Re: Is the Pacific Ocean at the same altitude as the Atlantic?

Hi Greg,

The answer depends on whether you're more interested in the Panama Canal, or more interested in sea-surface height.

If you're primarily interested in the Panama Canal or the engineering of the Panama Canal, the answer is that the canal itself is not at sea level. For instance, one of the two natural lakes which are part of the canal is 26 m (85 ft) above sea level (The Concise Columbia Encyclopedia, Columbia University Press, 1995). So the locks prevent the water in the canal from draining out both sides into the oceans.

If you're interested in sea-surface height in general, there's a lot to tell. Water does seek its own level, but in the oceans, it might be better to say that water is always seeking its own level; that is why it is always moving. Wind, uneven surface heating and cooling, evaporation and precipitation, and tidal effects all conspire to constantly un-level the oceans. If all these factors stopped and let the ocean settle down, it would eventually come to rest at sea-level. We can learn a lot about currents from knowing how far the sea-surface is from level at any point. This difference, which can be a meter or more, was impossible to measure until recently. Now, satellites such as TOPEX/Poseidon can measure the height of the sea surface from space, to within a few centimeters! More information about how this information is used in oceanography, as well as images of global sea-surface height, can be found at the TOPEX/Poseidon web site. As those images show, the height of the Pacific relative to the Atlantic depends on where in each ocean you are, and on the time of year, the vagaries of the weather, etc.

By the way, sea-level is not level! Because of variations in Earth's gravitational field, if the ocean were at rest, its surface would vary from a perfect ellipsoid by more than 50 meters in either direction. This surface is called the geoid, and a picture of it is available on the web.

Dan Goldner
goldner@mit.edu
MIT/Woods Hole Joint Program in Oceanography