A TRACER STUDY OF THE FLORIDAN AQUIFER IN SOUTHEASTERN GEORGIA - IMPLICATIONS FOR GROUNDWATER-FLOW AND PALEOCLIMATE

Distributions of stable isotopes of water, radiocarbon, noble gases, a nd chloride (Cl) in groundwater from the Upper Floridan aquifer in sou theastern Georgia suggest that down gradient of the Gulf Trough this a quifer contains waters representative of both regional and local groun dwater flow systems. In this area, locally recharged waters tend to re main near the top of the aquifer and do not mix substantially with the regional groundwater flow system. Noble gas temperatures suggest that this region of Georgia was 4.0 +/- 0.6 degrees C cooler during the la st glacial period (LGP). Similar temperature changes have been reporte d for southern Texas and northern New Mexico, suggesting that the sout hern United States cooled uniformly during the LGP. Stable isotopes of water became enriched down gradient from the recharge area. These enr ichments which have been observed before appear to result from local i nflux of shallow groundwater into the regional aquifer system rather t han representing a climate change signal. An inland gradient of the st able isotope composition (0.60 +/- 0.14 parts per thousand/100 km in d elta(18)O) was found in young (Holocene) water. After correcting for t he change in the stable isotope composition of the ocean during the LG P, water that was recharged during the LGP was found to be slightly de pleted in stable isotopes relative to modern recharge (Delta delta(18) O = 0.6 +/- 0.4 parts per thousand). Assuming the modern inland gradie nt, the change in delta(18)O is consistent with a shift in the coastli ne, which was caused by the lower sea level during the LGP.