Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation Tristan J. Horner a,∗ , Christopher W. Kinsley b , and Sune G. Nielsen c July 9, 2015 a Department of Marine Chemistry & Geochemistry, Woods Hole Oceanographic Institution, MA 02543-1050, USA b Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge MA 02139-4307, USA c NIRVANA Laboratories, Department of Geology & Geophysics, Woods Hole Oceanographic Institution, MA 02543-1050, USA ∗ Corresponding author: Tristan.Horner@whoi.edu Highlights • First full seawater depth profile of co-located [Ba]–δ 138/134 Ba NIST • Origin of Ba-isotopic variations are best explained by barite cycling • Regional circulation strongly influences depth structure of δ 138/134 Ba NIST • Data establish a baseline of Ba-isotopic variability in the marine realm Keywords: barium; isotopic fractionation; barite; seawater; biogeochemistry