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2 The Oceanic Environment

2 The Oceanic Environment. Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton. The Ocean. Geography and Bottom Features. The Ocean and Marginal Seas. The world’s oceans: oceans and marginal seas Oceans cover 71% of earth’s surface

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2 The Oceanic Environment

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  1. 2 The Oceanic Environment Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton

  2. The Ocean Geography and Bottom Features

  3. The Ocean and Marginal Seas • The world’s oceans: oceans and marginal seas • Oceans cover 71% of earth’s surface • Southern hemisphere 80%, Northern hemisphere 61% • 84% deeper than 2000m • Greatest depth ~ 11,000 m in Marianas Trench

  4. Marginal Seas • Examples: Gulf of Mexico, Mediterranean Sea • Affected strongly by • regional climate • precipitation-evaporation balance • river input of fresh water and dissolved solids • limited exchange with the open ocean (e.g., sill partially cutting Mediterranean from Atlantic) • Geological history

  5. Ocean as a Receptacle • Particulate mineral matter • Dissolved salts • Particulate organic matter (POM) • Dissolved organic matter (DOM) • Atmospheric precipitation • Volcanic sources • Water

  6. Water Relationships in the Ocean

  7. Topographic Features • Continental shelf (1° slope) • Continental slope (2.9° slope) • Continental Rise • Abyssal Plain • Submarine Canyons • Oceanic Ridge Systems

  8. Topographic Features

  9. Earth’s surface is divided into plates: borders are ridge systems, faults

  10. Magnetic anomalies led to discovery about movement of the oceanic crust.

  11. The Oceanic Crust: Crust is formed at ridges, moved laterally, and destroyed by subduction, which forms trenches Seafloor spreading

  12. Continents embedded in ocean crust, leading to extensive Continental Drift.

  13. The Ocean Seawater Properties

  14. Water Molecule • Asymmetry of charge distribution on water molecule - increases ability to form bonds with ions - makes water excellent solvent

  15. Water Properties • High heat capacity (0.9) • High heat of evaporation (590 cal/g) • High dissolving power • High transparency (absorbs infrared, ultraviolet)

  16. Latitudinal Gradient of Sea Water Temperature

  17. Vertical Temperature Gradient: Open Tropical Ocean

  18. Vertical Temperature Gradient: Shallow Temperate Ocean

  19. Temperature • Oceanic range (-1.9 to 40 °C) less than terrestrial range (-68.5 to 58 °C) • Deep ocean is cold (2 to 4 °C)

  20. Heat Changes in the Ocean

  21. Salinity • Definition: g of dissolved salts per 1000g of seawater; units are o/oo or ppt or psu (practical salinity unit) • Controlled by: + evaporation, sea-ice formation - precipitation, river runoff Salinity in open ocean is 32 to 38 o/oo

  22. Important Elements in Seawater • Chlorine (19,000 mg/l) • Sodium (10,500) • Magnesium (1,300) • Sulfur (900) • Calcium (400) • Potassium (380) • Bromine (65) • Carbon (28 - variable)

  23. Principle of Constant Element Ratios:Forchhammer’s Principle • Ratios between many major elements are constant all over the ocean, even though salinity varies

  24. Principle of Constant Element Ratios • Why? Because residence time of elements with constant ratios is much greater than time to mix them evenly throughout ocean by water currents (ca. 1000 y) Residence time

  25. Principle of Constant Element Ratios • Residence time of Na, Cl, Sr is on the order of millions of years • But mixing time of water is on order of thousands of years • Therefore ocean is well mixed, relative to input or removal

  26. Principle of Constant Element Ratios • Principle does not apply to elements that cycle rapidly, especially under influence of biological processes (e.g., nitrogen, phosphorous)

  27. Latitudinal Salinity Gradient Excess of evaporation over ppt in mid-latitudes Excess of ppt over evaporation at equator

  28. Measurement of Salinity • Chlorinity: g of chlorine per 1000 ml of seawater • Salinity = 1.81 x chlorinity • Measured by chemical titration, conductivity, index of refraction

  29. Seawater Density (mass/volume) • Influenced by salt, no maximum density at 4 °C (unlike freshwater) • Density measure of seawater at temperature t t= (density - 1) x 1000 t increases with increasing salinity t increases with decreasing temperature Special significance: vertical density gradients

  30. The Ocean Circulation in the Ocean

  31. Coriolis Effect - Earth’s Rotation

  32. Coriolis Effect - Movement of fluids, in relation to earth beneath, results in deflections

  33. Coriolis Effect and Deflection Ekman Spiral in Northern Hemisphere

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