This Document Contains Chapters 13 to 16 Chapter 13 The Ocean Floor The Ocean Floor begins with a brief overview of the extent and distribution of the world ocean and the techniques used to measure the depth of the oceans. Following an examination of the features associated with passive and active continental margins, the chapter continues with investigations of the ocean-basin floor and mid-ocean ridges. Also examined are seafloor sediments and how they are used to study climatic changes. The chapter concludes with a discussion of resources from the sea. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 13.1 Discuss the extent and distribution of oceans and continents on Earth. Identify Earth’s four main ocean basins. 13.2 Define bathymetry and summarize the various techniques used to map the ocean floor. 13.3 Compare a passive continental margin with an active continental margin and list the major features of each. 13.4 List and describe the major features associated with deep-ocean basins. 13.5 Summarize the basic characteristics of oceanic ridges. 13.6 Distinguish among three categories of seafloor sediment and explain why some of these sediments can be used to study climate change. 13.7 Discuss some important resources and potential resources associated with the ocean floor. TEACHING THE OCEAN FLOOR The topic of the ocean floor is a large one. In fact, entire textbooks and courses have been devoted to it. In the context of a geology course, it is not necessary to get into all the intricacies of oceanography. Focusing on the physical seafloor aspects of the ocean is the best approach. • Open by having students look at a globe or a world map. Have the students make observations about the ocean, e.g. how large it is, what hemispheres it tends to dominate, etc. Then have students come up with their own questions about the physical aspects of the seafloor. You can give them the example, maybe they’d want to know how deep it is. You can use this as a jumping off place for the topics in this chapter. • Some students have the misconception that the ocean floor is flat or has little topography. You can use various illustrations or have them watch the movie Drain the Ocean (see Additional Resources) to challenge this misconception. Ask students why they think the ocean is not flat. • Bring samples of the three different types of ocean sediments to class. Have students observe how they are different and how they are similar. • Sometimes students think that passive continental margins have no activity at all. Stress that they have no tectonic activity but there is plenty of activity in the form of turbidite currents and other features of this environment. • Often students are somewhat familiar with the idea of echo sounders or sonar. Ask them to describe other situations other than seafloor mapping where similar sounding devices might be put to use. Have them determine the similarity between those situations and seafloor mapping. They will relate an unfamiliar concept to a more familiar one in this way. • Using animations of subduction can give students a more concrete idea of how trenches form. • Some concepts in this chapter have been seen before in different contexts. Examples include midocean ridges and subduction zones. You can use these topics to reinforce earlier knowledge and to stress the interconnectedness of the Earth as a system. • Students will probably have memories of the BP Deepwater Horizons oil spill into the Gulf of Mexico. You can discuss this spill in the context of the seafloor as an energy resource. BP was drilling because these natural resources were under the seafloor; have students discuss the risks and benefits of doing so. CONCEPT CHECK ANSWERS Concept Check 13.1 1. How does the area of Earth’s surface covered by the oceans compare with that of the continents? Answer: The ocean makes up about 71% of Earth’s surface where the continents are about 29%. 2. Contrast the distribution of land and water in the Northern Hemisphere and the Southern Hemisphere. Answer: The Northern Hemisphere contains more continental landmass, with 39 percent of the surface as land and 61 percent as water. The Southern contains more ocean, with almost 81 percent of the surface as water. 3. Excluding the Southern Ocean, name the four main ocean basins. Contrast them in terms of area and depth. Answer: • Pacific Ocean – this is the largest in terms of both area and depth. • Atlantic Ocean – about half the area of the Pacific Ocean but not as deep. • Indian Ocean – slightly smaller than the Atlantic Ocean but about the same depth. • Arctic Ocean – about 7% the area of the Pacific Ocean and about 25% as deep as the rest of the oceans. 4. How does the average depth of the oceans compare to the average elevation of the continents? Answer: The average elevation of the continents is about 840 meters and the average depth of the oceans is 3729 meters. Concept Check 13.2 1. Define bathymetry. Answer: Bathymetry is the measurement of ocean depths and the charting of seafloor topography. 2. Describe how satellites orbiting Earth can determine features on the seafloor without being able to directly observe them beneath several kilometers of seawater. Answer: Satellites have radar altimeters that bounce microwaves off the sea surface; these sensors can measure very small variations in sea height. These data can be interpolated to determine ocean floor topography. 3. List the major provinces of the ocean floor. Answer: Continental margins, deep-ocean basin, and the mid-ocean ridge. Concept Check 13.3 1. List the three major features of a passive continental margin. Which of these features is considered a flooded extension of the continent? Which one has the steepest slope? Answer: These three features are the continental shelf, the continental slope, and the continental rise. The continental shelf is a flooded extension of the continent and the continental slope has the steepest slope. 2. Describe the differences between active and passive continental margins. Where is each type found? Answer: Passive continental margins are geologically inactive and located far from plate boundaries. Active continental margins are found along convergent plate boundaries. They are geologically active and typically feature trenches, earthquakes, and volcanic activity. 3. Discuss the process that is responsible for creating most submarine canyons. Answer: Most submarine canyons have been excavated by turbidity currents. Turbidity currents are fast-moving downslope movements of dense, sediment-laden water. These currents carve out the submarine canyons as they repeatedly flow down the same portion of the continental slope. 4. How are active continental margins related to plate tectonics? Answer: Active continental margins are located at the boundaries of tectonic plates and experience the same geological activity as the type of plate boundary with which they are associated. 5. Briefly explain how an accretionary wedge forms. What is meant by subduction erosion? Answer: An accretionary wedge forms when ocean floor sediments and crust are scraped from the descending ocean plate in a subduction zone. These sediments and rocks are then plastered against the edge of the overriding plate. Subduction erosion is also where sediment and rock are scraped off the bottom of the overriding plate in an active subduction zone, but these rocks and sediments are transported to the mantle by the subducting plate. Concept Check 13.4 1. Explain how deep-ocean trenches are related to plate boundaries. Answer: Deep-ocean trenches form at convergent plate boundaries, with the trenches forming where one plate is subducted under another. 2. Why are abyssal plains more extensive on the floor of the Atlantic than on the floor of the Pacific? Answer: The Atlantic has far fewer trenches to act as sediment traps, allowing for extensive plains on the Atlantic floor. 3. How does a flat-topped seamount, called a guyot, form? Answer: Guyots form when inactive volcanic islands are eroded to near sea level. As the tectonic plate on which they sit carries them away from elevated ocean ridges or hot spots, they sink below sea level. 4. What features on the ocean floor most resemble basalt plateaus on the continents? Answer: Oceanic plateaus. Concept Check 13.5 1. Briefly describe oceanic ridges. Answer: Oceanic ridges are elevated, extensive volcanic mountain chains that largely exist underwater and are the location of divergent plate boundaries. 2. Although oceanic ridges can be as tall as some mountains on the continents, list some ways that oceanic ridges are different from mountains. Answer: Oceanic ridges are volcanic and form from upwelling of magma where continental mountains form from compressional uplift forces. Oceanic ridges also tend to be basaltic and continental mountains are generally granitic. 3. Where do rift valleys form along the oceanic ridge system? Answer: Along the axes of some segments of the ridge system. 4. What is the primary reason for the elevated position of the oceanic ridge system? Answer: The ridge is hot rock that is less dense than the cooler rocks of the rest of the ocean basin. Concept Check 13.6 1. Distinguish among the three basic types of seafloor sediments. Give an example of each. Answer: • Terrigenous sediment – primarily mineral grains weathered from continental rocks and transported to the ocean. Beach sand is one example. • Biogenous sediment – consists of shells and exoskeletons of marine animals and algae. Calcareous ooze is one example. • Hydrogenous sediment – consists of minerals that crystallize directly from seawater. Manganese nodules are one example. 2. Why are seafloor sediments useful in studying past climates? Answer: Most seafloor sediments contain fossils of organisms that once dwelled near the sea surface. The numbers and types of organisms living in this zone vary with the climate. Scientists can study these fossils and make correlations between the climate at the time those organisms lived and the fossils in the seafloor sediment. Concept Check 13.7 1. Which seafloor resource is presently most valuable? Answer: Oil and natural gas. 2. What are gas hydrates? Will they likely be a significant energy source in the next 10 years? Answer: They are compact chemical structures of water and natural gas. They will likely be a significant energy source in the future, but not within the next 10 years. 3. What nonenergy seafloor resource is most valuable? Answer: Sand and gravel. GIVE IT SOME THOUGHT ANSWERS 1. Refer to the accompanying graph to answer the following questions: a. Water dominates Earth’s surface but not everywhere. In what Northern Hemisphere latitude belt is there more land than water? b. In what latitude belt is there no land at all? Answer: a. 30° to 60° degrees north latitude. b. 60° south latitude. 2. Assuming that the average speed of sound waves in water is 1500 meters per second, determine the water depth if a signal sent out by an echo sounder on a research vessel requires 6 seconds to strike bottom and return to the recorder aboard the ship. Answer: Depth = ½(1500 meters/sec. × echo travel time). Depth = ½(1500 meters/sec. × 6 seconds) = 4500 meters. 3. Refer to the accompanying map on the top of the next page, which shows the eastern seaboard of the United States to complete the following: a. Associate each of the following with a letter on the map: continental rise, continental shelf, continental slope, and shelf-break. b. How does the size of the continental shelf surrounding Florida compare to the size of the Florida peninsula? c. Why are there no deep-ocean trenches on this map? Answer: a. Continental slope =A, continental shelf = B, continental rise = C, shelf-break = D b. The continental shelf surrounding Florida is wider than the Florida peninsula. c. There are no deep-ocean trenches on the map because no convergent plate boundaries are found here. 4. Are the continental margins surrounding the Atlantic Ocean primarily active or passive? How about the margins surrounding the Pacific Ocean? Based on your response to the foregoing questions, indicate whether each ocean basin is getting larger, shrinking, or staying the same size. Explain your answer. Answer: The continental margins surrounding the Atlantic are primarily passive while the Pacific margins are mainly active. As a result, the Atlantic basin is getting larger as the continents on either side are moving away from the mid-ocean ridge (where “new” oceanic crust is forming). However, the Pacific basin is getting smaller due to the active subduction zones that surround this largest ocean. 5. Imagine that you and a passenger are in a deep-diving submersible such as the one shown here in the North Pacific Ocean near Alaska’s Aleutian Islands. During a typical 6- to 10-hour dive, you encounter a long, narrow depression on the ocean floor. Your passenger asks whether you think it is a submarine canyon, a rift valley, or a deep-ocean trench. How would you respond? Explain your choice. Answer: I would explain to them that it is most likely a deep-ocean trench. The Aleutian Islands have formed from an ocean to ocean collision boundary and deep-ocean trenches are associated with this type of plate boundary. I would explain that based on the location near the Aleutian Islands in the North Pacific Ocean, the long, narrow depression is likely a submarine canyon. These features are typically found closer to continental margins and are carved by underwater currents, distinguishing them from rift valleys (formed at divergent plate boundaries) and deep-ocean trenches (associated with convergent plate boundaries). 6. Examine the accompanying sketch, showing three sediment layers on the ocean floor. What term is applied to such layers? Are these layers more likely part of a deep-sea fan or an accretionary wedge? Answer: The sketch is an illustration of graded bedding. These deposits are created by turbidity currents, which are downslope movements of dense, sediment-choked water. These layers are most likely part of deep-sea fans that develop downslope of submarine canyons that have cut into the continental slope. The corals do indeed develop in shallow, warm, sunlit waters. However, as they are developing on the sides of a sinking, extinct volcano, they eventually sink as well, thus they are found in water depths much greater than where they formed. EXAMINING THE EARTH SYSTEM ANSWERS 1. Describe some of the material and energy exchanges that take place at the following interfaces: a. ocean surface and atmosphere b. ocean water and ocean floor c. ocean biosphere and ocean water Answer: a. Material and energy exchanges that take place between the ocean surface and atmosphere include the exchange of the gases carbon dioxide, oxygen, and water vapor as well as salt crystals and liquid water. Heat energy and wind energy (friction between the ocean surface and moving air) are also exchanged. b. Between the ocean water and ocean floor various chemicals are exchanged through outgassing and precipitation from the water. Energy in the form of heat and seismic energy, and energy from waves, currents, and tides is also exchanged. c. The ocean biosphere and ocean water exchange material as organisms extract and use the chemicals found in seawater to build shells and other structures, and return the material when they die, settle to the floor, and decay. The nutrients from the sea are the source of energy for marine life, and burrowing and other activities of organisms in the seafloor transfer energy to the floor and help mix and distribute sediment. 2. This image from a scanning electron microscope shows the shell (test) of a tiny organism called a foraminifera, that was collected from the ocean floor by a research vessel. When alive, the organism that created this shell lived in the shallow surface waters of the ocean. Relate this tiny shell to each of Earth’s four major spheres. Why are microscopic fossils such as this one useful in the study of climate change? Answer: Carbon dioxide from the atmosphere was dissolved in seawater, part of the hydrosphere. Microscopic organisms that are part of the biosphere uptake carbon dioxide that has undergone chemical reactions to become the calcium carbonate shell of these creatures. When these organisms die, they become part of the sediment of the geosphere. Microscopic fossils are useful for the study of climate change because the abundance and nature of organisms that live in shallow seas of a particular area varies as the climate varies. 3. Sediment on the seafloor often leaves clues about various conditions that existed during deposition. What do the following layers in a seafloor core indicate about the environment in which each layer was deposited?
▪ Layer 5 (top): A layer of fine clays
▪ Layer 4: Siliceous ooze
▪ Layer 3: Calcareous ooze
▪ Layer 2: Fragments of coral reef
▪ Layer 1 (bottom): Rocks of basaltic composition with some metal sulfide coatings
Explain how one area of the seafloor could experience such varied conditions of deposition. Answer: Layer 5 probably represents fine terrigenous sediment that was carried far out to sea from a terrestrial (land) source. The red color represents oxidation of iron-bearing minerals in the sediment or iron in the water. Layer 4 resulted from the accumulation of microscopic organisms composed of silicon dioxide. Such organisms prefer cooler surface waters in the ocean basins. Layer 3, the calcareous ooze, also represents the remains of microscopic organisms. However, calcium carbonate (source material for the calcareous ooze) is produced in warm, shallow waters. Also, calcareous tests will dissolve if they sink into the deeper parts of the ocean. Consequently, calcareous ooze does not accumulate in the deep-ocean basins. Layer 2 obviously represents the remnants of a former coral reef. As stated previously, coral reefs require warm, shallow, clear waters. Layer 1 was formed by lava flows that were near black smokers, which would explain the metal sulfide coatings on the basalt. The preceding sequence could represent one area of the seafloor that experienced changing water depths over millions of years. Layers 1 and 2 represent volcanic activity in shallow water followed by coral reef development on the margins of the volcano. Layer 3 could have formed as the volcano subsided and the ocean was still relatively shallow, as evidenced by the calcareous ooze. Finally, layers 4 and 5 represent sediment accumulations as water depths increased over time. 4. Reef-building corals are responsible for creating atolls – ring-shaped structures that extend from the surface of the ocean to depths of thousands of meters. These corals, however, can only live in warm, sunlit water no more than about 45 meters (150 feet) deep. This presents a paradox: How can corals, which require warm, sunlit water, create structures that extend to great depths? Explain the apparent contradiction. Answer: The corals do indeed develop in shallow, warm, sunlit waters. However, as they are developing on the sides of a sinking, extinct volcano, they eventually sink as well, thus they are found in water depths much greater than where they formed. In addition, the corals at the bottom of the atoll are no longer living; the living corals build their structures upon the exoskeletons of the dead corals. These living corals are in warm, sunlit water. ADDITIONAL RESOURCES DVDs and Movies • Earth Revealed, Episode 4: The Sea Floor (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/series78.html • Drain the Ocean (2009) National Geographic, 90 minutes. CGI animation shows seafloor topography if the ocean’s water were removed. Available on DVD. • Scientists “See” Ocean Floor via Sonar (2011) National Geographic, 5 minutes. Available for free streaming from http://video.nationalgeographic.com/video/news/environment-news/us-ocean-floormapping-vin/ • Changing Seas: Mission to Inner Space (2009) PBS, 26 minutes, 35 seconds. Available for streaming from http://video.pbs.org/video/1371376375/ • Cameron’s Long Way Down: Mariana Trench. National Geographic, 2 minutes. James Cameron shows what it is like to descend into Earth’s deepest ocean trench. • Deep Ocean Volcanoes. NOAA, 2 minutes. Contains actual footage of erupting underwater volcanoes. Available for live streaming at http://oceantoday.noaa.gov/deepoceanvolcanoes/ welcome.html • Exploring the Sea Floor with Sonar. NOAA, 2 minutes. Seafloor exploration with the NOAA ship Okeanos Explorer. Available for streaming in multiple formats at http://oceanexplorer.noaa.gov/ okeanos/media/movies/ex_podcast_video.html# Websites • NOAA Ship Okeanos Explorer Website. Information about a government research vessel that maps the ocean floor, its current and past missions, and general information about the ship. http://www.moc.noaa.gov/oe/ • Mariana Trench Dive Animation. From NOAA. Computer-generated animation uses vertical exaggeration to show the features in the deep sea trenches. http://www.ngdc.noaa.gov/mgg/image/ dives/marianas/marianarocky2.mov • Exploring Landscapes Beneath the Oceans. From National Geographic. Activity where students can use maps to locate ocean floor features. http://www.nationalgeographic.com/geobee/study-corner/ activity-2/ • Subduction animation. From the University of California, San Diego. Shows formation of an accretionary wedge and subduction of the oceanic plate. http://earthguide.ucsd.edu/eoc/teachers/ t_tectonics/p_subduction.html • Turbidity current videos and turbidite photos. From Carleton College. http://serc.carleton.edu/ NAGTWorkshops/sedimentary/visualizations/turbid.html • Coral atoll formation. From NOAA. http://oceanservice.noaa.gov/education/kits/corals/media/supp_ coral04a.html Chapter 14 Ocean Water and Ocean Life Ocean Water and Ocean Life begins with an examination of the composition of seawater, sources of sea salt, and the processes affecting seawater salinity. Following a discussion of ocean temperatures, seawater density and the ocean’s layered structure are explored. Global variations in salinity, ocean temperatures, and seawater density are discussed. The chapter discusses the different life forms that are found at different levels in the water column. Reasons for changes in ocean acidity are briefly mentioned. There is a special section devoted to hydrothermal vent communities of the deep ocean. The chapter closes with a discussion of oceanic feeding relationships, trophic level, food chains, and food webs. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 14.1 Define salinity and list the main elements that contribute to the ocean’s salinity. Describe the sources of dissolved substances in seawater and causes of variations in salinity. 14.2 Discuss temperature, salinity, and density changes with depth in the open ocean. 14.3 Distinguish among plankton, nekton, and benthos. Summarize the factors used to divide the ocean into marine life zones. 14.4 Contrast ocean productivity in polar, midlatitude, and tropical settings. 14.5 Define trophic level and discuss the efficiency of energy transfer between different trophic levels. TEACHING OCEAN WATER AND OCEAN LIFE • If you have access to a salinometer, it may be useful to bring it to class and demonstrate the salinities of different water. • Many students think that the ocean is salty due to the presence of what they know of as table salt. Stress that while sodium chloride does constitute a large proportion of what makes the ocean salty, there are other salts and minerals dissolved in the ocean water. Challenge them to think what these salts and minerals might be before providing instruction regarding them. • Often people harbor the misconception that ocean salinity does not vary globally. Show students Figure 14.4 and have them come up with their own ideas about why different salinities are found in different places. Draw their attention to locations of lower salinity and have them make plausible explanations for why salinity might be less at those places. Do the same for locations with higher salinity. • Although we have different names for different ocean basins, in reality all the oceans of the world are connected. Show students a map that illustrates this fact and ask them why they think we have different names for different oceans when, in reality, they are all one global ocean. • Students may think that nothing, or very little, lives in polar oceans. You can begin to dispel this misconception by showing them pictures of Antarctic benthos (see Additional Resources). Show students Figure 14.18 and have them draw their own conclusions as to why the idea of polar oceans being devoid of life is untrue. • Sometimes students think that glaciers, icebergs, and sea ice must be made of salt water since they are often frozen seawater. You can have them try this on their own or do as a demonstration over a few class periods: Have a cup of water that is noticeably salty. Have a student confirm this. Partially freeze the water. Have the students or a student taste the ice and the water. This illustrates how when water freezes, it leaves behind in solution anything dissolved in it. • Students may also think that as seawater evaporates, the salts dissolved in it also evaporate. You can do a demonstration or have people do this experiment on their own. Have a container full of salty water. Heat the container so that some of the water evaporates. Put a pie pan over the container to collect the evaporated water. Taste the evaporated water to confirm that it is not salty. • Many students are unfamiliar with concepts of life to which they have not been exposed. It may be difficult for them to envision life such as those in hydrothermal vent communities. Consider showing them the movie Volcanoes of the Deep Sea after having them read the GEO Graphics section of the chapter. Have students discuss how life can exist there. CONCEPT CHECK ANSWERS Concept Check 14.1 1. What is salinity, and how is it usually expressed? What is the average salinity of the ocean? Answer: Salinity is a measure of the total dissolved material in water. It is usually expressed in parts per thousand. The average salinity of the ocean is 35 parts per thousand. 2. What are the six most abundant elements dissolved in seawater? What is produced when the two most abundant elements combine? Answer: The six most abundant elements are sodium, chlorine, sulfur, magnesium, calcium, and potassium. Sodium chloride, or common table salt, is produced when the two most abundant elements combine. 3. What are the two primary sources for the elements that comprise the dissolved components in seawater? Answer: Chemical weathering of continental rocks and volcanic eruptions putting elements from Earth’s interior into the seawater. 4. List several factors that cause salinity to vary from place to place and from time to time. Answer: Processes that add freshwater to seawater, such as glacial melting, can decrease salinity. Increased evaporation due to increased temperatures can increase salinity. Surface salinity can vary seasonally at the poles as sea ice freezes and melts. 5. Is the pH of the ocean increasing or decreasing? What is responsible for the changing pH? Answer: The pH is decreasing. This changing pH is due to increased carbon dioxide in the atmosphere; this carbon dioxide is dissolved in the oceans, lowering the pH. Concept Check 14.2 1. Contrast temperature variations with depth in the high and low latitudes. Why do high-latitude waters generally lack a thermocline? Answer: At high latitudes, there is generally no temperature variation with depth. At low latitudes, temperature decreases with depth down to about 1000 meters, below which there is no temperature variation. High latitude waters generally lack a thermocline because the surface temperature is already cool, similar to the water temperatures at depth. 2. What two factors influence seawater density? Which one has the greater influence on surface seawater density? Answer: Temperature and salinity affect density. Temperature has the greater influence on surface density. 3. Contrast density variations with depth in the high and low latitudes. Why do high-latitude waters generally lack a pycnocline? Answer: At high latitudes, there is no density variation with depth. At low latitudes, density increases until a depth of about 750 meters, below which density remains constant. High latitudes generally lack a pycnocline because there is high-density cold water both at the surface and below. 4. Describe the ocean’s layered structure. Why does the three-layer structure not exist in high latitudes? Answer: At the surface, the surface mixed zone has nearly uniform temperatures and extends down to between 300 and 450 meters. It is the warmest zone. Below this layer is the transition zone, which has a prominent pycnocline and a prominent thermocline. It accounts for about 18% of ocean water. The bottom layer is the deep zone, where sunlight never reaches and water temperatures hover just above freezing. This threelayer structure does not exist in high latitudes because there is no thermocline or pycnocline, meaning all layers of the ocean can mix. Concept Check 14.3 1. Describe the lifestyles of plankton, nekton, and benthos, and give examples of each. Which group comprises the largest biomass? Answer: • Plankton – these are floaters. Some are algae, some are animals, and some are bacteria. They drift with ocean currents. Larvae and phytoplankton are examples. • Nekton – these are swimmers. They are capable of moving freely but are limited in lateral range by temperature, salinity, density, and availability of nutrients. Fish and dolphins are examples. • Benthos – these are bottom-dwellers. They may be attached to rocks or move along the bottom. Examples are sea stars and sponges. Plankton comprises the largest biomass. 2. List three physical factors that are used to divide the ocean into marine life zones. How does each factor influence the abundance and distribution of marine life? Answer: • Availability of sunlight – the photic zone has sunlit surface waters, allowing for phytoplankton and creatures that feed on plankton. The aphotic zone has no sunlight and many organisms are bioluminescent. • Distance from shore – close to the shoreline there is high biomass and a great diversity of species. There is low nutrient concentration and fewer species exist in the open ocean. • Water depth – deeper ocean layers have less sunlight and higher pressure, leading to sparse abundance of marine life. 3. Why are there greater numbers and types of organisms in the neritic zone than in the oceanic zone? Answer: The neritic zone often is shallow enough for sunlight to penetrate the entire water column, leading to higher nutrient abundances. The oceanic zone has fewer nutrients for organisms to feed on. Concept Check 14.4 1. List two methods by which primary productivity is accomplished in the ocean. Which one is most significant? What two factors influence it? Answer: Solar radiation and chemical reactions. Solar radiation is most significant and is influenced by availability of nutrients and the amount of solar radiation in the area. 2. Compare the biological productivity of polar, temperate, and tropical regions of the ocean. Answer: Polar regions have low productivity most of the year, but reach a peak greater than other parts of the globe at the height of summer when sunlight is most abundant. Temperate regions have a large productivity peak at the start of spring and a smaller peak as fall begins, with moderate productivity the rest of the year. Tropical oceans have low, fairly constant productivity all year. Concept Check 14.5 1. Discuss energy transfer between trophic levels. Answer: Energy transfer between trophic levels is very inefficient. At the plankton stage, there is about a 2% transfer efficiency. For higher trophic levels, there is roughly a 10% transfer efficiency. 2. Describe the advantage that a top carnivore gains by eating from a food web rather than a food chain. Answer: If one source of food disappears, the top carnivore has other options. A top carnivore benefits from a food web by having access to multiple prey species. This reduces dependency on a single food source, enhancing resilience to fluctuations in prey populations and ensuring a more stable food supply. GIVE IT SOME THOUGHT ANSWERS 1. The accompanying photo shows sea ice in the Beaufort Sea near Barrow, Alaska. How do seasonal changes in the amount of sea ice influence the salinity of the remaining surface water? Is water density greater before or after sea ice forms? Explain. Answer: When sea ice is formed, only the water portion of the ocean freezes, leaving behind all dissolved salts in the liquid ocean. This serves to increase the salinity. As sea ice melts, salinity decreases. Water density is greater after sea ice forms because there is a greater concentration of dissolved solids left behind in the water. 2. Say that someone brings several water samples to your laboratory. His problem is that the labels are incomplete. He knows samples A and B are from the Atlantic Ocean and that one came from near the equator and the other from near the Tropic of Cancer. But he does not know which one is which. He has a similar problem with samples C and D. One is from the Red Sea and the other is from the Baltic Sea. Applying your knowledge of ocean salinity, how would you identify the location of each sample? How were you able to figure this out? Answer: The salinity of Atlantic Ocean water near the equator would be less than the salinity of the sample from the Tropic of Cancer. In the dry subtropics near the Tropic of Cancer, high evaporation rates remove water and increase the salinity, while high rainfall at the equator results in lower salinity. The Red Sea is located near the Tropic of Cancer, another dry subtropical region with high water salinities. The Baltic Sea is at a high latitude, where salinities tend to be lower. 3. You are swimming in the open ocean near the equator. The thermocline in this location is about 1°C per 50 meters of depth. If the sea surface temperature is 24°C, how deep must you dive before you encounter a water temperature of 19°C? Answer: 5° total temperature drop × 1°/50 meters = 250 meters. 4. The accompanying graph depicts variations in ocean water density and temperature with depth for a location near the equator. Which line represents temperature and which represents density? Explain. Answer: The purple line represents temperature since it decreases with increasing depths (at lower latitudes). The green line represents density since it increases with increasing depth (due to decreasing temperatures). 5. After sampling a column of water from the surface to a depth of 3000 meters (nearly 10,000 feet), a colleague aboard an oceanographic research vessel tells you that the water column is isopycnal. What does this mean? What conditions create such a situation? What would have to happen in order to create a pycnocline? Answer: Isopycnal means that the density is the same for the entire column of water. These conditions exist when there is a cold layer of water at the surface and cold water at depth at well, such as is found at higher latitudes. A pycnocline would require an influx of warmer surface waters, perhaps due to ocean currents. 