26AI and 10Be: Oceanic Fractionation and Tracer Utilities

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9633469 KU Radioactive 26Al (half-life 0.7 My) and 10Be (1.5 My) on the earth are produced by the interaction of cosmic rays with atoms in the atmosphere and in the surface of rocks. They enter the ocean chiefly via wet/dry fallout, with nearly constant proportions primarily reflecting their atmospheric production ratios. Although these cosmogenic radionuclides and their stable isotopes (9Be and 27A1) differ in source functions, their pathways in geochemical reservoirs are linked through the isotopic kinship. Together, these isotopes can be used as powerful time and process tracers in geophysical studies. Such tracer studies have become feasible with recent improvements made in the analytical techniques, particularly the ability to measure 26Al in marine materials. Measurements will be made of authigenic 10Be/9Be ratios in sediments, concentrations of 10Be, 26Al, and U-unsupported 230Th in sediments, suspended particulate matter and sediment-trap material, and 10Be and 7Be in sea water. These measurements will improve our understanding of the factors governing the oceanic 26Al-10Be fractionation and distribution, and facilitate our use of the sedimentary signals of 10Be/26Al to trace paleoproductivity, and 26Al/230Th to trace past variations of cosmic-ray intensity. In addition, 26Al, 10Be and 7Be will be used to evaluate particle flux variations and particle dynamics in the water column.