9-15 lecture notes

9-15 lecture notes - The Oceans Cover about 71 of the...

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The Oceans Cover about 71% of the surface of the Earth. The greatest ocean depth of 11,035 m occurs in the Mariana Trench Have an average depth of 3,800 m. Have a present volume of about 1.35 billion cubic kilometers, but the volume fluctuates with the growth and melting of glacial ice. Salinity , a measure of amount of dissolved ions in the oceans, ranges between 33 and 37 parts per thousand. The dissolved ions have been concentrated in seawater as a result of chemical weathering (Na, Ca, Mg, S, K, Br, and HCO 3 ) and degassing of the mantle by volcanic activity (Cl Seawater would contain higher concentrations of dissolved ions if some were not removed by chemical precipitation, plants and animals, and absorption onto clay minerals. Salinity varies in the oceans (see figure 18.3a in your text) because: Surface waters evaporate, rain and stream water is added, and ice forms or thaws. Salinity is higher in mid-latitude oceans because evaporation exceeds precipitation Salinity is higher in restricted areas of the oceans like the Mediterranean and Red Seas (up to 41 parts per thousand). Salinity is lower near the equator because precipitation is higher. Salinity is low near the mouths of major rivers because of input of fresh water. The temperature of surface seawater varies with latitude, from near 0 o C near the poles to 29 o C near the equator. But restricted areas can have temperatures up to 37 o C. (See figure 18.3b in your text.) Properties of seawater also vary with depth. The density and salinity of seawater increase with depth. Temperature decreases with depth. Ocean Circulation Surface Ocean currents are result of drift of the upper 50 to 100 m of the ocean due to drag by wind. Thus, surface ocean currents generally follow the same patterns as atmospheric circulation with the exception that atmospheric currents continue over the land surface while ocean currents are deflected by the land. The surface currents have the following properties: Circulation is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. In each hemisphere cooler waters from higher latitudes circulate toward the equator where they are warmed and circulate back toward the poles.
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In addition to surface circulation, seawater also circulates vertically as a result of changes in density controlled by changing salinity and temperature (see figures 18.5, 18.6a, and 18.6b in your text). Such circulation, because it controlled by both temperature differences and differences in salinity of the water, is called thermohaline circulation . Ocean Tides Tides are due to the gravitational attraction of moon and to a lesser extent, the sun on the Earth. Because the moon is
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9-15 lecture notes - The Oceans Cover about 71 of the...

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