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Morphology of Ocean Basins

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Morphology of Ocean Basins Morphology Of Ocean Basins I Continental Margin •Continental Shelves •Epeiric Seas (In Past) •Continental Slope •Continental Rise II Ocean Basin •Mid Ocean Ridges, Rises, Fracture Zones •Abyssal Plains, Hills, Seamounts •Trench/Subduction Zones •Island Arcs •Back Arc Basins I Continental Margin •Atlantic Type (Trailing Edge -Passive) – Subsidence, sedimentation Broad •Pacific Type (Leading Edge -Active) – Volcanism, deformation, uplift Narrow •Continental Shelves Gentle, < 1o (1:500) slope 30m-1300km wide Break at ~ 130m depth •Epeiric Seas (In Past) 1:50,000 slope Very broad (1,000s of km) I Continental Margin (cont.) •Continental Slope Steeper (2-6o) 300-8,000m depth Submarine canyons •Continental Rise Submarine fans Turbidites Oil & gas reservoirs II Ocean Basins •Abyssal Plains, Hills, Seamounts - Plains <1:1000 slope, 4-6km depth 30% earth’s surface area (= total continental area) - Hills < 1000m relief - Seamounts are submerged volcanoes with high relief may be flat topped (guyots) •Mid Ocean Ridges, Rises, Fracture Zones - Vent communities, deep circulation and chemical reactions - Relation between spreading rates and rise slope (Pacific 10cm/yr, 0.1o slope; Atlantic 2-3cm/yr, 1o slope) - Locally high relief (1,000m cliffs) II Ocean Basins (cont.) •Trench/Subduction Zones -Up to 4o slopes - Mariana 11km (36,000’) deep - Peru-Chili 6,000 km long •Island Arcs •Back Arc Basins GEOLOGY OF THE WORLD’S OCEANS Ocean Sediments I Sampled by… II Value III Classification IV Types/Sources V Effects on Organisms VI Distribution of Sediment Types I Sediments are Sampled by •Grabs (hand sample, clamshell) •Cores (box, piston) •Drilling II Value of Sediment/Sedimentary Rocks •Archive of Earth history - Evolution/extinction - Climate change - Creation/destruction of ocean basins •Hydrocarbon reservoirs •Metallic mineral deposits III Classification – based on… •Origin - Clastic or chemical - Biotic or inorganic •Texture – Appearance - Size, sorting, - Shape, rounding - Grain-matrix relationships •Composition - Mineralogy - Biotic components IV Types/Sources •Terrigenous / clastic – from continents •Chemical / precipitate - form in ocean basins - Biogenous - organic - Hydrogenous - inorganic •Cosmogenous - from space IV Types/Sources (cont.) Terrigenous/clastic – from continents •Conglomerate, breccia •Sandstone •Siltstone •Shale / mudstone / red clays Clastic sediments are classified by particle size IV Types/Sources (cont.) Chemical/precipitate - form in ocean basins Biogenous – organic •Limestone/calcareous oozes CaCO3 – from forams & coccoliths – important sink for CO2 •Chert/siliceous oozes SiO2 – from radiolaria & diatoms, volcanic ash Hydrogenous – inorganic •Phosphates - ~CaPO4 •Manganese - MnO2 •Evaporites - Gypsum CaSO4, halite NaCl IV Types/Sources (cont.) Cosmogenous - from space •Glass spherules •Tektites V Sediment Effects on Organisms •High turbidity reduces light levels and may impact photosynthesis •High turbidity may interfere with suspension feeding •High sedimentation may bury sessile bottom dwellers •Fine sediment may preserve carbon for deposit feeders •Fine sediment may be oxygen poor and inhospitable for infauna VI Distribution of Sediment Types •Patterns •Controls - Energy levels - Depth - Latitude - Source GEOLOGY OF THE WORLD’S OCEANS Physical Properties of Seawater I Origin II The Marvelous Water Molecule: H2O III Physical properties IV Energy transmission I Origin •Volcanic outgassing •Comets II The Marvelous Water Molecule: H2O •Covalent bonds between H and O •Polar molecule (ends carry charges) •Hydrogen bonds between molecule (very strong) Water is the “universal solvent” III Physical properties •States - solid, liquid, gaseous Volume change with phase change •Density - 1g/cm3 @ 4oC Affected by temperature Affected by dissolved solids •Relatively incompressible (1.7% at 400 atm = 37m lowering of oceans) III Physical properties (cont.) •High heat capacity - Water 1.0 cal/g/oC, alcohol 0.23, lead 0.03 •Relatively high melting (0oC) and boiling (100oC) points - Affected by dissolved solids - Affected by atmospheric pressure •Viscous •Capillarity/surface tension IV Energy transmission •Light - Long wavelength (red) absorbed quickly - Short wavelength (blue) penetrates deeper - Great attenuation due to absorption and scatter - Refracted (bent) •Sound - Transmitted much better than in air (1500m/sec, 5 X faster) - Faster in warm water, faster under increased pressure •Heat - Inefficiently transferred downward through conduction GEOLOGY OF THE WORLD’S OCEANS Chemical Properties of Seawater I Sampled by… II Composition III Cycling of Dissolved Substances in Sea Water IV Chemical Properties I Water Chemistry Measured/ Sampled By CTD (Measures