Sea water salinity is expressed as a ratio of salt in grams to liter of water. In sea water there is typically close to 35 grams of dissolved salts in each liter. But as in weather, where there are areas of high and low pressure, there are areas of high and low salinity. Of the five ocean basins, the Atlantic Ocean is the saltiest. On average, there is a distinct decrease of salinity near the equator and at both poles, although for different reasons.
Near the equator, the tropics receive the most rain on a consistent basis. As a result, the fresh water falling into the ocean helps decrease the salinity of the surface water in that region. As one move toward the poles, the region of rain decreases and with less rain and more sunshine, evaporation increases. Fresh water, in the form of water vapor, moves from the ocean to the atmosphere through evaporation causing the higher salinity.
Toward the poles, fresh water from melting ice decreases the surface salinity once again. In summer the vertical temperature gradients increase mainly in mid latitudes leading to strong seasonal changes in these ocean areas. The surface water density is highest near the poles and decreases towards the equator.
The stratification, expressed as the difference in density between the sea surface and m depth, shows geographic variation in summer in the North Atlantic while in the southern hemisphere the change with latitude seems to be more uniform. Lower temperatures near the equator reflect the updoming or upwelling of waters from greater depth compared to the mid latitudes. This and the maximum in sea surface temperature give rise to the strong vertical temperature and density gradients in the tropical ocean.
The 'Global Conveyor Belt' visualization below shows a simplified model of how this type of circulation would work as an interconnected system. The ocean stores more heat in the uppermost three 3 meters than the entire atmosphere.
Thus density-controlled circulation is key to transporting heat in the ocean and maintaining Earth's climate. Excess heat associated with the increase in global temperature during the last century is being absorbed and moved by the ocean. In addition, studies suggest that seawater is becoming fresher in high latitudes and tropical areas dominated by rain, while in sub-tropical high evaporation regions, waters are getting saltier.
Such changes in the water cycle could significantly impact not only ocean circulation but also the climate in which we live. Throughout most of history, global understanding of ocean surface salinity was difficult because sampling by ships, buoys, drifters, and moorings was extremely limited. Between and AD, awareness of changes in salinity, temperature, and smell helped Polynesians explore the southern Pacific Ocean.
In the s, scientists aboard H. Challenger systematically measured salinity, temperature, and water density in the world's oceans. Over the years, techniques for measuring such ocean water properties have changed drastically in method and accuracy.
Salinity variations, one of the main drivers of ocean circulation, are closely connected with the cycling of freshwater around the planet and provide scientists with valuable information on how the changing global climate is altering global rainfall patterns.
The salinity sensor detects the microwave emissivity of the top 1 to 2 centimeters about an inch of ocean water — a physical property that varies depending on temperature and saltiness. The instrument collects data in kilometer-wide mile swaths in an orbit designed to obtain a complete survey of global salinity of ice-free oceans every seven days.
Data from Aquarius has unveiled a world of varying salinity patterns. The Arabian Sea, nestled up against the dry Middle East, appears much saltier than the neighboring Bay of Bengal, which gets showered by intense monsoon rains and receives freshwater discharges from the Ganges and other large rivers. As the water moves North or South it gives off heat and warms the atmosphere. Untitled Document. Three major factors influence salinity salt concentration in Pacific Ocean waters: precipitation , evaporation and winds.
Precipitation brings freshwater into the ocean, diluting its salt concentration. To understand how salty the sea is, start with mL of water 1 cup. To make seawater at home, add 35 grams of salt to a beaker, and then add tap water until the total mass is 1, grams, stirring until the salt is completely dissolved in the water. Tap water often contains lots of natural minerals found in seawater , such as magnesium and calcium. Therefore, the salinity is the highest in the equatorial region, but due to increase in temperature in equatorial region, the density is the lowest in the equatorial region.
Therefore, we can say, the sea water has the highest surface density at the polar latitudes than the equatorial region.
Definition of Salinity Because ocean water is so salty of course. The concentration of dissolved salt in a given volume of water is called salinity. Freshwater has very little salt, usually less than 0. Definition and units. Ocean salinity is generally defined as the salt concentration e. It is measured in unit of PSU Practical Salinity Unit , which is a unit based on the properties of sea water conductivity.
Water and soil salinity are measured by passing an electric current between the two electrodes of a salinity meter in a sample of soil or water.
The electrical conductivity or EC of a soil or water sample is influenced by the concentration and composition of dissolved salts. Seawater and brines have tens of thousands of parts per million ppm of salts, and typical drinking waters can have hundreds to well over 1, ppm, mostly less than ppm concentration ppm equals milligrams per liter of water.
0コメント