Relative REE abundances of porewater in Pacific pelagic sediment: estimation by equilibrium calculations based on REE composition of Mn-oxide and apatite components

Abstract

In order to reveal REE mobilization in sediment during early diagenesis, we estimate the REE com- position of porewater in Pacific sediments deposited in the Equatorial area. The Pacific sediment was divided chemically into leachate � (extracted by alkaline Na2S2O4), leachate 2 (extracted by 0. � 7 M HCl) and residue. The leachate � , leachate 2 and residue consist mainly of Mn oxide, carbonate fluor - apatite (CFA), and detrital materials, respectively. The Mn oxide and CFA component are considered to provide information about REE composition of porewater. Assuming that Mn oxide and CFA in the sediment were in chemical equilibrium with the porewater in terms of REE, the REE composition (REE/ Gd ratio) of the porewater in the sediment was estimated from the REE abundance of the leachateand 2. The estimated REE pattern (REE/Gd ratio) of the porewater shows La depletion and Ce enrichment relative to the deep-seawater. The difference of REE composition between deep-seawater and porewa- ter suggests that REE in pelagic sediment is mobilized during early diagenesis.