Ocean Basins - UW Oceanography

Ocean Basins - UW Oceanography

Reading Material (see website for course) Ocean Basins, from Oceanography M.G. Gross, Prentice-Hall Who Cares? Indonesia

tsunami New Orleans, Galveston earthquake landslide hurricane wind storm surge Oil & Gas Minerals (metals, fertilizer)

Sand and Gravel for concrete Fate of contaminated sediments Harbor siltation Beach erosion Sea-level rise Carbon burial, greenhouse gases, global warming History of Earth recorded by marine Ocean Basins

What creates the Earths surface? What is the shape of the surface below sea level (the seafloor)? What types of sediment are burying the seafloor? Hypsographic Curve

Earths Surface Hypsographic Diagram 30% land 10% continental margins (boundary) 60% deep sea Two distinct levels for Earth surface 0-1000 m above sea level 4000-5000 m below sea level

These represent two distinct types of crust (Earths rigid upper layer) continental crust thick, granite, not so dense oceanic crust thin, basalt, denser Plate Tectonics mechanism that moves crust Plates separate pieces of crust

move due to convection of heat in underlying layer (Mantle) plates can move in different directions, and collide Collisions a) two continental plates collide, form high mountain ranges e.g., Himalayas b) two ocean plates collide, form island arc and submarine trench e.g., Aleutian Islands, Aleutian Trench c) ocean and continental plates collide, form mountains and trench e.g., Andes and Peru-Chile Trench

Subduction occurs when ocean crust carried down into Mantle (e.g., b and c above) basalt and sediment heated to form volcanic magma Opening of new ocean and formation of mid-ocean ridge

Plate Tectonics mechanism that moves crust Plates separate pieces of crust move due to convection of heat in underlying layer (Mantle) plates can move in different directions, and collide Collisions a) two continental plates collide, form high mountain ranges

e.g., Himalayas b) two ocean plates collide, form island arc and submarine trench e.g., Aleutian Islands, Aleutian Trench c) ocean and continental plates collide, form mountains and trench e.g., Andes and Peru-Chile Trench Subduction occurs when ocean crust carried down into Mantle (e.g., b and c above) basalt and sediment heated to form volcanic magma

Bathymetry Mid-Ocean Ridges (underwater mountain ranges) water depth 2000-4000 m can be less where islands occur (e.g., Iceland) volcanic eruptions create new ocean crust hot basalt, thermal expansion creates elevation moves away from ridge axis in both directions Abyssal basins

water depth 4000-6000 m (only trenches are deeper) abyssal hills, include rough relief from volcanic formation abyssal plains, smooth surface due to burial by sediment Continental margins created by sediment from land that builds into ocean basins Sub-Environments on Continental Margins Continental shelf

smooth, gently dipping (less than 0.1 degrees) land surface during lowstand of sea level glacial ice melted and flooded portion of continent Continental slope steep (more than 4 degrees), rough topography edge of continental crust submarine canyons, larger than canyons on land not eroded by rivers directly (too deep), but by slurry of sediment

Continental rise more gentle gradient and relief sediment from land piled on ocean crust Trenches (collision of plates, deepest places in ocean) Abyssal plains (sediment from land buries abyssal hills) Trailing-Edge Margin Sub-Environments on Continental Margins

Continental shelf smooth, gently dipping (less than 0.1 degrees) land surface during lowstand of sea level glacial ice melted and flooded portion of continent Continental slope steep (more than 4 degrees), rough topography edge of continental crust submarine canyons, larger than canyons on land not eroded by rivers directly (too deep), but by slurry of

sediment Continental rise more gentle gradient and relief sediment from land piled on ocean crust Trenches (collision of plates, deepest places in ocean) Abyssal plains (sediment from land buries abyssal hills) Trailing-Edge Margin

Central California area of Monterey Canyon Monterey Canyon Sub-Environments on Continental Margins Continental shelf smooth, gently dipping (less than 0.1 degrees) land surface during lowstand of sea level glacial ice melted and flooded portion of continent

Continental slope steep (more than 4 degrees), rough topography edge of continental crust submarine canyons, larger than canyons on land not eroded by rivers directly (too deep), but by slurry of sediment Continental rise more gentle gradient and relief sediment from land piled on ocean crust

Trenches (collision of plates, deepest places in ocean) Abyssal plains (sediment from land buries abyssal hills) Trailing-Edge Margin Continental Margins Two types: Trailing-edge margins continental and oceanic plates move in same direction at same

speed examples margins around Atlantic Ocean contain: coastal plain (was continental shelf during higher sea level) broad continental shelf continental slope and rise Collision margins continental and oceanic plates move toward each other

examples margins around Pacific Ocean contain: coastal mountain range, volcanoes, earthquakes narrow, steep continental shelf continental slope and submarine trench Trailing-Edge Margin Continental Margins Two types:

Trailing-edge margins continental and oceanic plates move in same direction at same speed examples margins around Atlantic Ocean contain: coastal plain (was continental shelf during higher sea level) broad continental shelf continental slope and rise

Collision margins continental and oceanic plates move toward each other examples margins around Pacific Ocean contain: coastal mountain range, volcanoes, earthquakes narrow, steep continental shelf continental slope and submarine trench Collision Margin

Materials filling ocean basins Dissolved chemicals especially from rivers and mid-ocean ridges (volcanic eruptions) some remain dissolved (e.g., producing salt water) some precipitate inorganically (e.g., producing Manganese nodules) some precipitate organically (e.g., producing biogenic oozes) Solid particles, from: winds (aeolian) dust blown from land, only important in deepest

ocean forms red clay rivers (fluvial) most important source 90% mud (silt, clay), 10% sand glaciers (glacial) greatest impact at high latitudes supplies wide range of sizes (boulders to rock flour)

Authigenic Sediments (manganese nodules) and red clay Biogenic Sediments, microscopic in size Classification of marine sediments Lithogenic from disintegration of rock on land

aeolian, FLUVIAL, and glacial sources Biogenic organic precipitation of dissolved components dominated by single-celled plants and animals (create oozes) calcium carbonate (limestone) = calcareous silicon dioxide (opal) = siliceous Authigenic inorganic precipitation of dissolved components seawater becomes supersaturated with regard to some chemicals Cosmogenic from outside Earth

meteorites, usually very small (tektites) Cosmogenic Sediments tektites (micrometeorites)

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