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Crescent Beach Submarine Spring main view
Crescent Beach Submarine Spring
St. Johns County
Crescent Beach Submarine Spring is at least a second-magnitude spring. The spring is situated 59 feet below the surface of the Atlantic Ocean, and the spring boil can be seen at the sea surface on a calm day. The sea floor around the spring is level. However, numerous subsurface structures appear around the area of the spring (Kindinger 2000).
The interpreted seismic reflection profile reveals a well-defined vent feature that appears to have been developed and maintained from submarine discharge of artesian water (Swarzemski et al. 2001).
The profile also reveals multiple large collapse features directly adjacent to the Crescent Beach spring vent, as indicated by the presence of a series of fractures. The density difference between the freshwater discharges from the spring and seawater can be seen in the seismic reflection profile of the water column. The spring appears to be a recent, incised spring vent rather than a collapse structure. The northern side of the vent is higher than the southern side. For a more complete discussion of the seismic profiling and the visual scuba observations, the reader is directed to Brooks (1961) and Kindinger (2000).
No actual discharge measurements have been done at Crescent Beach Submarine Spring. Brooks (1961) estimated the discharge by two methods. Based upon the estimated volume of water rising to the surface, a maximum possible discharge of 1,500 cubic feet per second (cfs) was estimated. Based upon the mixing ratio of spring water to seawater, a discharge of 40 cfs was estimated. All in all, Brooks estimated that “true discharge is certainly between 10 cfs and 300 cfs.”
Crescent Beach Submarine Spring was sampled by St. Johns River Water Management District in 1995. Divers from the Jacksonville Reef Research Team, Continental Shelf Associates, and the U.S. Geological Survey assisted in the sampling of the spring. A sand point was attached to a weighted, vinyl tubing. Divers inserted the sand point into the sediment at the bottom of the spring, and the water was pumped through tubing for sample collection. The water quality data for selected variables are shown in the table below.
Summary statistics of water quality data at
Crescent Beach Submarine Spring
|Crescent Beach Submarine Spring||Value||Period|
|Alkalinity, total, mg/L as CaCO3||129.0||1995|
|Calcium, dissolved, mg/L as Ca||296.0||1995|
|Chloride, total, mg/L as Cl||3630.0||1995|
|Fluoride, total, mg/L as F||0.77||1995|
|Magnesium, dissolved, mg/L as Mg||252.00||1995|
|Potassium, dissolved, mg/L as K||64.10||1995|
|Sodium, dissolved, mg/L as Na||2040.00||1995|
|Specific conductance, field, µmhos/cm at 25°C||13010||1995|
|Specific conductance, lab, µmhos/cm at 25°C||11920||1995|
|Sulfate, total, mg/L as SO4||816.0||1995|
|Total dissolved solids, mg/L||7460||1995|
|Water temperature, °C||28.7||1995|
mg/L = milligrams per liter
cfs = cubic feet per second
Age of discharge water
The age of water discharging from Crescent Beach Submarine Spring was determined by measuring the concentrations of delta carbon-13 and carbon-14 in the spring discharge in August 1995. Crescent Beach Submarine Spring had a delta carbon-13 value of –5.22 parts per thousand and a carbon-14 concentration of 14% modern carbon, which suggests that the water is approximately 10,450 years old. The age of the water suggests that Crescent Beach Submarine Spring has a deep flow system and a regional area of influence.