The geothermal measurements made during and after Leg 166 have provided, for the first time, quantitative constraints to the thermal regime of the western margin of the Great Bahama Bank. Conductive heat flow through the seafloor varies systematically along the drilling transect of Sites 1003 through 1007. We believe that much of this variation is caused by topographic variation. The regional background heat flow seems nearly uniform at ~43 mW/m2, a reasonable value for the tectonic setting of an old continental margin. However, we do not have any strong evidence for rejecting the possibility that background heat flow indeed decreases upslope of the bank. More reliable heat-flow data, especially from the top of the bank, are needed for further examination.
Another important finding of this study is that the thermal regime of the top 50-100 mbsf of the sediments of this area is anomalous as indicated by the curvatures of the geothermal profiles. We examined three mechanisms as the potential cause of this anomaly: (1) thermal effect of sedimentation, (2) influx of seawater into the rock formation, and (3) temporal fluctuation of BWT. We ruled out the first as the primary cause. The second mechanism may explain the thermal data from Sites 1004 and 1005 but not those from other sites, particularly Site 1006, because of the thickness discrepancy in the zones of chemical and thermal anomalies. It is more likely that the third mechanism affected Site 1006 and possibly Sites 1003 and 1007. The history of BWT fluctuation reconstructed from the Site 1006 temperature data is very similar to the surface temperature records obtained at Key West and other parts of the east coast of the North America. However, it would probably not be consistent with the BWT histories for other drill sites of Leg 166. Perhaps, making measurements from additional closely spaced boreholes in this area would further our understanding.