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Author Topic: Why are the tides in the Mediterranean so small?  (Read 23237 times)

Offline chris

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Why are the tides in the Mediterranean so small?
« on: 24/03/2011 21:06:39 »
The Atlantic coast of Portugal and Spain have large tides, but the Mediterranean has a tidal reach of only a few feet if that. Why? Wouldn't the water rushing across the Atlantic all get trapped in the Med and "build up" because there's no way out?

Chris


 

Offline yor_on

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Why are the tides in the Mediterranean so small?
« Reply #1 on: 24/03/2011 22:31:04 »
"Tides are most pronounced along the coastline of the oceans and in bays where tidal range (the difference in height between low tide and high tide) is increased due to the topography and other factors. "Tidal bulges" which are the focus of attention in many textbooks, are in fact not due to rotation, but are simply due to the gravitational field of the moon, and the fact that this field has varying direction and strength over the volume of the Earth.

These bulges distort the shape of the solid Earth, and also distort the oceans. If the oceans covered the entire Earth uniformly, this would almost be the end of the story. But there are land masses, and ocean basins in which the water is mostly confined as the Earth rotates. This is where rotation does come into play, but not because of inertial effects, as textbooks would have you think. Without continents, the water in the ocean would lag behind the rotation of the Earth, due to frictional effects. But with continents the water is forced to move with them. However, the frictional drag is still important. Water in ocean basins is forced to "slosh around", reflecting from continental shelves, setting up ocean currents and standing waves that cause water level variations to be superimposed on the tidal bulges, and in many places, these are of greater amplitude than the tidal bulge variations.""

The last from Tidal Misconceptions.
 

Offline Geezer

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Why are the tides in the Mediterranean so small?
« Reply #2 on: 24/03/2011 23:07:04 »
I think there might be a simpler answer.

The Mediterranean is really just a very big lake, big enough that it actually has tidal action, but nowhere near as much as the major oceans. It is connected to the Atlantic, but the connection is so restricted that tides in the Atlantic have little effect on the Mediterranean.
 

Offline B4Real

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Re: Why are the tides in the Mediterranean so small?
« Reply #3 on: 17/10/2016 02:24:00 »
Yup- No need calling Bill Nye for this one! 👍
 

Offline alancalverd

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Re: Why are the tides in the Mediterranean so small?
« Reply #4 on: 17/10/2016 20:02:00 »
Indeed there is no way out for the Atlantic tide. But equally, there's no way in.
 

Offline evan_au

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Re: Why are the tides in the Mediterranean so small?
« Reply #5 on: 17/10/2016 21:29:15 »
As the following map shows, the Mediterranean basin actually consists of several smaller basins, each of which have relatively small tidal range. The center of the white areas are called amphidromic points, which have effectively no tide, while the surrounding blue areas have very little tide. (Unfortunately, this map splits the Mediterranean across the left and right edges.)

https://en.wikipedia.org/wiki/File:M2_tidal_constituent.jpg

There are other, smaller tidal constituents which will have different amphidromic points, but these will also be affected by the multiple small basins in the Mediterranean.
 

Offline evan_au

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Re: Why are the tides in the Mediterranean so small?
« Reply #6 on: 18/10/2016 21:25:27 »
Another thread is talking about Chladni's plates - patterns formed when sand is sprinkled on a vibrating plate. The sand will move away from areas with high amplitude vibrations (anti-nodes), and migrate to areas with little vibration (nodes).

The amphidromic points are the places in the ocean where the amplitude of tide variation is minimal (you could call them nodes).

Of course, the mode of vibration is very different in a solid and a liquid - stiffness plays a major part in the resonances of a solid, while stiffness does not really apply to the sloshing of a liquid like the ocean or a sea.
 

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Re: Why are the tides in the Mediterranean so small?
« Reply #6 on: 18/10/2016 21:25:27 »

 

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