FY 1994
Excess 222Rn above the Cleft Segment of the Juan de Fuca Ridge
Gendron, J.F., J.F. Todd, R.A. Feely, E.T. Baker, and D.C. Kadko
J. Geophys. Res., 99(B3), 50075015 (1994) |
The distributions of excess Rn above the North Cleft segment of the Juan de Fuca Ridge were determined from 1988 to 1991 in order to obtain a better understanding of the temporal variability of heat flux from this ridge segment. Based on the inventories of excess Rn, the hydrothermal heat flux was estimated to be 2.7 ± 1.3 GW in 1990. The large uncertainty results from errors in calculating the standing crop of Rn, the difficulty in determining the Rn to heat ratio, and the problem of entrainment of low-temperature waters into the rising plume. The high- resolution sampling program carried out in 1990 permitted the mapping of apparent plume ages for different sections of the neutrally buoyant plume. About 3 km to the east of the ridge axis there is a sharp gradient in the apparent age of the plume, while to the west the plume appears to be younger. This plume age distribution could indicate a current flow to the northwest during the time this transect was sampled. The mean Rn/heat ratios for the high- and low-temperature vent fluids were 0.0017 disintegrations per minute (dpm) g °C and 0.0044 dpm g °C, respectively. The extrapolated end-member concentrations of excess Rn in low-temperature vent fluids are a factor of 6 greater than the high-temperature fluids, based on the regressions of excess Rn activity and Mg concentration in North Cleft segment vent fluid samples. |