ture of shells and white sand which we brought up, upon sound-which we - PDF document

ture of shells and white sand which we brought up, upon sound-which we passed, told us we were nearly abreast of Chatham sve28079_ch04.pdf 10/15/03 1:01 PM Page 96 Seabed Resources000Sand and Gravel000Phosphorite000Sulfur000Coal000Oil and Gas000Gas Hydrates000Manganese Nodules000Sulfide Mineral Deposits000Laws and Treaties000Summary000Key Terms000Study Questions000Study Problems000Suggested Readings0004.1Measuring the DepthsMeasuring the Depths97Bathymetrics000Bathymetry of the Sea Floor000Continental Margin000Ocean Basin Floor000Giant Hawaiian Landslides000Sediments000Particle Size000Location000Rates of Deposit000Source and Chemistry000Patterns of Deposit on the Sea Floor000Formation of Rock000Sampling Methods000Sediments as Historical Records000 a fathom is the length be-grease confirmed the contact and brought a bottom sample tothe surface. This method was quite satisfactory in shallowLater, piano wire with a cannonball attached was used inIt was not until the 1920s, when acoustic sounding equip-graphic tool are discussed in chapter 5. A trace from a depth were large basins or depressions in EarthÕs crust, buttailed and as ocean travel and commerce increased, measurementof water depths and recording of seafloor features in shallowerregions became necessary to maintain safe travel and ocean com-merce. The secrets of the deeper oceanic areas had to wait fortury made it relatively easy to map and sample the sea floor. Itcuss their topography and geology. We examine the sources,4.1Measuring the DepthsIn about 85 ., a Greek geographer named Posidonius set sail,niusÕs question. Crude as this method was, it continued withminor modifications as the means of obtaining sve28079_ch04.pdf 10/15/03 1:01 PM Page 97 16.5 ft) spacing in a swath 240 m Very-large-scale seafloor surveys use satellite measure- from the ocean floor traces a depth profile as the ship sails a steady Figure 4.2This internally recording television camera isplaced on the sea floor, where it automatically photographs events untilit is retrieved by the researchers. The red boxcontains the cameraÕspower supply. sve28079_ch04.pdf 10/15/03 1:01 PM Page 98 Visualizing the sea floor began with single soundings made with aTodayÕs multibeam sound systems can take 293,000 measurementsper hour in 10 m of water and 20,000 measurements in 4000 m. Ad-vances in multibeam sound system technology and improved com-A single sound beam device releases a cone of sound; as thedepth of the water increases, the area of the sea floor from whichSide-scan measurements can be made from either a surfaceis pitching and rolling, the path of the sound beam from a surfacevessel will be displaced from its intended direction, resulting in in-of a conical sound beam that produces a smaller sound footprint.creases the scanned area for each cone of sound. The area sur-on either side of the sound device; no image is obtained from di-Side-scan acoustical images are the product of the reflectivityof the seafloor materials and the angle at which the sound beamsstrike the sea floor. Changes in the reflection of the sound comefrom the irregularities and the changing properties of the bottom 50 m5000 m60 km logical long-range inclined asdic) is one of the most sophisticated.Side-scan acoustical imaging also works very well to detectsunken ships, planes, or other structures, because the reflectingsurfaces of these structures are at an angle to the sea floor, andtheir acoustical properties are very different from those of the sea side-scan sonar. Note the shadow generated when sound was not re- sve28079_ch04.pdf 10/15/03 1:02 PM Page 99 100 Monica, and the central portion of San Francisco Bay. In 1998, theThe images obtained with these multibeam systems are providinginformation, fundamental for geological research and biologicalTo Learn More About BathymetricsGardner, J., P. Butman, and L. Mayer. 1998. Mapping U.S. ContinentalPratson, L.F., and W.F. Haxby. 1997. Panoramas of the Seafloor. Internet Referencesinformation over the shallow continental shelves. In the 1990s, theU.S. continental shelves using a system based on multiple soundthose found on land. Features of land topography, such as moun-Continental Margin maps are particularly valuable in the Southern Ocean, where4.2Bathymetry of the Sea FloorThe Grand Canyon, the Rocky Mountains, the desert mesas in the sve28079_ch04.pdf 10/15/03 1:03 PM Page 100 101 0û30ûE120ûE120ûW150ûE150ûW weblink Figure 4.3Color-shaded relief image of the bathymetry of the worldÕs ocean basins modeled from marine gravity anomalies mapped by satellite altimetry andchecked against ship depth soundings. sve28079_ch04.pdf 10/15/03 1:03 PM Page 101 102margins: passive, or Atlantic, margins and active, or Pacific,margins. Passive margins have little seismic or volcanic activityand involve a transition from continental crust to oceanic crust inthe same lithospheric plate. They form after continents are riftedapart, creating a new ocean basin between them. Passive marginstend to be relatively wide. Active margins are tectonically activeand associated with earthquakes and volcanism. Most are associ-ated with plate convergence and subduction of oceanic litho-sphere beneath a continent. Active margins are plate boundariesand are frequently relatively narrow. The continental margin ismade up of the continental shelf, shelf break, slope, and rise. Thecontinental shelflies at the edge of the continent; continentalshelves are the nearly flat borders of varying widths that slopevery gently toward the ocean basins. Shelf widths average about65 km (40 mi) but are typically much narrower along active mar-gins than passive margins. The width of the continental shelf canbe as much as 1500 km (930 mi). Water depth at the outer edgeof the continental shelf varies from 20Ð500 m (65Ð1640 ft), withan average of about 130 m (430 ft).The distribution of the worldÕs continental shelves is shownin figure 4.5. The width of the shelf is often related to the slopeof the adjacent land; it is wide along low-lying land and narrow Figure 4.4Computer-drawn topographic profiles from the western coast of Europe and Africa to the Pacific Ocean. The elevations anddepths above and below 0 m are shown along a line of latitude by using the latitude line as zero elevation. For example, the ocean depth at 40¡N and60¡W is 5040 m (16,531 ft). The vertical scale has been extended about 100 times the horizontal scale. If both the horizontal and vertical scales werekept the same, a vertical elevation change of 5000 m would measure only 0.05 mm (0.002 in). E120E180W120W90W60W60E90 Figure 4.5Distribution of the worldÕs continental shelves (shown in light blue). The seaward edges of these shelves are at an average depthof approximately 130 m (430 ft). sve28079_ch04.pdf 10/15/03 1:04 PM Page 102 4.2Bathymetry of the Sea Flooralong mountainous coasts. Note the narrow shelf along themay erode continental shelves (fig. 4.6), and, in some areas,When sea level was low, erosion deepened valleys, waves (c)(c)Salt domesCoral reefs (i)(ii)(iii)(iv)(v)(vi) Figure 4.6 sve28079_ch04.pdf 10/15/03 1:04 PM Page 103 to place. The slope may be short and steep (for example, thedepth may increase rapidly from 200 m [650 ft] to 3000 m horizontal extent of each subdivision. The aver-slope, and rise. The vertical scale is 100 times 05 km (a)(b) weblink ©1963 by Francis P. Shepard. Reprinted by permission of Addison-Wesley Educational Publishers. sve28079_ch04.pdf 10/15/03 1:04 PM Page 104 spreads, and the sediments settle. Because of their speed and4.2Bathymetry of the Sea Floor of the Colorado River. A submarine canyon is also shown in 2 m link Figure 4.9This beach cliff shows an ancientturbidite deposit that has been uplifted and then exposed by wave ero-sion. Turbidites are graded deposits, with the largest particles in the de-posit at the bottom of the turbidite and the smallest at the top. sve28079_ch04.pdf 10/15/03 1:04 PM Page 105 caused by a turbidity current that ran for 800 km (500 mi) atrine organisms within the basin are effectively cut off from E120E180W120W90W60W60E90 Figure 4.11dark blue) are separated by ridges, rises, and continents. sve28079_ch04.pdf 10/15/03 1:04 PM Page 106 high, and Oceans, coral reefs and coral islands are formed in associa-Ridges,Rises,and