ALBERT

Description: The possibility of using the 15% excess U234 activity in oceanic uranium for dating pelagic sediments in the age range 100,000 years to more than 1 m.y. has been explored. Results from a series of analyses of bulk samples, mechanical separates, and acid leach fractions indicate that separation of authigenic uranium from detrital uranium by either mechanical or chemical means is impractical. Measurements on totally dissolved samples reveal that the sediments do not form a closed system; post-depositional migration of U234 in the sedimentary column takes place. Based on the experimental data obtained from three red-clay cores with sedimentation rates ranging from 2 to 6 mm/1000 yr, a model depicting diffusion of the U234 generated within the sediments is proposed. The diffusion equation includes three parameters: sedimentation rate, diffusion coefficient for U234, and fraction of the internally produced U234 subject to mobility. If the amount of U234 lost from these cores is typical, a sizeable part of the U234 excess in the sea must be from this source.

Description: The steady motion of a liquid drop in another liquid of comparable density and viscosity is studied theoretically. Both inside and outside the drop, the Reynolds number is taken to be large enough for boundary-layer theory to hold, but small enough for surface tension to keep the drop nearly spherical. Surface-active impurities are assumed absent. We investigate the boundary layers associated with the inviscid first approximation to the flow, which is shown to be Hill's spherical vortex inside, and potential flow outside. The boundary layers are shown to perturb the velocity field only slightly at high Reynolds numbers, and to obey linear equations which are used to find first and second approximations to the drag coefficient and the rate of internal circulation.

Description: The Jeffreys-Bullard theory of the topographic correction to geothermal gradients cannot be applied with confidence if the height of the relief is large relative to the horizontal distance and depth of the measurement points. It cannot be generally applied to shallow probe measurements in the ocean bottom if bold relief occurs on a scale exceeding a few meters, or on continents to observation in shallow boreholes in extremely rugged terrain. In an important special case, where the measurement depth is small relative to the distance to the relief, the ‘superficial’ gradient anomaly may be approximated by the value applicable at zero depth. A fairly general two-dimensional steady-state theory for this case can be based on the solution for heat flux through an inclined plane of arbitrary height and slope angle. These two parameters are easily visualized and represented graphically so that models which approximate or bracket real topography can be identified quickly. The results can be applied to stations on planes, valleys, ridges, or benches bounded by irregular slopes. They are valid for points arbitrarily close to slopes of any height or inclination. Finite slope and curvature of the surface at the station can be accommodated if they are not too great. Even if other theories of the topographic correction are applicable, the present method can be useful, as it leads to rapid estimates by graphical means and to useful limits even if the superficial condition is not satisfied. Curvature in an ocean-bottom temperature profile justifies suspicion of a topographic disturbance from undetected relief. The temperature probe's length should be 2 or 3 times the uncertainty in local elevation difference, and measured curvature should be negligible for reasonable assurance that undetected relief is not causing gradient errors greater than ±10%. Relief not detectable with conventional echo sounders, but of the type observed with deeply towed sounding equipment, can cause heat-flow anomalies of 50–100%, and relatively little curvature will be indicated by probes a few meters long. The very high oceanic heat flows are difficult to explain by undetected relief, but the very low ones are not.