Revealing the climate of snowball Earth from Δ¹⁷O systematics of hydrothermal rocks
2015
Herwartz, Daniel | Pack, Andreas | Krylov, Dmitri | Xiao, Yilin | Muehlenbachs, Karlis | Sengupta, Sukanya | Di Rocco, Tommaso
The oxygen isotopic composition of hydrothermally altered rocks partly originates from the interacting fluid. We use the triple oxygen isotope composition ( ¹⁷O/ ¹⁶O, ¹⁸O/ ¹⁶O) of Proterozoic rocks to reconstruct the ¹⁸O/ ¹⁶O ratio of ancient meteoric waters. Some of these waters have originated from snowball Earth glaciers and thus give insight into the climate and hydrology of these critical intervals in Earth history. For a Paleoproterozoic [∼2.3–2.4 gigayears ago (Ga)] snowball Earth, δ ¹⁸O = −43 ± 3‰ is estimated for pristine meteoric waters that precipitated at low paleo-latitudes (≤35°N). Today, such low ¹⁸O/ ¹⁶O values are only observed in central Antarctica, where long distillation trajectories in combination with low condensation temperatures promote extreme ¹⁸O depletion. For a Neoproterozoic (∼0.6–0.7 Ga) snowball Earth, higher meltwater δ ¹⁸O estimates of −21 ± 3‰ imply less extreme climate conditions at similar paleo-latitudes (≤35°N). Both estimates are single snapshots of ancient water samples and may not represent peak snowball Earth conditions. We demonstrate how ¹⁷O/ ¹⁶O measurements provide information beyond traditional ¹⁸O/ ¹⁶O measurements, even though all fractionation processes are purely mass dependent.
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