Trenchestrace the Japan-Kuril Trench, the Aleutian Trench, the Philip-4.2Bathymetry of the Sea Floor ShelfShelf breakSlopeRiseAbyssal hillsGuyot Figure 4.12An idealized portion of ocean basin floor with abyssal hills (less than 1000 m of elevation), a guyot (a flat-topped seamount),and an island on the abyssal plain. The island was previously a seamount before it reached the surface. Seamounts and guyots are known to be vol-canic in origin (vertical sve28079_ch04.pdf 10/15/03 1:04 PM Page 107 by Dr. David Claguecritical new data or observations; it lasted until 1986. At that time,that extended 200 miles from all U.S. land. One of the participantshad made the initial highly controversial suggestion more thantem because it could create a complete image of the sea floor byOahu showed numerous angular blocks ranging in size from theThe new data clearly demonstrated that the seafloor topogra-landslide and that Moore had been correct in his hypothesis inmon. We now know they can be found along the entire Hawaiianvolcanic chain as far west as Midway Island. In all, seventeen sep-Two main types of slide deposits were recognized: rotationalslumps and debris avalanches. The rotational slumps are up totend far from shore, whereas the debris avalanches are less thanenough momentum to eventually run up hill. These characteristics Nuuanu DebrisAvalancheWailau DebrisAvalanche 00'157 30'157 00'156 30'22 00'21 30'22 00'21 30'157 00'156 D.A., and J.G. Moore. 2002. ÒThe Proximal Part of The Giant Sub- sve28079_ch04.pdf 10/15/03 1:05 PM Page 108 question: Can we identify the conditions that will lead to the nextlecting high-resolution multibeam bathymetry to better define thedistribution and sizes of blocks, amassing deep seismic data totypes of rocks made up the landslide blocks. An Ocean DrillingScience and Technology Center ran a series of four cruises over afive-year period with a major goal of exploring the blocks from sev- 1 North KaulKAUAI W158 W156HAWAII MAUI OAHUClark NIIHAUNuuanuWallauWaianaeKonaPololu050100150 Papau Moore, J.G., D.A. Clague, R.T. Holcomb, P.W. Lipman, W.R. Normark, and M.E. Torresan. 1989. Prodigious Submarine Landslides on We have been successful in determining what slid and, to alesser degree, when it slid. We are beginning to get a three-dimensional picture of the structure of the slides. However, theReferencesClague, D.A., and J.G. Moore. 2000. The Proximal Part of the Giant Sub-Moore, J.G., D.A. Clague, R.T. Holcomb, P.W. Lipman, W.R. Normark,and M.E. Torresan. 1989. Prodigious Submarine Landslides on theInternet References sve28079_ch04.pdf 10/15/03 1:07 PM Page 109 110of South America. To the north, the Middle America Trenchborders Central America. The Peru-Chile and Middle AmericaTrenches are associated with volcanic chains on land. In the In-dian Ocean, the great Sunda-Java Trench runs for 4500 km(2800 mi) along Indonesia. In the Atlantic, there are only twocomparatively short trenches: the Puerto Rico-Cayman Trenchand the South Sandwich Trench, both associated with chains ofvolcanic islands. To view the bathymetry of the ocean floor as itis known to exist today, see figure 3.9.In figure 4.16, the topography of the land and the bathyme-try of the sea floor are summarized as percentages of EarthÕsarea. Compare the tectonically active areas of trenches andridges, as well as the area of low-lying land platforms with thearea of the ocean basins. Figure 4.13Types of coral reefs and the steps in the forma-tion of a coral atoll shown in profile. (a) Fringing reef. (b) Barrier reef.(c) Atoll reef.