6. Tropical environments on land are well known for their abundant life; rain forests are an example. By contrast, biological productivity in tropical oceans is meager. Why is this the case? Answer: Biologic productivity is low in tropical regions of the open ocean due to a permanent thermocline that produces a stratification of the water and prevents mixing between surface waters and nutrient-rich deeper waters. The thermocline essentially acts as a barrier that eliminates the supply of nutrients from deeper waters below. 7. The accompanying graph relates to the abundance of ocean life (productivity) in a polar region of the Northern Hemisphere. Which line represents phytoplankton, and which represents zooplankton? How did you figure this out? Why are the curves so low from November through February? Answer: The red line represents phytoplankton and the green line zooplankton. A springtime surge of diatoms is followed by an associated increase of zooplankton. The curves are low from November through February because of a lack of sunlight. 8. Refer to Figure 14.19. What is the average efficiency of energy transfer between trophic levels? Use this efficiency to determine how much phytoplankton mass is required to add 1 gram of mass to a killer whale, which is a third-level carnivore. Answer: The average efficiency of energy transfer between trophic levels is about 10 percent. It would take 100 grams of phytoplankton mass to add 1 gram of mass to a killer whale. (Going from level 1— phytoplankton to level 3—killer whale with a 90% loss between each level) 100 grams × 90% loss = 10 grams; 10 grams × 90% loss = 1 gram. 9. How might the removal of the top carnivore affect a food web? How would the removal of the primary producer affect the food web? Which change would be more significant? Answer: Removal of a top carnivore would allow the organisms on which it feeds to proliferate and flourish. This could cause overpopulation and eventual death of many of these mid-level species due to lack of sufficient food to support these communities. The primary producer is the base of the food web. Removal of the primary producer could cause collapse of the entire food web due to lack of original source of nutrients; therefore primary producer removal would be more significant. EXAMINING THE EARTH SYSTEM ANSWERS 1. Reef-building corals are tiny invertebrate colonial animals that live in warm, sunlit marine environments. They extract calcium carbonate from seawater and secrete an external skeleton. Although individuals are small, colonies are capable of creating massive reefs. Many other organisms also make the reef structure their home. Corals are a part of the biosphere that inhabit the hydrosphere. The solid calcium carbonate reefs they build may ultimately become the sedimentary rock limestone, a part of the geosphere. Can you relate coral reefs to the atmosphere? Can you come up with more than one connection? Answer: Corals are related to the atmosphere because oceans dissolve carbon dioxide from the atmosphere; this carbon dioxide chemically reacts in seawater to become a product that corals can uptake to build their calcium carbonate exoskeletons. Coral reefs are also dependent upon specific water temperatures. If Earth’s atmosphere warms, this in turn will warm the ocean, stressing the corals and causing them to die. Coral reefs require a specific amount of sunlight as well. If Earth warms and melts glaciers, sea level may rise to the point where corals are not receiving enough sunlight to survive. As more carbon dioxide is put into the atmosphere by human activities, the dissolution of this CO2 in seawater acidifies the ocean. Corals cannot survive outside of a specific range of pH. 2. A storm near the coast produces sediment-rich runoff that causes water in the euphotic zone to become cloudy. Describe how this would affect the plankton, nekton, and benthos. Answer: The plankton would experience a decrease in sunlight that is necessary for phytoplankton to generate biomass via photosynthesis; therefore phytoplankton biomass would decrease. Zooplankton that feed on phytoplankton would have a reduced food source and decrease in abundance as well. Nekton that feed on plankton would also find their nutrient source less abundant and would migrate elsewhere to find food or die off. Nutrients that filter through the water column to provide nutrients to the benthos would be less abundant. Sessile benthos would be stressed or die due to lack of food and mobile benthos would need to relocate or die also. 3. Hydrothermal vents, such as the one shown here, occur on the ocean floor along mid-ocean ridges. The GEO graphics in this chapter on page 442 examined these features, where very hot, mineral rich water is emitted into the cold water of the deep-ocean environment. a. What category of sediment is created by the process described above – hydrogenous, biogenous, or terrigenous? b. How are hydrothermal vents related to the biosphere? How can there be life in these deep, cold, and dark environments? Explain. Answer: a. Hydrogenous. b. Hydrothermal vents provide the nutrients and sustenance for the animals that live there. The life that lives in these cold, deep, and dark environments evolved there and are thus adapted to that environment. These species are dependent upon the sulfur and other things emitted by the hydrothermal vents, and have evolved to withstand the extreme low temperatures and high pressures. ADDITIONAL RESOURCES DVDs and Movies • Planet Earth: The Blue Planet (1986) WQED and the National Academy of Sciences, 1 hour. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/ series49.html • Blue Planet: Seas of Life (2007) BBC, 392 Minutes. Available on DVD. • Oceans (2010) Disneynature, 85 minutes. Narrated by Pierce Brosnan. Available on DVD. • Oceans: Why the Ocean Matters. From National Geographic, 3 minutes. Available for free streaming from http://video.nationalgeographic.com/video/environment/habitats-environment/habitats-oceansenv/why-ocean-matters/ • Australia Revealed: Great Barrier Reef. Discovery Channel, 2 minutes. Available for free streaming from http://www.discovery.com/video-topics/other/other-topics-earth-videos.htm • IMAX Secrets of the Deep (2002) IMAX, 35 minutes. Kelp forests, corals, and nekton. Available on DVD. • Volcanoes of the Deep Sea (2003) IMAX, 40 minutes. Explores deep-sea hydrothermal vent communities. Available on DVD. Websites • All About the Ocean. From National Geographic. http://ocean.nationalgeographic.com/ocean/ • Tropical Oceans Animals. From Missouri Botanical Garden. http://mbgnet.net/salt/coral/animals/ index.htm • Australian Great Barrier Reef. From the Australian government. http://www.gbrmpa.gov.au • Antarctic Benthos Gallery. From the Alfred Wegener Institute. http://www.awi.de/en/news/images_ video_audio/image_galleries/picture_gallery_antarctic_benthos/ • Hydrothermal Vent Creatures. From the Smithsonian Institution. http://ocean.si.edu Chapter 15 The Dynamic Ocean The Dynamic Ocean opens with a discussion of ocean surface currents and their importance. Deep-ocean (thermohaline) circulation is also briefly examined. Following a detailed presentation on waves, shoreline erosional and depositional features, as well as stabilization of the shore and coastal classification, are investigated. The chapter concludes with a discussion of tides, tidal patterns, and tidal currents. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 15.1 Discuss the factors that create and influence ocean currents and describe the affect ocean currents have on climate. 15.2 Explain the processes that produce coastal upwelling and the ocean’s deep circulation. 15.3 Explain why the shoreline is considered a dynamic interface and identify the basic parts of the coastal zone. 15.4 List and discuss the factors that influence the height, length, and period of a wave and describe the motion of water within a wave. 15.5 Describe how waves erode and move sediment along the shore. 15.6 Describe the features typically created by wave erosion and those resulting from sediment deposited by longshore transport processes. 15.7 Summarize the ways in which people deal with shoreline erosion problems. 15.8 Contrast the erosion problems faced along different parts of America’s coasts. Distinguish between emergent and submergent coasts. 15.9 Explain the cause of tides, their monthly cycles, and patterns. Describe the horizontal flow of water that accompanies the rise and fall of tides. TEACHING THE DYNAMIC OCEAN • Sometimes students readily confuse ocean surface currents with ocean thermohaline circulation. It is important to make this distinction early so that students are not working with this active misconception. • It can be helpful to show students a map of global wind belts and then show them a map of global surface currents. This can help students make the connection that surface currents are generated by wind flows. Have them detect similarities or differences in the two maps. • If you have ready access to a coast, this is a good unit during which to take a field trip to the beach. Have students identify various beach features, such as the berm, the dunes, and other coastal landforms indigenous to your area. • Regardless of whether or not you are able to visit a beach, use of many visuals is important for this unit. Since you are talking about the movement of the ocean, it is critical to have something concrete for students to see. It may be difficult for some people to abstractly relate the ocean dynamics of which you will be speaking to actual processes they cannot see. • Early in Alfred Hitchcock’s movie The Birds, there is aerial footage of a character driving along the California coastline. Using just this brief segment from this movie can be a good way to have students identify coastal features. Have them determine if this is an emergent or submergent coastline. You might also ask the students if this ocean view were something they would see on the U.S. East Coast or Gulf Coast. Have them tell you why or why not. • Hurricane Sandy is a fairly recent event that most people will be able to recall. Use the video clip about repairing the beach after this storm (see Additional Resources) to show students what beach nourishment looks like. You can use this to begin a discussion of hard stabilization and alternatives. • Show students a map of the U.S. with average temperatures for various cities along the coasts. You can use seasonal maps or yearly average maps. Have them discuss why San Francisco seems to be cool for its latitude. Likewise, have them discuss why New York might be warm for its latitude. Use this lesson to introduce the concept of how oceans and ocean currents can affect local climates. CONCEPT CHECK ANSWERS Concept Check 15.1 1. What is the primary driving force of surface-ocean currents? Answer: Wind. The primary driving force of surface-ocean currents is wind. Wind generates frictional drag on the ocean's surface, transferring energy to the water and causing it to move in the direction of the prevailing winds. 2. How does the Coriolis effect influence ocean currents? Answer: The Coriolis effect causes the deflection of the path of moving objects, including the path of surface currents, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection generates the large ocean gyres that flow in a circular path in the oceans. 