Publication Date:
2019
Description:
〈span〉〈div〉Abstract〈/div〉Plate tectonics, the principal vehicle for dissipation of planetary energy, is believed to buffer the δ〈sup〉18〈/sup〉O of seawater at its near-modern value of 0‰ SMOW (Standard Mean Ocean Water) because the hot and cold cells of hydrothermal circulation at oceanic ridges cancel each other. The persistence of plate tectonics over eons apparently favors attribution of the well-documented oxygen isotope secular trends for carbonates (cherts, phosphates) to progressively warmer oceans, from 40–70 °C in the early Paleozoic to 60–100 °C in the Archean. We argue that these oceanic hydrothermal systems are dominated by low-temperature (〈350 °C) cells that deplete the percolating water in 〈sup〉18〈/sup〉O. Seawater δ〈sup〉18〈/sup〉O is therefore a proxy for, rather than being buffered by, the intensity of plate tectonics. Detrending the Phanerozoic carbonate δ〈sup〉18〈/sup〉O〈sub〉c〈/sub〉 secular trend for its “tectonic” component yields a stationary time series that, interpreted as a proxy for Phanerozoic climate, indicates low-latitude shallow ocean temperatures oscillating between 10 and 30 °C around a baseline of 17 °C, attributes comparable to modern temperature values.〈/span〉
Print ISSN:
0091-7613
Electronic ISSN:
1943-2682
Topics:
Geosciences
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