Test: Oceanography - 2

• The strong gravitational pull exerted by the Sun and the Moon on the Earth’s surface causes the tides. The tides are caused by the strong gravitational pull exerted on the surface of the Earth by the Sun and the Moon. Under the influence of the gravitational force of the Moon, the Earth’s water closer to the Moon is pulled and causes high tide.

• The intensity of tides can be magnified by the shape of bays and estuaries. Especially funnel-shaped bays can dramatically alter the magnitude of ' the tide. The classic example of this effect is the Bay of Fundy in Nova Scotia, which has the highest tides in the world (15 km). Incoming tides are scattered by the narrow inlets and shallow water. Strong seasonal flows in the spring can severely alter or mask the incoming tide in estuaries with strong tidal rivers, e.g. the Delaware River and Columbia River.

• Powerful offshore winds move water away from coastlines, magnify low tide exposures. Onshore winds can pile up water on the shoreline, virtually eliminating exposures to low tide. Sea levels are depressed by high-pressure systems, leading to clear sunny days with extremely low tides. By contrast, low-pressure systems that contribute to cloudy, rainy conditions typically are associated with tides that are much higher than predicted.

• The tides are caused by the strong gravitational pull exerted on the surface of the Earth by the Sun and the Moon. Under the influence of the gravitational force of the Moon, the Earth’s water closer to the Moon is pulled and causes high tide.

• The Sun, the Moon and the Earth are in the same line during the full moon and the new moon days, and the highest tide called spring tides can be seen on those days.

• But at the first and last quarters of the Moon, the ocean waters are drawn by the gravitational pull of Sun and Earth in diagonally opposite directions, resulting in low tides called neap tides.

• The California Current is a Pacific Ocean current that moves southward along the western coast of North America, beginning off southern British Columbia and ending off southern Baja California Peninsula.

• It is considered an Eastern boundary current due to the influence of the North American coastline on its course.

• It is also one of five major coastal currents affiliated with strong upwelling zones, the others being the Humboldt Current, the Canary Current, the Benguela Current, and the Somali Current.

• The California Current is part of the North Pacific Gyre, a large swirling current that occupies the northern basin of the Pacific.

• When cold and warm ocean current meets, the warm ocean current condenses after getting in contact with cold air and it results in fog.

• It also leads to a high rate of precipitation in the region. The circulation in the area where the Labrador Current and Gulf Stream meet is one of the most complex and variable regions in the world.

• Surface currents are generated largely by the wind. Their patterns are determined by wind direction, Coriolis forces from the Earth’s rotation, and the position of landforms that interact with the currents.

• Near the equator, the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.

• Solar energy makes the current warm or cold and decides their circulatory patterns.

• It flows down the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is even suggested that the Agulhas is the largest western boundary current in the world ocean. The Agulhas acts as an oceanic convergence zone.

• Due to mass continuity, this drives surface waters down, resulting in the upwelling of cold, nutrient-rich water south of the current.

• Unlike waves that break along the shore, Rossby waves are huge, undulating movements of the ocean that stretch horizontally across the planet for hundreds of kilometres in a westward direction.

• Also known as planetary waves, they naturally occur in rotating fluids.

• They are so large and massive that they can change Earth’s climate conditions.

(i) Cold currents are usually found on the west coast of the continents in the low and middle latitudes (true in both hemispheres) and on the east coast in the higher latitudes in the Northern Hemisphere.

(ii) Warm currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres). In the Northern Hemisphere, they are found on the west coasts of continents in high latitude.

• Equatorial counter-currents are major surface flows that carry water eastwards in the Atlantic, Indian, and Pacific Oceans.

• They are located near the equator and are sandwiched between two westward flowing currents, the North Equatorial Current and the South Equatorial Current.

• Equatorial counter-currents are unique, in that they flow in the opposite direction of the surface winds. The other major surface currents in the tropics flow in the same direction as the prevailing winds.

• The equatorial counter-currents are thus driven by a distinct surface wind pattern in the tropics. Strong westward trade winds result in westward surface flow in most of the tropical Atlantic and Pacific Oceans.

• A convergence zone is a region in the atmosphere where two prevailing flows meet. It is not a meeting of all major ocean currents.

• There is an upwelling of cold, nutrient-rich water south of the current. Additionally, the convergence tends to increase the concentration of plankton in and around the Agulhas.

Both Of These factors result in the area being one of enhanced primary productivity as compared to the surrounding waters.

• The Antarctic Circumpolar Current (ACC) (West Wind Drift) is an ocean current that flows clockwise from west to east around Antarctica.

• It is the largest ocean current. The ACC connects the Atlantic, Pacific and Indian Oceans, and serves as a principal pathway of exchange between them. The circumpolar current is driven by the strong westerly winds in the latitudes of the Southern Ocean.

• The current is circumpolar due to the lack of any landmass connecting with Antarctica and this keeps warm ocean waters away from Antarctica, enabling that continent to maintain its huge ice sheet. It means that in the Southern Hemisphere since there is no obstruction of the Antarctica continent, the west wind drifts across the Pacific, the Atlantic and the Indian Ocean in the south, forming a circulation (also known as the westerly circulation).

In the North Indian Ocean, a complete reversal of direction of Monsoon Current, twice a year is observed between summer and winter because the Monsoon winds change their direction according to seasons. South-West Monsoon Current (warm).

• In the summer season, the monsoon winds blow from south-west to north-east. Consequently, the ocean current also flows from south-west to north-east direction.

• The main current moves in the Arabian Sea and the Bay of Bengal along the coast of India. North-East Monsoon Current (warm)

• In the winter season, the monsoon winds blow from northeast to south-west. The ocean current also flows from northeast to south-west under the influence of these winds.

• Associated with the monsoon, it sees the migration of deep-sea oxygen minimum zone (OMZ) towards the coast. During the northeast monsoon, strong upwelling occurs along the western coast of India.

• During the southwest monsoon, upwelling occurs off the Somali and Arabian coasts and south of Java. It is most intense between 5° and 11° N, with the replacement of wanner surface water by the water of about 14 °C.

• It involves wind-driven motion of dense, cooler, and usually, nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton.

• Live coral is colonies of small animals embedded in calcium carbonate shells. It is a mistake to think of coral as plants or rocks. Coral heads consist of accumulations of individual animals called polyps, arranged in diverse shapes.

• Reef-building or hermatypic corals live only in the photic zone (above 50 m), the depth to which sufficient sunlight penetrates the water, allowing photosynthesis to occur.

• Coral polyps do not photosynthesise, but have a symbiotic relationship with zooxanthellae; these organisms live within the tissues of polyps and provide organic nutrients that nourish the polyp. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight.

• Coral reefs are vital to the world’s fisheries. They film the nurseries for about a quarter of the ocean’s fish and thus provide revenue for local communities as well as national and international fishing fleets.

• Coral reefs break the power of the waves during storms, hurricanes, typhoons, and even tsunamis. By helping to prevent coastal erosion, flooding, and loss of property on the shore, the reefs save billions of dollars each year in terms of reduced insurance and reconstruction costs and reduced need to build costly coastal defences.

• A new class of proteins capable of blocking HIV from penetrating T-cells has been discovered. The proteins have been found in a coral from Australia’s northern coast. Coral reefs are also being used in the treatment of cancer.