The Oceans

1. The Oceans The Oceans • Oceanographyis the scientific study of Earth’s oceans, including its inhabitants, it’s physical and chemical properties. In the late 1800s, the British Challengerexpedition became the first research ship to use relatively sophisticated measuring devices to study the oceans. It studied ocean currents, temperature, sediments, and topography.

2. The Oceans Modern Oceanography • In the 1920s, the German research ship Meteor used sonar for the first time to map the seafloor features, the mid-Atlantic ridge, of the South Atlantic Ocean.

3. Modern Oceanography • Sonar, which stands for sound navigation and ranging, uses the return time of an echo and the known velocity of sound in water to determine water depth. • The velocity of sound in water is 1500 m/s. • To calculate the distance to the ocean floor, multiply the time by 1500 m/s, then divide by 2. - Side-scan sonar is a technique that directs sound waves to the seafloor at an angle, so that the sides of underwater hills and other topographic features can be mapped.

4. Side scanning SONAR How SONAR works

5. The Oceans Modern Oceanography • Today we can use SONAR and satellites to study the oceans. • Satellites such as the Topex/Poseidon continually monitor the ocean’s surface temperatures, currents, and wave conditions. • Submersibles, or underwater vessels, investigate the deepest ocean trenches.

6. Submersibles

7. The Oceans Origin of the Oceans Where did the water come from? • Scientists hypothesize that Earth’s water could have originated from two sources. • Comets occasionally collide with Earth and release water on impact–possibly enough to have filled the ocean basins over geologic time.

8. The Oceans Origin of the Oceans Volcanism • Shortly after the formation of Earth, violent volcanism released huge amounts of water vapor, carbon dioxide, and other gases, which combined to form Earth’s early atmosphere. • As Earth’s crust cooled, the water vapor gradually condensed into oceans.

9. The Oceans Distribution of Earth’s Water “The Blue Planet” • Approximately 71 percent of Earth’s surface is covered by oceans. • Because most landmasses are in the northern hemisphere, oceans only cover 61 percent of the surface. • Water covers 81 percent of the southern hemisphere.

10. The Oceans Distribution of Earth’s Water • The oceans contain 97 percent of all of the water found on Earth. • The remaining 3 percent is freshwater located in the frozen ice caps of Greenland and Antarctica and in rivers, lakes, and underground sources. • The percentage of ice has ranged from near zero to as much as 10 percent of the hydrosphere over geologic time.

12. The Oceans Distribution of Earth’s Water • Sea levelis the level of the oceans’ surfaces. • It is currently rising due to melting ice caps. • Tectonic forces that lift or lower portions of the seafloor has also affected sea level. • Sea level has risen and fallen by hundreds of meters in response to melting ice during warm periods and expanding glaciers during ice ages. • We’ll talk more about sea level at the end of the unit

13. The Oceans Distribution of Earth’s Water Major Oceans • There are four major oceans: • The largest ocean, the Pacific, contains roughly half of Earth’s seawater and is larger than all of Earth’s landmasses combined. • The second-largest ocean, the Atlantic, extends from Antarctica to the arctic circle, north of which it is often referred to as the Arctic Ocean. • The third-largest ocean, the Indian, is located mainly in the southern hemisphere. • The smallest is the Arctic Ocean.

14. The Oceans Distribution of Earth’s Water Major Oceans

15. The Oceans Distribution of Earth’s Water Seas • Seas are smaller than oceans and are partly or mostly landlocked. • The Mediterranean Sea is located between Africa and Europe and was the first sea to be explored and mapped by ancient peoples. • Notable seas in the northern hemisphere include the Gulf of Mexico, the Caribbean Sea, and the Bering Sea, which is located between Alaska and Siberia. • All seas and oceans belong to one global ocean whose waters are thoroughly mixed.

16. The Oceans Section Assessment 3. Identify whether the following statements are true or false. ______ Oceans contain 97 percent of the water found on Earth. ______ Oceans cover 71 percent of Earth’s surface. ______ The Earth’s major oceans are isolated from each other by landmasses. ______ Presently, average global sea level is decreasing 1 to 2 cm per year. true true false false

17. End of Section 1

18. Seawater Seawater • Seawater is a solution of about 96.5 % pure water and 3.5 % dissolved salts. • The most abundant salt in seawater is sodium chloride (NaCl). • Most elements on Earth are present in seawater. • Because these substances are dissolved, they are in the form of ions.

19. Seawater Seawater

20. Seawater Chemical Properties of Seawater • Salinity is a measure of the amount of dissolved salts in seawater that is expressed as grams of salt per kilogram of water, or parts per thousand (ppt). • The total salt content of seawater is, on average, 35 ppt, or 3.5 percent. • Seawater also contains dissolved gases and nutrients.

21. Seawater Chemical Properties of Seawater • The actual salinities of the oceans vary. • Salinities may be decreased by precipitation, runoff, icebergs melting and sea ice melting. These all add fresh water into the salty ocean water. (32ppt) • Salinity can be increased by evaporation. When more water evaporates than precipitation falls, there is more water leaving, and thus leaving the salts behind. (37 ppt) • Salinity can also be increased when sea water freezes in polar areas. When water freezes, it does not freeze with the salt in the water. Therefore, the salt is left behind.

