Geologists are aware that the level of the ocean surface is not fixed, but
instead a dynamic feature of our planet. Sea-level during the Last Glacial
Maximum (LGM, 20,000 years ago) was 125 - 130 m lower than it is at the present
time. The image below shows the modern margin of the Gulf of Mexico.
Using digital elevation data, geologists can develop maps showing the continental
margins during episodes of lowered sea-level. The image below shows the margin
of the Gulf of Mexico and other parts of the western Atlantic (a portion of
Cuba and the Bahamas) as they would have appeared 20,000 years ago during
the sea-level lowstand. Note that large areas of the continental shelf and
the Bahamas platforms are exposed well above sea-level.
Geologists can also model sea-level rise using the same types of digital
data. In the view below, sea-level is 15 m higher than at present. Note the
dramatic change in the outline of the Gulf of Mexico as much of south Florida
is inundated. Also note that the Bahamas are completely submerged, and a narrow
strip of land is all that remains of Cuba.
To learn more about sea-level changes and the geologic processes that shape
coastal areas, read chapter 14 of your textbook.