Discussion:

Light Transmission in Seawater
Oceanic Climatic Regions

Air-Sea Interaction

Light Transmission in Seawater

The sun radiated energy across the entire electromagnetic spectrum.
The most intense radiation radiated by the sun is in the visible region of the electromagnetic spectrum.
Within 1 m of the surface of the ocean, only 40% of the incident visible light remains, i.e. 60% is absorbed.
At a depth of 100 m, only 1-2% of incident visible light remains.

Differential absorption of visible light occurs in water.
The longer red wavelengths are absorbed rapidly, whereas the shorter blue-green wavelengths are transmitted to deeper depths.

Oceanic Climatic Regions

There are six open-ocean climatic regions that trend east-west:

1. equatorial
2. tropical
3. subtropical
4. temperate
5. subpolar
6. polar

Climatic regions have surface waters with different T and S that result from differing degrees of:

• insolation (amount of solar energy adsorbed)
• precipitation
• evaporation

Changes in T and S result in surface waters of different densities.

Equatorial Region

The equatorial climatic region straddles the equator, 0^o.
Earth's meteorological equator, the ITCZ, is located about 4^o N.
It is a region of low atmospheric pressure, which results in ascending air.
It is a region of weak winds called the Doldrums.
The surface waters in the equatorial region are warm all year.
It is a region of heavy precipitation.
Throughout the year, precipitation > evaporation at the equator.
This results in lower than average salinity, <34.7 ppt.

Tropical Region

This is the region of strong Trade Winds.
The strong winds cause strong equatorial currents.
Relatively warm surface water all year.

Subtropical Region

The subtropical regions straddle 30^o north and 30^o south.
It is a region of high atmospheric pressure, which results in descending air.
Cool, dry air descends from the upper atmosphere.
It is a region of weak winds called the Horse Latitudes.
Small changes in surface water temperature with the seasons are observed.
It is a region of high evaporation.
Throughout the year, evaporation > precipitation in the subtropical region.
This results in the highest salinity in the open ocean, as high as 37 ppt.

Temperate Region

The boundary between the temperate and the subpolar climatic regions is 60^o north and 60^o south.
Near 60^o is a region of low atmospheric pressure, which results in ascending air.
The temperate climatic region contains strong winds, the Westerlies.
The strong winds cause strong surface currents.
In this climatic region, the largest seasonal changes in surface water temperatures occur, the water is cold in the winter and warm in the summer.
Heavy precipitation occurs in the low pressure part of the temperate region near 60^o.
Throughout the year, precipitation > evaporation.
This results in lower than average salinity in the surface waters, as low as 33 ppt.

Subpolar Region

This climatic region contains the Polar Easterlies.
Here the surface water is cold all year, > 5^oC.
Ice forms in the winter, which creates the densest water in the open ocean.
This is the region of deep water formation.

Polar Region

The polar region is an area of high atmospheric pressure, which results in descending air.
The temperatures are near freezing all year.
However, the atmosphere is not in contact with the ocean in this climatic region.
The continent of Antarctica is at the south pole, and the Arctic Ocean at the north pole is covered with ice.