(b) Mid-ocean ridgeAxis of rift valleyAseismic ridge or rise Figure 4.14The mid-ocean ridge and rise system of divergent plate boundaries. Locations of major aseismic (no earthquakes) ridges andrises are added. Aseismic ridges and rises are elevated linear features thought to be created by hot-spot activity. sve28079_ch04.pdf 10/15/03 1:07 PM Page 110 4.3Sediments E120E90 E180W120W90W60 Figure 4.15Major ocean trenches of the world. The deepest ocean depth is 11,020 m (36,150 ft), east of the Philippines in the MarianaTrench. It is known as the Challenger Deep. 050% Land area1005050% Ocean area100 s. 4.3Sediments sve28079_ch04.pdf 10/15/03 1:07 PM Page 111 Particle SizeWhen a sediment sample is collected, it can be dried andcoastal environment, when poorly sorted sediment is trans- 4th edition, Duxbury, Duxbury,reserved. Descriptive NameDiameter (mm)Cobble64Ð256Pebble4Ð64Granule2Ð4Very coarse1Ð2Coarse0.5Ð1Medium0.25Ð0.5Fine0.125Ð0.25Very fine0.0625Ð0.125Silt0.0039Ð0.0625 Sediment Size Classifications 210.50.20.1.05.02.01.005.002.001.0005Sediment particle diameter (mm)Percentage of sample by weight 210.50.20.1.05.02.01.005.002.001.0005Sediment particle diameter (mm)Percentage of sample by weight Figure 4.17(a) A poorly sorted sample. Particles fall into awide variety of size ranges in approximately equal amounts. (b) Awell-sorted sample. One size range predominates in a limited distribu-tion of sizes. sve28079_ch04.pdf 10/15/03 1:07 PM Page 112 ganic remains, often small shells calledpellets have been deposited on the bot-4.3Sediments he particles are spherical andhave a density similar to that of quartz. Estimates of the speed of deep currents vary. A conservative estimate of 5 cm/s is chosen for purposes ofillustration.Fundamentals of Oceanography,4th edition, Duxbury, Duxbury, and Sverdrup. Copyright 2000 The McGraw-Hill Companies. All rights reserved. Approximate Time for a Vertical Horizontal Distance Traveled Sediment SizeSinking Rate (m/s)Fall of 4 km (days)in a 5 cm/s Current (km)Very fine sand9.8 4.720.4Silt9.8 4702040Clay9.8 47,000204,000 Sediment Sinking Rate and Distance Traveled LandRiver Figure 4.18Classification of sediments by location of deposit. The distribution patternis partially controlled by proximity to source and rate of supply. sve28079_ch04.pdf 10/15/03 1:08 PM Page 113 Source and ChemistryThese are also commonly called chlorite, illite, kaolinite, and montmorillonite. The distribution (a) (b) link Figure 4.19(a) Manganese nodules resting on red clay photographed on deck in natural light. Nodules are 1Ð10 cm in diame-ter. (b) A cross section of a manganese nodule showing concentric layers of formation. sve28079_ch04.pdf 10/15/03 1:08 PM Page 114 than 50% of the clay minerals. Illite forms under a variety ofSediments derived from organisms are classified aspelagic sediments are more than 30% biogenous material byspecifically, either a 4.3Sediments weblink Distribution of the principal sediment types on the deep-sea floor. Sediments are usually a mixture but are sve28079_ch04.pdf 10/15/03 1:08 PM Page 115 acidic (this is discussed in detail in the sections on the pH offalls below 20% of the total sediment is called the careous tests. The oceans are undersaturated in silica every- (c) (a)(b) sve28079_ch04.pdf 10/15/03 1:09 PM Page 116 (phosphorus in the form of phosphate in crustsIn addition, hy-in diameter. In the present oceans, there are relatively fewmuch as 25 cm (10 in) in diameter or in beds of sand-sizeprecipitated or separated from solution and then deposited onchloride. Studies of precipitated material on the floor of theOcean tend to have the highest concentrations of metals, withspectively, while the average weight percent of nickel, cobalt,influenced by their position on the sea floor with respect toOn the deep-sea floor, manganese nodules form black or4.3Sediments (Ni), cobalt (Co), and copper (Cu) in manganese nodules from theOcean Chemistry and Deep-Sea Sediments,Pergamon Press, Average for All ElementAtlanticPacificIndianThree OceansMn16.1819.7518.0317.99Fe21.214.2916.2517.25Ni0.2970.7220.5100.509Co0.3090.3810.2790.323Cu0.1090.3660.2230.233 Average Chemistry of ManganeseNodules from the Three Ocean Basins (Ni), cobalt (Co), and copper (Cu), and the manganese-to-iron ratio inOcean Chemistry and Deep-Sea Sediments,Pergamon Press, ActiveContinentalAbyssal ElementSeamountsRidgesMarginsDepthsMn14.6215.5138.6917.99Fe15.8119.151.3417.25Ni0.3510.3060.1210.509Co1.150.4000.0110.323Cu0.0580.0810.0820.233Mn/Fe0.920.8128.91.04 Average Chemistry of ManganeseNodules from Different Environments sve28079_ch04.pdf 10/15/03 1:09 PM Page 117 very slowly: 1Ð10 mm (0.004Ð0.04 in) per million years forPatterns of Deposit on the Sea Floormajority of this sediment enters the tropical and subtropical 8.33cm6.35cm These