Magna Tomas

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Magna
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Tomas
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  • Article
    Groundwater discharge impacts marine isotope budgets of Li, Mg, Ca, Sr, and Ba
    (Nature Research, 2021-01-08) Mayfield, Kimberley K. ; Eisenhauer, Anton ; Santiago Ramos, Danielle ; Higgins, John A. ; Horner, Tristan J. ; Auro, Maureen E. ; Magna, Tomas ; Moosdorf, Nils ; Charette, Matthew A. ; Gonneea, Meagan E. ; Brady, Carolyn E. ; Komar, Nemanja ; Peucker-Ehrenbrink, Bernhard ; Paytan, Adina
    Groundwater-derived solute fluxes to the ocean have long been assumed static and subordinate to riverine fluxes, if not neglected entirely, in marine isotope budgets. Here we present concentration and isotope data for Li, Mg, Ca, Sr, and Ba in coastal groundwaters to constrain the importance of groundwater discharge in mediating the magnitude and isotopic composition of terrestrially derived solute fluxes to the ocean. Data were extrapolated globally using three independent volumetric estimates of groundwater discharge to coastal waters, from which we estimate that groundwater-derived solute fluxes represent, at a minimum, 5% of riverine fluxes for Li, Mg, Ca, Sr, and Ba. The isotopic compositions of the groundwater-derived Mg, Ca, and Sr fluxes are distinct from global riverine averages, while Li and Ba fluxes are isotopically indistinguishable from rivers. These differences reflect a strong dependence on coastal lithology that should be considered a priority for parameterization in Earth-system models.
  • Article
    The vanadium isotope composition of Mars: Implications for planetary differentiation in the early solar system
    (European Association of Geochemistry, 2020-09-30) Nielsen, Sune G. ; Bekaert, David V. ; Magna, Tomas ; Mezger, Klaus ; Auro, Maureen E.
    The V isotope composition of martian meteorites reveals that Bulk Silicate Mars (BSM) is characterised by δ51V = −1.026 ± 0.029 ‰ (2 s.e.) and is thus ∼0.06 ‰ heavier than chondrites and ∼0.17 ‰ lighter than Bulk Silicate Earth (BSE). Based on the invariant V isotope compositions of all chondrite groups, the heavier V isotope compositions of BSE and BSM relative to chondrites are unlikely to originate from mass independent isotope effects or evaporation/condensation processes in the early Solar System. These differences are best accounted for by mass dependent fractionation during core formation. Assuming that bulk Earth and Mars both have a chondritic V isotopic compostion, mass balance considerations reveal V isotope fractionation factors Δ51Vcore-mantle as substantial as −0.6 ‰ for both planets. This suggests that V isotope systematics in terrestrial and extraterrestrial rocks potentially constitutes a powerful new tracer of planetary differentiation processes accross the Solar System.