TY - JOUR
T1 - Molybdenum isotope behaviour in groundwaters and terrestrial hydrothermal systems, Iceland
AU - Neely, Rebecca A.
AU - Gislason, Sigurdur R.
AU - Ólafsson, Magnus
AU - McCoy-West, Alex J.
AU - Pearce, Christopher R.
AU - Burton, Kevin W.
PY - 2018/3/15
Y1 - 2018/3/15
N2 - Molybdenum (Mo) isotopes have proved useful in the reconstruction of paleoredox conditions. Their application generally relies upon a simplified model of ocean inputs in which rivers dominate Mo fluxes to the oceans and hydrothermal fluids are considered to be a minor contribution. To date, however, little attention has been paid to the extent of Mo isotope variation of hydrothermal waters, or to the potential effect of direct groundwater discharge to the oceans. Here we present Mo isotope data for two Icelandic groundwater systems (Mývatn and Þeistareykir) that are both influenced by hydrothermal processes. Relative to NIST 3134 = +0.25‰, the cold (<10 °C) groundwaters (δ98/95MoGROUNDWATER = −0.15‰ to +0.47‰; n=13) show little, if any, fractionation from the host basalt (δ98/95MoBASALT = +0.16‰ to −0.12‰) and are, on average, lighter than both global and Icelandic rivers. In contrast, waters that are hydrothermally influenced (>10 °C) possess isotopically heavy δ98/95MoHYDROTHERMAL values of +0.25‰ to +2.06‰ (n=18) with the possibility that the high temperature endmembers are even heavier. Although the mechanisms driving this fractionation remain unresolved, the incongruent dissolution of the host basalt and both the dissolution and precipitation of sulfides are considered. Regardless of the processes driving these variations, the δ98Mo data presented in this study indicate that groundwater and hydrothermal waters have the potential to modify ocean budget calculations.
AB - Molybdenum (Mo) isotopes have proved useful in the reconstruction of paleoredox conditions. Their application generally relies upon a simplified model of ocean inputs in which rivers dominate Mo fluxes to the oceans and hydrothermal fluids are considered to be a minor contribution. To date, however, little attention has been paid to the extent of Mo isotope variation of hydrothermal waters, or to the potential effect of direct groundwater discharge to the oceans. Here we present Mo isotope data for two Icelandic groundwater systems (Mývatn and Þeistareykir) that are both influenced by hydrothermal processes. Relative to NIST 3134 = +0.25‰, the cold (<10 °C) groundwaters (δ98/95MoGROUNDWATER = −0.15‰ to +0.47‰; n=13) show little, if any, fractionation from the host basalt (δ98/95MoBASALT = +0.16‰ to −0.12‰) and are, on average, lighter than both global and Icelandic rivers. In contrast, waters that are hydrothermally influenced (>10 °C) possess isotopically heavy δ98/95MoHYDROTHERMAL values of +0.25‰ to +2.06‰ (n=18) with the possibility that the high temperature endmembers are even heavier. Although the mechanisms driving this fractionation remain unresolved, the incongruent dissolution of the host basalt and both the dissolution and precipitation of sulfides are considered. Regardless of the processes driving these variations, the δ98Mo data presented in this study indicate that groundwater and hydrothermal waters have the potential to modify ocean budget calculations.
KW - groundwater
KW - hydrothermal
KW - Mo isotopes
KW - ocean mass balance
UR - http://www.scopus.com/inward/record.url?scp=85044747528&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2017.11.053
DO - 10.1016/j.epsl.2017.11.053
M3 - Article
AN - SCOPUS:85044747528
SN - 0012-821X
VL - 486
SP - 108
EP - 118
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -