The Application of Thermal Ionization Mass Spectrometry to the Study of Thorium Scavenging in the Oceans

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This proposal is aimed at examining the partitioning of Th between the dissolved phase and various naturally occurring colloidal and suspended particulate surfaces. This information will be used to examine in more detail the mechanisms of scavenging. In particular, such measurements would allow for a separation of the processes of sorption onto particle surface from the aggregation and disaggregation of colloids and suspended particles. %%% Increased analytical sensitivity is needed for the proposed Th- 230 and Th-232 determinations, as traditional radiochemical analyses of these isotopes require thousands of liters of seawater. It is proposed to develop techniques which utilize thermal ionization mass spectrometry (TIMS) for these analyses. Sub-liter (for Th-232) and 1-10 liter (for Th-230) natural seawater samples could thereby be used for this study. A number of samples under differing particle regimes will be examined, ranging from vertical profiles in the open ocean, to coastal waters collected during periods of intense biological activity (spring and summer) and periods of physical resuspension (fall and winter).