splash-form tektites were collected in Fundamentals of Oceanography,4th edition, Duxbury, Duxbury, and Sverdrup. Copyright 2000 The McGraw-Hill Companies. All rights reserved. TypeSourceAreas of Significant DepositExamples airborne dustLiving organismsChemical precipitationfrom seawaterSpaceDominantly neritic, pelagic in areas oflow productivityareas of upwelling, dominantly pelagic,sediment types, neritic and pelagicturbidites, red clayCalcareous ooze (above the CCD),siliceous ooze (below the CCD), coralMetal sulfides, manganese nodules,phosphates, some carbonatesMeteorites, space dust sve28079_ch04.pdf 10/15/03 1:09 PM Page 118 retained, the sediments will move across the shelf into theof low river discharge in summer and fall. The floods bringIn shallow coastal areas, cycles of climate change causedeep bottom deposits, allowing them to remain relatively un-of 50¡Ð60¡N and S latitude and in equatorial regions where coldLarge rock particles of land origin are also moved out toto the sea floor. In addition, sea ice formed in shallow water4.3Sediments Figure 4.23A deep-sea sediment core obtained by thedrilling ship Glomar Challenger.Note the layering of the sediments. sve28079_ch04.pdf 10/15/03 1:09 PM Page 119 deposition of larger rocks by this rafting process is infrequentFormation of Rockthe sediments puts pressure on the lower sediment layers, and Figure 4.24Frequency of haze as a result of airborne dust during the Northern HemisphereÕs (a) winter and (b) summer. Values are givenin percentages of total observations. sve28079_ch04.pdf 10/15/03 1:09 PM Page 120 nents, and on land where they have been thrust upward along4.3Sediments (a)(b)Figure 4.25(a) Rocks can be recovered from the sea floorwith a dredge having a chain basket. Sediments and other fine mater-ial escape through the chains. (b) Basalt dredged from a depth of about8 km (5 mi) near the Tonga Trench in the western Pacific Ocean. Thedredge is in the foreground. sve28079_ch04.pdf 10/15/03 1:09 PM Page 121 ilar to the techniques used to study the interior of Earth (seeMarine sediments and the skeletal materials in them providecurrent, extending to depths of 3000Ð4000 m (9800Ð13,000 ft), ),both in open positions. Grabs take surface sediment samples.America had not yet separated from Antarctica. Marine sedi-cates that the organism had not been spread to other areas bylowed the ACC to first flow around the continent, carryingcalcareous hard parts (see the discussion of foraminiferans ininto the sediment. During warmer, interglacial periods, the sve28079_ch04.pdf 10/15/03 1:09 PM Page 122 Figure 4.27(a) The Phleger corer is a free-fall gravity corer.The weights help to drive the core barrel into the soft sediments. Insidethe corer is a plastic liner. The sediment core is removed from the corerby removing the plastic tube, which is capped to form a storage con-tainer for the core. (b) A sketch of a piston corer in operation. Thecorer is allowed to fall freely to the sea bottom. The action of the pis-ton moving up the core barrel owing to the tension on the cable allowswater pressure to force the core barrel into the sediments. (c) Loading apiston corer with weights to prepare it for use. (d) A gravity corerready to be lowered. (e) A box corer is used to obtain large, undis-turbed seafloor surface samples. (c)(e)(d) sve28079_ch04.pdf 10/15/03 1:10 PM Page 123 at 36 million tons. The United States, Australia, and Southtoo deep for exploitation, considering the present demand andnental shelf and slope. The nodules contain about 30% phos-California, Mexico, Peru, Australia, Japan, and northwestern 4.4Seabed Resourcesnology development, and environmental studies, especially inSand and Graveltons. The United Kingdom and Japan each take 20% of their sve28079_ch04.pdf 10/15/03 1:10 PM Page 124 Oil and gas represent more than 95% of the value of all re-ally be converted to oil and gas. It must first accumulate inrocks above. This upward migration continues until the fluidsPetroleum-rich marine sediments are more likely to accu-In recent years, interest has been growing in gas hydrates4.4Seabed Resources Figure 4.28The oil-drilling platform Hibernia, located 320 km (200 mi) offshore