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Seawater Properties

Learn about the chemical processes and sources that contribute to the high salinity of seawater. Explore the composition of salts and how changes in salinity, temperature, and density affect the properties of seawater. Discover the importance of dissolved gases and transparency in the ocean.

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Seawater Properties

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  1. Seawater Properties

  2. Seawater • How did the water get salty? 1. Chemical weathering of rocks on land 2. From the Earth’s interior

  3. Salt Composition • 6 ions make up over 98% of the solids in seawater • Sodium and Chloride account for 85% of those solids.

  4. Salinity • Is defined as: the total amount of salt dissolved in seawater. • Average salinity of the ocean is 35 ‰ or 35 parts per thousand. • Salinity is also expressed in grams/liter. • Changes in salinity are controlled by the addition (rain or snow) or removal (evaporation or freezing) of pure water.

  5. Temperature (T), Salinity (S)and Density (D) • Temperature varies greatly in the ocean (between -2 ºC to 30 ºC). This has a strong influence on density. • Density is mass/volume. It is measured in g/cm3, g/ml or g/L. • A Hydrometer is the instrument used to determine density. • Salinity and temperature affect the density of water (as salinity and temperature decrease, density increases).

  6. TSD Diagram

  7. Ideal Aquarium Conditions • Temperature: 25-26.6ºC • Salinity: 35 parts per thousand (ppt), ‰ • Density: 1.020-1.024 g/cm3

  8. Dissolved gasses • 3 most important gasses in the ocean: • Oxygen • Carbon Dioxide • Nitrogen • Gasses dissolve better in cold water. • Marine animals affect the amount of dissolved gasses in the ocean.

  9. Dissolved Oxygen (D.O.) • 0-9 mg/L in seawater. • 21% in atmosphere. • Major source of D.O. is photosynthesis. • 50% of atmospheric O2 is from diffusion from the ocean. • At the surface an increase in temperature or salinity = decrease in the amount of D.O. that can be dissolved.

  10. Transparency • Seawater is relatively transparent so sunlight can penetrate fairly deep into the ocean (which helps plants to grow). • Transparency depends on what is suspended and dissolved in the water. • Different colors of light penetrate to different depths of the ocean. Blue light penetrates the deepest, red light the least.

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