Chapter 15 Physical Oceanography. (Humpback whale breaching near Auke Bay, Juneau, Alaska)

Transcription

1 Chapter 15 Physical Oceanography (Humpback whale breaching near Auke Bay, Juneau, Alaska)

2 NC Earth Science Essential Standards EEn Analyze patterns of global climate change overtime. EEn Differentiate between weather and climate. EEn Explain changes in global climate due to natural processes. EEn Analyze the impacts that human activities have on global climate changes (such as burning hydrocarbons, greenhouse effect, and deforestation). EEn Attribute changes to Earth s systems to global climate change (temperature change, changes in ph of ocean, sea levels changes, etc.).

3 Reading Assignment: Read Chapter 15; pages: Objective: -Identify methods used by scientists to study Earth s oceans; -Discuss the origin and composition of the oceans; -Describe the distribution of oceans and major seas; -Compare and contrast the physical and chemical properties of seawater; -Explain ocean layering; -Describe the formation of deep-water masses; -Describe the physical properties of waves; -Explain how tides from; -Compare and contrast various ocean currents. Vocabulary: Oceanography Side-scan sonar Sea level Salinity Temperature profile Thermocline Wave Crest Trough Breaker Tide Density current Surface current Upwelling

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

5 The Oceans 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.

6 The Oceans How SONAR works Side scanning SONAR

7 The Oceans Oceanography : scientific study of oceans, and its inhabitants, it s physical and chemical properties. Challenger expedition investigated ocean currents, water temperature, and chemical composition, seafloor sediments, topography and marine life. German ship Meteor used sonar for the first time to map the seafloor features of the South Atlantic Ocean. Sonar and satellites study the oceans; satellites like Topex/Poseidon, Tera, Aqua, and Jason, to name a few, that continually monitor the ocean s surface temperatures, currents, and wave conditions.

8 Modern Oceanography The Oceans Today we can use SONAR and satellites to study the oceans. Submersibles, or underwater vessels, like Alvin, investigate the deepest ocean trenches. Large portions of the seafloor have been mapped using side-scanned sonar, 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.

9 The Oceans Where did the water come from? Scientists hypothesize that Earth s water could have originated from two sources: comet and volcanoes. Comets occasionally collide with Earth and release water on impact and possibly enough to have filled the ocean basins over geologic time.

10 Volcanoes Volcanism The second belief for the formation of water, was 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.

11 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 level is 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 At present, average global sea level is slowly rising at a rate of 1 to 2 mm per year in response to melting glaciers.

13 The Oceans 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.

14 The Oceans 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.

15 Major Oceans

16 Sea Ice The Oceans Sea ice covers Arctic and Antarctic oceans during the winter and somewhat breaks up in the summer. Ice is less dense than water and floats Sea ice crystals first form, then ice crystal slush, eventually solidifies into round pancake ice, eventually thickens and freezes into continuous ice cover called pack ice During coldest winter regions, pack ice may be more than 1000 km wide and several meters thick.

17 Seas The Oceans 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.

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 or ionic form.

19 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.

20 Chemical Properties of Seawater The actual salinities of the oceans vary. Seawater 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.

21 Seawater

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23 Seawater Sources of Sea Salt Geological evidence indicates that the salinity of ancient seas was not much different from that of today s oceans. One evidence is the amount of magnesium in the calcium-carbonate shells of marine organisms. Volcanic gases contain chlorine and sulfur dioxide, which 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 such as, sodium, calcium, potassium, iron, and magnesium. These ions are then flushed into rivers and transported to oceans.

24 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 which removes quantities of sodium, chloride, calcium sulfate and other sea salts. 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. All these processes remove immense quantities of salt ions from the ocean.

25 Seawater Salts are added to seawater by volcanic eruptions and by the weathering and erosion of rocks. Salts are removed from seawater by the formation of evaporates and biological processes.

