ABSTRACT

The Nd and Sr isotopes of the acetic-acid-soluble, hydrochloric-acid-soluble, hydrofluoric-acid-soluble (siliceous) fractions of settling particles collected in the highly diatom productive Bering Sea were measured. The siliceous fraction exhibits ε_Nd values higher than that of the acetic acid extractable fraction or that dissolved in North Pacific seawater. Recent studies concluded that the siliceous fraction of settling particles collected in an area of extremely high diatom production consists almost exclusively of diatom frustules, that diatom frustules are a major Nd transporter in the ocean water column, and that half the Nd in diatom frustules should be supplied from an unknown input other than that diffused/advected from the deep seawater. The Nd isotope system of the siliceous fraction provides the first evidence that diatoms transport the high ε_Nd signature to the oceanic system. The unknown input is the dissolution of silicate rocks which are somehow supplied to the sea surface. In the Bering Sea one of the sources of the high ε_Nd values was identified to be island arcs. This diatom-mediated dissolution of silicate particles may be a mechanism to explain the rather pervasive island arc Nd isotope signature in the Pacific Ocean where there are surrounding island arcs.