This three-year research program is aimed at wrapping up studies of the marine geochemistry of uranium while beginning a new study of Th cycling in the ocean. the uranium work will include completing analysis of samples collected during the 1988 expedition to the Black Sea, processing sediment and pore water samples already collected from continental slopes sites off the east and west coasts of the U.S., and collecting and processing new pore water samples to quantify the contribution by colloids to the operationally defined dissolved (<0.45 micron) U concentration in pore waters. high Resolution mass Spectrometric (HRMS) studies of TH concentration and isotopic composition in the ocean will use the new VG ISOLAB 110 mass spectrometer to be installed at Lamont by the end of 1988. the high sensitivity performance of this new instrument allows for a tenfold improvement of precision, for a factor of 100 reduction of sample size and for a factor of 300 shorter measurement-time, compare to traditional alpha-counting techniques. The concentration of 232 Th will be measured as a function of size-distribution in filtered sea water samples, in order to check for the existence of the colloidal Th species (<0.4u), recently assumed by Honeyman and Santschi (1988) in their "Brownian pumping" model; and demonstrate the capability to measure 230 Th concentrations in seawater and in time-series sediment-traps sample (e.g., for GOFS) in order to evaluate the response of deep-sea scavenging to temporally variable processes in surface waters.
