EARTH SCIENCE geology, the environment, and the universe 2008 (17)

The Marine Environment BIG Idea The marine environment is geologically diverse and contains a wealth of natural resources Coral and tunicates 16.1 Shoreline Features MAIN Idea The constant erosion of the shoreline and deposition of sediments by ocean waves creates a changing coastline 16.2 Seafloor Features MAIN Idea The ocean floor contains features similar to those on land and is covered with sediments of several origins GeoFacts • Coral reefs cover only percent of the ocean floor, yet about 25 percent of all marine fish species are found living on coral reefs Coral reef environment • A chemical from the Caribbean sea whip, a soft coral, is used to make skin-care products because it has anti-inflammatory properties • The blood of tunicates—softbodied organisms closely related to vertebrates—contains high levels of the rare metal vanadium 436 (t)Reinhard Dirscherl/Visuals Unlimited, (b)Gary Bell/zefa/CORBIS, (bkgd)B.S.P.I./CORBIS Start-Up Activities Seafloor Features Make this Foldable to diagram the major geologic features of continental margins and ocean basins LAUNCH Lab Where does chalk form? Although you might not live near a coast, parts of your environment were shaped by the ocean For example, you might be just a few meters away from former seafloor deposits that are now part of the bedrock underground One such seafloor deposit is chalk How can you tell that chalk formed on the seafloor? Procedure Read and complete the lab safety form Use a mortar and pestle to grind a small piece of natural chalk into a powder Make a slide of the powdered chalk Observe the chalk powder through a microscope Analysis Describe the powder Are the grains irregular in shape or size? Do some of the grains have patterns? Analyze your data and hypothesize the origin of the chalk On what evidence you base your conclusion? STEP Fold a horizontal sheet of paper in half from side to side STEP Fold into thirds Unfold and draw lines lightly along the fold lines to indicate three tabs Label the uncut tabs Continent, Continental Margin, and Ocean Basin Draw a diagram of these seafloor features here STEP Cut along the fold lines to make three tabs after your diagram is complete STEP Continent Continental Ocean Basin Margin Continent Continental Ocean Basin Margin FOLDABLES Use this Foldable with Section 16.2 As you read this section, diagram the major features of the seafloor When you finish your diagram, cut the tabs as described in Step Summarize the features shown in your diagram under each of the tabs Visit glencoe.com to study entire chapters online; explore • Interactive Time Lines • Interactive Figures • Interactive Tables animations: access Web Links for more information, projects, and activities; review content with the Interactive Tutor and take Self-Check Quizzes Chapter Section 16 ••XXXXXXXXXXXXXXXXXX The Marine Environment 437 Section Objectives ◗ Explain how shoreline features are formed and modified by marine processes ◗ Describe the major erosional and depositional shoreline features ◗ Identify protective structures used near shore Review Vocabulary breaker: collapsing wave that forms when a wave enters shallow water Vocabulary beach wave refraction longshore bar longshore current barrier island Shoreline Features MAIN Idea The constant erosion of the shoreline and deposition of sediments by ocean waves creates a changing coastline Real-World Reading Link Have you ever picked up a smoothly polished pebble on the beach? A sculptor forms a masterpiece out of a chunk of wood or stone by chipping away one tiny bit at a time Waves are nature’s chisel, and beaches display the carefully carved features The Shore Shown in Figure 16.1, the shore is the area of land between the lowest water level at low tide and the highest area of land that is affected by storm waves Shores are places of continuous, often dramatic geologic activity—places where you can see geologic changes occurring almost daily The shoreline is the place where the ocean meets the land Shorelines are shaped by the action of waves, tides, and currents The location of the shoreline constantly changes as the tide moves in and out As waves erode some shorelines, they create some of the most impressive rock formations on Earth In other areas, waves deposit loose material and build wide, sandy beaches Beaches Long stretches of U S coasts are lined with wide, sandy beaches A beach, shown in Figure 16.1, is the area in which sediment is deposited along the shore Beaches are composed of loose sediments deposited and moved about by waves along the shoreline The size of sediment particles depends on the energy of the waves striking the coast and on the source of the sediment Beaches pounded by large waves or formed on rocky coasts usually consist of coarse materials such as pebbles and cobbles ■ Coast Figure 16.1 The location of the shoreline changes as the tide moves in and out Identify How is a beach related to a shore? Shore Waves Beach High-tide shoreline Low-tide shoreline 438 Chapter 16 • The Marine Environment Beach Shallow water Bay Beach ■ Figure 16.2 Wave crests advance toward the shoreline and slow down when they encounter shallow water This causes the wave crests to bend toward the headlands and move in the direction of the arrows Beach Shallow water Headland Bay Cliff Headland Cliff Bay Formation of Shoreline Features Large breaking waves can hurl thousands of metric tons of water, along with suspended rock fragments, against a shore with such force that they are capable of eroding solid rock Erosional features Waves move faster in deep water than in shallow water This difference in wave speed causes initially straight wave crests to bend when part of the crest moves into shallow water, a process known as wave refraction, illustrated in Figure 16.2 Along an irregular coast with headlands and bays, the wave crests bend toward the headlands As a result, most of the breaker energy is concentrated along the relatively short section of the shore around the tips