Rare earth elements in the North Atlantic, part II: Partition coefficients
International audience This study presents the first basin scale section of the partition coefficients (Kd) of 14 rare earth elements (REE)along the GEOVIDE (GEOTRACES GA01 cruise) transect, in the subpolar North Atlantic (May–June 2014, R/VPourquoi Pas?). Although Kd data are very scarce in the lit...
Published in: | Chemical Geology |
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Main Authors: | , , , , |
Other Authors: | , , , , , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2024
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Subjects: | |
Online Access: | https://hal.univ-brest.fr/hal-04674291 https://hal.univ-brest.fr/hal-04674291/document https://hal.univ-brest.fr/hal-04674291/file/1-s2.0-S0009254124003784-main.pdf https://doi.org/10.1016/j.chemgeo.2024.122298 |
Summary: | International audience This study presents the first basin scale section of the partition coefficients (Kd) of 14 rare earth elements (REE)along the GEOVIDE (GEOTRACES GA01 cruise) transect, in the subpolar North Atlantic (May–June 2014, R/VPourquoi Pas?). Although Kd data are very scarce in the literature, it is a key parameter of element cyclemodeling, controlling the scavenging efficiency by particles. Because of this lack of data, Kd are generallyadjusted in the models to obtain the best agreement between modeled and observed concentrations. Thisshortcoming likely contributes to make the modeling of the oceanic REE cycles challenging. This is well illus-trated by the difficulty to satisfactorily simulate both Nd concentrations and isotopic compositions.Here, we determined Kd(REE) at 10 stations, calculated from previously published dissolved and particulateREE concentrations, and from suspended particulate matter (SPM) concentrations. The data required for thecalculation of SPM concentrations were obtained in the framework of the GEOVIDE cruise. Kd profiles displayedminimum values at the surface, variations in the upper 400 m, and an increase with depth below 400 m. Theexpression of the ratio of particulate to dissolved REE concentrations as a function of SPM concentrations showedthat manganese oxides (MnO2) were the main driver of REE scavenging, followed by the lithogenic phase andiron hydroxides (Fe(OH)3). Our study also highlighted that REE scavenging preferentially depended on therelative proportion of these three phases rather than on their absolute concentrations. These conclusions wereevaluated by a Pearson correlation test, with correlation coefficients of 0.83, 0.84, and 0.75 between Kd(Nd) andthe MnO2, lithogenic, and Fe(OH)3 fractions, respectively.Finally, we proposed two Kd(Nd) parameterizations as a function of the particulate phase fractions. The firstparameterization included MnO2 and Fe(OH)3, phases that are currently not represented in Nd cycle models, andshowed a good agreement between ... |
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