Density-dependent groundwater flow in the Floridan aquifer system (FAS) depends on chloride concentrations and fluid temperature. Previous studies addressing the role of chloride concentration and temperatures on groundwater flow in the FAS have relied on observation data or simplified two-dimensional numerical models. A three-dimensional hydrologic analysis of FAS in peninsular Florida was performed using a modified version of SUTRA (SUTRA-MS) capable of simulating multi-species solute and heat transport. SUTRA-MS was developed during this investigation and is capable of reproducing results for several problems with known solutions.The model was developed using available geometric and hydraulic parameter data and calibrated using hydraulic head, chloride concentrations, and temperatures representative of conditions prior to significant groundwater pumpage from the FAS. The calibrated model is capable of reproducing observed pressures and temperatures but in general ov er-simulates chloride concentrations. The inability of the model to simulate observed chloride concentrations suggests chloride concentrations in the FAS are not in equilibrium with current sea level. Previous hydrologic studies of the FAS have attributed anomalous chloride concentrations to incomplete flushing of relict seawater that entered the aquifer during previous sea-level highstands.Three hypothetical, sinusoidal sea-level changes occurring over 100,000-years were used to evaluate how the aquifer responds to sea-level fluctuations. Model results indicate pressure equilibrates most rapidly and is followed by temperatures and then chloride concentrations. Confining unit thicknesses directly affect response times of pressure, temperature, and chloride concentrations in the FAS.Simulation of the system with ("geothermal case") and without ("isothermal case") the geothermal component reveals that the inflow of seawater from the Florida Straits would be similar without the heat f low but the distribution would differ significantly. The addition of heat flow also reduces the asymmetry of the circulation. Simulations evaluating aquifer responses to sea-level fluctuations and the thermal component indicate that the complicated three-dimensional setting of the FAS is a key component of the groundwater flow system and steady state conditions may not exist for relatively thick coastal aquifers that have experienced multiple sea-level cycles.