of the rocky headlands, while the remaining wave energy is spread out along the much longer shoreline of the bays The headlands thus undergo severe erosion The material eroded from the headlands is swept into the bays, where it is deposited to form crescent-shaped beaches The headlands are worn back and the bays are filled in until the shoreline straightens Wave-cut platforms Many headlands have spectacular rock for- mations Generally, as a headland is worn away, a flat erosional surface called a wave-cut platform is formed The wave-cut platform terminates against a steep wave-cut cliff, as shown in Figure 16.3 Original headland Figure 16.3 A headland can be modified by wave erosion The dotted lines indicate the original shape of the headland ■ Wave-cut cliff Wave-cut platform Section • Shoreline Features 439 Elio Ciol/CORBIS ■ Figure 16.4 The sea stack and sea arch shown here, along the coast of France, were formed by wave refraction at a rocky headland Sea stacks Differential erosion, the removal of weaker rocks or rocks near sea level, produces many of the other characteristic landforms of rocky headlands As shown in Figure 16.4, a sea stack is an isolated rock tower or similar erosional remnant left on a wave-cut platform A sea arch, also shown in Figure 16.4, is formed as stronger rocks are undercut by wave erosion Sea caves are tubelike passages blasted into the headlands at sea level by the constant assault of the breakers Longshore currents Suppose you stood on a beach at the edge of the water and began to walk out into the ocean As you walked, the water might get deeper for a while, but then it would become shallow again The shallow water offshore lies above a sandbar, called a longshore bar, that forms in front of most beaches, as illustrated in Figure 16.5 Waves break on the longshore bar in the area known as the surf zone The deeper water between the shore and longshore bar is called the longshore trough The waves striking the beach are almost parallel to the shoreline, although the waves seaward of the longshore bar are generally not parallel to the shore This is another case of wave refraction The slowing of the waves in shallow water causes the wave crests to bend toward the shore Figure 16.5 A typical beach profile includes longshore troughs and bars within the surf zone Explain What is the difference between a longshore trough and a longshore bar? ■ Dunes Shore Longshore trough 440 Chapter 16 • The Marine Environment Surf zone Longshore bar Waves approach shore at an angle Path of sand particles Direction of sediment movement Longshore current ■ Figure 16.6 Longshore currents are driven by incoming waves Interactive Figure To see an animation of longshore currents, visit glencoe.com As water from incoming breakers spills over the longshore bar, a current flowing parallel to the shore, called the longshore current, is produced This current varies in strength and direction from day to day Over the course of a year, because of prevailing winds and wave patterns, one direction usually dominates Movement of sediments Longshore currents, shown in Figure 16.6, move large amounts of sediment along the shore Fine- grained material, such as sand, is suspended in the turbulent, moving water, and larger particles are pushed along the bottom by the current Additional sediment is moved back and forth on the beach by incoming and retreating waves Incoming waves also move sediment at an angle to the shoreline in the direction of wave motion Overall, the transport of sediment is in the direction of the longshore current On both the Atlantic and Pacific coasts of the United States, longshore transport moves generally toward the south Reading Check Explain how the longshore current moves sediments Rip currents Wave action also produces rip currents, which flow out to sea through gaps in the longshore bar Rip currents, shown in Figure 16.7, return the water spilled into the longshore trough to the open ocean These dangerous currents can reach speeds of several kilometers per hour If you are ever caught in a rip current, you should not try to swim against it, instead swim parallel to shore to get out of it Figure 16.7 Rip currents return water through gaps in the longshore bar out to sea Rip currents spread out and weaken beyond the longshore bar ■ Shoreline Longshore bar Longshore current Rip current Longshore bar Section • Shoreline Features 441 Lagoon Lagoon Bay Spit Spit Mainland beach Baymouth bar Longshore Barrier islands current Tombolo Figure 16.8 Depositional features of coastlines include tombolos, spits, baymouth bars, lagoons, and barrier islands ■ Depositional features As a result of wave erosion, longshore transport, and sediment deposition, most seashores are in a constant state of change Sediments are eroded by large storm waves and deposited wherever waves and currents slow down Sediments moved and deposited by longshore currents build various characteristic coastal landforms, such as spits and barrier islands, illustrated in Figure 16.8 Spit A narrow bank of sand that projects into the water from a bend in the coastline is called a spit A spit, which forms where a shoreline changes direction, is protected from wave action When a growing spit crosses a bay, a baymouth bar forms ■ Figure 16.9 This barrier island off the coast of North Carolina is one of many that line the eastern coast Barrier islands Long ridges of sand or other sediment, deposited or shaped by the longshore current, that are separated from the mainland are called barrier islands Barrier islands, like the ones shown in Figure 16.9, can be several kilometers wide and tens of kilometers long Most of the Gulf Coast and the eastern coast south of New England is lined with an almost continuous chain of barrier islands Baymouth bars A baymouth bar, shown in Figure 16.10, forms when a spit closes off a bay The shallow, protected bodies of water behind baymouth bars and barrier islands are called lagoons, which are saltwater coastal lakes that are connected to the open sea by shallow, restricted outlets Tombolo Another coastal landform is a tombolo, shown in Figure 16.10 A tombolo is a ridge of sand that forms between the mainland and an island and connects the island to the mainland When this happens, the island is no longer an island, but is the tip of a peninsula Reading Check Describe how a tombolo is formed 442 Chapter 16 • The Marine Environment Dr Frank M Hanna/Visuals Unlimited (tl)Joseph Melanson/Aero Photo Inc/www.skypic.com, (tr)Joseph Melanson/Aero Photo Inc/www.skypic.com, (bl)T Michot/USGS, (bc)T Michot/USGS Baymouth bar Tombolo Natural and human effects on the coast All of these depositional coastal landforms, including large barrier islands, are unstable and temporary Occasionally, major storms sweep away entire sections of barrier islands and redeposit the material elsewhere Figure 16.11 shows the existence of South Gosier Island, a barrier island off the coast of Louisiana in August of 2004, a month before Hurricane Ivan passed over it The island was completely destroyed by the strong waves generated by Hurricane Ivan Even in the absence of storms, however, changing wave conditions can slowly erode beaches and rearrange entire shorelines For example, the shoreline of Cape Cod, Massachusetts, is retreating by as much as m per year People are drawn to coastal areas for their rich natural resources, mild climate, and recreation opportunities Coastal areas in the United States make up only 17 percent of contiguous land areas, but are currently home to over half of the population in the nation Increasing population has caused substantial coastal environmental changes, including pollution, shoreline erosion, and wetland and wildlife-habitat loss These coastal changes in turn increase the susceptibility of the communities to natural hazards caused by hurricanes and tsunamis Before After ■ Figure 16.10 Baymouth bars and tombolos are examples of features formed by the deposition of sediments ■ Figure 16.11 The island of South Gosier, a barrier island off the coast of Louisiana, was completely washed away by Hurricane Ivan in September, 2004 Section • Shoreline Features 443 Groins Erosion of sand Deposition of sand Sand movement Erosion of sand Jetties Figure 16.12 Seawalls deflect the energy of waves on the beach Groins and jetties deprive downshore beaches of sand ■ Protective Structures In many coastal areas, protective structures such as seawalls, groins, jetties, and breakwaters are built in an attempt to prevent beach erosion and destruction of oceanfront properties However, these artificial structures interfere with natural shoreline processes and can have unexpected negative effects ■ Figure 16.13 A breakwater causes the longshore current to slow down, which results in sediment being deposited behind the structure Seawalls Structures called seawalls, shown in Figure 16.12, are built parallel to shore, often to protect beachfront properties from powerful storm waves Seawalls reflect the energy of such waves back toward the beach, where they worsen beach erosion Eventually, seawalls are undercut and have to be rebuilt larger and stronger than before Groins and jetties Groins, shown in Figure 16.12, are walllike structures built into the water perpendicular to the shoreline for the purpose of trapping beach sand Groins interrupt natural longshore transport and deprive beaches down the coast of sand The result is aggravated beach erosion down the coast from groins Similar effects are caused by jetties, which are walls of concrete built to protect a harbor entrance from drifting sand Jetties are also shown in Figure 16.12 Breakwaters Structures like the one shown in Figure 16.13 that are built to provide anchorages for small boats or a calm beach area are called breakwaters Breakwaters are built parallel to the shoreline When the longshore current slows down behind a breakwater and is no longer able to move sediment, it is deposited behind the breakwater If the accumulating sediment is left alone, it can eventually fill an anchorage To prevent this, anchorages have to be dredged regularly 444 Chapter 16 • The Marine Environment (t)Sexto Sol/Getty Images, (b)Tom Bean/CORBIS Deposition of sand Changes in Sea Level At the height of the last ice age, approximately 10,000 years ago, the global sea level was about 130 m lower than it is at present Since that time, the melting of most of the ice-age glaciers has raised the ocean to its present level In the last 100 years, the global sea level has risen 10 to 15 cm It continues to rise slowly; estimates suggest a rise in sea level of mm/year Many scientists contend that this continuing rise in sea level is the result of global warming During the last century, Earth’s average surface temperature has increased by approximately 0.5°C As Earth’s surface temperature rises, seawater warms up and expands, which adds to the total volume of the seas In addition, higher temperatures on Earth’s surface cause glaciers to melt, and the meltwater flowing into the oceans increases their volume VOCABULARY ACADEMIC VOCABULARY Estimate a rough or approximate calculation The estimate for the new roof was $3000 Effects of sea level changes If Earth’s remaining polar ice sheets in Greenland and Antarctica melted completely, their meltwater would raise sea level by another 70 m This rise would completely flood some countries, such as the Netherlands, along with some coastal cities in the United States, such as New York City, and lowlying states, such as Florida and Louisiana Measurements from NASA’s GRACE satellite, launched in 2002, have indicated that the Greenland ice sheet is melting at an accelerating rate The West Antarctic Ice Sheet has also been thinning according to a decade of satellite measurements A complete melt of the Greenland Ice Sheet would lead to a sea level rise of about to m Many of the barrier islands of the Atlantic and Gulf Coasts might be former coastal dunes that were drowned by rising sea levels Other features produced by rising sea levels are the fjords of Norway, shown in Figure 16.14 Fjords (fee ORDZ) are deep coastal valleys that were scooped out by glaciers during the ice age and later flooded when these glaciers melted Figure 16.14 Fjords are flooded U-shaped valleys that can be up to 1200 m deep ■ Section • Shoreline Features 445 Anders Blomqvist/Lonely Planet Images Jerome Neufeld/The Experimental Nonlinear Physics Group/The University of Toronto ■ Figure 16.18 Turbidity currents flow along the seafloor because the seawatersediment mixture of the current is denser than seawater alone Scientists study turbidity currents in the lab by simulating them in glass tanks, as shown Continental rise The gently sloping accumulation of deposits from turbidity currents that forms at the base of the continental slope is called a continental rise A continental rise can be several kilometers thick The rise gradually becomes thinner and eventually merges with the sediments of the seafloor beyond the continental margin In some places, especially around the Pacific Ocean, the continental slope ends in deeper depressions in the seafloor, known as deep-sea trenches In such places, there is no continental rise at the foot of the continental margin Reading Check Differentiate between the continental slope and the continental rise PROBLEM-SOLVING Lab Interpret Graphs How surface elevations compare? A useful comparison of the heights of the continents to the depths of the oceans is given by the curve in the graph below Depth (km) Elevation (km) Surface Elevations on Earth 10 2 10 Land 29.2% Ocean 70.8% Mountains Analysis Approximately how tall is the highest mountain on Earth’s surface in kilometers? At about what depth would you begin to find trenches on the ocean floor? What percentage of Earth’s surface is above current sea level? What percentage of Earth’s surface is represented by the continental margin? Ocean surface Continents Trenches Continental margins Ocean basins 20 40 60 80 100 Think Critically Calculate The oceanic crust is the part of the crust that is at a depth of km or more below sea level What percentage of Earth’s surface lies above the oceanic crust? Percentage of Earth’s surface Section • Seafloor Features 449 Master Page used: NGS Visualizing the Ocean Floor Figure 16.19 The ocean floor has topographic features, including mid-ocean ridges, trenches, abyssal plains, seamounts, and guyots Fracture zones run perpendicular to mid-ocean ridges Abyssal plains are smooth, flat areas of the deep ocean covered with fine-grained sediments Seamounts are submerged volcanoes that are more than km high Mid-ocean ridges run through all ocean basins Trenches are the deepest areas of the ocean To explore more about the ocean floor, visit glencoe.com 450 Chapter 16 • The Marine Environment Marie Tharp (t)Marie Tharp, (b)Science VU/NGDC/Visuals Unlimited Deep-Ocean Basins Beyond the continental margin are ocean basins, which represent about 60 percent of Earth’s surface and contain some of Earth’s most interesting topography Figure 16.19 shows the topography of the ocean basin beneath the Atlantic Ocean Abyssal plains The flattest parts of the ocean floor or km below sea level are called abyssal plains Abyssal plains, shown in Figure 16.19, are plains covered with hundreds of meters of finegrained muddy sediments and sedimentary rocks that were deposited on top of basaltic volcanic rocks Deep-sea trenches The deepest parts of the ocean basins are the deep-sea trenches, which are elongated, sometimes arc-shaped depressions in the seafloor several kilometers deeper than the adjacent abyssal plains Many deep-sea trenches lie next to chains of volcanic islands, such as the Aleutian Islands of Alaska, and most of them are located around the margins of the Pacific Ocean Deep-sea trenches are relatively narrow, about 100 km wide, but they can extend for thousands of kilometers The Peru-Chile trench, shown in Figure 16.20, is almost 6000 km long and has an average width of 40 km Mid-ocean ridges The most prominent features of the ocean basins are the mid-ocean ridges, which run through all the ocean basins and have a total length of more than 65,000 km—a distance greater than Earth’s circumference Mid-ocean ridges have an average height of 1500 m, but they can be thousands of kilometers wide The highest peaks in mid-ocean ridges are over km tall and emerge from the ocean as volcanic islands Mid-ocean ridges are sites of frequent volcanic eruptions and earthquake activity The crests of these ridges often have valleys called rifts running through their centers Rifts can be up to km deep Mid-ocean ridges not form continuous lines They are broken into a series of shorter, stepped sections, which run at right angles across each mid-ocean ridge The areas where these breaks occur are called fracture zones, shown in Figure 16.21 Fracture zones are about 60 km wide, and they curve gently across the seafloor, sometimes for thousands of kilometers ■ Figure 16.20 The Peru-Chile trench runs along the west coast of South America FOLDABLES Incorporate information from this section into your Foldable ■ Figure 16.21 There are many fracture zones along the Mid-Atlantic Ridge Fracture zone Fracture zone Section • Seafloor Features 451 Black smoker White smoker Hydrothermal vents A hydrothermal vent is a hole in the seafloor through which fluid heated by magma erupts Most hydrothermal vents are located along the bottom of the rifts in mid-ocean ridges When the heated fluid that erupts from these vents contains metal oxides and sulfides, they immediately precipitate out of the fluid and produce thick, black, smokelike plumes This type of hydrothermal vent, known as a black smoker, ejects superheated water with temperatures of up to 350°C Figure 16.22 illustrates the black smokers found in the rift valley of a mid-ocean ridge A second type of vent, known as a white smoker, also shown in Figure 16.22, ejects warm water Smokers are caused by seawater circulating through the hot crustal rocks in the centers of midocean ridges The fundamental cause of mid-ocean ridges and the volcanic activity associated with them is plate