oceans - Fish OCEAN S Hypsometric Curve Hypsometric •...

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Unformatted text preview: Fish OCEAN S Hypsometric Curve Hypsometric • Diagram of % of Earth’s surface above certain elevation. • Two dominant physiographic provinces - continents (0-5000 m elevation), - ocean basins (mean depth 3800m) 29% land 71% ocean Five Major Oceans Five Major Oceans Pacific, Atlantic, Indian, Arctic, Southern… Each has distinct characteristics (size, temperature, salinity) 81% of Land in Northern Hemisphere Hemisphere MARGINS Passive continental margin (trailing edge) broad shelf gentle slope Fig. 18.05 a, b, d National Geophysical Data Center/NOAA Active continental margin (leading edge) narrow shelf steep slope adjacent trench Mapping the Seafloor Mapping • • • • Satellite measurements Echo sounding profiles Side-scan sonar Manned and unmanned submersibles • Deep Sea Drilling 1872-1876: dredged ocean floor, measured water depths Glomar Challenger - first research vessel designed in late 1960s for drilling and taking core samples from deep ocean floor. JOIDES Resolution - deep-sea drilling ship of 1990s. Heezen/Tharp physiographic maps - basic physiography, cartoon based on large, spotty PDR data set. PDR 1954 Precision Depth Recording 1954 1952 - 6 profiles 1952 based on soundings taken in North Atlantic on cruises of Atlantis. Atlantis. 1977 Topography of the Ocean Floor Mean depth 3729 m or 4 km Greatest Depth - Marianas Trench (11000 m) Bathymetry mapping of oceans has delineated: Bathymetry 1) Ocean Trenches 2) Ocean Basin Floor 3) Continental Margins 4) Mid-Ocean Ridges 3) Atlantic Atlantic Atlantic Ocean • Long and sinuous. • MOR in center. • Prominent fracture zones. • Well developed continental shelves. Fracture zones - fossil transform fault 10-100 km wide; 100's to 3500 km long; displace MOR North Atlantic profile North Atlantic Bathymetric Features Atlantic • • • • • • Continental shelf Continental slope Continental rise Abyssal plains Seamounts Mid-ocean ridge Cross-section of a passive margin! Cross-section Continental Shelf Continental ­ Broad, flat from shoreline to continental slope ­ < 200 m deep, may be 100’s km offshore ­ Underlain by continental crust ­ 0.3o slope Continental Shelf Continental No vertical exaggeration • Shallow shelf affected by waves & tidal currents. • Dominant sediments ­ sand, silt, & mud. • Sediment input from weathering of the continent. • New Jersey Shelf formed from weathering of Appalachian Mountains. Sediment transported by rivers to shelf. Shelf Sediment Mud Silt/Clay Silty Sand Sand Continental Shelf off New Jersey Continental Extension of adjacent continent Continental Slope Continental - Steeper - 2o - Typically mud-draped - Marks edge of continental shelf - Extend down to 4 km - Canyons cut through it, transporting sediment from shelf to continental rise Submarine Submarine Canyons Canyons • Cut into slope during LOW sea level. • Some > Grand Canyon • Often w/ submarine landslides & turbidity currents Turbidity currents – density currents move down slope 50­100 km/hr + create large deposits Graded bedding Fig. 7.26a Stephen Marshak Produce Turbidites Graded (upward) bedding Turbidity Current Turbidity • Flow of muddy water down a slope • Forms deposits known as turbidites • Active on the continental slope and continental rise Turbidite Formation Turbidite Continental Rise Continental • Gently sloping sediment apron (contourites) • Sands & muds deposited from continental slope • Depths of 4 - 4.5 km • Large submarine fans with kms of sediment Submarine Canyon fan system Submarine • • • • • • Few kilometers to over Few 2000 km across 2000 Fed by Submarine Fed canyons canyons Comprise the Comprise Continental rise Continental Sediment coarsest at Sediment source, becomes finer away! away! Sand and gravel, or Sand graded beds (Bouma graded Bouma sequence) are best sequence are preserved in proximal fan fan Fine sand and mud Fine dominate distal fan dominate Abyssal Plain Abyssal • Deep, quiet ocean seafloor • Thick accumulation of sediments • ~4-5 km water depth • Flattest surface on Earth • Forms LARGEST part of ocean • Contains submerged volcanoes - seamounts. Bathymetry mapping of ocean Bathymetry mapping of ocean basins has delineated major units: Ocean Basin Floor Abyssal Plain Guyot Guyot flat­topped seamount flat­topped seamount w/reef growing on w/reef growing on top top Seamount Seamount isolated submarine mountain isolated submarine mountain former hot­spot volcano former hot­spot volcano Marine Sediments Abyssal plains marine plankton terrestrial detritus windblown dust ice-rafted debris MORs - usually bare rock because: MORs too young for blanket of plankton too too elevated for terrestrial detritus too too far from land (/young) for windblown too ice-rafted only at high latitudes ice-rafted MOR sediment basalt Types of Deep Sea Sediment Sea • Terrigenous material eroded from the continents - clay. • Biochemically precipitated shells of marine organisms. Sources of sediment Sources Derived from land Deep sea sediment distribution map H H H HH H Pacific Ocean Pacific Ocean • Surrounded by linear Pacific mountain chains, trenches, island arcs, marginal seas • “Ring of Fire” • Narrow continental margins • Mid Ocean ridge really isn’t in middle! • Large number HOT Spot volcanic islands Trenches - topographic expression of subduction zone. common in Pacific remarkably long and narrow, depths up to 11 km Peru-Chile 5900 km long ...
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