REORGANIZATION OF GROUNDWATER FLOW DURING SEA LEVEL RISE

The distribution of dissolved noble gases, delta O-18, radiocarbon, and TDS indicates four distinct groundwaters can be found in the Floridan Aquifer System in south Florida. These water masses consists of Holocene age saltwater, Holocene age freshwater, last glacial period freshwater and mixed groundwater with locations best explained by a reorganization of groundwater flow following a rise in sea level. During the low sea level stand of the last glacial period, the entire Floridan Aquifer System was filled with meteoric water. After sea level rose, the increased hydraulic head of the ocean trapped last glacial period freshwater within this system. Most of the groundwater that presently exists in the upper portion of the Floridan aquifer system and is withdrawn by the large coastal cities of South Florida for water supply purposes was recharged during the last glacial period. As sea level rose, the increased ocean water head also initiated saltwater circulation in the lower Floridan aquifer. Today this aquifer is nearly entirely filled with Holocene age saltwater that is geochemically similar to the Straits of Florida bottom water, where ocean water is known to enter the aquifer off of the continental shelf. The saline water has been altered slightly by mixing with last glacial period freshwater that is present within the lower Floridan aquifer.