Revealing the climate of snowball Earth from Delta O-17 systematics of hydrothermal rocks

Abstract

The oxygen isotopic composition of hydrothermally altered rocks partly originates from the interacting fluid. We use the triple oxygen isotope composition (O-17/O-16, O-18/O-16) of Proterozoic rocks to reconstruct the O-18/O-16 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 [similar to 2.3-2.4 gigayears ago (Ga)] snowball Earth, delta O-18 = -43 +/- 3 parts per thousand is estimated for pristine meteoric waters that precipitated at low paleo-latitudes (<= 35 degrees N). Today, such low O-18/O-16 values are only observed in central Antarctica, where long distillation trajectories in combination with low condensation temperatures promote extreme O-18 depletion. For a Neoproterozoic (similar to 0.6-0.7 Ga) snowball Earth, higher meltwater delta O-18 estimates of -21 +/- 3% imply less extreme climate conditions at similar paleolatitudes (<= 35 degrees N). Both estimates are single snapshots of ancient water samples and may not represent peak snowball Earth conditions. We demonstrate how O-17/O-16 measurements provide information beyond traditional O-18/O-16 measurements, even though all fractionation processes are purely mass dependent.