Determination of Ra-226 concentrations in seawater and suspended particles (NW Pacific) using MC-ICP-MS
Résumé
We report vertical profiles of radium-226 (Ra-226) concentrations determined in seawater and suspended particles collected in the North-West Pacific using Multi Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS). Dissolved Ra-226 concentrations were determined in small size water samples (between 110 and 250 ml volume) with a precision usually better than 5% (internal error, two standard error, 2 sigma(m)) using a chemical protocol slightly modified compared to previous studies that provides a chemical recovery of 90%. The Ra-226 activities thus obtained are in good agreement with the Ra-226 activities determined using low-background gamma spectrometry. In this work, we report the first Ra-226 activities determined in marine suspended particles using MC-ICP-MS. We thus show that this method is very useful to determine Ra-226 concentrations in suspended particles that have been poorly studied up to now because they display very low Ra-226 activities (i.e. two orders of magnitude lower than the Ra-226 activity in seawater). Such a sensitive method can thus be used to build high-resolution vertical profiles of dissolved and particulate Ra-226 activities, which would allow us to better understand the impact of biology on the oceanic Ra cycle. (C) 2011 Elsevier B.V. All rights reserved.