conductivity, temperature, depth) Niskin bottles retrieve water samples II Composition •Dissolved gases •Dissolved solids •Particulates (clays and organic matter) II Composition (cont.) - Dissolved gases CO2, N2 , O2 •Concentrations differ from atmosphere •CO2 and O2 will affect the distribution of organisms •CO2 will affect ph and dissolution/ precipitation of minerals (e.g. CCD) •Gas concentrations vary with depth - why? •Gas solubility is affected by water temperature Oceanic gases are mainly CO2 and O2 Note changes in concentration with increasing depth - Why? II Composition (cont.) - Dissolved solids (total = salinity = 3.5 % or 35 ppt o/oo, not 35 % (e.g. 35 gm salt per 1.0 liter water) •Major constituents (99.4% of dissolved solids) Cl, Na, SO4, Mg, Ca, K Measured in ppt -- “Conservative” •Traces I, Ba, Li, Cu, Ni, Se, Zn, others Can be important to organisms, e.g. iodine •Nutrients Si, N, P Measured in ppb -- “Nonconservative” Required for growth – influence marine productivity - Nutrients •Important for growth •Concentrated in ocean bottom waters •Supplied to surface waters through Upwelling Rivers II Composition (cont.) - Dissolved solids •Salinity varies with latitude and depth - why? •Salinity varies with environments e.g. hypersaline and hyposaline environments •Organisms vary in their ability to tolerate excursions from “normal marine” e.g. stenohaline corals, echinoderms euryhaline snails, clams, algae II Composition (cont.) - Particulates (Clays and Organic Matter) •Scatter light •Raise depth of photic zone III Cycling of Dissolved Substances in Sea Water •Added by - Volcanic outgassing - Reactions at mid ocean ridges and fracture zones - Weathering of continental rocks - Weathering of marine rocks - Marine life (photosynthesis, respiration) •Removed by - Biotic processes (esp Ca and Si) - Evaporite deposits - Sea spray - Adsorption onto clays IV Chemical Properties •Universal solvent •Catalyst Why? GEOLOGY OF THE WORLD’S OCEANS The Atmosphere •Gaseous envelope surrounding our planet - energized by solar radiation •Generated by volcanic outgassing and biologic processes (photosynthesis). •Has evolved over time – initially CO2, H?, N rich •Oxygenated (1% PAL) by 2.0 Ga I Earth’s Heat Budget •Insolation varies with latitude •Water has high heat capacity •62% of solar energy absorbed at earth’s surface is transferred to atmosphere through evaporation •Oceans show relatively little fluctuation in surface temperatures •Oceans moderate terrestrial climates II Atmospheric Circulation Models (Note -warm air less dense, humid air less dense) 1) Non-rotating, water-covered Earth (no continents) 2) Rotating, water-covered Earth (no continents) 3) Rotating, with oceans and continents II Atmospheric Circulation Models 1) Non-rotating, water-covered earth (no continents) • Latitudinally-controlled temperature differences • Simple cells with N surface winds in northern hemisphere (winds named based on where they are from) 2) Rotating, water-covered earth (no continents) • Coriolis Effect On a rotating sphere, velocity varies (e.g. 1700km/hr at equator, 850km/hr at 60oN) • Generates 6 cells (e.g. Hadley cells) - gives surface winds (Westerlies, Trades) separated by zones of vertical movement (Doldrums and Horse Latitudes) II Atmospheric Circulation Models (cont.) 3) Rotating, with oceans and continents •At mid latitudes, seasonal difference between land and oceans drive winds/pressure systems (e.g. high over cool continents, low over warm oceans) flow is from high to low •Monsoons - spring time, continents warm more rapidly, cool oceanic air flows landward, rises and releases water •Lows spawn hurricanes/cyclones •Daily patterns Sea-Land Breezes (e.g. “Undertaker Wind”) Mountain-Valley Winds (e.g. local canyon winds) III Storms Cyclones (Indian Ocean), Typhoons (W. Pacific), Hurricanes (Atlantic, E. Pac.), Willi-Willis (Australia) •Form between 10o-25o lat.; Require warm, moist air •Established over lows, draw heat energy from water phase change •Circulate ccw in N hemis., cw in S hemis. (Coriolis gives spin) •Move at 5-40km/hr;1000 km wide; 15 km high; 5-10 days avg life •Energy loss due to: Moving over land, moving into cooler waters •Damage due to: Wind (120 - 250 km/hr), floods, storm surge GEOLOGY OF THE WORLD’S OCEANS Ocean Circulation I Layered Oceans II Mechanisms III Influenced By IV Current Types V Surface Current Zones VI El Nino (ENSO) and La Nina I Layered Oceans •Subsurface masses of different densities - Due to a combination of salinity and temperature (and pressure) - Salinity and temperature controlled by climate at surface (related to latitude) - Pycnocline, thermocline or halocline may separate water masses •Mixed surface zone (down to ~ 100m) - Due to wave action - Temperature, oxygen, salinity relatively constant II Mechanisms •Wind - Surface cohesion
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