RESULTS

Uranium concentrations for the samples are uniformly high, ranging from 2.6 to 4.4 ppm (Table 3). Thorium-232 concentrations range from 23 to 98 ppb and are sufficiently low that corrections for scavenged Th remain reasonably small. The uppermost sample from each core has ²³⁴U(0) values close to the modern seawater value of 149 (Stirling et al., 1995). Deeper samples from Sites 1005 and 1006 show a general decrease in ²³⁴U(0) with depth, while samples from Site 1007 and particularly Site 1003 show more scatter and are close to the secular equilibrium value of zero. Three samples from Site 1003 have ²³⁴U(0) of less than zero.

Measured (²³⁰Th/²³⁸U) ratios are low for the uppermost sample in each core (0.1-0.3). With the exception of Sample 6-2 with a ratio of ~0.7, all other samples have (²³⁰Th/²³⁸U) greater than 0.97. For samples from Sites 1003, 1006, and 1007, the values are generally close to 1.0, but for deep samples from Site 1005, (²³⁰Th/²³⁸U) values are all significantly greater than 1.0, ranging to 1.2.

Raw U-Th ages calculated from this data are shown in Table 3, together with ages corrected for initial ²³⁰Th scavenged from seawater by assuming a ²³²Th/²³⁰Th atom ratio for seawater of 12,000 ± 6,000. This range of values easily incorporates observed values of the ²³²Th/²³⁰Th ratio for seawater from close to the Bahamas (Hoff et al., in press) and also fits with initial ²³²Th/²³⁰Th ratios calculated from modern Bahamas sediment (Slowey et al., 1996). The uncertainty in the value of the ratio used to make this correction introduces error to the final corrected age, which in most cases is larger than the analytical uncertainty.

Corrected ages for the uppermost sample from each site are <25 ka and yield ²³⁴U(T) values close to modern seawater. Sample 6-2 gives an age of 109 ka and also yields a ²³⁴U(T) close to modern seawater. All other samples either do not yield ages, or return ages that are older than 280 ka with ²³⁴U(T) values very different from modern seawater.