tectonics, which you will read about in Chapter 17 Reading Check Identify where most hydrothermal vents are located Seamounts and guyots Satellite data have revealed that the ocean floor is dotted with tens of thousands of solitary mountains These mountains are not located near areas of active volcanism How, then, did they form? You have learned that the ocean basins are volcanically active at mid-ocean ridges and fracture zones The almost total absence of earthquakes in most other areas of the seafloor suggests that volcanism in those areas must have ceased a long time ago Thus, most of the mountains on the seafloor are probably extinct volcanoes Investigations of individual volcanoes on the seafloor have revealed that there are two types: seamounts and guyots (GEE ohz) Seamounts are submerged basaltic volcanoes more than km high Many linear chains of seamounts, such as the Emperor seamount chain, are stretched out across the Pacific Ocean basin in roughly the same direction Guyots are large, extinct, basaltic volcanoes with flat, submerged tops 452 Chapter 16 • The Marine Environment (tc)B Murton/Southampton Oceanography Centre/Photo Researchers, (tr)NOAA/www.oceanexplorer.noaa.gov ■ Figure 16.22 Black smokers form when metal oxides and sulfide precipitate out of fluid heated by magma White smokers form when elements such as calcium and barium precipitate out of warm water ejected from rifts in mid-ocean ridges Steve Gschmeissner/Photo Researchers Marine Sediments The sediments that cover the ocean floor come from a variety of sources, but most come from the continents Land-derived sediments include mud and sand washed into the oceans by rivers, as well as dust and volcanic ash blown over the ocean by winds Much of the coarser material supplied by rivers settles out near shorelines or on beaches, but fine-grained material such as silt and clay settles so slowly through water that some tiny particles take centuries to reach the bottom Terrigenous sediments Ocean currents disperse fine silt, clay, and volcanic ash from land, called terrigenous sediments, throughout the ocean basins Thus, the dominant type of sediment on the deep ocean floor is fine-grained, deep-sea mud Deep-sea mud usually has a reddish color because the iron present in some of the sediment grains becomes oxidized during the descent to the ocean bottom Closer to land, the sediments become mixed with coarser materials such as sand, but some sandy sediments occasionally reach the abyssal plains in particularly strong turbidity currents ■ Figure 16.23 The shells of microscopic marine organisms, such as diatoms, as well as shell fragments and hard parts from larger marine organisms make up biogenous sediments SEM: magnification unknown Biogenous sediments Deep-sea sediments that come from biological activity are called biogenous sediments When some marine organisms die, such as the diatoms shown in Figure 16.23, their shells settle on the ocean floor Sediments containing a large percentage of particles derived from once-living organisms are called oozes Most of these particles are small and consist of either calcium carbonate or silica The oozes and deep-sea mud of the deep ocean typically accumulate at a rate of only a few millimeters per thousand years Measure Sediment Settling Rates How fast sediment grains sink? Procedure Read and complete the lab safety form Obtain sediment grains with approximate diameters of 0.5 mm, mm, mm, mm, and 10 mm Draw a data table with these headings: Type of Particle, Diameter (mm), Distance (cm), Time (s), and Settling Speed (cm/s) Measure and record the diameters of each specimen using a set of sieves Fill a 250-mL graduated cylinder with cooking oil Measure the height of the cooking oil Drop the largest specimen into the oil Use a stopwatch to measure and record the time it takes for the specimen to sink to the bottom of the cylinder Repeat Step for the remaining specimens Analysis Calculate the settling speed for each specimen, and fill in your data table Plot the settling speed (cm/s) against particle diameter (mm) on a graph Explain How settling speeds change as particle sizes decrease? Section • Seafloor Features 453 Inst of Oceanographic Sciences/NERC/Photo Researchers Figure 16.24 Metals, such as manganese, precipitate directly from seawater These manganese nodules consist of manganese and iron ■ Hydrogenous sediments While terrigenous sediments are derived from land and biogenous sediments are derived from biological activity, another sediment type, called hydrogenous sediments, is derived from elements in seawater For example, manganese nodules, shown in Figure 16.24, consist of oxides of manganese, iron, and copper and other valuable metals that have precipitated directly from seawater The precipitation happens slowly, therefore growth rates of manganese nodules are extremely slow Growth rates of manganese nodules are measured in millimeters per million years Manganese nodules cover huge areas of the deep-sea floor Although some have tried to mine manganese nodules for their valuable metals, the difficulty and cost involved in removing them from a depth of 5000 to 6000 m has made progress slow Section 16.2 Assessment Section Summary Understand Main Ideas ◗ The oceans cover parts of the continental crust as well as oceanic crust ◗ A continental margin consists of the continental shelf, the continental slope, and the continental rise Summarize the differences between deep-sea mud and oozes ◗ Deep-ocean basins consist of abyssal plains, trenches, mid-ocean ridges, seamounts, and guyots ◗ Most deep-sea sediments are finegrained and accumulate slowly MAIN Idea Describe the features of deep-ocean basins Identify which sediment sinks faster — pebbles or sand grains Compare and contrast the characteristics of the three major areas of the continental margin Think Critically Suggest If there is little volcanic activity on abyssal plains, yet they are dotted with thousands of seamounts, from where did these extinct volcanoes come? Earth Science Suppose you are taking side-scan sonar