Overview[ edit ] The global conveyor belt on a continuous-ocean map The movement of surface currents pushed by the wind is fairly intuitive. For example, the wind easily produces ripples on the surface of a pond.
Temperature and salinity Temperature The oceans tend to be stratified, the principal factor being temperature; the bottom waters of the deep parts are intensely cold, with temperatures only slightly above freezing. The surface zone, where temperature variations are perceptible, is between and 1, feet and metres thick.
It is more compressed in the temperate eastern Pacific, along the coasts of North and Central America, where cold water appears at a shallower depth compared with the central and western Pacific. Ocean temperatures in the North Pacific tend to be higher than those in the South Pacific because the ratio of land to sea areas is larger in the Northern Hemisphere and because Antarctica also influences water temperature.
The mean position of the thermal equator the line on the Earth on which the highest average air temperatures are found; the line migrates latitudinally with the changing angular distance from the Equator of the Sun in the Pacific, although it lies in the Northern Hemisphere, is nearer to the geographic equator than in the Atlantic and Indian oceans.
There is a pronounced difference in temperature and salinity between the surface and deep zones of the Pacific. Salinity The salinity patterns of the surface waters of the Pacific are influenced largely by wind and by precipitation and evaporation patterns. The waters within the belt of calm and variable winds near the Equator have lower salinities than those in the trade-wind belts.
In the equatorial belt, relatively large amounts of rain fall and little evaporation occurs, both because of low wind speeds and because of the generally cloudy skies; salinity in the equatorial belt runs as low as 34 parts per thousand.
Latitudinal variation in precipitation and evaporation and its relationship to major wind belts and oceanic salinity. The highest surface salinities in the open Pacific occur in the southeastern area, where they reach 37 parts per thousand; in the corresponding trade-wind Ocean water salinity at equator in the North Pacific, the maximum salinity seldom reaches 36 parts per thousand.
Pacific waters near Antarctica have salinities of less than about 34 parts; the lowest salinities—less than about 32 parts—occur in the extreme northern zone of the Pacific. The heavy rainfall of the western Pacific, associated with the monsoons of the region, gives Ocean water salinity at equator to relatively low salinities.
Seasonal variations are significant in the western Pacific as well as in the eastern Pacific, caused by seasonal changes in surface currents. Squeezed between the equatorial currents is a well-defined countercurrentthe axis of which is always north of the Equator and which extends from the Philippines to the shores of Ecuador.
The major part of the North Equatorial Current swings northward in the vicinity of the Philippines to form the warm Kuroshio also called the Japan Current. To the east of Japan the Kuroshio swings eastward to form the Kuroshio Extension.
The surface waters of the Bering Sea circulate in a counterclockwise direction. The cold, southeast-flowing California Current forms the eastern segment of the returning branch of the North Equatorial Current system. The main part of the South Equatorial Current divides into three large branches as it flows westward.
The two westernmost branches, on reaching the east coast of Australiaswing south to form the East Australian Currentwhich, becoming the Tasman Current, turns back to the northeast and dissipates west of New Zealand. This event is associated with the appearance of unusually warm ocean conditions off the tropical coast of South America and with changes in tropical atmospheric patterns called the Southern Oscillation that can adversely affect fishing, agriculture, and precipitation patterns along the west coast of South America.
Deepwater circulation Observations of temperature and salinity at different levels in the ocean reveal well-defined layers, each forming a water mass distinguished by its own temperature and salinity characteristics. It appears that the most important influence on the vertical circulation of the Pacific is the cold water generated around the Antarctic continent.
This dense circumpolar water sinks and then spreads northward to form the bottom layer of the greater part of the Pacific.
It is thought that cold, deep water flows northward in the western Pacific in a relatively well-defined current from the vicinity of Antarctica to Japan. Branches from this deep main stream convey cold water eastward and then poleward in both hemispheres.
Deepwater circulation is influenced by the descent of surface water at zones of convergence of neighbouring water flows. In the Pacific Tropical Convergence, which coincides with the Equatorial Countercurrentwater sinks to a depth of about feet 90 metres before it spreads laterally.
Water that sinks at the convergences spreads laterally at increasing depths as the distance from the Equator increases. The Antarctic Convergence lies in the zone of the southern westerly winds.
A corresponding Arctic Convergence is prominent in the northeastern Pacific. To compensate for downward-moving water, some water rises at zones of divergence, particularly along the so-called cold-water coasts of both North and South America, where upwelling of cold water is a well-marked phenomenon.
Tides In contrast to the tides of the Atlantic—which are almost always semi diurnal twice-daily occurrences—those of the Pacific include many instances of diurnal daily and mixed tides. In the diurnal type of tidal oscillation, only a single high water and a single low water occur each tidal day which lasts for about 24 hours and 50 minutes.
Mixed tides, in which both diurnal and semidiurnal oscillations appear, are characterized by large inequalities in successive high or low water heights. This type of tide is prevalent along much of the Pacific coast. Mangroves Rhizophora apiculata at low tide on the coast of Thailand.
At certain places in the South Pacific, the natural period of oscillation of the sea accentuates the solar tidal oscillation. At those locations the time of the am or pm high or low water occurs at approximately the same time for several days in succession, instead of getting later each day by about 50 minutes as is generally the case.
The tide at Tahitifor example, follows the Sun and not the Moon—the time of high water occurring, day after day, at about midnight and noon and that of low water at about 6 am and 6 pm.
In general, tidal ranges within the Pacific are small. That at Tahiti is about 1 foot 0. However, in the upper reaches of the Gulf of California and in Korea Baytidal ranges of 40 feet 12 metres are common, while around most of Australia tides range from 6 to 33 feet 1.
The circumglobal mixing of water in the southern and, to a much more limited extent, northern polar reaches of the Pacific permits the intermingling of flora and fauna from other oceanic regions, while temperate and tropical surface waters of the Pacific are more likely to have indigenous biotas.The properties of the sea water, productivity.
Temperature The temperature of the surface of the Earth, the atmosphere, depends on a delicate balance between solar radiation from the sun and the Earth radiating it out back into space. The following simulations come from the Ocean Sciences Sequence for Grades The Ocean-Atmosphere Connection and Climate lausannecongress2018.com simulation is part of a complete activity or series of activities on a particular topic within the curriculum sequence.
Lecture 3: Temperature, Salinity, Density and Ocean Circulation Two of the most important characteristics of seawater are temperature and salinity – together they control its density, which is the major factor governing the vertical.
What is the Cryosphere? When scientists talk about the cryosphere, they mean the places on Earth where water is in its solid form, frozen into ice or snow. When fresh water is added for example by rivers, or precipitation, the salinity of the ocean will decrease. That explains why some oceans are less salty than others Factors like the melting of ice, the inflow of river water, rain, snowfall, evaporation, wind, wave motion and currents affect the salinity.
The movements of ocean waters are influenced by numerous factors, including the rotation of the Earth (which is responsible for the Coriolis effect), atmospheric circulation patterns that influence surface waters, and temperature and salinity gradients between .