Pa and
Be
Pa and
Be
Be in dissolved and particulate phases throughout the water column
at the location of each EqPac sediment trap mooring. Annual composites of
material collected by each sediment trap will be analyzed, as will be
fine-grained particles collected by in situ filtration.
Individual time-series samples will be analyzed from the site showing the
greatest seasonal variability of particle flux. Detailed profiles of
radionuclides will be measured in the uppermost 10 to 20 cm of sediments
collected by box cores, and additional samples from dated piston cores
will be analyzed, going back to ~200 ky BP.
Th,
Pa),
Be carrier, and~1000 mg of
iron as FeCl (cleaned by extraction into isopropyl ether and back
extraction into water) are added to acidified samples and allowed to sit
for ~24 hours. Ammonia is then added to raise the pH to between 7 and 8
to induce precipitation of FeO, which carries with it the radionuclides
of interest. Precipitates are concentrated by settling. Supernate
solutions are decanted and discarded. Precipitates are shipped back to
the lab for purification of the radionuclides.Iron-hydroxide precipitates are freed of residual salts by resuspension in high purity water, and further concentrated by centrifugation. Precipitates are dissolved in redistilled HCl. Fe is extracted into isopropyl ether and discarded. The acid phase, containing the radionuclides, is evaporated by heating, with addition of HNO3 and HF. Final purification of the radionuclides is by ion exchange following a scaled-down version of the procedure described by Anderson et al. (1990). Th and Pa are measured by mass spectrometry. 10Be is measured by accelerator mass spectrometry (AMS). Uranium is not measured because its concentration in seawater can be calculated from the constant U/salinity ratio.
U,
Th and
Pa isotopic
yield monitors and
Be carrier using a mixture of HCl, HNO , HF and HClO
following the method of Fleisher and Anderson (1991). Individual nuclides are purified by ion exchange, following a
scaled-down version of the procedure described by Anderson et
al. (1990). U, Th and Pa are measured by mass spectrometry;
Be by AMS. Analysis of sediments follows the procedure of
Anderson et al. (1990), including total dissolution of
sediments and purification of nuclides by ion exchange.
Be will
be measured by AMS. At the time of this writing, it is uncertain
whether U, Th and Pa analyses will be by alpha spectrometry or by
ICP-MS.
Be and
Pa. Earth and Planetary Science Letters,
90: 287--304.