The oceans are anything but level
The lay person imagines that, since all the world’s oceans are interconnected, they must all be at the same height – sea level. While that assumption is true on the small scale, it is fallacious on the world-scale. Ignoring waves and tides, the oceans have different levels, and the levels vary within an ocean. The causes of these different levels are numerous. First, the earth is not a perfect sphere, or even a perfect ellipsoid. Rather, it is a lumpy rock. Heavy material is not evenly distributed, resulting in variations in the effects of gravity. Ocean currents, such as the Gulf Stream, cause regional accumulations or diminishments of water. Thus, sea level in Bermuda (in the middle of the Gulf Stream) is almost one meter higher than sea level in Charleston, South Carolina (which is outside of the Gulf Stream’s flow). Salinity is a significant factor. The higher salinity (and density) of the Atlantic Ocean is a major reason that its level, on average, is 20 cm lower than that of the Pacific Ocean. The height difference at the Isthmus of Panama is 10cm, making a true “sea level” canal a physical impossibility. Temperature causes water to expand and become lighter. Sea water in warmer climes has a higher level (all other things being equal) than does water in cooler regions. As with many other subjects, on close examination sea level is much more complex than it first appears.