EARTH'S SHALLOW SPHERES
OCEANS (COMPOSITION/STRUCTURE)
Water is a very Peculiar Solvent:
Water is so commonplace that it is easy to overlook that, chemically, it is a very peculiar substance.
The water molecule is bent:
108o
d+ H H
\ /
d- O
/ \ lone pairs of electrons (unshared out of 6)
The net result is a deficiency of negative charge on the hydrogen end, making a polar molecule with a distinct positive and negative end.
This polarity is responsible for the dramatically peculiar behavior of WATER. The polarity enables the molecule to act as a dipole (equal BUT opposite charges of a fixed distance apart in the same molecule).
FOR EXAMPLE: Salts of NaCl will dissolve very well in water because ion interaction (pairing) is made difficult by the fact that the Na+ is surrounded by the negative (O) end of the water, and the Cl- is surrounded by the negative charge of the positive end (H) of the water.
HENCE: Supersolvent for ionic salts.
Furthermore, water can also interact with itself through a dipole-dipole interaction. This is seen most clearly in the structure of ice, less dense than water.
HENCE: High viscosity
High surface tension
High boiling point
High specific heat – heat to raise 1 kg by 1 deg (heat capacity)
High latent heat of vaporization
Unusually high liquid state temperature range (100 deg-C)
ALL these combined makes the "ROLE" of water quite unique on Earth.
SURFICIAL PROCESSES – how the above will impact? Climate (buffer – the first 2.5 m of ocean matches entire atmosphere heat capacity), weathering (solution and frost cracking), organism habitat (ion/nutrient diffusion), contaminant/solute transport.
Although we are not going to discuss it, one can only imagine how the same properties are essential to the functioning of LIFE itself.
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Ocean Chemistry:
l Residence times (amount of time needed to replenish all of the oceans' content of the elements). Long means better mixed. Same as atmosphere.
l What controls this chemical composition ? INPUT vs. PROCESSES
l Vertical Temperature-Salinity Profiles. Mixed layers.
l Global Carbon Cycle: (1) carbon dioxide and seawater, (b) the biological pump, and (c) circulation of the oceans. Missing SINK?
l Ocean currents, geostropic (wind)/thermohaline (density) circulation
Northern Atlantic circulation, Gulf Stream, Downwelling and Upwelling Zones
l El Nino Southern Oscilation (ENSO), Atmospheric- Ocean Coupling
Different environments under the sea. Broadly, we have:
(2) benthic environments where sessile (live in place) and vagrant (mobile) organisms are found (clam, mussels).
All life in the oceans (like on land) depends on the net primary productivity. As we already noted, because of nutrient and light requirements and NPP is highest in coastal shallow regions.