Currents and Tides Help (page 3)

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By — McGraw-Hill Professional
Updated on Sep 4, 2011


We learned that water is divided into layers depending on temperature, salinity, pressure, and density. Currents and tides move seawater around changing the density. These movements change the depth of the thermocline layer. Underwater vehicles have to adjust their buoyancy to maintain a stationary depth.

When the Moon, Earth, and Sun line up, a happening called syzygy , shorelines experience the greatest change in high- and low-tide water levels. These spring tides take place twice a month, during the full and new Moon.

When the Moon is at perigee , or its closest distance to the Earth in its orbit, the tides are extremely high or low.

Then when the Sun and Moon form a 90° angle, like at the time of a half moon, their gravitational forces fight each other and there is a smaller change between high and low tides. These are known as neap tides .

There are other things that play into the equation. For example, when the Moon goes around the Earth, the planet’s tilt, ocean depth, and ocean topography all affect tides. This is why not all coasts have two high and low tides a day.

Semidiurnal tides happen twice a day. The Atlantic Ocean has semidiurnal tides. It has two high tides and two low tides in one day.

Diurnal tides take place once a day. The Gulf of Mexico has only one high tide and one low tide in a 25-hr period.

Then there are the exceptions to the rule, some seas and ocean sections, including parts of the Pacific Basin, have mixed tides . They don’t follow any set pattern, but many have one low tide followed by two high tides.

The Bay of Fundy , between New Brunswick and Nova Scotia holds the record for the highest tides in the world. The change in water level between high tide and low tide can be over 16 m; more than half the length of a football field.

Practice problems of this concept can be found at: Oceans Practice Test

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