Data report: dissolved rare earth elements (REEs) in the pore fluids of Sites U1378, U1380, U1381, and U1414 drilled during IODP Expeditions 334 and 344

Abstract

In this report, we present the concentrations of dissolved rare earth elements (REEs) in pore fluids recovered during International Ocean Discovery Program (IODP) Expeditions 334 and 344 from the active margin of Costa Rica. We measured dissolved REEs at three sites on the Costa Rica margin: Sites U1378/U1380 on middle slope of the continental margin and Sites U1381 and U1414 on the incoming Cocos plate. Pore fluids recovered from these cores were filtered and acidified after sampling and stored until the dissolved REEs could be measured directly using an automated chromatography preconcentration system attached to an inductively coupled plasma–mass spectrometer at Oregon State University. At Sites U1378/U1380 on the continental slope, the measured REE concentrations in the pore fluid were variable in the upper 200 meters below seafloor (mbsf), ranging from 9 to 162 pM, 24 to 120 pM, and 29 to 145 pM for La, Dy, and Yb, respectively, representing the light, middle, and heavy REEs. Deeper than 200 mbsf at Sites U1378/U1380, measured concentrations decreased from 100 to 17 pM, 10 to 4 pM, and 50 to 10 pM for La, Dy, and Yb. At Site U1381 on the incoming Cocos plate, measured concentrations peaked at 192 (La), 43 (Dy), and 74 pM (Yb) at 20 mbsf. Deeper than 80 mbsf, measured concentrations increase, particularly for the light and middle REEs, with averages of 273 (La), 38 (Dy), and 26 pM (Yb). At the second site on the incoming plate, Site U1414, measured REE concentrations peak in the upper 75 mbsf and return to relatively constant values deeper than 75 mbsf. Peak concentrations of 834 (La), 223 (Dy), and 207 pM (Yb) are followed by average concentrations of ~25 (La), ~10 (Dy), and ~20 pM (Yb) deeper than 75 mbsf. Dissolved REE concentrations in the pore fluids were normalized to Post-Archean Australian Shale (PAAS) to evaluate relative abundances of light, middle, and heavy REEs. For all three sites, normalized concentrations show a greater abundance of heavy REEs relative to light and middle REEs. The trend for this greater relative abundance of heavy REEs is greatest for the upper portion of the sediment and becomes less pronounced downcore.