I have done some rough calculations and simulations for questions concerning evaporation of the Gulf of Mexico and sea level.
Surface area of Gulf of Mexico: 15 million square km
Estimated depth evaporation rate: 1 meter/yr
Estimated volume evaporation rate for Gulf of Mexico: 1.7 trillion liters/hr
Normal volume flow of Mississippi R.: 23 billion liters/hr
An est. volume flow of Amazon R: 300 billion liters/hr
I have included flows of large rivers for comparison with the evaporation rate. So, for example, the flow of about 100 Mississippi Rivers are needed to compensate evaporation in the Gulf of Mexico. Only about 5 or 6 Amazon Rivers would be needed. It is stated that the Amazon flow represents about 20% of all the fresh water flowing into the oceans on earth. So given somehow that the Gulf of Mexico could be isolated from the oceans, I estimate it could take anywhere between 700 to 2100 years for the water level of the Gulf of Mexico to drop about 2000 ft due to evaporation, depending on the amount of water flowing from rivers, reduction of surface area, etc.
To isolate the Gulf of Mexico as it now stands seems to require essentially damming the lengths of the straight of Florida and the Yucatan channel. Each of these run about 200 kms shortest distance between land masses. BTW - this does not seem out of reach of immense human possibilities if we ever wanted to make a man-made dam:)
The depths of these I have been unable to determine exactly, but I estimate they could average anywhere between 2000 to 3500 ft. Is it possible that they are less, or that there is a path which is less, or perhaps there was smaller lengths due to since dissipated land mass?
This is all towards determining whether or not it could have been possible that the Gulf of Mexico was isolated or partially isolated enough so it could have a water level lower by approximately 2000 ft below today's sea level.
To get an idea of the competition between evaporation and inflow through ocean channels, e.g. through the straight of Florida, I have calculated some scenarios using a quasi-steady Bernoulli-like flow model. This allows consideration of the width and depth of channels connecting the Gulf of Mexico to the ocean with the Gulf of Mexico at a lower level than the ocean. This has assumed a drop at the channel.
1) Assume current effective channel width of 400 km, and try to maintain a difference of 2000 ft. The pressure is about 1000 psi. This is unsustainable from evaporation. It would take only about three days for the difference to decrease by 1000 ft.
2) Determine the maximum width of the channel and water level difference necessary to maintain an equilibrium with evaporation, ignoring additional inflow from rivers.etc:
Channel width Equilibrium difference in level ------------------
-------------------------
-------- 400 km .................. 41 cm
200 km .................. 65 cm
40 km ................... 1.9 m
4 km .................... 8.8 m
1 km .................... 22 m
0.5 km .................. 35 m
7 m ..................... 2000 ft
3) Given the width of the channel, determine the change of the level with time for a variety of initial levels. This allows the possibility to determine time dependant scenarios, e.g. given some catastrophic or otherwise sudden event leaving the gulf very low, could the rise to equilibrium have been slow enough to take a long time >100 yrs? Or given that the channel width was decreased by some event, how long would it take to drop the level? I have attached a series of red arrow flow graphs showing the result with certain inital conditions as lines. These graphs are of the difference between sea level and gulf level in units of centimeters on the vertical scale and units of hours on the horizontal scale. The difference between sea level and gulf level means that a positive increase on the graph represents a lowering of the relative level of the gulf. Each is titled according to the width of the channel in kilometers. Note that the scale of the axis does change from graph to graph.
The summary from graphs is essentially the gulf fills up pretty quickly away from equilibrium except for the smallest channel widths less than 4 km. The symmetry from above and below equilibrium is interesting and useful for analysis. An isolation event creating a channel 4km will take about 6 years to drop the gulf by half its equilibrium level of 8.8 meters below sea level. Even a 0.5 km channel will take only about 25 years to reach half its equilibrium value of 35 meters. A 50 meter channel takes about 100 yrs to drop halfway to its equilibrium drop of about 160 m. As shown by the fact that only a 7 meter wide channel can sustain 2000 ft indefinitely, the only way to have sustain such large diifferences in depths is to have a very narrow channel - or of course, no channel at all.
(Frankly, I was suprised to hear anymore about this subject but, they apparently were pretty excited about the prospect. This is just a small sampling of the correspondense on this subject. I did not include all the charts and graphs. This communication refers to the Gulf Of Mexico somewhat isolated but with a deep channel to the ocean.)
Figure 1 gives a topographic map of the sea floor in the Yucatan Straits. It is about 2000 meters deep.
Your calculations don't include an estimate of precipitation over the Gulf of Mexico. The net evaporation may be a lot smaller than 1 m/yr.