Protactinium determination in manganese crust VA13/2 by thermal ionization mass spectrometry (TIMS)

Here we present the first high precision (231)Protactinium measurements in a manganese crust applying thermal ionization mass spectrometry (TIMS) using the double filament technique. The detection limit using TIMS is at least one order of magnitude lower, the statistical uncertainty 6-8 times better than for alpha-spectrometry. Thus, older sections of manganese crust VA13/2 from the Northern Equatorial Pacific could be measured precisely for their Pa-231 activity. Our results reveal significant Variations in Pa-231(xs) activity for the last 150 ka which corroborate existing alpha-spectrometric data. If the growth rate was constant between 0 and 450 ka, the protactinium flux from the water column into manganese encrustations must have been variable. Thus, 231Pa(xs) is not suitable for dating marine Mn/Fe deposits. (C) 1999 Elsevier Science B.V. All rights reserved.