Determination of 226Ra concentrations in seawater and suspended particles (NW Pacific) using MC-ICP-MS

We report vertical profiles of radium-226 (226Ra) 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 226Ra 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, 2σm) using a chemical protocol slightly modified compared to previous studies that provides a chemical recovery of 90%. The 226Ra activities thus obtained are in good agreement with the 226Ra activities determined using low-background gamma spectrometry. In this work, we report the first 226Ra activities determined in marine suspended particles using MC-ICP-MS. We thus show that this method is very useful to determine 226Ra concentrations in suspended particles that have been poorly studied up to now because they display very low 226Ra activities (i.e. two orders of magnitude lower than the 226Ra activity in seawater). Such a sensitive method can thus be used to build high-resolution vertical profiles of dissolved and particulate 226Ra activities, which would allow us to better understand the impact of biology on the oceanic Ra cycle.