3. Name the five subtropical gyres and identify the main surface currents in each. Answer: • North Atlantic Gyre – Gulf Stream, North Atlantic Drift, Canary Current, and North Equatorial Current. • South Atlantic Gyre – Brazil Current, South Equatorial Current, and Benguela Current. • North Pacific Gyre – California Current, North Equatorial Current, Kuroshito Current, and North Pacific Current. • South Pacific Gyre – South Equatorial Current, Peru Current, West Wind Drift, and East Australian Current. • Indian Ocean Gyre – South Equatorial Current, Agulhas Current, West Wind Drift, and West Australian Current. 4. How do ocean currents influence climate? Provide at least three examples. Answer: Ocean currents influence climate because the currents are major redistributors of heat and energy throughout the globe. Warm currents such as the Gulf Stream cause regions that would normally be cold to be warmer. For example, New York is warm for its latitude. Cold currents cause the air above them to be cooler. San Francisco is relatively cool in the summer because of the presence of the cool California Current off its coastline. Cold currents also increase the aridity of an area. The Peru Current off the coast of South America causes stable atmospheric conditions that resist cloud formation and moisture-bringing precipitation. Concept Check 15.2 1. Describe the process of coastal upwelling. Why is an abundance of marine life associated with these areas? Answer: Coastal upwelling occurs when wind blow surface waters laterally. Cold, nutrient-rich water from lower ocean layers moves upward to fill the space. There is an abundance of marine life in these areas because of the dense nutrient concentrations in these upwelled waters. 2. Why is deep-ocean circulation referred to as thermohaline circulation? Answer: Deep-ocean circulation is a global circulation pattern that relies on temperature and density differences to determine if the current will flow at the surface or on the ocean floor. 3. Describe or make a simple sketch of the ocean’s conveyor-belt circulation. Answer: See Figure 15.7. Warm surface waters flow from the mid-Pacific, through the Indian Ocean basin, and upwards to the North Atlantic. In the North Atlantic, these waters become more dense as they cool, and they sink to the ocean floor, where they flow back to the Indian and Pacific Oceans as deep-ocean currents. The ocean's conveyor-belt circulation, also known as thermohaline circulation, involves the sinking of dense, cold water near the poles (due to cooling and increased salinity) and the upwelling of warmer water in the equatorial regions. This global circulation helps redistribute heat and nutrients throughout the oceans, influencing climate patterns worldwide. Concept Check 15.3 1. Why is the shoreline considered an interface? Answer: An interface is a boundary where different parts of a system interact; the shoreline is a boundary between the ocean processes and those found on land and in the atmosphere. 2. Distinguish among shore, shoreline, coast, and coastline. Answer: The shore is the area that ranges from the lowest tide level to the furthest reaches of land affected by storm waves, while the shoreline is the line that demarcates between land and sea. The coast is the area that extends from the shore to as far as ocean-related features can be found, where the coastline marks the coast’s seaward edge. 3. What is a beach? Distinguish between beach face and berm. Answer: A beach is where sediment accumulates along the landward edge of an ocean or a lake. The beach face is the part of the beach that is wet and sloping, extending from the berm to the shoreline. The berm is relatively flat and adjacent to coastal dunes or cliffs; they mark a change in slope. Concept Check 15.4 1. List three factors that determine the height, length, and period of a wave. Answer: Wind speed, length of time the wind has blown, and fetch, which is the distance wind has travelled across the open water. 2. Describe the motion of a floating object as a wave passes. Answer: The floating object will bob up and down as the water underneath it moves in a vertical circular pattern. 3. How do the speed, length, and height of a wave change as the wave moves into shallow water and breaks? Answer: The speed decreases while the length of the wave also decreases. The height increases, eventually breaking on the shore. Concept Check 15.5 1. Describe two ways in which waves cause erosion. Answer: The force of the water in a wave exerts a great deal of pressure on rocks, causing rock fragments to break loose and enlarging fractures. Waves also cause erosion due to abrasion from rock fragments and large sediment carried by them. 2. Why do waves that are approaching the shoreline often bend? Answer: Wave refraction occurs as part of the wave approaching at an angle becomes a shallow water wave, thus slowing down, while part of the wave is still a faster-moving deep water wave. 3. What is the effect of wave refraction along an irregular coastline? Answer: You will find erosion of the headlands and deposition in the bays. 4. Describe the two processes that contribute to longshore transport. Answer: Beach drift is when incoming waves hit the beach at an angle, causing a zigzag motion of the water and the sediment contained in it down the beach. The longshore current also contributes to longshore transport; as the longshore current is the current that runs parallel to the beach. Concept Check 15.6 1. How is a marine terrace related to a wave-cut platform? Answer: A wave-cut platform is generated as waves erode coastal cliffs over time. A wave-cut platform can become a marine terrace if it is uplifted by tectonic forces. 2. Describe the formation of the features labeled in Figure 15.20 and Figure 15.21. Answer: In Figure 15.20 we see a sea stack and a sea arch. These form due to wave erosion as refracted waves aggressively erode extending headlands. If there are caves on opposite sides of the headland, a sea arch with a hole in the middle of the rock may form. In Figure 15.21 we see a spit, a bay mouth bar, and a tidal delta. A spit is formed as longshore transport generates an elongated ridge of sand that extends into a hook shape into a bay. A bay mouth bar is also caused by longshore transport if a ridge of sand completely seals off a bay. A tidal delta is a bay ward deposit of sand caused by the ocean breaking through the ridge of sand. 3. List three ways that barrier islands may form. Answer: They can originate as spits that were severed from the mainland, they may be formed when turbulent coastal waters deposit long ridges of sand, or they may be former sand dunes that had the areas around them flooded as sea level rose after the last glacial period. Concept Check 15.7 1. List three examples of hard stabilization and describe what each is intended to do. How does each affect sand distribution on a beach? Answer: • Jetty – built in pairs and run perpendicular to the shoreline at the entrance to rivers and harbors. They are intended to prevent deposition in the river channels. They cause sand to accumulate on the side from which the longshore current is coming and to erode on the other side. • Breakwater – built parallel to the shoreline with the intent of protecting boats from the force of breaking waves. Sand may accumulate behind a breakwater close to the shore. • Seawall – designed to protect structures and property on the coast from breaking waves. The beach on the seaward side of the seawall will generally experience significant sand erosion. 2. What are two alternatives to hard stabilization, and what potential problems are associated with each? Answer: • Beach nourishment – sand is manually replaced on beaches where it has been eroded. The transported sand has to come from another beach, it is expensive, it is temporary, and it generally replaces eroded sand with sand that is different in size, shape, sorting, and composition. • Relocation – moving buildings. People do not always want to move and it is another expensive solution. Concept Check 15.8 1. Briefly describe what happens when storm waves strike an undeveloped barrier island. Answer: Waves may move sand from the beach to the offshore region or the dunes. Over wash may move sand as far as the bay side of the barrier island. The whole island is capable of moving sediment with whatever waves hit it. 2. How might building a dam on a river that flows to the sea affect a beach? Answer: It would restrict the flow of continental sediments to the beach, depriving the beach of a sand source. 3. What is an observable feature that would lead you to classify a coastal area as emergent? Answer: An elevated marine terrace. An observable feature that would lead to classifying a coastal area as emergent is the presence of exposed marine terraces or raised shorelines. These indicate that the land has risen relative to sea level, typically due to tectonic uplift or a decrease in sea level over time. 4. Are estuaries associated with submergent or emergent coasts? Explain. Answer: They are associated with submergent coasts. As sea level rises, drowned river mouths that have been submerged become estuaries. Estuaries are associated with submergent coasts. This is because estuaries form in areas where sea level has risen relative to the land, resulting in the submergence of river valleys or coastal plains. Estuaries typically occur at the mouths of rivers where freshwater mixes with seawater in a partially enclosed coastal body of water. Concept Check 15.9 1. Explain why an observer can experience two unequal high tides during one day. Answer: The Moon’s position will vary with respect to the observer. If the Moon is located in a position where it pulls strongly on the tide in one part of the day and more weakly during the other part of the day, the observer can experience two unequal tides. 2. Distinguish between neap tides and spring tides. Answer: When the Sun and the Moon are aligned with the Earth, both influence the tidal bulges, which will be greater than normal; this is a spring tide. When the Moon is in the first or third quarter position, the tidal bulges produced by the Sun are at right angles to those produced by the Moon, and these bulges will be smaller than normal. These are neap tides. 3. How is a mixed tidal pattern different from a semidiurnal tidal pattern? Answer: A mixed tidal pattern is when there are two high tides and two low tides of unequal height during the day and a semidiurnal tidal pattern is when there are two high tides and two low tides of equal height during the day. 4. Contrast flood current and ebb current. Answer: Tidal currents that advance into the coastal zone as the tide rises are flood currents and currents that recede with low tide are ebb currents. GIVE IT SOME THOUGHT ANSWERS 1. In this chapter you learned that global winds are the force that drive surface ocean currents. A glance at the accompanying map, however, shows a surface current that does not exactly coincide with the prevailing wind. Provide an explanation. Answer: Upwelling and the Coriolis effect could account for the surface current off of the southwestern African coast that is not moving in the same direction as the prevailing winds. 2. During a visit to the beach, you get in a small rubber raft and paddle out beyond the surf zone. Tiring, you stop and take a rest. Describe the movement of your raft during your rest. How does this movement differ, if at all, from what you would have experienced if you had stopped paddling while in the surf zone? Answer: Beyond the surf zone the movement of the raft is more up and down, due to the waves moving, but not touching the bottom. Had you stopped in the surf zone, the raft would move more laterally toward the shore, due to the asymmetrical nature of the waves created by touching the bottom. 