deepoceans

deepoceans - OCEANS Fish And OCEANOGRAPHY Oceans The Water...

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Unformatted text preview: OCEANS Fish And OCEANOGRAPHY Oceans The Water Planet ­ 70% Why are there Oceans? Why are there Oceans? Why is there water? Water vapor from outgassing from volcanoes (& comets) cooling ­­> rain ­­> oceans ball of ice + Why is there LIQUID water? dust If Earth were 13% closer to Sun --> too hot for liquid water If If Earth were farther from Sun or less CO2 -> too cold for liquid water If 81% of Land is in the N. Hemisphere 81% of Land is in the N. Hemisphere Five major oceans Five major oceans Pacific, Atlantic, Indian, Arctic, Southern… Each has distinct characteristics (size, temperature, salinity) Atlantic Ocean Atlantic Atlantic • Relatively long and sinuous • MOR in the center • Prominent fracture zones • Well developed continental shelves reflects ancient rifting and subsequent weathering Pacific Pacific Pacific • Mean 3900 m depth • Surrounded by linear mountain chains, trenches, island arcs, marginal sea • Your “Ring of Fire” • Narrow continental margins • Mid Ocean ridge really isn’t in the middle! • Large number volcanic islands caused by HOT Indian Indian Indian Ocean • Cross between Atlantic and Pacific Oceans • Ridges are central (generally) • Several triple junctions! • Some subduction zones, Island arc ­ (e.g., Indonesian arc) • Some long hotspot traces • 90 East ridge traces plate motion of India! • Abyssal plains & fans Plate Tectonics Plate Tectonics The bathymetry, shape, and history of the Oceans can all be related to Plate Tectonics Mid-Ocean Ridges Margins Subduction & Trenches Hot spots & Seamounts Bathymetry of the Ocean Floor Bathymetry of the Ocean Floor Bathymetry mapping of ocean basins has delineated major units: Bathymetry mapping of ocean basins has delineated major units: 1) Ocean Trenches 3) Ocean Basin Floor 2) Continental Margins 4) Mid­Ocean Ridges North Atlantic profile North Atlantic profile What tools do we use to measure bathymetry? (depth of the sea­floor…useful for identifying features, and their “elevation” several dozen echo sounding beams Oceanic Features! Oceanic Features! What are they? What do we call them? 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 Deep-ocean trench - convergent boundaries where lithospheric Deep-ocean plates subduct into the mantle ­ long, relatively narrow ­ deepest parts of ocean (most >8 km; 11 km) ­ most are in Pacific Continental Shelf Continental Shelf ­ Broad, flat from shoreline to continental slope ­ < 200 m deep, may be 100’s km offshore ­ Underlain by continental crust ­ 0.3o slope No vertical exaggeration ­ Shallow shelf affected by waves & tidal currents; ­ Dominant sediments ­ sand, silt, & mud. ­Land­derived sediment input from the weathering of the continents! ­ In New Jersey’s case the Shelf was formed from the weathering and erosion of the Appalachian Mountains. Sediment was transported by rivers before deposition on the shelf! Cross­section of a passive margin! Cross­section of a passive margin! Continental Shelf off of New Jersey Continental Shelf off of New Jersey Continental shelf ­ extension of adjacent continent (1:1000) Continental shelf overlies continental crust Continental slope and rise may overlie the continental­ Continental slope and rise may overlie the continental­ oceanic crust transition on passive margins Continental Slope Continental Slope ­ Steeper (2o) ­ Typically mud­draped, marks edge of continental shelf ­ Can extend down to 4 km ­ Canyons cut through this, transporting sediment from the shelf to the continental rise ­ Submarine canyons are important features, cut into the slope during LOW sea level! ­ Often dissected by submarine canyons (some > Grand Canyon) ­ Often w/ submarine landslides & turbidity currents Seafloor Features: Continental Margins Submarine canyons Submarine (cut into the c. slope) (cut Abyssal plain Continental shelf Continental rise Abyssal plain Continental slope Continental Rise Continental ­ Gently sloping sediment apron (contourites) ­ Sands & muds deposited from continental slope ­ Depths of 4­4.5 km ­ Large submarine fans with kms of sediment Some sediment transported from shelf via slope Some sediment transported from shelf via slope Submarine Canyon fan system Submarine Canyon fan system Submarine fans Submarine • • • • • • A few kilometers to over few 2000 km across 2000 Fed by Submarine Fed canyons canyons Comprise the Comprise Continental rise Continental Sediment coarsest at the Sediment source, becomes finer away! away! Sand and gravel, or Sand graded beds (Bouma graded Bouma sequence) are best sequence are preserved in the proximal fan proximal Fine sand and mud Fine dominate in the distal fan fan Continental shelf Continental rise Continental slope Cape Hatteras Abyssal Plain Abyssal Plain ­ Beyond the continental rise, deep sea ­ Think of the quiet ocean seafloor, away from tectonic processes, wave and tide energy at the sea surface, and turbidites coming off the shelf ­ ~4­5 km water depth ­ Flattest surface on the Earth ­ Forms LARGEST part of ocean ­ Contains submerged volcanoes called seamounts. Abyssal plains Abyssal plains divergent oceanic plate boundary sediment Fig. 18.05 c W. W. Norton basalt Abyssal hills broad fairly flat seafloor > ~ 4 km central rift valley Marine Sediments Abyssal plains marine plankton terrestrial detritus windblown dust ice-rafted debris MORs are 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 Sources of sediment Sources of sediment Derived from land Deep­Sea Oozes Deep­Sea Oozes BUGS!­ Planktonic Foraminifera BUGS!­ CaCO3 Radiolarians­ Rich in Silica Siliceous microfossils Siliceous microfossils Surface Currents Surface Currents controlled by: Wind Coriolis effect Deep Currents controlled by: Temperature & Salinity = Density eddy ­ isolated ring­ shaped current The Coriolis Effect ­ the Earth spins “faster” at equator The Coriolis Effect ­ the Earth spins “faster” at equator Coriolis (rotation of planet) deflects: right (clockwise) in N left (counterclockwise) in S Winds drive surface currents in the oceans Winds drive surface currents in the oceans Wind pattern without continents: Coriolis + temperature gradient Continents complicate wind patterns: gain/lose heat faster than oceans mountains deflect winds block ocean currents but not wind Surface ocean currents – wind­driven Fig. 18.10 gyre ­ large circular flow pattern of surface currents W. W. Norton. Adapted from Getis et al., 1991 Coriolis Effect ­ clockwise (N), counterclockwise (S) Surface currents redistribute global heat surface currents Sea surface temperature during August Upwelling/Downwelling Upwelling/Downwelling Wind What is the prevailing wind direction? Ocean Currents Ocean Currents Large ocean gyres Sea Surface Temperatures Sea Surface Temperatures • Warmest at equator (28°C) •Freezing at high latitudes • Mean annual temperature is 17°C Sea Surface Salinity Sea Surface Salinity Atlantic ocean is saltier than The Pacific! Why? Latitude… Evaporation… Landmass… • Mediterranean • Enclosed, semi­arid climate • Isthmus of Panama • Narrow land separates two water bodies Evaporation > precipitation + runoff ­­> Evaporation > precipitation + runoff ­­> salinity increases Average surface salinity of the oceans Seawater T controls density Sea surface temperature during August Evaporation > precipitation + runoff ­­> Evaporation > precipitation + runoff ­­> salinity increases Dead sea a unique, but Excellent example… Ocean temperature Ocean temperature with depth Temperature varies little beneath the thermocline Atlantic water masses Atlantic water masses • Like the atmosphere, oceans are stratified – by temperature (cooler at bottom) – by chemistry (saltier at bottom) • • Atlantic Ocean is more saline than Pacific but the Pacific is deeper. Sinking of North Atlantic Deep Water (NADW) drives a "conveyor belt" Sinking ocean circulation - the thermohaline circulation thermohaline Thermohaline Circulation Thermohaline Circulation “The Great Conveyor Belt” Seawater ­ density­driven layers Seawater ­ density­driven layers Abrupt vertical density change that separates surface & deep ocean Salinity Halocline + + Temperature Thermocline = = Density Pycnocline Above the pycnocline (surface water currents): lateral circulation driven by wind, Coriolis Below the pycnocline (deepwater currents): vertical circulation driven by density differences (T, S) discrete water masses distinguished by temperature, salinity Fig. 18.16 Ocean conveyor belt W. W. Norton. Adapted from Deepwater Currents Skinner and Porter, 1995 are driven by density differences density = temperature + salinity ...
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