Chapter 3 Bathymetry Bathymetry Measures the vertical distance from the oceans surface to mountains valleys plains and other sea floor features Topography shape of the ocean floor Poseidonus conducted the first recorded attempt to measure the ocean s depth a sounding 85 BC Stuck a probe out until the line hit the bottom Fathom standard unit of measurement for measuring ocean depth HMS Challenger first systematic measurements Echo Sounder sends a sound signal ping from the ship downward into the ocean where it produces echoes when it bounces off any density difference Most of our knowledge of ocean bathymetry has been provided by the echo sounder Precision Depth Recorder PDR uses a focused high frequency sound beam to measure depths to a resolution of about 1 meter Seabeam first multibeam echo sounder made it possible for a survey ship to map the features of the ocean floor along a strip up to 60 km Seismic reflection profiles sounds penetrate benath the sea floor and reflect off the boundaries between different rock or sediment layers used to measure ancient bathymetry Measuring Ancient Bathymetry air guns strong low frequency sounds details ocean structure beneath the sea floor Ocean Floor Provinces continental margins deep ocean basins mid ocean ridge the provinces are formed by the plate tectonic process Hypsographic Curve shows relationship between height of land and depth of ocean 70 8 of Earth covered by oceans Average ocean depth is 3729 meters average land elevation is 840 meters uneven distribution of areas of different depths elevations Variations suggest plate tectonics at work Continental Margins shallow water areas close to continents Deep Ocean Basins deep water areas farther from land Mid Ocean Ridge composed of shallower areas near the middle of an ocean Continental margins classified as either passive or active depends on proximity to plate boundaries Passive margins embedded within the interior of lithospheric plates and are therefore not in close proximity to any plate boundary usually lack major tectonic activity Ex East Coast of USA Active margins associated with lithospheric plate boundaries and are marked by a high degree of tectonic activity Two types Convergent active margins associated with oceanic continental convergent plate boundaries Transform active margins less common and are associated with transform plate boundaries Offshore faults usually parallel the main transform plate boundary fault and create linear islands banks and deep basins close to shore Continental Margins Continental shelf defined as a generally flat zone extending from the shore beneath the ocean surface to a point at which a marked increase in slope angle occurs Shelf break marked increase in slope angle on a continental shelf Continental borderland high degree of relief that marks a continental shelf Continental slope lies beyond the shelf break where the deep ocean basins being Similar to mountains Continental Slope Chapter 4 OCE1001 Marine Sediments Sediment eroded rock particles and fragments Deposit by settling through water column Oceanographers decipher Earth history through studying sediments Useful for providing clues to past geographic distributions of marine organisms movements of the ocean floor ocean circulation patterns climate changes on Earth and even global extinction events Lithified when sediment turns into rock and form sedimentary rock Mountains contain telltale marine fossils which indicate that these rocks originated on the ocean floor in the geologic past Mount Everest included Texture the size and shape of particles clues to sediment origins are found in the texture Paleoceanography study of how ocean atmosphere and land interactions have produced changed in ocean chemistry circulation biology and climate How are marine sediments collected and what historical events do they reveal Collecting Marine Sediments floor for analysis Dredge bucket like device used to scoop up sediment form the deep ocean Gravity corer hollow steel tube with heavy weight on top thrust into the sea floor to collect the first cores cylinders of sediment and rock depth of penetration was limited Rotary drilling performed by specially designed ships collect larger deeper cores Deep Sea Drilling Project used the Glomar Challenger its tall drilling rig resembling a steel tower to collect cores by drilling into the ocean floor in water up to 6000 meters deep o Scientists confirmed from these cores the age of the ocean floor increased progressively with distance from the mid ocean ridge sediment thickness increased progressively with distance from the mid ocean ridge Earth s magnetic filed polarity reversals were recorded in ocean floor rocks Ocean Drilling Program when the Deep Sea Drilling Project went international it became this o Used the JOIDES Resolution the new ship had a tall metal drilling rig to conduct rotary drilling pipe was 8200 meters long with a drill bit on the end and could drill 2100 meters deep into the Earth Integrated Ocean Drilling Program took over after the ODP used many ships to drill instead of just one o Used Chikyu can drill up to 7000 meters into the sea floor How do scientists study sediments Deep water cameras Clamshell samplers Piston corers Core libraries Seismic profilers Marine Sediment Classification Lithogenous or Terrigenous derived from rocks on land Classified by origin Biogenous derived from organisms Hydrogenous derived from water Cosmogenous derived from outer space Lithogenous Sediments Derived from pre existing rock material that originates on the continents or islands from erosion volcanic eruptions or blown dust Origin Begin as rocks on land until weathered down by water temperature and chemical effects When in smaller pieces they are eroded and transported It is transported by streams wind glaciers and gravity The greatest quantity is around continental margins Composition Discrete crystals minerals Quartz most abundant chemically stable durable mineral composed of silicon and oxygen in the form SiO2 same as glass It is resistant to abrasion to it is easily transported Courser sediments stay close to shore finer sediments go farther from shore Sediment Texture one of the most important properties of Lithogenous sediments Distribution Litho Sediments are ubiquitous found all over the ocean o Neritic deposits found on continental shelves and in shallow water near islands generally course grained o Pelagic deposits found in the deep ocean
View Full Document
Unlocking...