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Earth’s Oceans

Earth’s Oceans. Part 2: Properties of Ocean Water. Composition. Ocean water is a mixture of gases and solids dissolved in pure water. 96.5% H 2 O 3.5% or 35 0/00 (parts per thousand) dissolved salts Most of the 90 naturally occurring elements have been found in seawater.

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Earth’s Oceans

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  1. Earth’s Oceans Part 2: Properties of Ocean Water

  2. Composition • Ocean water is a mixture of gases and solids dissolved in pure water. • 96.5% H2O • 3.5% or 35 0/00 (parts per thousand) dissolved salts • Most of the 90 naturally occurring elements have been found in seawater Image credit: HannesGrobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

  3. Salts in Ocean Water • Salinity – the amount of dissolved salts in water • # of grams of dissolved salts in 1 kg of water = parts per thousand (0/00) • Average for ocean water is 35 0/00 • Range is ~33-37 0/00 • If the mass of all the oceans combined is about 1.4 × 1021kg, how much salt is there dissolved in all? • 1.4 × 1021kg x .035 kg/kg = 4.9 x 1018kg of salt = 4,900,000,000,000,000,000 = 4.9 billion billion kg FYI: This is enough salt to cover all the Earth’s land surface with a layer of salt 500 ft. thick.

  4. Salts in the Ocean Video: http://www.youtube.com/watch?v=aFXn1d5baCo Sources of Salts • Weathering and erosion of rock of the Earth’s crust, including wave action • Dissolving of salts by rains and running water that carry them to the sea • Volcanic activity in oceans (gases and solids that escape from vents) Credit: NSF and NOAA

  5. Salts in Ocean Water • Note lower salinity to the north of the Amazon River • Most of very high or low readings right at coastlines are due to satellite signal distortion http://earthobservatory.nasa.gov/IOTD/view.php?id=78250&src=flickr

  6. Salts in the Oceans • Various factors affect salinity at a given location. Examples: • Near the Amazon, Mississippi, and Congo River basins salinity is lower due to large influx of fresh water • High rates of evaporation in tropical regions, such as the Red Sea area, causes higher salinity • Freezing of water into ice in the polar regions increases salinity as the salts are left behind in the liquid water • Living organisms reduce the amount of calcium salts from what would be otherwise expected as they use them to make their shells

  7. Gases in Ocean Water • Most abundant are nitrogen, oxygen, argon, and carbon dioxide. • Highest amounts are near the ocean’s surface, where these gases are exchanged with the atmosphere. • Oxygen and carbon dioxide are necessary for respiration and photosynthesis respectively. • Much of the carbon dioxide converts into carbonic acid or bicarbonate • Bicarbonate, as calcium bicarbonate, is needed to by organisms to form shells

  8. Gases in Ocean Water Factors that affect the amount of gas dissolved: • Temperature of the water - cold water holds more gas than warm water • Salinity – low salinity water can hold more gas than high salinity water • Depth – as depth increases pressure increases and more gas can be dissolved • Amount of living organisms in the water– water with a lot of photosynthesizing organisms will be oxygen-rich • Oxygen is carried to deep waters when the water cools, as in polar areas, or becomes more saline (both cause an increase in density).

  9. Temperature of Ocean Water Surface Zone: • Sun warms the surface. • Heat is transferred downward by the mixing action of waves and currents • Extends 100 to 400 meters deep and temperature remains fairly constant through the zone • Temperature varies with location and season

  10. Temperature of Ocean Water Thermocline: • Temperature drops off rapidly • Depth of thermocline varies depending on season and the flow of currents • Occurs because warm surface water and cold deep water do not easily mix Graph showing a tropical ocean thermocline (depth vs. temperature). Note the rapid change between 100 and 200 meters.

  11. Temperature of Ocean Water Deep Zone: • Extends from the bottom of the thermocline to depths of 4,000 m or more • Temperature decreases only slightly • Below 1,500 m the temperature is about 4°C • In the polar oceans the three zones do not exist as even the surface waters are very cold. • Video: http://oceantoday.noaa.gov/takingtheoceanstemp/

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