The rhenium isotope composition of Atlantic Ocean seawater

The concentrations and isotopic compositions of rhenium are presented from seawater samples obtained from the primary station for the Bermuda Atlantic Time Series Study in the North Atlantic Ocean and from the 40 degrees S UK GEOTRACES expedition in the South Atlantic Ocean. Salinity-normalized Re concentrations in both locations range between similar to 6.8-7.7 ppt between 50-5000 m depth, consistent with previously published concentration data from the North Atlantic and North Pacific Oceans. Rhenium isotope values (expressed as delta Re-187/185 relative to NIST 3143) exhibit minimal variation around an average value of -0.17 +/- 0.12 parts per thousand (n = 12, 2 S.D.), irrespective of water depth or water mass. These results confirm that the isotopic composition of perrhenate (ReO4-) in seawater is uniform. The new data establish a baseline for evaluating the isotopic mass balance of Re, and for future assessments of whether this global cycle can be disturbed by changes in seafloor redox and/or global weathering rates. (C) 2020 Elsevier Ltd. All rights reserved.