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, < 1 o (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 (2-6 o ) 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, 0.1 o slope; Atlantic 2-3cm/yr, 1 o slope) - Locally high relief (1,000m cliffs)

II Ocean Basins (cont.) Trench/Subduction Zones -Up to 4 o 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

Origin III Classification based on - Clastic or chemical - Biotic or inorganic Texture Appearance Composition - Size, sorting, - Shape, rounding - Grain-matrix relationships - 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 CaCO 3 from forams & coccoliths important sink for CO 2 Chert/siliceous oozes SiO 2 from radiolaria & diatoms, volcanic ash Hydrogenous inorganic Phosphates - ~CaPO 4 Manganese - MnO 2 Evaporites - Gypsum CaSO 4, 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: H 2 O III Physical properties IV Energy transmission

I Origin Volcanic outgassing Comets

II The Marvelous Water Molecule: H 2 O 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/cm 3 @ 4 o C 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/ o C, alcohol 0.23, lead 0.03 Relatively high melting (0 o C) and boiling (100 o C) points - Affected by dissolved solids - Affected by atmospheric pressure Viscous Capillarity/surface tension

IV Energy transmission Light Sound Heat - Long wavelength (red) absorbed quickly - Short wavelength (blue) penetrates deeper - Great attenuation due to absorption and scatter - Refracted (bent) - Transmitted much better than in air (1500m/sec, 5 X faster) - Faster in warm water, faster under increased pressure - 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 CO 2, N 2, O 2 Concentrations differ from atmosphere CO 2 and O 2 will affect the distribution of organisms CO 2 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 CO 2 and O 2 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, SO 4, 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 CO 2, 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. equator, 850km/hr at 60 o N) 1700km/hr at 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 10 o -25 o lat.; Require warm, moist air Established over lows, draw heat energy from water change Circulate ccw in N hemis., cw in S hemis. (Coriolis phase 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 of water (due to hydrogen bonds) - Considerable inertia - Ekman spiral Density differences (thermohaline circulation) - Temperature - Salinity Tides (attraction of sun and moon)

III Currents Influenced By Continents e.g. pile up on western side of ocean basins Submarine features e.g. mid- ocean ridges

IV Current Types Surface Currents wind generated, relatively rapid Deep Currents thermohaline, carry O 2 - North Atlantic Deep Water NADW - Antarctic Bottom Water AABW Vertical Currents slow, - Upwelling with divergence (supply nutrients) - Downwelling with convergence

V Surface Currents Gyres - Boundary Currents (with western intensification) - Western currents - narrow, deep, fast (e.g. The Gulf Stream) - Eastern currents - broad, shallow, slow (e.g. The California Current) Ekman Spiral Equatorial Counter Current Convergence Zones Divergence Zones

VI El Nino (ENSO) and La Nina Influence weather in western hemisphere Control ocean productivity off South America Driven by changing high/low pressure zones in Pacific

GEOLOGY OF THE WORLD S OCEANS I Anatomy of a Wave II Mechanisms Waves III Capable of Erosion, Transport and Deposition IV Giant Waves/Rogue Waves V Tsunamis/Seismic Sea Waves not tidal waves VI Waves as Energy Sources

I Anatomy of a Wave Wave height (H) Wave length (λ) Wave period (P) Crest Trough Swells Open-ocean waves Shallow-water waves

II Mechanisms Energy from wind Velocity, duration, distance (fetch) Surface cohesion important Water moves in circular orbits - Orbital diameter decreases with depth - Orbits feel bottom at depth ~ ½ λ Orbits become more elliptical Wave length decreases Wave height increases Breakers form

III Capable of Erosion, Transport and Deposition of Sediment Erosion Entrainment & Transport of Grains Sedimentary Structures Land Forms

III Erosion (cont.) Erosion Major destructive force in coastal settings Pressure and abrasion Energies concentrated by refraction Influenced by bedrock vs unconsolidated sediments Combated with jetties, sea walls, breakwaters, beach nourishment

III Erosion (cont.) Entrainment of grains Size Mass Shape Flow velocity III Transport of Sediment Swash & backwash Beach drift Long shore drift Rip tides

III Sedimentary Structures (small-scale features) Oscillation/ symmetrical ripples Asymmetrical/ current ripples Dunes and Forms (large-scale features) Erosional - Wave cut terraces and sea cliffs - Sea arches and stacks Depositional -Spits - Barrier islands - Bay mouth bars

IV Giant Waves/Rogue Waves Wave energies concentrated, additive effects In open ocean often at the shelf edge esp. S. Africa Up to 58m high, 50 km/hr speeds May break large ships V Tsunamis/Seismic Sea Waves (Not tidal waves) Generated by earthquakes and landslides Travel quickly across ocean basins Long wavelength waves (λ 200km, H 0.5m, P 20 min, V 760km/hr)

VI Waves as Energy Sources Lift objects Use orbital motion Compress air in cylinders Difficulties - unpredictable timing - possibly too strong

GEOLOGY OF THE WORLD S OCEANS Ocean Tides I Mechanism II Timing III Effects IV Energy from Tides

I Mechanism Interaction with moon and sun s gravity Centrifugal/inertial forces Ellipticity of earth and moon s orbits Declination of moon and sun relative to earth Influenced by shape of ocean basins Focused by local topography (e.g. tidal bores up rivers)

Daily II Timing - Diurnal - 1 high, 1 low - Semidiurnal - 2 equal highs, 2 equal lows - Semidiurnal mixed - 2 unequal highs, 2 unequal lows Tides arrive 50 min later each day why? Monthly Spring Tides - constructive (additive) effect of sun and moon, occurs with new and full moon Neap Tides - destructive effect of sun and moon, occurs with first and third quarter moon

III Effects Influenced by tidal range and topography (gentle or steep) Expose sea floor, cause pronounced zonation -Supratidal zone -Intertidal zone - Subtidal zone Generate strong currents - Carry food and nutrients - Erode and transport sediment Tidal channels Ripples/dunes Herringbone

IV Energy from Tides Water wheels/mills Proven technology in North Sea Turbines - Require sufficient tidal range and dams Downside may restrict migration of marine life