readings as your ship moves across the Pacific Ocean from east to west Describe how you would interpret the sonar data and which features are beneath the surface 454 Chapter 16 • The Marine Environment Self-Check Quiz glencoe.com Ralph White/CORBIS eXpeditions! ON SITE: Surveying the Deep Ocean Floor here are a variety of vessels that can Tcollect data on the deep ocean floor ranging from human-occupied submersible vehicles to free-moving autonomous robots to remotely operated vehicles These vessels are used by oceanographers to learn more about the topography, biology, and chemistry of the deep ocean Submersibles Alvin is one of several humanoccupied deep-sea submersibles used worldwide In Alvin, the trip to the bottom of the ocean takes about two hours, and it takes two hours to return to the surface Under the immense pressure of thousands of kilograms of water and in the darkness and cold of the deep ocean, scientists have about four hours of bottom time to record video and collect water, sediment, and biological samples Using Alvin, scientists got their first view of hydrothermal vents in 1977, a major discovery for both geologists and biologists Autonomous underwater vehicles The Autonomous Benthic Explorer (ABE) has a mass of over 500 kg and is m long, but, thanks to computer systems, the bulky vehicle is able to dive into narrow trenches and zip around seamounts at depths as deep as 5000 m Autonomous underwater vehicles are able to move around independent of a pilot, ship, or submersible Alvin is a human-occupied submersible vehicle that is used to study hydrothermal vents and other deep-sea features The ABE has completed over 150 dives to the deep seafloor, recording videos of the deep sea environment and taking temperature and water chemistry samples Remotely operated vehicles Jason/Medea is a remotely operated vehicle (ROV) system that can collect data at depths as deep as 6000 m An ROV is deployed from a ship, but unlike the ABE, it needs a pilot, an engineer, and a navigator to control its operations from the ship In 2006, Jason/Medea explored part of the western Pacific Ocean near the Marianas Trench, collecting data on water chemistry near active undersea volcanoes and hydrothermal vents Each dive provided scientists with views—from glowing, red, hot lava pouring out a vent from a volcano, to black-smoker hydrothermal vents and the unique organisms that live near them—that were never disappointing nce Earth Scie ation ore inform m h rc a of the Rese ploration Time Line x e f o ry vessels at histo -occupied about the n a m u h that disusing time line deep sea a te a re logical om C nt techno glencoe.c a rt o p im s of is area plays date ries in th e v o c is d and advances National Geographic Expeditions 455 Davis Barber/Photo Edit MAPPING: IDENTIFY COASTAL LANDFORMS Background: Topographic maps of coastal areas show a two-dimensional representation of coastal landforms You can identify an emergent coast by the landforms along the coastline as well as landforms found inland Question: How can you identify and describe the coastal landforms of an emergent coast on a topographic map? Materials metric ruler drafting compass graph paper calculator Procedure Read and complete the lab safety form Determine the map scale and the contour interval On the inset map, plot a west-east cross section of the coast just north of Islay Creek from the 60-ft depth contour to a point 5000 ft inland Use a scale of 1:24,000 and a vertical exaggeration of 4 Use both maps to answer the following questions Analyze and Conclude Describe What kind of coastal landform is the Morro Rock Peninsula? Explain What kind of feature is Pillar Rock, and how was it formed? Interpret On what coastal feature is Morro Bay State Park located? How was the feature formed? Identify What are the irregular sand hills in Morro Bay State Park? Infer What is the direction of the longshore transport along Morro Bay? Apply Your west-east cross section shows an elevated flat area next to the shoreline What kind of coastal landform is this? How was it formed? Morro Rock is located off the coast of California Draw Conclusions If sea level dropped 10 m, how would the shoreline change? How far would it move seaward? Would it become more regular or irregular? What would happen to Morro Bay? Suggest three major changes that could occur to the coastal region if sea level rose m APPLY YOUR SKILL Compare and contrast this coastal section with a section of the Texas coast between Corpus Christi and Galveston Which coastal features are similar? Which are different? 456 GeoLab GeoLab 457 BIG Idea The marine environment is geologically diverse and contains a wealth of natural resources Vocabulary Key Concepts Section 16.1 Shoreline Features • barrier island (p 442) • beach (p 438) • longshore bar (p 440) • longshore current (p 441) • wave refraction (p 439) MAIN Idea • • • • The constant erosion of the shoreline and deposition of sediments by ocean waves creates a changing coastline Wave erosion of headlands produces wave-cut platforms and cliffs, sea stacks, sea arches, and sea caves Wave action and longshore currents move sediment along the shore and build depositional features Artificial protective structures interfere with longshore transport Sea levels in the past were 130 m lower than at present Section 16.2 Seafloor Features • abyssal plain (p 451) • continental margin (p 447) • continental rise (p 449) • continental shelf (p 447) • continental slope (p 448) • deep-sea trench (p 451) • guyot (p 452) • mid-ocean ridge (p 451) • seamount (p 452) • turbidity current (p 448) 458 Chapter 16 X ••Study StudyGuide Guide MAIN Idea • • • • The ocean floor contains features similar to those on land and is covered with sediments of several origins The oceans cover parts of the continental crust as well as oceanic crust A continental margin consists of the continental shelf, the continental slope, and the continental rise Deep-ocean basins consist of abyssal plains, trenches, mid-ocean ridges, seamounts, and guyots Most deep-sea