RARE EARTH ELEMENT CYCLING IN THE PORE WATERS OF THE BERING SEA SLOPE (IODP EXP. 323)

Abstract

We studied the diagenetic behavior of rare earth elements in a highly productive passive margin setting of the Bering Sea Slope. Pore water concentrations of fourteen REEs were determined to a depth of ~140 meters below seafloor (mbsf). Site U1345 was drilled during the Integrated Ocean Drilling program (IODP) Expedition 323 at a water depth of 1008 m presently in the center of an oxygen minimum zone. The concentrations of REEs were enriched in the pore water relative to deep seawater indicating that there is significant liberation from sediment during diagenesis. There was a peak at ~ 10 mbsf, which was more pronounced for the HREE, whose depth coincided with those of dissolved iron and manganese and below the sulfate-methane transition zone (~6.3 mbsf). In the upper 1 mbsf, there is a minor peak in HREE. Below ~40 mbsf, the concentration profiles were relatively constant. The positive Ce anomaly was relatively constant (average shale-normalized Ce/Ce*=1.1±0.2) throughout the depth profile indicating that Ce depletion in seawater is completely regenerated and maintained. HREE-enrichment is observed for the entire 140 mbsf except for the upper ~1 mbsf where there is MREE-bulge. REE release in the shallow depths (upper ~1 m) is attributed to preferential release of LREEs and MREEs during organoclastic reduction of Fe, Mn hydroxides in anoxic sediments. The high HREE concentrations observed Site U1345 was drilled during the Integrated Ocean Drilling program (IODP) Expedition 323 at a water depth of 1008 m presently in the center of an oxygen minimum zone. The concentrations of REEs were enriched in the pore water relative to deep seawater indicating that there is significant liberation from sediment during diagenesis. There was a peak at ~ 10 mbsf, which was more pronounced for the HREE, whose depth coincided with those of dissolved iron and manganese and below the sulfate-methane transition zone (~6.3 mbsf). In the upper 1 mbs