22. Seawater

24. Seawater Chemical Properties of Seawater Sources of Sea Salt • The sources of sea salts has remained the same over time. • Chlorine and sulfur dioxide dissolve in water and form the chlorine and sulfate ions of seawater. • The weathering of crustal rocks generates most of the other abundant ions in seawater. • These ions are then flushed into rivers and transported to oceans. • Volcanoes also contribute.

25. Seawater Chemical Properties of Seawater Removal of Sea Salts • Salts are removed from the ocean at the same rate as they are added. • The removal of sea salts involves several processes. • Some sea salts precipitate from seawater near arid, coastal regions. • Salty spray droplets from breaking waves are picked up by winds and deposited inland. • Marine organisms remove ions from seawater to build their shells, bones, and teeth.

26. Seawater Sea Surface Temperatures • Ocean surface temperatures range from –2°C in polar waters to 30°C in equatorial regions. • What causes the differences in surface temperatures? • The average surface temperature being 15°C.

29. Water Density 11. Water density is influenced by two factors: temperature and salinity. 12. Cold water is denser; it sinks to the bottom whereas warm water is less dense and would rise. 13. The higher the salinity, the denser the water is. It sinks more. 14. Therefore, the densest combination of water would be cold&salty water. 15. The differences in temperature and salinity in the ocean cause vertical layering within the ocean. 16. These differences are also what account for the currents that exist in the oceans.

30. Seawater Ocean Layering • Ocean water temperatures decrease significantly with depth. • A typical ocean temperature profileplots changing water temperatures with depth.

31. Seawater Ocean Layering • Based on temperature variations, the ocean can be divided into three layers. • Ocean water is warmest in the surface zone. (from the sun’s heat) Then temperature decreases with depth. • The thermocline is a zone of rapid temperature change. The temperatures are decreasing with depth. • The bottom zone is at the bottom. Sunlight never reaches it and it is very cold, just above freezing. • 80% of ocean water is found here.

33. Seawater Ocean Layering

34. Seawater Physical Properties of Seawater Absorption of Light • Water absorbs light, which gives rise to another physical property of oceans—they are dark. • In general, light penetrates only the upper 100 m of seawater. • Red light penetrates less than blue light. • Light sufficient for photosynthesis exists only in the top 100 m of the ocean.

35. Ocean Life Zones • 1. Ocean life zones are classified based on sunlight, distance from shore and water depth. • 2. The zones are: intertidal, neritic, and open-sea. • 3. The intertidal is where the land and sea meet and overlap. Sometimes it is underwater and sometimes it is dry, depending on the tides. • 4. The neritic zone covers the gently sloping continental shelf. • 5. The oceanic zone or open-sea zone reaches great depths to the ocean floor.

36. -The open-sea zone is further divided up into three sections based on depth. • The photosynthetic zone which is at the top. • The bathyal zone is in the middle • The abyssal zone is the bottom.

37. Open Sea zone Photosynthetic zone Neritic zone Bathyal zone Abyssal

38. Ocean Life • 1.Marine organisms can be classified according to where they live and how they move. • 2.Plankton drift with ocean currents. Examples are: bacteria, algae

39. Nekton are animals that swim. Examples are: fish, squid and mammals like whales, seals, etc. Nekton

40. Benthos are animals living in or on the ocean bottom. Examples are: starfish and crabs Benthos

41. Seawater Water Masses • Cold water migrates toward the equator as a cold, deep water mass along the ocean floor. • To start, sea ice that forms in the polar regions does not incorporate salt ions into growing ice crystals, causing them to accumulate beneath the ice. • As the cold water beneath the ice becomes saltier and denser than the surrounding seawater, it sinks. • Surface currents in the ocean also bring relatively salty midlatitude or subtropical waters into polar regions where they cool and sink. • The dense, salty water then migrates toward the equator as a cold, deep water mass along the ocean floor.

42. Seawater Water Masses • Three water masses account for most of the deep water in the Atlantic Ocean. 1. Antarctic Bottom Water forms when antarctic seas freeze during the winter and water temperature drops below 0°C. 2. North Atlantic Deep Water forms in a similar manner offshore from Greenland. 3. Antarctic Intermediate Water forms when the relatively salty waters of the Antarctic Ocean decrease in temperature during winter and sink.

43. Seawater Water Masses • The Indian and Pacific Oceans contain only the two deep antarctic water masses.

44. End of Section 2

45. Ocean Movements • Ocean water is constantly moving in three ways: waves, tides and currents. • A wave is a rhythmic movement that carries energy through space or matter, such as ocean water. • As an ocean wave passes, the water moves up and down in a circular pattern and returns to its original position.

46. 1.Most ocean waves are caused by wind moving over the water’s surface. The energy is what is moving. The water is not moving!

47. Ocean Movements Wave Characteristics • The crestis the top of a wave. • The trough is the bottom of a wave. • Wave height is the vertical distance between crest and trough • Wavelength is the horizontal distance from crest-to-crest or trough to trough.

49. Ocean Movements Wave Characteristics Wave Height depends on three things: • 1. Wind speed • 2. Length of time the wind has blown • 3. The distance wind has blown across the surface

50. Ocean Movements Wave Characteristics Breaking Waves • Ocean waves begin to lose energy and slow down near the shore because of friction with the ocean bottom. • As the water becomes shallower, incoming wave crests gradually catch up with the slower wave crests ahead. • Breakers are waves where the crests collapse forward when the wave becomes higher, steeper, and unstable as it nears shore.