| 1. Heating and Cooling
the Earth's Surface: |
| Learning Objectives: |
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Understanding of the factors that control the Earth's heat budget
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Recognition of the role of the oceans in the distribution of heat on Earth
|
| Distribution of Solar Radiation: |
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Solar constant (Without atmosphere heat received 2 cal cm-2
/min: .
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Greatest heat received (1.6 cal cm-2 /min)
in equatorial regions
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imprint of solar radiation more disperesed at high latitudes
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Heat absorbed by atmosphere
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decreases with increasing latitude as radiation more oblique.
|
| Heat Budget: |
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Heat gains and losses:
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Reflection of solar radiation:
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31% by atmosphere, 4% by Earth's surface
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Adsorption of solar radiation:
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17.5% by atmosphere, 47.5% by Earth's surface.
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Reradiation
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combined 65% is lost, 59.5% by atmosphere, 5.5% by Earth's surface
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Transfer of heat from surface to atmosphere:
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total 42%, 29.5% by evaporation, 12.5% by conduction
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Heat gain in equatorial regions, most heat lost in polar regions.
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Sea surface temperature show strong latitudinal gradients.
|
| Annual Cycles of Solar Radiation, Heat Capacity
of the Oceans: |
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Seasonal changes in radiation and temperature
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greatest change at mid and high latitudes.
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summer at high latitudes: long duration of low intensity radiation.
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Annual temperature ranges:
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variation controlled by heat capacity of oceans
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oceans dominant role in southern hemisphere.
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range on land at high latitudes is greater than in oceans.
|
| 2. Density Structure and Vertical Circulation: |
| Learning Objectives: |
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Understanding controls on seawater density and its description
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Recognition of the layered structure and movement of the ocean
|
| Surface Processes: |
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Temperature and salinity variations control density
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As temperature increases, density decreases
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As salinity increases (or pressure), density increases
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less dense water at surface
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Higher density water formed at polar latitudes sinks into deep ocean.
|
| Changes with Depth: |
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Three depth zones:
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surface (mixed layer to ~100m, 2%)
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pycnocline (100 - 1000m, 18%)
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deep ocean (>1000m, 80%).
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Pycnocline: zone of density change,
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Thermocline: depth zone where marked changes in temperature occur
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Halocline: depth zone where marked changes in salinity occur
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Density structure:
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increases with depth: stable
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unstable where denser water overlies less dense water
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isopycnal: lines (depths) of equal density
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isothermal: lines (depths) of equal temperature,
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isohaline: lines (depths) of equal salinity
|
| Density-driven Circulation: |
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Thermohaline circulation
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convective exchange and vertical circulation;
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controlled by temperature and salinity
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seasonal temperature changes create seasonal thermocline
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affect surface density
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can form sinking water masses, or freshwater lid.
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Sigma-t (st):
measure of seawater density
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defined as (density - 1) x 1000.
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1.02677 becomes 26.77 st.
|
| Movement of Water: |
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Upwelling: ascending water masses
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Downwelling: sinking water masses
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maintain continuity of flow, vertical movement (0.1 - 1.5m/day)
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Sinking waters may take 1000 years to reach great depths.
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Horizontal water movement:
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convergence (meeting) and divergence (spreading out).
|
| Chemical Tracers: |
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Used to study water movement in the oceans
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e.g. tritium, the radioactive isotope of H.
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