Newfoundland, produced its first oil in November 1997. sve28079_ch04.pdf 10/15/03 1:10 PM Page 125 sumption of the United States. In 1997, the U.S. Geologicalknown conventional natural gas reserves. Japan, interested inidentified that may be related to the presence of gas hydrates.tools and aircraft engines. The nodules grow very slowly, butthe 1980s. The concentration of cobalt in these deposits isProgress in mining cobalt from the sea floor continued toorganization of twelve South Pacific Island nations (Cook Is-Sulfide Mineral DepositsStates have found sulfides of zinc, iron, copper, and possibly sve28079_ch04.pdf 10/15/03 1:10 PM Page 126 Laws and Treatiescoastal nations, the developing nations of the world feel theyUnited States, Belgium, France, West Germany, Italy, Japan,national cooperation for the exploration and exploitation ofThe UN Convention on the Law of the Sea (UNCLOS)undeveloped land sources combine to make rapid commercial- around the seamounts to form fringing reefs. A barrier reef is sve28079_ch04.pdf 10/15/03 1:10 PM Page 127 Sediment classifications are based on their size, location,Sediments formed from particles of preexisting rocks areby red clay. Red clay dominates marine sediments only in re-along mid-ocean ridges. Sediments containing particles thatremains, the seasonal variations in river flow, waves and cur-are mined. Phosphorite nodules are the raw material of fertil-tional law, high mining costs, and low market prices. Sulfide sve28079_ch04.pdf 10/15/03 1:10 PM Page 128 1.Are calcareous oozes more common in the southern Pacific2.What is a turbidity current? Where would you expect a tur-3.List the four basic sediment types classified by source.4.Discuss the future of commercial development and ex-5.Imagine that you are in a submersible on the ocean bottom.6.What processes form submarine canyons?7.What is the continental margin? What pattern of sediment8.What combination of factors is required to form a coral atoll?9.What is a relict sediment? Where would you be likely to10.Describe several ways in which a continental shelf may be11.Describe methods used to recover sediment samples from12.What is the average depth of the oceans in meters? In13.How is particle size used in understanding the pattern of14.What are the implications for the marine environment as15.The Grand Banks is an extensive, relatively shallow area1.If underwater cables are spaced 14 km apart on the sea2.If the average concentration of suspended sediment in the3.In how many days will each of the particles listed in theParticleParticle Settling Rate TypeDiameter (mm)(V) (cm/s)Very fine sand0.16.6 Silt0.062.4 Clay0.0041.05 4.Assuming a constant sedimentation rate of 0.4 cm per Bambach, R.K., C.R. Scotese, and A.M. Ziegler, 1980. BeforeMacdonald, K.C., and P.J. Fox. 1990. The Mid-Ocean Ridge.Nittrouer, C.A., and G.J. Brunskill. 1994. The Gateway forNormark, W.R., and D. Piper. 1993/94. Turbidite Sedimenta-Pratson, L.F., and W.F. Haxby. 1996. What Is the Slope of thePratson, L.F., and W.F. Haxby. 1997. Panoramas of theRea, D.K. 1993/94. Terrigenous Sediments in the PelagicRice, A.L. 1991. Finding Bottom. sve28079_ch04.pdf 10/15/03 1:10 PM Page 129 Small, C., and D.T. Sandwell. 1996. Sights Unseen. Smith, W.H.F., and D.T. Sandwell. 1997. Global Sea FloorStephenson, A.G. 1977. Hydrographic Surveying. Pages 34Ð38ences, 2nd ed., R.G. Pirie. Oxford University Press, NewSuess, E., etal. 1999. Flammable Ice. Broadus, J.M. 1987. Seabed Materials. Cruickshank, M.J. 1991. Ocean Mining: For the Future a GoodCruickshank, M.J. 1991. Mining: A Significant Non-Action forics in Conflict. Pages 55Ð83 in E.M. Borgese and N. Ginsberg. University of Chicago,Edmond, J.M., and K. Von Damm. 1983. Hot Springs on theEllers, F.S. 1982. Advanced Offshore Oil Platforms. Mottl, M.J. 1980. Submarine Hydrothermal Ore Deposits.Pagano, S.S. 1999. Offshore Oil and Gas: Amid Uncertainty,Ryan, P.R. (ed.). 1983. Weldon, C. 2000. Ocean Action 1999: SomeÑBut Still a Long¥Ocean Bathymetry¥The Marine Sea Floor¥The Coast and the Continental Shelf¥Miscellaneous Geological Oceanography¥Gas Hydrates¥Politics and Law weblink sve28079_ch04.pdf 10/15/03 1:10 PM Page 130