10Be in Ocean Sediments as an Indicator of past Changes in Cosmic ray Flux Produced by Terrestrial and ExtraterrestrialProcesses

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There is increasing evidence that the geomagnetic dipole moment was less than one half of its present value prior to 15,000 B.P. This would lead to an increase in 10Be and 14C production by 40%. Short term variations in the cosmic ray flux are also thought to have occurred. For example, two spikes in 10Be concentrations in the Vostok ice core from Antarctica have been found. It seems unlikely that they were formed due to a change in climatic conditions. The increase of 10Be is probably due to an increase in production of 10Be due to increased cosmic ray activity in the atmosphere induced by supernovae or geomagnetic excursions. A hemipelagic sediment core from the Blake Outer Ridge and a varved sediment core from the Gulf of California offer a good opportunity to observe variations in 10Be and 14C production during the last 100,000 years because of continuous, constant, and high rate of sedimentation on the cores. Ocean sediments should provide an important archive of data concerning changes in 10Be production. Unlike the ice cores, the ca. 300-year residence time of 10Be in the sea minimizes local variations due to climate. Correlation of 10Be "events" between both cores should establish whether the events are of worldwide or local origin. In addition, paleomagnetic data have already been measured in the cores making correlation possible with the 10Be production curve. Sedimant samples are to be analyzed for 10Be and 14C at the TAMS facility at the University of Arizona. 9Be will be measured by atomic absorption spectrophotometry. Reservoir models will be evaluated to define the nature of the event.