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Science: Ocean Circulation & Climate |
Ocean salinity's influence on the environment can be summarized by looking at earth's three major latitude zones: high latitudes (i.e., 60 degrees -90 degrees), mid-latitudes (i.e., 30 degrees-60 degrees), and tropics (i.e., from 30 degrees N - 30 degrees S). Salinity's influence on ocean circulation and climate may be most profound at earth's high latitudes. For example, the North Atlantic is a primary source for sinking of cold, high-salinity water masses ; this process triggers the thermohaline circulation that extends thoughout the world's oceans. Thermohaline circulation accounts for much of the oceanic heat transport that regulates climate. Moreover, recent studies show that past climate shifts are linked to significant changes in the strength of thermohaline circulation. Other research shows that over the past few decades, vast regions of abnormal sea surface salinity (SSS) - called Great Salinity Anomalies - have propagated around far north Atlantic, bringing unusual weather to Europe. At mid-latitudes, salinity influences the depth to which water masses sink and how far they extend through the ocean. The location and depth of these water masses controls how heat and salts are transported between the tropics and high latitudes. Like atmospheric fronts that bring unstable weather, ocean fronts -- found at the interface between water masses - are areas of high activity often correlated with important fisheries such as tuna. In the tropics, SSS is greatly controlled by rainfall and river runoff; these sources of freshwater regulate how the oceans interact with the atmosphere . Affecting almost half of the world's human population each year, monsoons are driven by exchanges at the air-ocean boundary. Likewise, El Niño has profound effects on humankind and is -- to an unknown extent -- governed by ocean salinity. In fact, recent studies indicate that understanding salinity's effect on upper ocean buoyancy may be the key to better El Niño forecasts. After the launch of Aquarius in 2010, scientists will investigate how salinity variations modify ocean density and influence ocean circulation from the tropics to the poles. Thus SSS from Aquarius is key to better discerning how ocean circulation is tied to global climate and how both these systems are changing through time.
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Glossary Words |
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atmosphere: Gaseous layer surrounding a planet; the whole mass of air surrounding the earth.
buoyancy: The tendency or capacity to remain afloat in a liquid; the upward force that a fluid exerts on an object less dense than itself. climate: The prevailing or normal pattern of weather at a place, or in a region, averaged over a long period of time; in contrast to weather, which is the state of the atmosphere at a particular time. conductivity: A measure of the ability of a material to conduct or transmit an electric charge. density: Mass per unit volume of a substance. Usually expressed as grams per cubic centimeter. For ocean water with a salinity of 35 at 0°C, the density is 1.028 grams per cubic centimeter. front: interface between two masses of different physical characteristics. monsoon: A name for seasonal winds derived from the Arabic word for season, mausim. The term was originally applied to winds over the Arabian Sea that blow from the southwest during summer and the northeast during winter, subsequently extended to similar seasonal winds in other parts of the world. practical salinity unit (psu): Used to describe the concentration of dissolved salts in water, the UNESCO Practical Salinity Scale of 1978 (PSS78) defines salinity in terms of a conductivity ratio, so it is dimensionless. Salinity was formerly expressed in terms of parts per thousand (ppt) or by weight (parts per thousand or 0/00). That is, a salinity of 35 ppt meant 35 pounds of salt per 1,000 pounds of seawater. Open ocean salinities are generally in the range between 32 and 37. runoff: The downward movement of surface water under gravity in channels ranging from small rills to large rivers. salinity: A measure of the quantity of dissolved solids in ocean water. In general, salinity reflects the total amount of dissolved solids in ocean water in parts per thousand by weight after all carbonate has been converted to oxide, the bromide and iodide to chloride, and all the organic matter oxidized. Salinity is now measured as pratical salinity units (psu). system: 1) A regularly interacting or interdependent group of items forming a unified whole. 2) A manner of classifying. 3) A group of interacting bodies under the influence of related forces. thermohaline circulation: The vertical movement of ocean water driven by density differences resulting from the combined effects of variations in temperature and salinity. water mass: A body of water identifiable by its temperature, salinity, or chemical content. |
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