sediments are fine-grained and accumulate slowly Vocabulary PuzzleMaker glencoe.com Vocabulary PuzzleMaker biologygmh.com (t)Joseph Melanson/Aero Photo Inc/www.skypic.com Download quizzes, key terms, and flash cards from glencoe.com Vocabulary Review Write the definition for each vocabulary term listed below barrier island beach longshore bar wave refraction Complete the sentences below using vocabulary terms from the Study Guide can create submarine canyons by cutting through bottom sediments and bedrocks of seafloors The deepest part of an ocean basin is a The is the part of a continent that is submerged under the ocean Submerged basaltic volcanoes more than km high are Understand Key Concepts Which coastal features are usually found in the bays along irregular coasts with headlands? A sea stacks C wave-cut platforms B wave-cut cliffs D beaches 10 Which coastal landform is not produced by longshore transport? A barrier island C baymouth bar B sand spit D sea stack 11 Which is the correct order of features on the continental margin moving from land out to sea? A continental slope, continental shelf, continental rise B continental rise, continental trench, continental shelf C continental shelf, continental slope, continental rise D continental slope, continental shelf, continental trench Chapter Test glencoe.com 12 What percentage of Earth’s surface is represented by ocean basins? A 10 percent B 30 percent C 50 percent D 60 percent 13 What the sediments of the abyssal plains mostly consist of? A sand and gravel B oozes C seashells D mud 14 Where are most deep-sea trenches located? A in the Atlantic Ocean B in the Pacific Ocean C in the Indian Ocean D in the Arctic Ocean 15 Which is the longest mountain system on Earth? A the Emperor seamount chain B the mid-ocean ridge system C the Himalayas D the Rocky Mountains Use the diagram below to answer Questions 16 and 17 A B C D 16 Which letter indicates the continental shelf? A A B B C C D D 17 Which feature is indicated by the letter A? A guyot B continental slope C continental rise D trench Chapter 16 • Assessment 459 18 Which marks the true edge of a continent? A submarine canyon C continental shelf B continental slope D abyssal plain 19 Which seafloor feature can be found along rifts in the mid-ocean ridges? A hydrothermal vents B manganese nodules C deep-sea trenches D seamounts 25 Explain the relationship between oozes and the sedimentary rock known as chalk 26 Illustrate the effect that wave refraction has on incoming wave crests that approach the shore of a straight coast at an angle Use the diagram below to answer Question 27 20 Which represents the flattest part of Earth’s surface? A deep-sea trenches B continental margins C abyssal plains D mid-ocean ridges Use the diagram below to answer Question 21 Original headland Wave-cut cliff Wave-cut platform 27 Apply Copy the diagram above onto a sheet of paper, and label the following features: shore, beach, low-tide shoreline, high-tide shoreline, coast, and waves 28 Illustrate how incoming waves along a shoreline create the longshore current 29 Apply If a coast has elevated marine terraces, is it rising or sinking? Explain 21 Which features are not caused by erosion? A wave-cut platforms C original headlands B wave-cut cliffs D sea stacks 22 Which features of the seafloor are cut by turbidity currents? A longshore bars C abyssal plains B submarine canyons D baymouth bars 23 Which are not associated with mid-ocean ridges? A black smokers C fracture zones B guyots D hydrothermal vents 30 Differentiate between a baymouth bar and a tombolo 31 Discuss all the processes that can cause sea level changes 32 Compare and contrast seamounts and guyots How are they formed? 33 Analyze Why does deep-sea mud usually have a reddish color? 34 Compare and contrast the origins of marine sediments and their rates of deposition Constructed Response 24 Explain Is global sea level currently rising, falling, or staying the same? During the last ice age, was the sea level higher, lower, or the same as at present? 460 Chapter 16 • Assessment Think Critically 35 Hypothesize Form a hypothesis that explains why seamounts are extinct volcanoes Chapter Test glencoe.com 36 Suppose you are surfing at a beach in California Describe which near-shore currents might affect your position relative to where you start out on the beach after each cycle of surfing Will you come back to the same point? 37 Suggest Evidence shows that woolly mammoths moved from Siberia to North America during the last ice age How could they have crossed the two continents? 38 Suppose that you are swimming in the ocean toward the shoreline, and you suddenly find that, despite all your efforts to swim ahead, you remain in the same location Explain why this might happen, and describe the path in which you should swim to get yourself out of this situation Additional Assessment 43 Earth Science Write an editorial article for a newspaper that discusses some of the risks involved in living in a low-lying coastal area Document–Based Questions Data obtained from: National assessment of shoreline change: part historical shoreline changes and associated land loss along the U.S Gulf of Mexico Report 2004–1043 U.S Geological Survey The graph below shows the average annual sea level based on tide data for a 100-year period for two cities on the Gulf Coast of the United States Sea Level Changes 39 Assess Is it possible to have a coast that is sinking when global sea level is falling? Sea Level (mm) Use the diagram below to answer Question 40 7800 7600 Key West, FL 7400 7200 7000 6800 Galveston, TX 6600 1905 1925 1945 1965 1985 2005 Year 40 Evaluate The arrow is pointing to what ocean floor feature? What is the significance of this feature? 