Measuring production–dissolution rates of marine biogenic silica by 30Si-isotope dilution using a high-resolution sector field inductively coupled plasma mass spectrometer

François Fripiat, Rudolph Corvaisier, Jacques Navez, Marc Elskens, Véronique Schoemann, Karine Leblanc, Luc André, Damien Cardinal

Limnol. Oceanogr. Methods 7:470-478 (2009) | DOI: 10.4319/lom.2009.7.470

ABSTRACT: Regional and seasonal variability of the Si dissolution:production ratios in the surface ocean have not been well assessed. Here, we propose a new method for determining these rates, using the 30Si-isotopic dilution technique with a high-resolution sector field inductively coupled plasma mass spectrometer (HR-SF-ICP-MS). Relative analytical precision of the isotopic measurement is better than 1%, similar to that obtained by thermal ionization–quadrupole mass spectrometry (TIMS). Accuracy and reproducibility of the isotopic measurements have been checked on artificial and natural solutions by intercomparison between two HR-SF-ICP-MS instruments and one TIMS. Measurements of real Si production and dissolution rates are illustrated for two contrasted situations with an average relative precision of 10%, including one from waters with low Si content (2 µmol L–1), which required an additional purification step by cation exchange chromatography. Si production rate from this later incubation was not significantly different from the one measured by radioactive 32Si. The new method is faster and simpler than TIMS or isotope ratio mass spectrometry (IRMS). Its sensitivity is more than one order of magnitude better than TIMS, and it can cover the whole range of Si concentrations encountered in the ocean.