Warm Up – top of page 25 1.What are the 3 major wind patterns in the Northern Hemisphere? 2.How does the Great Ocean Conveyor Belt work? 3.What is a seasonal thermocline? 4.Briefly explain how the Ekman spiral works?
Tides Oceanography
Ocean Tides Tides are the periodic rise and fall of the sea surface. They have several purposes: –expose and submerge organisms on the shore –drive the circulation of bays and estuaries –trigger spawning of some marine organisms.
Tides Tides are caused by the gravitational pull of the moon and sun and the rotations of the earth, moon, and sun. One object doesn’t rotate around another because of gravity; instead they both rotate around a common point (the center of their combined masses). This rotation produces centrifugal forces which cause water to bulge on the outside of the rotation.
Ebb and Flow Because water flows, it is also pulled toward objects that have a large gravitational pull, causing a bulge toward the moon or sun. These bulges are high tides. Low tides are the areas where water is not bulging. Ebb & Flow- term referring to the decrease in water/water flowing away from coast (ebb) and increase in water (flow)
Tides Because the earth takes about 24 hours to completely rotate, any point on earth with water will have two high tides and two low tides each day. The effect of the sun is only about half as much as the moon. Their effects add together and can cause tides that are much larger.
Spring and Neap Tides Tidal range is the difference in water level between successive high and low tides. This is larger when the sun and moon are in line with each other and are known as spring tides because they seem to surge up like a spring of water. Neap tides occur when the sun and moon are at right angles and their effects partially cancel one another. The tidal range is smaller during this time.
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Semidiurnal Tides Tides vary across the earth depending on location and type of basin. The east coast of North America, most of Europe and Africa have semidiurnal tides. Two high and low tides each day. The west coast of the US and Canada have mixed semidiurnal tides which causes high tides of different height.
Diurnal Tides Diurnal tides occur when there is only one high and one low tide each day. Not very common at all. They occur on the coasts of Antarctica, part of the Gulf of Mexico, Caribbean, and Pacific. Tidal waves (not to be confused with tsunamis!) occur when the leading edge of the tide forms a wave.
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