Presentation on theme: "OCEAN SALINITY OCEAN SALINITY by Robert Perry. DISCLAIMER: The images, maps and diagrams in this presentation were taken from the public domain on the."— Presentation transcript:
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SALINITY The amount of salts dissolved in the ocean water.
Why is the ocean salty? The ocean is salty because of the weathering of rocks in the early stages of the formation of the oceans and continents. The ocean probably is continuing to become saltier very slowly (on geologic time scales) as rivers bring dissolved material to the sea. Even though the concentrations of dissolved salts in "fresh" river water is tiny, evaporation from the ocean surface (which is how water gets back to the rivers) removes only pure water so whatever salt enters from rivers remains in the sea and slowly builds up. Sea water is 35 o / oo or 3.5% salt by weight, which means the total quantity of dissolved salt, if dried, would form a layer 45m thick over the entire earth, or 153m thick over the present land area.
The salt in sea water is composed of a variety of components, primarily sodium chloride (table salt), magnesium chloride, magnesium sulfate and calcium carbonate, along with many trace elements. One of the remarkable aspects of ocean salinity is how constant the relative ratios of these constituents are in sea water, no matter where in the oceans one looks. This suggests that the oceans are "well-mixed" on the time scale of salt input. Total salinity, however, varies from about 3.3% to 3.8% in open- ocean surface waters, depending on the rainfall, evaporation, and river runoff in different regions. Salinity in bays or near the mouths of rivers is less, for example the salinity of Puget Sound near Seattle is about 2.9-3.2%. Deep-ocean salinity is much less variable.
SALINITY MEASUREMENTS: Oceanographers report salinity (total salt content) and the concentrations of individual chemical constituents in sea water -- chloride, sodium, or magnesium for example -- in parts per thousand, for which the symbol o/oo (or ppt) is used. That is, a salinity of 35 o/oo means 35 pounds of salt per 1,000 pounds of sea water. Similarly, a sodium concentration of 10 o/oo means 10 pounds of sodium per 1,000 pounds of water.
THERMOMETER HYDROMETER Here’s an easy way to measure the salinity of a water sample…
SST and DENSITY determine the SALINITY 22.3 John Jones 6 Sept. 21, 2000 9:10 am 0.0 2 310 green 7 90 % 20.02 4 5
LET’S FIND SALINITY: If our SST was 20.0 O C and our density was 1.0245 g/cm 3.
The salinity is: 34.5 o/oo Here’s where the lines intersect.
22.3 John Jones 6 Sept. 21, 2000 9:10 am 0.0 2 310 green 7 90 % 20.02 4 534.5 The amount of dissolved salts in the ocean is controlled by temp- erature, which increases evaporation and causes the salinity to increase. Also, during the winter rainy season, large volumes of fresh water (especially from the Pacific Northwest region) can dilute the salt content and lower salinity values. SALINITY
A rosette or cluster of water sampling bottles is ready to be lowered into the sea. This is one way ocean salinities are determined at different depths below the surface.
Regions of higher evaporation Regions of higher evaporation Regions of higher precipitation Regions of higher precipitation Regions of higher precipitation The red line shows surface salinity vs. latitude. The dashed line shows evaporation minus precipitation. (Areas above zero are dry and those below zero are wet). Note the similarity in the lines.
North Atlantic Deep Water Antarctic Bottom Water Higher evaporation than precipitation Higher evaporation than precipitation Atlantic Ocean Salinity Cross Section