Triple oxygen isotope mass balance for the Earth's oceans with application to Archean cherts

Abstract

The oxygen isotope composition of the Earth's oceans is buffered by high- and low-T exchange with the lithosphere. We present a triple oxygen isotope mass balance model for the Earth's oceans. The model is based on triple oxygen isotope measurements of rocks from various reservoirs including high- and low-T alteration products. The modern ocean water composition can be well-matched if the ratio between continental weathering and high-T seafloor alteration is ~25% higher than previously assumed. The mass balance suggests that putative Precambrian low-δ18O ocean water would fall on a trend with slope λ = 0.51 passing through “modern” ice-free-world seawater. Exemplified application to a published Phanerozoic and Archean chert data suggest precipitation in cool oceans with modern-like δ18O followed by diagenetic alteration with involvement of meteoric water.