West Florida Continental Shelf Research Articles

Geothermal springs of the West Florida continental shelf: Evidence for dolomitization and radionuclide enrichment

On the sea bed of the West Florida continental shelf about 45 km SSW of Ft. Myers, Florida, an 85-km 2 area has been discovered in which six thermal springs discharge warm, chemically altered seawater from vents and seepage zones. The spring water apparently originates in the subsurface ocean around the Florida Platform and penetrates the highly porous strata of the platform about 500–1000 meters below sea level. It percolates toward the interior of the platform and is geothermally heated to about 40°C en route. Then it rises along more vertical flow channels and is discharged in warm submarine springs. Beneath the platform, several chemical processes alter the percolating seawater. One process seems to be a secondary dolomitization of the limestone of the platform because, in the discharging seawater, magnesium is lower by 2.7 mmole/kg and calcium higher by 3.6 mmole/kg than in normal seawater with the same chlorinity. Other reactions within the sediments of the platform enrich the spring effluents 1000-fold in 226Ra, 10,000-fold in 222Rn, and 90-fold in 228Ra compared to the seawater surrounding the platform. Thus, the springs may be important sources of radionuclides for the Gulf of Mexico. The percolating seawater also loses all of its oxygen and nitrate to reduction processes, loses most of its phosphate and 40% of its 238U, and roughly quadruples its silica content. Coastal carbonate platforms are fairly common geological features. Thus, processes like those beneath the West Florida Shelf may function on a world-wide basis to play an important role in the diagenesis of carbonate sediments.

The landward distribution of oceanic plankton and micronekton over the west Florida continental shelf as related to their vertical distribution

The landward distribution of oceanic plankton and micronekton over the west Florida continental shelf as related to their vertical distribution

Some Observations of Baroclinic Diurnal Tides over a Near-Critical Bottom Slope

Abstract The time-depth structure of the baroclinic diurnal tide has been examined with the aid of current and temperature profiles on the West Florida Continental Shelf. Of interest is the fact that the diurnal frequencies (e.g., the K1 and O1 tides) are near the “critical frequency” corresponding to the bottom slope and density stratification at the experimental location. The baroclinic semidiurnal tide was rather weak and most of the semidiurnal tidal energy was contained in the barotropic currents. This large ratio of barotropic-to-baroclinic, semidiurnal tidal energy is in agreement with the results obtained by Koblinsky (1979) from previous (current meter) measurements in the same area. In contrast, the baroclinic diurnal tide is quite strong and exhibits appreciable structural variations with time. The diurnal oscillations are predominantly of low vertical modal order, and there is no evidence of the concentrated “beams” of internal tidal energy which have sometimes been observed in other areas (e....

Magnetic Anomalies and Crustal Structure in Eastern Gulf of Mexico

A marine magnetic survey made during 1965 has led to the construction of an anomaly map of the total magnetic field in the eastern Gulf of Mexico. Elongate anomalies with northeast-southwest trend characterize the northern part of the west Florida continental shelf. Anomalies indicative of volcanic-type source rocks lie within a 180-kilometer-wide strip across the central part of the west Florida shelf; it is inferred that a belt of volcanic rocks trends northeast-southwest across Florida, the west Florida shelf, and the abyssal plain to the Campeche Scarp. The eastern Gulf is thus dominated by northeast-southwest (commonly called Appalachian) structural trends in the basement. Depth to the basement in the marine volcanic province is estimated, from the magnetic anomali s and from available seismic refraction evidence, probably to be not much less than 9 kilometers. The west-central part of the map is devoid of large magnetic anomalies and probably corresponds with oceanic-type crust under thick sedimentary cover. North of the eastern part of the Campeche Bank a large negative magnetic anomaly strikes ESE.-WNW. This feature may indicate a synclinal downwarp in the oceanic crust there; it is shown that the theoretical anomaly for a syncline of triangular section fits the observations whereas a graben does not. There is no magnetic expression of the steep escarpment which terminates the west Florida shelf; this suggests that there is no basement faulting at the scarp involving the magnetic source rocks.