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potassium, and strontium.
The pressure in the oceans rises
one atmosphere for every 10m of depth.
The freezing point of seawater becomes lower as the salinity gets higher. Seawater typically freezes at -2°C. The colder and saltier water is, the more dense it becomes, and the more it tends to sink.
Seawater does not have a freezing pattern the same as fresh water. Fresh water is most dense at 4°C. When it freezes, it becomes less dense (the reason why ice floats on water). Seawater, on the other hand, continues to increase in density all the way down to its freezing point.
Seawater and the air above it
are continually exchanging gases, including water vapor. However, the proportions of each gas in the air are different from those in the sea because some gases in the air are more soluble in water than others. Oxygen is very soluble in water, and the percentage of oxygen in water is about one and a half times as great as the percentage of oxygen in the air.
The amounts of carbon dioxide and oxygen in seawater are also greatly affected by sea life because animals use oxygen and give out carbon dioxide, whereas plants use carbon dioxide and give out oxygen.
The sea appears blue. That is because light entering the water is scattered by the water so that more red light is absorbed than blue. If the sea appears green, that is due to a large number of microscopic plankton in the water, which are yellow. The combination of blue and yellow makes the green color.
The occasional growth of vast numbers of plankton make the sea appear red. The Red Sea derives its name from this phenomenon, which is common there.
Sediment
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Sediment
Material that has been carried
by rivers and then deposited. Sediment that has settled out on a river bed or flood plain may also be called alluvium.
Sediment can be large, in which case it is called boulders, cobbles, and pebbles; it may be of medium size—gravel and sand; it may be fine—silt; or very fine— clay, or mud.
The finest materials are carried in suspension and do not easily settle out on the bottom of
the river. The medium-
sized materials
 Sediment—This picture shows a river carrying so much sediment in suspension that it has turned the water light gray. A tributary enters, carrying little sediment, and is a clearer dark blue. The waters only mix much further downstream.
only move during times when the river is full of water, and then they mostly hop along the river bed. The largest sediment moves only in times of flood, and then it rolls along the river bed. (See also: Delta and Pothole.)
 Sediment—This is suspended sediment. The silt has settled out, leaving the clay to color the water.