26 Physical Properties of Seawater Freshwater has a maximum density of 1.00 g/cm 3 Because salt ions are heavier than water molecules, they increase the density of water Seawater is then denser than freshwater Temperature also affects density; cold water is denser than warm water: 1.02 g/cm 3 to 1.03 g/cm 3 ; these differences are small but significant. Variations in salinity also cause the freezing point of seawater to be somewhat lower than freshwater: -2ºC in saltwater compared to 0ºC in freshwater

27 Absorption of Light In water, intensity of light decreases with depth; water also absorbs light, reasons oceans are dark below 100 m. Light penetrates only in the upper 100 m of seawater. Red light penetrates less than blue light, red objects appear black below depth of red light. Photosynthesis exists only in the top 100 m of the ocean.

28 Open Sea zone Neritic zone Photosynthetic zone Bathyal zone Abyssal The photosynthetic zone which is at the top. The bathyal zone is in the middle The abyssal zone is the bottom.

29 Ocean Layering Ocean surface temperatures range from 2 C in polar waters to 30 C in equatorial regions. Average surface temperature being 15 C. A typical ocean temperature profile plots changing water temperatures with depth. Ocean water temperatures decrease significantly with depth.

30 Ocean Layering Based on temperature variations, the ocean can be divided into three layers. Ocean water is warmest in the surface layer (from the sun s heat) Then temperature decreases with depth. The thermocline is characterized by rapidly decreasing temperatures with depth. The bottom layer is cold and dark with temperatures near freezing. (Dense cold water the bottom layer and warm less dense water is near surface).

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32 Water Masses The temperature of the bottom layer of ocean water is near freezing even in tropical oceans, where surface temperatures are warm. The source of all this cold water comes from Earth s polar seas. When seawater freezes during the artic or antarctic winter, sea ice forms. With the growing of sea ice, salt ions begin to precipitate out of the sea water and begin to accumulate beneath the ice. Consequently, the cold water beneath the ice becomes saltier and denser than the surrounding seawater, and this saltier water sinks. This salty water then migrates toward the equator as a cold, deep water mass along the ocean floor.

33 Water Masses Three water masses account for most of the deep water in the Atlantic Ocean. Antarctic Bottom Water forms when antarctic seas freeze during the winter; with water temperatures below 0 C, this water is the coldest and densest in all the waters. North Atlantic Deep Water forms is a similar manner offshore from Greenland; it is warmer and less dense than the Antarctic Bottom Water and rides on top of it. Antarctic Intermediate Water forms when the relatively salty waters of the Antarctic Ocean decrease in temperature during winter and sink. Being slightly warmer and less dense than both of the other cold water masses, it overrides the other two deep-water masses. As for the Indian Ocean and Pacific Ocean they only contain the two deepest deep-water masses.

34 Water Masses The three deep-water masses in the Atlantic Ocean.

35 Oceanic Circulation The component of general oceanic circulation are controlled by horizontal differences in temperature and salinity, which continually replaces seawater at the depths with water from the surface and slowly replaces surface water elsewhere with water rising from deeper depths. Ocean thermohaline conveyor system that transports warm, salty waters into the North Atlantic, tempering the climate of Northern Europe. If the conveyor should collapse on its return loop near Greenland and Iceland, Britain's climate could resemble Labrador.

36 Thermohaline Circulation The paths of the thermohaline circulation of ocean water are caused by the differences in density of ocean water. Blue paths represent deep-water currents, while red paths represent surface currents.

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39 Ocean Movements Wave Characteristics 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.

40 Ocean Movements Wave Characteristics The crest is 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.

41 Ocean Movements Wave Characteristics In a wave, water moves in circles that decrease in size and depth. At a depth equal to half the wavelength, water movement stops. Wave characteristics include wave height, wavelength, crest, and trough. Wave height depends upon three factors: wind speed, wind duration, and fetch, which refers to the expanse of water (meaning the distance) that the wind blows across.

42 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.

