Characterization of settling particles in the Bering Sea and implications for vertical transportation of multiple elements by diatom frustules

To understand the contribution of carbonate, oxide, organic and siliceous matter to the vertical transportation of elements, sequential chemical leaching was applied to sediment-trap samples collected in and near the Bering Sea. A total of eleven samples representing periods of high to low opal flux were analyzed for elements in carbonate, oxide and silicate. Two samples from high and low opal flux periods were analyzed further for those in organic matter. Siliceous matter may be an important carrier for most elements (Li, Mg, Al, Sc, Ti, V, Cr, Fe, Co, Ge, As, Rb, Zr, Nb, Sn, Sb, Cs, Hf, Ta, W and Th); carbonate may be important for Na, K, Ca, Mn, Ni, Sr, Pd, Ag, Cd, Ba, Pb, Bi and U and organic matter for B, P, Cu and Ga. Carbonate, oxide and siliceous fractions almost equally contribute to transportation of Y and lanthanides (REEs). The concentrations of most elements in the siliceous fraction exhibit hyperbolic relationships against opal flux, where the asymptotes are always non-zero. The non-zero asymptotes lead to two possible interpretations. 1) Diatom frustules are pure opal; when diatom production is extremely high, it is accompanied with supply of terrigenous matter whose amount is proportional to diatom production. 2) Diatom frustules are not pure opal (SiO2), but contain significant amounts of other elements; the observed increase of elemental concentrations at smaller productivity results from selective dissolution of opal or terrigenous matter mixing. We argue that the second interpretation is more plausible, and the composition of diatom frustules is estimated as that of the silicate fraction of the high productive group, with an opal flux greater than 200 mg m−2 day−1. This indicates the potential of diatom frustules as effective vertical carriers of multiple elements.