Ocean Current | The Canadian Encyclopedia

Ocean Current

An ocean current is a large ( 100 kilometer or more ), largely permanent, horizontal movement of water at all depths in the oceans. Currents are generated by winds, excessive cooling or dehydration at the ocean come on ( thermohaline processes ) and tidal forces .

Wind-Driven Currents

In the Atlantic and Pacific oceans north of the equator, the blend effects of the potent westbound winds ( between 30 and 60° N ) and the northeastern deal winds ( 10-20° N ) cause the near-surface waters to circulate in 2 large, clockwise gyres. Wind puff on the water is the primary drive coerce. The rotation of the Earth then causes the net motion of the upper layer ( internet explorer, Ekman layer, from 0-100 molarity depth ) to be to the right of the tip commission ( the Coriolis effect ). A convergence of water develops in the Ekman level between the westerlies and the trade winds, creating a hard-hitting area in the ocean around which water circulates clockwise. In the Atlantic this subtropical coil includes the Gulf Stream and the North Atlantic, Canary and North Equatorial currents ; in the North Pacific, the North Equatorial, Kuroshio, North Pacific and California currents .
north of the westerlies, divergences in the Ekman layers create low-pressure areas leading to counterclockwise subpolar gyres. The North Atlantic subpolar coil includes the North Atlantic, Irminger, Greenland and Labrador currents ; the North Pacific subpolar coil, the North Pacific, Alaska and Oyashio currents. The main currents in BAFFIN BAY are partially an extension of the North Atlantic subpolar coil .
These ocean-scale gyres are asymmetrical : currents on the western side of the oceans, the Gulf Stream and the Kuroshio, are constrict ( 100 kilometer ) and strong ( up to 2.5 m/sec ). zonal currents ( those running west to east or east to west ), and those on the easterly sides of the oceans are across-the-board ( 500-1000 kilometer ) and slow ( 0.2 m/sec ). The intensification on the western side results from an increase in the Coriolis impression between the equator and the North Pole, caused by the Earth ‘s ball-shaped shape. Speeds in the major currents decrease with increasing depth, quickly in the upper 300 megabyte, but there are meaning manifestations of the strongest currents at the ocean bottom. The Gulf Stream and the Kuroshio are each estimated to transport, at their utmost, 15 ten 107 m3/sec of water. This volume is roughly 15 000 times the average hang of the St Lawrence River or enough to fill Lake Superior in about one day.

South of the equator, the predominate winds render counterclockwise subtropical gyres that are alike but less acute than those in the northern oceans. The southerly subpolar gyres merge to form a circumpolar stream around Antarctica, as there are no landmasses to break up the stream into gyres. ocean currents vary from day to day but, averaged over a month or so, they appear as constant features .
variability can be caused by long-period waves ( 100 hour ), specially when the current is in contact with the continental gradient. away from the coasts, the Gulf Stream and Kuroshio exhibit large meanders in their paths that have typical periods of 75 days. The meanders may be started by inner instabilities or by encounters with bomber mountains.

Thermohaline Currents

The second group of currents, those driven by thermohaline processes, are found below the wind-driven currents down to the bottomland of the ocean. They are not significant to high-seas commerce and are broadly known only to oceanographers. Most of these cryptic flows are created by acute cool of the ocean coat water in the Arctic and Antarctic. Cooling increases the density of water, causing it to sink. This new water ( because it was recently at the sea surface ) then moves away from the sinking region in distinct currents. gamey dehydration, eg, in the Mediterranean, besides increases density and subsequent sink by increasing the salt of the urine.

In the mid-ocean, alternate layers of urine come from different locations. For exemplar, in most of the North Atlantic Ocean, water at the penetrate comes from the Antarctic, but north of 45° N and west of the middle atlantic Ridge, the bottom water comes from the Iceland Sea, through the Denmark Strait between Greenland and Iceland. Above this layer is the water known as the North Atlantic Deep Water that partially originates in the norwegian Sea and flows into the Atlantic across the ridge between Iceland and the Faroe Islands. next highest ( at 1500-2000 m depth ) are the intermediate waters. Labrador Sea water, renewed during hard winters in the deep water east of the pack ice off Labrador, is found in the North Atlantic ( north of 45° N ). This water is recognizable by its low salt relative to the waters above and below. mediterranean water flows out of the Strait of Gibraltar and is recognized over much of the North Atlantic by its eminent brininess, a consequence of excessive vaporization in the Mediterranean Sea .

Effects

Currents have 2 very significant effects : they influence both FISHERIES and climate. Currents provide a intend by which the deep, nutrient-rich waters are raised up to the sunlit surface layers, thus promoting biological productivity. They besides transport significant quantities of hotness which strongly influences climate in coastal areas. For Canadians, the most crucial currents are the LABRADOR CURRENT off the East Coast, and the North Pacific Current, off the West Coast. The Labrador Current gives rise to one of the universe ‘s largest fisheries on the Labrador Continental Shelf and the GRAND BANKS of Newfoundland. The North Pacific Current provides a huge reservoir of heat and water that is partially transferred to coastal BC to produce a balmy climate and a big, generative afforest industry .
See besides COASTAL WATERS ; TIDE .