44 Estimate the sea level change for Key West, Florida, and Galveston, Texas, by roughly fitting a straight best-fit line through the data points Concept Mapping 45 The global mean sea level rise for the past century is estimated to be about 0.18 m Which location has a sea level rise closer to the global mean? 41 Use the following terms to construct a concept map about the continental margin: continental shelf, continental slope, continental rise, turbidity currents, and submarine canyons Refer to the Skillbuilder Handbook for more information 46 What is one possible cause for global sea level rise? What is one reason that a local sea level change can be much larger than the global average? Challenge Question 47 What are the four most common foliated metamorphic rocks? (Chapter 6) 42 Investigate the causes and effects of a natural disaster that occurred in the past five years and resulted in coastal erosions in the United States or in any other country Chapter Test glencoe.com Cumulative Review 48 Describe the process that creates supercell thunderstorms (Chapter 13) Chapter 16 • Assessment 461 Standardized Test Practice Multiple Choice Which ocean movement is slow-moving and occurs in deep waters? A surface currents C density currents B upwelling D gyres If the northern hemisphere is experiencing long hours of darkness and cold weather, what season is it in the southern hemisphere? A spring C winter B summer D fall Use the illustration below to answer Questions and Use the illustration below to answer Questions 7–9 B What instrument is shown? A thermometer C barometer B hygrometer D rain gauge If a barometer records high pressure, what type of weather can be expected? A storms C fair weather B cloudy weather D hot weather Why does the silica content of seawater in the Pacific and Atlantic Oceans increase as the depth of the water increases? A The chemical makeup of the water at the surface of the oceans dissolves more silica B When shelled organisms die, their shells fall to the floor of the ocean and dissolve, releasing silica into the water C Wave action at the surface of the oceans dilutes the silica D Oxygen entering the surface water pushes silica down into deeper water How might volcanic activity affect changes in the climate? A Volcanic dust blocks incoming radiation causing lower global temperatures B Volcanic dust traps radiation in the Earth’s atmosphere raising global temperatures C Lava running along Earth’s surface increases the temperature thus increasing global temperature D Lava thrown into the air increases the atmospheric temperature thus increasing global temperatures 462 Chapter 16 • Assessment C What shoreline feature is indicated by B? A a tombolo C a lagoon B a spit D a beach The material in the section indicated by the B is very coarse What conclusions can be drawn about the waves and sediment source? A The area is rocky and pounded by heavy waves B The area is rocky and hit with light waves C The area consists of fine-grained material that has been hit by heavy waves D The area consists of fine-grained material that has been hit by light waves Which forms the area indicated by C? A large storm waves B gaps in the longshore bar C the longshore current D a rip current 10 Limestone that is exposed to enough heat and pressure is transformed into A marble B slate C quartzite D gneiss Standardized Test Practice glencoe.com Reading for Comprehension Short Answer Use the illustration below to answer Questions 11 and 12 Underwater Hot Spots Scientists think that underwater hot spots might host unique, previously unknown forms of life Hydrothermal vents at ocean ridges are an essential part of the chemical balance of seawater They support ecosystems not found anywhere at the surface and are thought to have been the sites of the early formation and evolution of life The study of these organisms will give scientists insight to the flexibility and adaptability of life The water that spews forth from hydrothermal vents can reach temperatures of 350°C and is rich in chemicals such as sulfur and salt Some microorganisms have adapted to the environments on these vents creating rich underwater ecosystems that some scientists think might represent some of the earliest lifeforms on Earth 11 Describe the process that is occurring in the illustration Article obtained from: Roach, J Hydrothermal vents found in Arctic Ocean National Geographic News January 23, 2003 12 How does a greenhouse mimic radiation and Earth’s atmosphere? 13 How does a greenhouse benefit gardeners? 14 Describe the hypothesis of how a comet might have created Earth’s early oceans 18 Which is NOT an importance of hydrothermal vents? A They support unique ecosystems B They create rich underwater environments C They help underwater creatures to adapt to extremely hot temperatures D They are an essential part of the chemical balance of seawater 19 Why is it rare to find life-forms around hydrothermal vents? A They are extremely hot B They are along ocean ridges C They are not chemically balanced with the rest of the ocean D No life-form is able to survive due to the sulfur in the area 15 Discuss a location where an analog forecast could be more beneficial than a digital forecast 16 If a sonar signal takes s to be emitted and received by an oceanographer mapping the ocean floor, what is the ocean depth in that location? 17 If air is rising due to uneven heating of Earth’s surface within an air mass, what can you expect to occur? 20 Why is studying these hydrothermal vents so important to scientists? NEED EXTRA HELP? If You Missed Question Review Section 15.3 12.3 11.2 15.2 14.3 14.3 16.1 16.1 16.1 Standardized Test Practice glencoe.com 10 5.2 11 12 13 14 15 16 17 11.1 11.1 11.1 15.1 12.4 15.1 13.1 Chapter 16 • Assessment 463 ... tombolo is a ridge of sand that forms between the mainland and an island and connects the island to the mainland When this happens, the island is no longer an island, but is the tip of a peninsula... on the longshore bar in the area known as the surf zone The deeper water between the shore and longshore bar is called the longshore trough The waves striking the beach are almost parallel to the. .. almost daily The shoreline is the place where the ocean meets the land Shorelines are shaped by the action of waves, tides, and currents The location of the shoreline constantly changes as the tide