Notes – Chapter 12 Ocean Waters and the Ocean Floor

1. Notes – Chapter 12Ocean Waters and the Ocean Floor

2. The Vast World Ocean • Area of Continents and Oceans • Seventy one percent (71%) of the globe is covered with oceans or seas. • Continents and islands compose the remaining twenty nine percent (29 %).

3. The Vast World Ocean • Distribution of Continents and Oceans • Northern Hemisphere - 61% Water / 39% Land • Southern Hemisphere – 81% Water / 19% Land

4. The Vast World Ocean • Volume of Continents vs Oceans • Volume of land above sea level (continents) is 1/18 the volume of the ocean.

5. The Vast World Ocean • Height vs Depth • Average elevation of continents is 840 meters above sea level. • Average depth of oceans is 3800 meters below sea level. • If the Earth were perfectly smooth and spherical the oceans would cover it to a uniform depth of 2000 meters.

6. The Vast World Ocean • Comparison of Major Oceans • Pacific Ocean • Largest ocean, equal to the Atlantic and Indian together • Contains > half the world’s ocean water • Greatest average depth, 3940 meters

7. The Vast World Ocean • Comparison of Major Oceans • Atlantic Ocean • Greatest north-south extension • Shallowest, average depth 3310 meters

8. The Vast World Ocean • Comparison of Major Oceans • Indian Ocean • Smallest of the three major oceans • Mostly located in the southern hemisphere

9. Composition of Seawater • Seawater – complex solution of salts, consisting of about 3.5 % dissolved mineral substances (normally range between 3.3% and 3.7% in the open ocean). • If all water evaporated a layer of salt 60 meters thick would cover the ocean floor.

10. Composition of Seawater • Salinity – proportion of dissolves salts to pure water, expressed in either parts-per-thousand or percentages (%)

12. Composition of Seawater • Component Elements – Mostly sodium chloride (NaCl) but seawater contains more than 70 of Earth’s 92 naturally occurring elements.

14. Composition of Seawater • Variation in Salinity – based on differences in the percentage of water, not differences in types of salts. • High Salinities – found where evaporation is high (sub tropics) Ex. Persian Gulf and the Red Sea – exceeds 4.2% • Low Salinities – found where heavy precipitation dilutes ocean water (near the mid latitudes and equator) Ex. Baltic Sea – less than 1.0%

16. Composition of Seawater • Source of Salts – • Chemical Weathering of Rocks • Volcanic Eruptions

17. Resources From Seawater • Salt • Fresh Water • Desalinization • Gold

19. The Ocean’s Layered Structure • Determined by differences in temperature and salinity at different depths

20. The Ocean’s Layered Structure • Shallow Surface Mixed Zone • Warmest • Higher Salinity

21. The Ocean’s Layered Structure • Transition Zone (Thermocline/Halocline) • Greatest Drop in Temperature

22. The Ocean’s Layered Structure • Deep Zone • Coldest – Temperatures below 4 C • Lowest Salinity

24. Earth Beneath the Sea • H.M.S. Challenger (1872-1876) • Trip went through every ocean except the Arctic • Sampled depths using a weighted line

25. Earth Beneath the Sea • Echo Sounder (1920s) • Transmitted sound toward the ocean bottom and a receiver measured how long it took for the sound waves to return. • Had to know how fast sound travels in water (1500meters or 5000 feet per second)

26. Earth Beneath the Sea

27. Continental Margins • Includes continental shelf, continental slope and continental rise.

28. Continental Margin

29. Continental Margin

30. Continental Margins • Continental Shelf –gently sloping submerged surface extending from the shoreline toward the deep-ocean basin at the shelf break. • Flooded extension of continents, it can vary in size. • Can be a source of important minerals, petroleum, etc.

31. Continental Margins • Continental Slope and Rise • Continental Slope – edge of the continental shelf leading into deep waters and is the true edge of the continent. • Continental Rise – gradual incline further seaward from the continental slope, sometimes nonexistent where the slope descends into a submarine canyon.

32. Submarine Canyons and Turbidity Currents • Submarine Canyons • Extend to depths as great as 3 kilometers • Created by processes operating below the Earth’s surface as well as turbidity currents

33. Submarine Canyons

34. Submarine Canyons and Turbidity Currents • Turbidity Currents • downslope movement of dense sediment laden waters • eroding and accumulating more sediment as it moves toward the ocean basin.

35. The Ocean Basin Floor • Comprises 30% of Earth’s surface.

36. The Ocean Basin Floor • Deep Ocean Trenches – long narrow troughs that are the deepest part of the ocean • Challenger Deep in the Marianna Trench is more than • 11,000 meters deep • Sites where crustal plates are plunging back into the mantle

37. The Ocean Basin Floor • Abyssal Plains – flattest places on Earth • Turbidity currents deposit their sediments here

38. The Ocean Basin Floor • Seamounts – isolated volcanic peaks, maybe be islands or submerged • Some form from hotspots, some near plate boundaries

39. Mid Ocean Ridges • Form an almost continuous underwater mountain chain through all major oceans • Comprise 20% of Earth’s surface

40. Mid Ocean Ridges • Rift zone – region where magma from the asthenosphere moves upward to create new crust

41. Coral Reefs and Atolls • Coral Reefs • Constructed from the skeletal remains and secretions of corals and certain algae, built up over time • Thrive in warm waters and rarely occur elsewhere, they require clear, sunlit waters with very little variation in temperature

42. Coral Reefs and Atolls • Atolls • Remains of coral reefs surround volcanic islands that have since sank back into the ocean

43. Seafloor Sediments • Terrigenous Sediment – “derived from land” • Weathered continental rock transported to the ocean • Biogenous Sediment –“derived from organisms” • Shells or skeletons of marine animals and plants • Hydrogenous Sediment – “derived from water” • Minerals that crystallize directly from seawater

44. Marianas Trench • http://www.youtube.com/watch?v=KuPfn5faawE