Diatoms spread a high εNd-signature in the North Pacific Ocean

Copyright © 2014 by The Geochemical Society of Japan. columns in the North Pacific Ocean (Akagi et al., 2011). The surface concentrations of dissolved REEs, expressed as “leftover”, in any oceans have been well explained by the diatom-incorporation theory (Akagi, 2013). Briefly, in this theory, a surface-to-deep concentration ratio is smaller in the Pacific Ocean than in the Atlantic Ocean, because the portion of REEs complexed with silicic acids is greater in the silica-rich Pacific Ocean, and thus more effectively incorporated in diatom frustules together with dissolved silica. This theory also derives the equation of distribution coefficients of REEs in diatom opal to predict the REEs concentration in diatom frustules in any ocean. The surface-to-deep concentration ratio explained by the theory implies that diatom frustules should be the dominant vertical carrier of REEs in all oceans except the Arctic Ocean, where no/small vertical gradient in the REE profiles is seen, resulting from the absence of dissolved silica throughout the water columns. The study also implied the presence of unknown input of REEs to diatom frustules to satisfy the steady-state condition, indicating the presence of unknown sources of REEs in surface water (Akagi, 2013). The conclusion of model studies (Arsouze et al., 2009; Rempfer et al., 2011) is challenged by the idea of input in surface water by Akagi (2013) and Nd isotope dynamics of diatom silica frustules needs to be assessed. Diatoms spread a high eNd-signature in the North Pacific Ocean