3. You and a friend set up an umbrella and chairs at a beach. Your friend then goes into the surf zone to play Frisbee with another person. Several minutes later your friend looks back toward the beach and is surprised to see that she is no longer near where the umbrella and chairs were set up. Although she is still in the surf zone, she is 30 or 40 yards away from where she started. How would you explain to your friend why she moved along the shore? Answer: I would explain to my friend that waves generally approach the shore at an angle and this produces a current in the surf zone that moves parallel to the coast. Such movements are called longshore currents and they tend to transport sediment (and in this case a person) parallel to the shore. 4. Examine the accompanying aerial photo that shows a portion of the New Jersey shoreline. What term is applied to the wall-like structures that extend into the water? What is their purpose? In what direction are beach drift and longshore currents moving sand? Is sand moving toward the top or toward the bottom of the photo? Answer: The structures are called groins and they are designed to trap sand that is moving parallel to the shore. The beach drift and longshore currents are moving the sediment from the bottom towards the top of the photograph. 5. A friend wants to purchase a vacation home on a barrier island. If consulted, what advice would you give your friend? Answer: Although they may appear to be relatively stable, barrier islands are essentially low ridges of sand that parallel the coastline. They typically originate as spits that are separated from the shore by turbulent waters that scour sediment from the seafloor. Because they are nothing more than deposits of sand, barrier islands are often heavily eroded or altered during hurricanes or severe storms. Also, the natural processes along the shore will influence the alteration or formation of barrier islands over time. Therefore, I would advise my friend against purchasing a vacation home on a barrier island. 6. The force of gravity plays a critical role in creating ocean tides. The more massive an object, the stronger the pull of gravity. Explain why the Sun’s influence is only half that of the Moon, even though the Sun is much more massive than the Moon. Answer: The Sun’s gravitational influence is much less than that of the Moon because it is much further away from the Earth. The Sun is much more massive than the Moon, but it is also approximately 400 times further away and because of this the Moon exerts much more gravity on the Earth than does the Sun. 7. This photo shows a portion of the Maine coast. The brown muddy area in the foreground is influenced by tidal currents. What term is applied to this muddy area? Name the type of tidal current this area will experience in the hours to come. Answer: This muddy area is a tidal flat. It will experience a flood tide. EXAMINING THE EARTH SYSTEM ANSWERS 1. Palm trees in Scotland? Yes, in the 1850s and 1860s, amateur gardeners planted palm trees on the western shore of Scotland. The latitude here is 57° north, about the same as the northern portion of Labrador across the Atlantic in Canada. Surprisingly, these exotic plants flourished. Suggest a possible explanation for how these palms can survive at such a high latitude. Answer: The warm Gulf Stream transports large amounts of very warm water from equatorial regions northward up the East Coast of North America. From there, this current merges with the North Atlantic Drift, which brings warm water to the northern tip of Scotland. These warm waters off the coast of Scotland moderate the climate enough to allow these trees to grow. 2. If wastage (melting and calving) of the Greenland Ice Sheet were to dramatically increase, how would the salinity of the adjacent North Atlantic be affected? How might this influence thermohaline circulation? Answer: Wastage of this ice sheet would dump a large quantity of fresh water into the North Atlantic, decreasing the salinity. It is in this vicinity that the warm current portion of thermohaline circulation becomes dense enough to sink to the bottom of the ocean and return through the Atlantic Ocean as a bottom current. Since salinity affects density, it is likely that the decreased salinity of the water could shut down thermohaline circulation as the water is no longer saline, or dense, enough to sink. 3. In this chapter the shoreline was described as a “dynamic interface.” What is an interface? List and briefly describe some other interfaces in the Earth system. You need not confine yourself to examples from this chapter. Answer: An interface is a common boundary where different parts of a system interact. Student answers will vary, but some other examples of Earth system interfaces include the mantle–core boundary, the asthenosphere–lithosphere boundary, and where rivers erode rock. 4. This dam in the San Gabriel Mountains near Los Angeles was built on a river that flows into the Pacific Ocean. What impact might this artificial structure have on coastal beaches? Answer: Sand on coastal beaches is usually eroded continental material that has been transported by rivers. If you dam the river that transports sediment oceanward, you will cut off the supply of beach sand that replenishes and nourishes the beach environment. ADDITIONAL RESOURCES DVDs and Movies • Earth Revealed, Episode 24: Waves, Beaches and Coasts (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/ series78.html • Coasts and Islands: Rio Beach. National Geographic, 2 minutes. Preserving the Brazilian coastline from environmental issues. Available for free streaming from http://video.nationalgeographic.com/ video/places/parks-and-nature-places/coasts-and-islands/brazil_riobeach/ • Repairing the Beach After Sandy. NOVAScienceNow, PBS, 3 minutes. Beach nourishment project in New Jersey after Hurricane Sandy. Available for free streaming from http://www.pbs.org/wgbh/nova/ earth/beach-nourishment.html • How Rip Currents Are Formed and How to Avoid Drowning. NMANews Direct, 1 minute. http://www.youtube.com/watch?v=d8c7RJx5pBg Websites • Breaking Waves. From NOAA. Interactive website where you can see how steepness of the beach affects how waves break. http://oceanexplorer.noaa.gov/edu/learning/9_ocean_waves/activities/ breaking_waves.html • Savage Seas Wave Simulator. From PBS Online. Interactive website where you can create your own ocean wave and learn about its characteristics. http://www.pbs.org/wnet/savageseas/multimedia/ wavemachine.html • Rip Current. From NOAA. Short video clip of a rip current at a beach. http://www.ripcurrents.noaa.gov/multimedia/Rip3.mov • How Headlands and Bays Form and Erode. Animation from BBC. http://www.bbc.co.uk/schools/ riversandcoasts/coasts/change_coast/pg_05_flash.shtml • Perpetual Ocean Global Ocean Currents Animation. From NASA and LiveScience. http://www.livescience.com/19662-animation-reveals-ocean-currents.html Chapter 16 The Atmosphere: Composition, Structure, and Temperature The Atmosphere: Composition, Structure, and Temperature introduces the subject of meteorology by presenting its definition, noting the differences between weather and climate, and listing the elements of weather. Included is a discussion of the major gases (nitrogen and oxygen) and variable components (water vapor, aerosols, and ozone) of the atmosphere. The structure and extent of the atmosphere are also examined. The discussion of atmospheric heating begins with an examination of Earth’s motions. The variables that control the quantity of solar radiation intercepted by a particular place are also discussed. This is followed by a detailed investigation of the seasons. After an examination of radiant energy and the common mechanisms of heat transfer, atmospheric heating by solar and terrestrial radiation is discussed. Various temperature measurements are also explained. The factors that cause variations in temperature, such as differential heating of land and water, altitude, geographic position, cloud cover, and albedo, are investigated. The chapter concludes with a short description of the global distribution of Earth’s surface temperatures. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 16.1 Distinguish between weather and climate and name the basic elements of weather and climate. 16.2 List the major gases composing Earth’s atmosphere and identify the components that are most important to understanding weather and climate. 16.3 Interpret a graph that shows changes in air pressure from Earth’s surface to the top of the atmosphere. Sketch and label a graph that shows atmospheric layers based on temperature. 16.4 Explain what causes the Sun angle and length of daylight to change during the year and describe how these changes produce the seasons. 16.5 Distinguish between heat and temperature. List and describe the three mechanisms of heat transfer. 16.6 Sketch and label a diagram that shows the paths taken by incoming solar radiation. Summarize the greenhouse effect. 16.7 Calculate five commonly used types of temperature data and interpret a map that depicts temperature data using isotherms. 16.8 Discuss the principal controls of temperature and use examples to describe their effects. 16.9 Interpret the patterns depicted on world maps of January and July temperatures. TEACHING THE ATMOSPHERE: COMPOSITION, STRUCTURE, AND TEMPERATURE • Students should already be familiar with the idea of conduction after studying the solid Earth chapters and discussing mantle upwelling. Be prepared to make this connection that conduction can occur with any type of fluid, and in the case of the atmosphere, air behaves as a fluid. • There are some novelty lamps on the market that have a rotating tube that projects images on the wall as the light bulb in the lamp heats up. You can use one of these lamps to illustrate the process of convection. Turn it on at the beginning of class. The tube will begin to rotate after several minutes, as the heat in the lamp increases and convection drives the circulation of the tube. Show this demonstration to students and ask them what is going on before you explain it. • You can use the example of a boiling pot of water to discuss the difference between conduction and convection. Since most students are familiar with what a boiling pot of water looks like, it is not necessary to have one on hand. You can ask them which part of this system represents conduction and which represents convection. Then explain that when the pot itself is in contact with a hot burner, this is conduction. As the water at the bottom of the pot heats up, it rises in a mass movement to the top of the pot, where it cools and sinks again. Make the connection between this and what happens in Earth’s atmosphere. • Give students a chart that lists layers of the atmosphere and their relative thicknesses. Have the students create a scale model of the atmosphere layers either in their notebooks or you can provide larger paper for them to work on. • Many students harbor the misconception that Earth’s seasons are directly tied to proximity to the Sun. They mistakenly believe that when we are closer to the Sun, we have summer. You can start to challenge this misconception by asking how this can be true if there are opposite seasons in opposite hemispheres. Show a graphic of Earth’s nearly circular orbit and then introduce the concept of Earth’s tilt affecting the seasons. • You can demonstrate varying radiation on Earth’s surface by using a tilted globe and a flashlight. Hold the flashlight steady and show how the beam is more direct at some locations than at others; use this as an analogy for solar radiation. • Ozone and the ozone hole are important environmental issues. However, many students think that the problems of global warming and the ozone hole are the same thing. It is important to clarify that they are completely different issues, especially before exploring the topic of climate change in future chapters. • A common misconception is that the air is mostly oxygen. • To illustrate the moderating effects of the ocean, you can demonstrate with a heat lamp, a container of water, and a dark solid surface. Turn the heat lamp on so that it shines equally on your container of water and on your solid surface. After a few minutes invite a few students to feel the temperature difference between the solid and the water. You can relate this small-scale demonstration to the high specific heat of water and how on a large scale water can moderate climate. • To help students remember that temperature decreases with altitude in the troposphere, you can use the example of snow-capped mountains. Ask why the snow is on the tops of mountains but not necessarily on the sides. Explain that the mountaintop is higher in the troposphere than other parts of the mountain and thus will be experiencing cooler temperatures. CONCEPT CHECK ANSWERS Concept Check 16.1 1. Distinguish between weather and climate. Answer: Weather is short-term atmospheric conditions for a given location. Climate is long-term atmospheric conditions for a region. Climate must include averages and extremes. 