FN Archimer Export Format PT J TI Ge and Si isotope signatures in rivers: A quantitative multi-proxy approach BT AF BARONAS, J. Jotautas TORRES, Mark A. WEST, A. Joshua ROUXEL, Olivier GEORG, Bastian BOUCHEZ, Julien GAILLARDET, Jerome HAMMOND, Douglas E. AS 1:1;2:1;3:1;4:2;5:3;6:4;7:4;8:1; FF 1:;2:;3:;4:PDG-REM-GM-LCG;5:;6:;7:;8:; C1 Univ Southern Calif, Dept Earth Sci, Los Angeles, CA 90089 USA. Ctr Brest, Inst Francais Rech Exploitat Mer, Technopole Brest Iroise, F-29280 Plouzane, France. Trent Univ, Water Qual Ctr, Peterborough, ON K9L 1Z8, Canada. Univ Paris Diderot, Sorbonne Paris Cite, IPGP, CNRS, F-75231 Paris, France. C2 UNIV SOUTHERN CALIF, USA IFREMER, FRANCE UNIV TRENT, CANADA UNIV PARIS 07, FRANCE SI BREST SE PDG-REM-GM-LCG IN WOS Ifremer jusqu'en 2018 copubli-france copubli-univ-france copubli-int-hors-europe IF 4.637 TC 24 UR https://archimer.ifremer.fr/doc/00460/57196/59370.pdf LA English DT Article DE ;germanium;silicon;isotopes;rivers;weathering;fractionation AB Solutes derived from the dissolution of silicate minerals play a key role in Earth’s climate via the carbon and other biogeochemical cycles. Silicon (Si) is a unique constituent of silicate minerals and a biologically important nutrient, so tracing its behavior in near-surface environments may provide important insights into weathering processes. However, Si released by weathering is variably incorporated into secondary mineral phases and biota, obscuring signals derived from primary weathering processes. Due to chemical similarities, Germanium (Ge) may help better understand the Si cycle and its relationship to chemical weathering. With this aim, we report new measurements of the concentration and isotopic composition of Ge for both the dissolved and particulate phases of a variety of global rivers. These measurements are combined with analyses of concentration and isotopic ratio of Si on the exact same sample set in order to make direct comparisons of the behavior of these two elements in natural river systems. With this dataset, we develop a new modeling framework describing the full elemental and isotopic systems of these solutes in rivers (i.e., Ge/Si, δ74Ge, and δ30Si). This multi-proxy approach allows us to ascertain the relative importance of biological versus mineral uptake in modulating the fluxes of these elements delivered to the modern ocean. Dissolved δ74Ge composition of rivers studied thus far range from 0.9 to 5.5 ‰ with a discharge-weighted global average of 2.6±0.5 ‰. The Ge isotope composition of riverine suspended and bedload sediments is indistinguishable from silicate source rocks, which is consistent with mass balance expectations. The multi-proxy modeling suggests that, among the watersheds studied here, the isotopic fractionation of Si during secondary mineral phase precipitation (∆30Sisec) ranges from -2.7 to -0.2 ‰, which removes between 19-79% of the initial dissolved Si sequestration, while between 12-54% is incorporated by biota. For Ge, modeling indicates that 79-98% of the dissolved load is incorporated into secondary mineral phases with a ∆74Gesec ranging from -4.9 to -0.3 ‰. The fractionation induced by biological uptake is calculated to range from -2.6 to -1.3 ‰ for ∆30Sibio and -0.7±0.7 ‰ for ∆74Gebio. In addition to improving our understanding of the coupled Ge and Si cycles, our study provides a framework for using multiple isotopic tracers to elucidate the chemical behavior of solutes in natural waters PY 2018 PD DEC SO Earth And Planetary Science Letters SN 0012-821X PU Elsevier Science Bv VL 503 UT 000449246100019 BP 194 EP 215 DI 10.1016/j.epsl.2018.09.022 ID 57196 ER EF