decade. This trend continued through 2010 and 2011 when weak convection was observed in relation with negative North Atlantic Oscillation. Deep convection was observed again in 2012 with the Labrador Sea Water reaching 1400m, corresponding with a positive North Atlantic Oscillation similar to those seen in the early 1990s.
See also
*
Labrador Sea
The Labrador Sea (French: ''mer du Labrador'', Danish: ''Labradorhavet'') is an arm of the North Atlantic Ocean between the Labrador Peninsula and Greenland. The sea is flanked by continental shelves to the southwest, northwest, and northeast. It ...
*
North Atlantic Deep Water
North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the ...
*
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
*
North Atlantic Oscillation
The North Atlantic Oscillation (NAO) is a weather phenomenon over the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the ...
References
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Oceanography