TY - JOUR
T1 - The evolution of the global selenium cycle
T2 - secular trends in Se isotopes and abundances
AU - Stüeken, Eva E.
AU - Buick, R.
AU - Bekker, A.
AU - Catling, D.
AU - Foriel, J.
AU - Guy, B. M.
AU - Kah, L. C.
AU - Machel, H. G.
AU - Montañez, I. P.
AU - Poulton, S. W.
N1 - The project was financially supported by a University of Washington Royalty Research grant to R.B., the National Science Foundation grant EAR0921580 to R.B., NASA Exobiology Program Grant NNX10AQ90G to D.C., and the NAI Virtual Planetary Laboratory at the University of Washington. We thank the UW Isotope Geochemistry Lab and the UW Isolab for technical support.
PY - 2015/8/1
Y1 - 2015/8/1
N2 - The Earth’s surface has undergone major transitions in its redox state
over the past three billion years, which have affected the mobility and
distribution of many elements. Here we use Se isotopic and abundance
measurements of marine and non-marine mudrocks to reconstruct the
evolution of the biogeochemical Se cycle from ∼3.2 Gyr onwards. The six
stable isotopes of Se are predominantly fractionated during redox
reactions under suboxic conditions, which makes Se a potentially
valuable new tool for identifying intermediate stages from an anoxic to a
fully oxygenated world. δ82/78Se shows small fractionations
of mostly less than 2‰ throughout Earth’s history and all are
mass-dependent within error. In the Archean, especially after 2.7 Gyr, we find an isotopic enrichment in marine (+0.37 ± 0.27‰) relative to non-marine samples (−0.28 ± 0.67‰), paired with increasing Se abundances. Student t-tests
show that these trends are statistically significant. Although we
cannot completely rule out the possibility of volcanic Se addition,
these trends may indicate the onset of oxidative weathering on land,
followed by non-quantitative reduction of Se oxyanions during fluvial
transport. The Paleoproterozoic Great Oxidation Event (GOE) is not
reflected in the marine δ82/78Se record. However, we find a major inflection in the secular δ82/78Se trend during the Neoproterozoic, from a Precambrian mean of +0.42 ± 0.45‰ to a Phanerozoic mean of −0.19 ± 0.59‰.
This drop probably reflects the oxygenation of the deep ocean at this
time, stabilizing Se oxyanions throughout the water column. Since then,
reduction of Se oxyanions has likely been restricted to anoxic basins
and diagenetic environments in sediments. In light of recent Cr isotope
data, it is likely that oxidative weathering before the Neoproterozoic
produced Se oxyanions in the intermediate redox state SeIV, whereas the fully oxidized species SeVI became more abundant after the Neoproterozoic rise of atmospheric oxygen.
AB - The Earth’s surface has undergone major transitions in its redox state
over the past three billion years, which have affected the mobility and
distribution of many elements. Here we use Se isotopic and abundance
measurements of marine and non-marine mudrocks to reconstruct the
evolution of the biogeochemical Se cycle from ∼3.2 Gyr onwards. The six
stable isotopes of Se are predominantly fractionated during redox
reactions under suboxic conditions, which makes Se a potentially
valuable new tool for identifying intermediate stages from an anoxic to a
fully oxygenated world. δ82/78Se shows small fractionations
of mostly less than 2‰ throughout Earth’s history and all are
mass-dependent within error. In the Archean, especially after 2.7 Gyr, we find an isotopic enrichment in marine (+0.37 ± 0.27‰) relative to non-marine samples (−0.28 ± 0.67‰), paired with increasing Se abundances. Student t-tests
show that these trends are statistically significant. Although we
cannot completely rule out the possibility of volcanic Se addition,
these trends may indicate the onset of oxidative weathering on land,
followed by non-quantitative reduction of Se oxyanions during fluvial
transport. The Paleoproterozoic Great Oxidation Event (GOE) is not
reflected in the marine δ82/78Se record. However, we find a major inflection in the secular δ82/78Se trend during the Neoproterozoic, from a Precambrian mean of +0.42 ± 0.45‰ to a Phanerozoic mean of −0.19 ± 0.59‰.
This drop probably reflects the oxygenation of the deep ocean at this
time, stabilizing Se oxyanions throughout the water column. Since then,
reduction of Se oxyanions has likely been restricted to anoxic basins
and diagenetic environments in sediments. In light of recent Cr isotope
data, it is likely that oxidative weathering before the Neoproterozoic
produced Se oxyanions in the intermediate redox state SeIV, whereas the fully oxidized species SeVI became more abundant after the Neoproterozoic rise of atmospheric oxygen.
UR - https://www.sciencedirect.com/science/article/pii/S0016703715002392?via=ihub#s0085
U2 - 10.1016/j.gca.2015.04.033
DO - 10.1016/j.gca.2015.04.033
M3 - Article
SN - 0016-7037
VL - 162
SP - 109
EP - 125
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -
