Physics

• Crust:

  • 30-50 km
  • Low density
  • Al, Si, O
• Mantle:

  • ~2900 km
  • Dense
  • Hot rocks
  • Mg, Si, Fe, O
• Core:

  • Very Dense
  • 3500 km
  • Inner - Solid
  • Outer - Molten
  • Fe, Ni
• Litosphere:

  • Crust
  • Upper mantle
  • Brittle
• Asthenosphere:

  • Mantle
  • Plastic
• Mesophere:

  • Below 350 km
  • More rigid
• Shelf:

  • Nearly flat
  • 1-1000 km wide
  • ~0.5 degrees
• Shelf Break:

  • 1-4 degrees
  • ~130 m depth
• Slope:

  • ~4 degrees slope to 2-3 km depth
  • Submarine canyons
• Rise:

  • ~500 km offshore
  • ~1 degree slope
  • ~4 km depth
• Continents:

  • 29% of the surface
  • Mean height = 0.84 km
  • Granitic rocks
  • Igneous - Al, O, Si
  • 2700kg/m^3
  • 30-40 km thick
• Ocean Basins

  • 71% of the surface
  • Mean depth 3.8km
  • Balsatic rocks
  • Volcanic - Mg, O, Si
  • 2900kg/m^3
  • 4-10 km thick
• Addition of solutes or solid particles -> Increase in mass of material in fluid volume -> Increase in fluid density
• Removal of solutes or particles -> decrease in mass of material in fluid volume -> decrease in fluid density.
• Typical seawater has a salinity of ~35 ppt
• Cation (+) sources:

  • Weathering igneous rocks
  • Transport via rivers
• Anion (-) sources:

  • From mantle
  • From early atmosphere
  • Released by volcanoes
• Ocean salinities remain constant for ~1.5 billion years
• Salt removal processes:

  • Sea spray
  • Evaporite formation
  • Adsorption onto particles
  • Incorporation by organisms
  • Harvesting by organisms
  • Formation of insoluble products by ion-ion interactions
• Thermocline:

  • Zone of rapid transition in temperature
  • Depth of 200-1000m
• Seasonal thermocline forms at mid-latitudes: 40-100m

  • Spring/summer heating lowers density of surface waters
  • Cooling and wind/wave mixing removes stratification in winter
• Small-scale diurnal thermocline can form at <12m
• Surface salinity is controlled by balance of precipitation and evaporation.

  Dependent on:

  • Climate
  • Local influence of river run-off
• Evaporation of sea surface salt is dominant in 20-35 degrees N and S
• Halocline - uniform salinity at depth (unaffected by surface processes)
• Seawater density increases with:

  • Decreasing temperature
  • Increasing salinity
  • Increasing pressure
• Pycnocline - region of rapid change of density with depth
• High temperature + Low salinity = Lower density
• Low temperature + High salinity = High density
• 75% of ocean:

  • T = 0-5 degrees C
  • S = 34-35 ppt
• Types of water masses:

  • Deep (>~2km)
  • Intermediate (~1-2km)
  • Central (~0-1km)
• Thermohaline - temperature and salinity differences
• Thermohaline circulation:

  • Temp decreases with latitude + depth
  • Cold air cools surface ice formation, raises salinity
  • Dense water sinks + spreads throughout ocean basins
  • Mixing raises deep water upwards to surface
  • Solar heating offsets high evaporation
  • Thin layer of salty water
• Deep water masses only form in:

  • Polar seas
  • Relatively shallow basins
• NADW - North Atlantic Deep Water

  • Close to Greenland (cooling/evaporation)
  • High production -> Large volume
• MIW - Mediterranean Intermediate Water

  • Formed in Mediterranean Sea (evaporation)
  • Flows out through Strait of Gilbraltar and sinks
• PSW - Pacific Subartic Water
• AAIW - Antarctic Intermediate Water

  • Formed in antarctic
  • Flows North to meet AIW
• AABW - Antarctic Bottom Water

  • Weddell Sea (Ice formation)
  • Very cold and salty (densest sea in the oceans)
• AADW: Antarctic Deep Water

  • Less extreme latitudes
  • Slightly less cold and salty than AABW