2. Write two brief statements about your current location: one that relates to weather and one that relates to climate. Answer: Weather in my current location is sunny with clear skies and a gentle breeze. The climate here is generally temperate, characterized by mild winters and warm summers. 3. What is an element? Answer: It is a quantity or property that is measured regularly. 4. List the basic elements of weather and climate. Answer: Air temperature, humidity, type and amount of cloudiness, type and amount of precipitation, air pressure, and speed and direction of the wind. Concept Check 16.2 1. Is air a specific gas? Explain. Answer: Air is not a specific gas because it contains a mixture of several different gases. 2. What are the two major components of clean, dry air? What proportion does each represent? Answer: 78% nitrogen, 21% oxygen. 3. Why are water vapor and aerosols important constituents of Earth’s atmosphere? Answer: Water vapor is an important greenhouse gas that makes the planet habitable. It also contains huge amounts of latent heat that provide the power for weather systems globally. Aerosols are small solid particles suspended in the air. They can serve as nuclei on which water can condense and they can absorb, scatter, and reflect incoming solar radiation. 4. What is ozone? Why is ozone important to life on Earth? What are CFCs, and what is their connection to the ozone problem? Answer: Ozone is three oxygen molecules bonded together. It is important because it blocks much of the harmful UV radiation from the Sun. CFCs are chlorofluorocarbons and chemically interact with ozone molecules to break them apart; when this happens enough an ozone hole may be generated. Concept Check 16.3 1. Does air pressure increase or decrease with an increase in altitude? Is the rate of change constant or variable? Answer: Air pressure decreases with increased altitude. The rate of change is variable. 2. Is the outer edge of the atmosphere clearly defined? Explain. Answer: It is not well defined. Only a tiny fraction of Earth’s gases exist at the top of the thermosphere and it is difficult to determine where it ends. 3. The atmosphere is divided vertically into four layers, on the basis of temperature. List and describe these layers in order, from lowest to highest. In which layer does practically all our weather occur? Answer: • Troposphere – temperature decreases with increasing height. Has the highest pressure of all four layers. • Stratosphere – temperature increases with increasing height. This layer contains most of Earth’s protective ozone layer. • Mesosphere – temperature decreases with increasing height and contains the coldest temperatures in the atmosphere. It is the least explored of the four layers. • Thermosphere – temperature increases with increasing height up to the edge of space. Temperatures can be very high. Almost all of Earth’s weather occurs in the troposphere. 4. What is the environmental lapse rate, and how is it determined? Answer: This is the temperature decrease with altitude in the troposphere. It is determined by sending a radiosonde balloon up to make temperature measurements. 5. Why do temperatures increase in the stratosphere? Answer: This is where there is an abundance of ozone, which absorbs ultraviolet radiation from the Sun. This heats up this layer. 6. Why are temperatures in the thermosphere not strictly comparable to those experienced near the Earth’s surface? Answer: The atmosphere and gas concentration in the thermosphere is very sparse and thin. Concept Check 16.4 1. Do the annual variations in Earth–Sun distance adequately account for seasonal temperature changes? Explain. Answer: No, because Earth is tilted on its axis. Distance from the Sun is negligible in seasonal temperature changes. 2. Create a simple sketch to show why the intensity of solar radiation striking Earth’s surface changes when the Sun angle changes. Answer: See Figure 16.4. Sure, here's a simple sketch: This sketch illustrates how the angle of sunlight (represented by "X") affects the intensity of solar radiation on Earth's surface. As the angle increases (moving from left to right), the same amount of solar energy is spread over a larger area, reducing its intensity. 3. Briefly explain the primary cause of the seasons. Answer: The tilt of Earth on its axis allows some locations on Earth to receive more direct solar radiation at some times of the year because those locations are tilted towards the Sun; this would be summer. When a hemisphere is tilted away from the Sun it receives less direct radiation and experiences winter. 4. What is the significance of the Tropic of Cancer and the Tropic of Capricorn? Answer: These represent the most northern and most southern locations on Earth at which the noon sun will ever be directly overhead. The Tropic of Cancer and the Tropic of Capricorn mark the northernmost and southernmost points, respectively, where the Sun can appear directly overhead at noon on the solstices. They define the limits of the tropics, influencing the Earth's climate and weather patterns. 5. After examining Table 16.1, write a general statement that relates the season, latitude, and the length of daylight. Answer: Regions closer to the equator experience little variation in day length among the seasons, while areas closer to the poles experience extremely long hours of daylight in summer and little to none in winter. Concept Check 16.5 1. Distinguish between heat and temperature. Answer: Temperature is the average speed of air molecules, while heat is a measure of energy transfer between objects or regions of different temperatures. 2. Describe the three basic mechanisms of heat transfer. Which mechanism is least important as a means of heat transfer in the atmosphere? Answer: • Convection – this is mass movement or circulation of heat in a substance. • Radiation – this is radiant energy that reaches Earth from the Sun. • Conduction – this is heat transfer from molecule to molecule within a substance. It is the least important in the atmosphere. 3. In what part of the electromagnetic spectrum does the Sun radiate maximum energy? How does this compare to Earth? Answer: The Sun emits its maximum energy in the visible portion of the spectrum. Earth is much cooler and emits most of its radiation as longwave radiation. 4. Describe the relationship between the temperature of a radiating body and the wavelengths it emits. Answer: Hotter objects emit radiation at shorter wavelengths. Concept Check 16.6 1. What three paths does incoming solar radiation take? Answer: It can be scattered, reflected, or absorbed. 2. What factors cause albedo to vary from time to time and from place to place? Answer: Cloud cover, particulate matter in the air, angle of the Sun’s rays, nature of the surface. 3. Explain why the atmosphere is heated chiefly by radiation emitted from Earth’s surface rather than by direct solar radiation. Answer: Earth’s atmospheric gases are more efficient at trapping longer wavelengths of radiation such as those emitted by the Earth; these gases tend to allow solar radiation to pass through the atmosphere. 4. Prepare a sketch with labels that explains the greenhouse effect. Answer: See Figure 16.4. Simple sketch with labels explaining the greenhouse effect: Label 1: Incoming Solar Radiation - Energy from the Sun reaches the Earth's surface. Label 2: Outgoing Infrared Radiation - Some of this energy is absorbed and re-emitted by greenhouse gases, trapping heat in the atmosphere. Concept Check 16.7 1. How are the following temperature data calculated: daily mean, daily range, monthly mean, annual mean, and annual range? Answer: • Daily mean – adding the maximum and minimum daily temperatures and dividing by two. • Daily range – finding the difference between the maximum and minimum temperature for a day. • Monthly mean – adding the daily means for each day of the month and dividing by the number of days in that month. • Annual mean – averaging the 12 monthly means. • Annual range – finding the difference between the highest and lowest monthly means. 2. What are isotherms, and what is their purpose? Answer: Isotherms are lines of equal temperature on a weather map. They connect places that have the same temperature and show temperature gradients and distribution patterns. Concept Check 16.8 1. List the factors that cause land and water to heat and cool differently. Answer: Water’s relatively high specific heat, transparency of water, vertical mixing of water, evaporation from water is greater than that from land. 2. Quito, Ecuador, is located on the equator and is not a coastal city. It has an average annual temperature of only 13°C (55°F). What is the likely cause for this low average temperature? Answer: Quito is at a high elevation. The likely cause for Quito's low average temperature despite its equatorial location and lack of coastal influence is its high altitude. Quito sits at an elevation of about 2,850 meters (9,350 feet), where temperatures typically decrease with altitude due to lower atmospheric pressure and thinner air. 3. In what ways can geographic position be considered a control of temperature? Answer: Places close to an ocean will experience the moderating effects of an ocean. A windward coast will experience more prevailing winds than a leeward coast also. 4. How does cloud cover influence the maximum temperature on an overcast day? How is the nighttime minimum influenced by clouds? Answer: Cloud tops have a high albedo and reflect much incoming sunlight away from Earth’s surface, making temperatures at the surface cooler on an overcast day. Clouds absorb outgoing nighttime radiation from the Earth, acting as a blanket and keeping minimum temperatures warmer than they otherwise would be. Concept Check 16.9 1. Why do isotherms generally trend east–west? Answer: The heating of Earth’s surface by solar radiation is a function of latitude and similar latitudes have similar temperatures. 