43 The surf is the zone where the waves break on shore.

44 Ocean Movements Tides are the periodic rise and fall of sea level. The highest level to which water rises is known as high tide, and the lowest level is called low tide. Because of differences in topography and latitude, the tidal range the difference between high tide and low tide varies from place to place. In the Gulf of Mexico, the tidal range is less than1 meter, where as in New England, it can be as high as 6 meters. Generally, a daily cycle of high and low tides takes 24 hours and 50 minutes.

45 Ocean Movements Causes of Tides The Sun s Influence The gravitational attraction of the Sun and Earth s orbital motion around the Sun also generate tides. Lunar tides are more than twice as high as those caused by the Sun because the Moon is much closer to Earth. Solar tides can either enhance or diminish lunar tides. Spring tides occur when the Sun, the Moon, and Earth are aligned, causing high tides to be higher than normal and low tides to be lower than normal. During neap tides, high tides are lower and low tides are higher than normal.

46 Tides Difference in topography and latitude cause three different daily tide cycles. Areas with semidiurnal cycles experience two high tides per day. Areas with mixed cycles have one pronounced and one smaller high tide each day. Areas with diurnal cycles have one high tide per day.

47 Ocean Movements Two types of Ocean Currents Currents are masses of ocean water that flow from one place to another. Density currents are vertical currents that result from different densities of water. (Denser water sinks) Surface currents are movements of water that flow horizontally in the upper part of the ocean s surface. They develop due to wind. Surface currents follow predictable patterns influenced by Earth s global wind systems.

48 Gyres A gyre is a huge circular surface current. Ocean Movements There are five major gyres: the North Pacific, the North Atlantic, the South Pacific, the South Atlantic, and the Indian Ocean. Because of the Coriolis effect, the gyres of the northern hemisphere circulate in a clockwise direction, where as, those in the southern hemisphere circulate in a counterclockwise direction. The parts of all gyres closest to the equator move towards the west as equatorial currents. When they encounter a landmass, they are deflected towards the poles. These poleward-flowing waters carry warm, tropical water into higher colder latitudes. Once there they gradually cool and move back to the equator.

49 Ocean Currents Ocean Movements

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51 The Gulf Stream Current The Gulf Stream is a powerful current in the Atlantic Ocean. It starts in the Gulf of Mexico and flows into the Atlantic at the tip of Florida, accelerating along the eastern coastlines of the United States and Newfoundland.

52 Upwelling In addition to moving horizontally, ocean water moves vertically; the upward motion of ocean water is called upwelling. Upwelling waters originate from the bottom of the ocean and thus are cold. Areas of upwelling exist mainly off the western coasts of continents in the trade-wind belts. Upwelling waters are rich in nutrients, which support abundant populations of marine life.

53 Ocean Life Marine organisms can be classified according to where they live and how they move - either as plankton, nekton, or benthos. Plankton are organisms that live in the water column, but that either cannot swim or cannot swim faster than currents. Examples include microscopic foraminifera, radiolarian, diatoms, dinoflagellates, and the larvae of many marine animals.

54 Nekton Nekton are organisms that spend most of their time in the water column and can swim freely and faster than currents. Examples include whales, seals, most fish, and squid.

55 Benthos Benthos are organisms that live on or in the seafloor sediment. These organisms can be attached or freely moving, but must be unable to swim. Examples include anemones, clams, sea stars, crabs, and most seaweeds, which attach to rocks by holdfasts.

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

58 Ocean Movements Section Assessment 1. Match the following terms with their definitions. D crest B trough C tide A upwelling breakers E A. the upward motion of ocean water, caused by an offshore wind B. the lowest point of a wave C. the periodic rise and fall of sea level. D. the highest point of a wave E. waves that become higher, steeper, and unstable which causes their crest to collapse

59 Ocean Movements Section Assessment 3. Identify whether the following statements are true or false. false Gyres rotate in a counterclockwise direction in the northern hemisphere. false The water in a wave moves steadily forward. true Wave speed increases with wavelength. false Spring and neap tides alternate every four weeks.

60 Chapter Assessment Multiple Choice 1. Approximately how much of Earth s surface is covered by oceans? a. 51 percent c. 71 percent b. 61 percent d. 81 percent Because most landmasses are located in the northern hemisphere, oceans cover only 61 percent of the surface there. However, 81 percent of the southern hemisphere is covered by water.

61 Chapter Assessment Multiple Choice 2. Of the areas listed below, which generally has the lowest ocean salinity? a. subtropical regions c. temperate regions b. tropical regions d. polar regions In the polar regions, seawater is diluted by melting sea ice. On a localized level, the lowest salinities often occur where large rivers empty into the oceans.

62 Chapter Assessment Multiple Choice 3. Which term below best describes the tide when the Sun, the Moon, and Earth form a right angle? a. spring tide c. high tide b. neap tide d. low tide During a neap tide, high tides are lower than normal and low tides are higher than normal. During a spring tide the solar and lunar tides are aligned, causing high tides to be higher than normal and low tides to be lower than normal. Spring and neap tides alternate every two weeks.

63 Chapter Assessment Multiple Choice 4. What is the average ocean surface temperature? a. 8ºC c. 15ºC b. 12ºC d. 18ºC Surface temperature of Earth s oceans varies between 2ºC in the polar regions to 30ºC in equatorial regions.

64 Chapter Assessment Multiple Choice 5. Which of the following is the most prevalent ion in seawater? a. chloride c. sodium b. sulfate d. magnesium Chloride has a concentration of ppt in seawater. It is followed by sodium (10.76 ppt), sulfate (2.71 ppt), and magnesium (1.29 ppt).

65 Chapter Assessment Short Answer 6. What are the three factors that determine wave height? The three factors that determine wave height are wind speed, wind duration, and fetch. Fetch refers to the expanse of water that the wind blows across.

66 Chapter Assessment Short Answer 7. What are the three basic ocean layers and are they distributed evenly throughout the oceans? The three basic ocean layers are the surface layer, the thermocline, and the bottom layer. They are not distributed evenly. Both the thermocline and surface layer are absent in polar seas, where water temperatures are cold from top to bottom.

67 Chapter Assessment True or False 8. Identify whether the following statements are true or false. false Oceanography is usually considered to have started with the Meteor expedition. true Some water molecules in the atmosphere are continually being destroyed by ultraviolet radiation from the Sun. false Blue light does not penetrate as far as red light in the ocean. true The Moon and Earth revolve around a common center of gravity.

68 Section 15.1 Study Guide Section 15.1 Main Ideas Oceanography is the scientific study of Earth s oceans. Oceanographers use sonar, satellites, and submersibles, among other tools, to explore the ocean. Earth s first oceans likely formed more than 4 billion years ago. Some water may have come from impacting comets or from deep within Earth s interior. Scientists theorize that water from within Earth s interior was released by volcanism. Approximately 71 percent of Earth s surface is covered by oceans. The major oceans are the Pacific, Atlantic, Indian, Arctic, and Antarctic.

69 Section 15.2 Study Guide Section 15.2 Main Ideas Seawater contains 96.5 percent water and 3.5 percent dissolved salts. The average salinity of seawater is 35 ppt. The salinity of the ocean remains constant because salts are removed from the ocean at the same rate as they are added. Ocean surface temperatures range from 2 C in polar waters to 30 C in equatorial waters. Seawater density changes with changes in salinity and temperature. Ocean water temperatures decrease with depth. The ocean can be divided into three layers: the surface layer, the transitional thermocline, and the bottom layer.

70 Section 15.3 Study Guide Section 15.3 Main Ideas Ocean waves are generated by wind. Water in a wave moves in a circular motion but does not move forward. When waves reach shallow water, friction with the ocean bottom slows them, and they become breakers. Tides are caused by the gravitational attraction among Earth, the Moon, and the Sun. Lunar tides are twice as high as solar tides. Density currents are deep currents generated by salinity and temperature differences. Wind-driven surface currents affect the upper few hundred meters of the ocean. Upwelling occurs when winds push surface water aside and the surface water is replaced by cold, deep water.