2. Why do isotherms shift north and south from season to season? Answer: There is differential heating of different latitudes with the seasons depending upon the angle at which the Sun is striking them. 3. Where do isotherms shift most, over land or water? Explain. Answer: They shift most over land because water has a high specific heat and takes longer to heat up and cool off. 4. Which area on Earth experiences the highest annual temperature range? Answer: Asian continental interior. GIVE IT SOME THOUGHT ANSWERS 1. Determine which statements refer to weather and which refer to climate. (Note: One statement includes aspects of both weather and climate.) a. The baseball game was rained out today. b. January is Omaha’s coldest month. c. North Africa is a desert. d. The high this afternoon was 25°C. e. Last evening a tornado ripped through central Oklahoma. f. I am moving to southern Arizona because it is warm and sunny. g. Thursday’s low of -20oC is the coldest temperature ever recorded for that city. h. It is partly cloudy. Answer: a. weather b. climate c. climate d. weather e. weather f. climate g. weather and climate h. weather 2. This map shows the mean percentage of possible sunshine received in the month of November across the 48 contiguous United States. a. Does this map relate more to climate or to weather? b. If you visited Yuma, Arizona, in November, would you expect to experience a sunny day or an overcast day? c. Might what you actually experience during your visit be different from what you expected? Explain. Answer: a. Climate b. Sunny c. You could experience different conditions. This map represents climate, which is an overall generalization. It does not account for variability in day-to-day weather conditions. 3. Refer to the graph in Figure 16.3 to answer the following questions about temperatures in New York City: a. What is the approximate average daily high temperature in January? In July? b. Approximately what are the highest and lowest temperatures ever recorded? Answer: a. 4 degrees C (42°F) in January. 29 degrees C (84°F) in July. b. Highest = 42°C (108°F). Lowest = −19°C (0°F). 4. Which of the three mechanisms of heat transfer is clearly illustrated in each of the following situations? a. Driving in a car with the seat heater turned on. b. Sitting in an outdoor hot tub. c. Lying inside a tanning bed. d. Driving a car with the air conditioning turned on. Answer: a. Conduction b. Conduction c. Radiation d. Convection 5. The circumference of Earth at the equator is 24,900 miles. Calculate how fast someone at the equator is rotating in miles per hour. If the rotational speed of Earth were to slow down, how might this impact daytime highs and nighttime lows? Answer: 24,900 miles/24 hours = 1038 miles/hour. If Earth’s rotational speed were to slow down, daytime high temperatures would be higher and nighttime low temperatures would be lower. 6. Rank the following according to the wavelengths of radiant energy each emits, from the shortest wavelengths to the longest: a. A light bulb with a filament glowing at 4000°C. b. A rock at room temperature. c. A car engine at 140°C. Answer: a, c, b. Ranking the wavelengths of radiant energy emitted from shortest to longest: 1. a. A light bulb with a filament glowing at 4000°C (emits shorter wavelengths in the visible and infrared spectrum due to its high temperature). 2. c. A car engine at 140°C (emits longer wavelengths in the infrared spectrum). 3. b. A rock at room temperature (emits even longer wavelengths in the far infrared and microwave spectrum). 7. Imagine being at the beach in this photo on a sunny summer afternoon. a. Describe the temperatures you would expect if you measured at the surface of the beach and at a depth of 12 inches in the sand. b. If you stood waist deep in the water and measured the water’s surface temperature and its temperature at a depth of 12 inches, how would these measurements compare to those taken on the beach? Answer: a. The temperature of the surface sand would be warm or hot from the solar radiation. Since radiation does not penetrate deep into the earth, the temperature at a 12 inch depth would be cooler. b. The water temperatures would be cooler than those on the land, and would be similar at the surface and at a 12 inch depth. 8. On which summer day would you expect the greatest temperature range? Which would have the smallest range in temperature? Explain your choices. a. Cloudy skies during the day and clear skies at night. b. Clear skies during the day and cloudy skies at night. c. Clear skies during the day and clear skies at night. d. Cloudy skies during the day and cloudy skies at night. Answer: Choice c would provide the greatest temperature range because clear skies during the day allow a great deal of solar radiation to reach the surface and clear skies at night allow Earth’s longwave radiation to escape. Choice d would have the smallest range because cloudy skies would allow little shortwave radiation into the atmosphere and clouds at night would prevent radiation from escaping. 9. The accompanying sketch map represents a hypothetical continent in the Northern Hemisphere. One isotherm has been placed on the map. a. Is the temperature higher at City A or City B? b. Is the season winter or summer? How are you able to determine this? c. Describe (or sketch) the position of this isotherm 6 months later. Answer: a. City A. b. Summer. The continent has heated up more quickly than the ocean due to a combination of increased solar radiation and the high specific heat of water. c. This isotherm will be flatter and more southward in 6 months. 10. This photo shows a snow-covered area in the middle latitudes on a sunny day in late winter. Assume that 1 week after this photo was taken, conditions were essentially identical, except that the snow was gone. Would you expect the air temperatures to be different on the two days? If so, which day would be warmer? Suggest an explanation. Answer: Air temperatures would be warmer 1 week later. Cold snow has a cooling effect on the air directly above it. In addition, snow has a high albedo, causing much of the incoming solar radiation to be reflected rather than absorbed. 11. The Sun shines continually at the North Pole for 6 months, from the spring equinox until the fall equinox, yet temperatures never get very warm. Explain why this is the case. Answer: Despite the long period of solar radiation continually reaching the North Pole, the temperatures never get very warm because the sun angle is quite low and never gets above 23½° during this entire time, thus the intensity of solar radiation is always low as well. 12. The data below are mean monthly temperatures in degrees Celsius for an inland location that lacks any significant ocean influence. Based on annual temperature range, what is the approximate latitude of this place? Are these temperatures what you would normally expect for this latitude? If not, what control would explain these temperatures? Answer: The approximate latitude is zero degrees. These are not temperatures you would normally expect; the control would be a high elevation. EXAMINING THE EARTH SYSTEM ANSWERS 1. Earth’s axis is inclined 23½° to the plane of its orbit. What if the inclination of the axis changed? Answer the following questions that address this possibility: a. How would seasons be affected if Earth’s axis were perpendicular to the plane of its orbit? b. Describe the seasons if Earth’s axis were inclined 40°. Where would the Tropics of Cancer and Capricorn be located? How about the Arctic and Antarctic Circles? Answer: a. If Earth’s axis were perpendicular to the plane of its orbit instead of being inclined 23½°, the equator would receive vertical (90°) rays from the Sun throughout the entire year. Therefore, the altitude of the noon Sun and length of day would remain the same at each latitude throughout the year, and no seasonal variations would occur. b. If this were the actual tilt of the Earth’s axis, seasonal variations would be more extreme than they are now—warmer summers and colder winters in both hemispheres. The Tropics of Cancer and Capricorn would be at 40° North and South latitudes and the Arctic and Antarctic Circles would be at 80° North and South. 2. Speculate on the changes in global temperatures that might occur if Earth had substantially more land area and less ocean area than at present. How might such changes influence the biosphere? Answer: Land heats more rapidly and to higher temperatures than water and cools more rapidly and to lower temperatures than water. If Earth had substantially more land and less ocean, (1) daytime temperatures, especially in the interiors of landmasses, would be higher and get hotter sooner, and (2) night temperatures, again especially in the interiors, would get colder and colder sooner. Along the coastal margins of the new landmasses, the effects would be less noticeable because of the modification of temperatures by the ocean. Eventually the effect would be alteration of Earth’s entire global climate. The influence such changes would have on the biosphere would be significant. Organisms in the interiors of continents would have to become more tolerant of the larger daily ranges of temperatures and the arid conditions that could develop because they would be more removed from moisture supplied by the oceans. Eventually, owing to the overall impact on global climates, all species would be affected to some degree. 3. The accompanying photo shows the explosive 1991 eruption of Mt. Pinatubo in the Philippines. How would you expect global temperatures to respond to the ash and debris that this volcano spewed high into the atmosphere? Speculate about how a change in temperature might impact one or more of the spheres in the Earth system. Answer: Following a major volcanic eruption that sends huge volumes of debris and gases into the atmosphere, global temperatures tend to decrease over a period of several months to perhaps a year or two. The volcanic debris and aerosols (primarily droplets of sulfuric acid) serve to block and reflect a portion of the incoming solar radiation, thus reducing the amount of heat energy that reaches Earth’s surface. A change in temperature might impact the biosphere because many species are adapted to specific temperatures. 4. Figure 16.21 shows that about 30 percent of the Sun’s energy is reflected and scattered back to space. If Earth’s albedo were to increase to 50 percent, how would you expect average surface temperatures to change? Explain. Answer: An increase in total albedo to 50% would undoubtedly lead to lower surface temperatures. The additional 20% would result in less radiation available to heat the surface and resulting lower temperatures. ADDITIONAL RESOURCES DVDs and Movies • The Weather (2003) BBC, 230 minutes. Includes subheadings Wind, Wet, Cold, and Heat. Available on DVD. • Earth Weather 101. National Geographic, 3 minutes. Brief introduction to weather. Available for free streaming from http://video.nationalgeographic.com/video/science/earth-sci/weather-101-sci/ • Earth: Climate and Weather. National Geographic, 3 minutes, 30 seconds. Available for free streaming from http://video.nationalgeographic.com/video/science/earth-sci/climate-weather-sci/ Websites • University Corporation for Atmospheric Research. http://www2.ucar.edu • National Oceanic and Atmospheric Administration (NOAA) Weather. http://www.noaa.gov/wx.html • NOAA Climate. http://www.noaa.gov/climate.html • National Weather Service. http://www.weather.gov/ • Weather and Climate Events. American Museum of Natural History. Interactive animation showing recent global weather and climate events. http://www.amnh.org/sciencebulletins/climate/ Solution Manual for Earth Science Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa 9780321928092, 9780321934437
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