On plate tectonics and ocean temperatures

Figure 3. Linearly detrended d18Oc (c – carbonate) data (black line; ± 1 s in grey; from the same data as per Fig.1). Note that y-axis for d18Oc data is inverted to project increases in temperature upwards.
SMOW – Standard Mean Ocean Water; Geological time scale from the International Commission on Stratigraphy (Cohen et al., 2013; updated in 2018); Cb. — Cambrian; Ordo. — Ordovician; Sil. — Silurian; Carbo. — Carboniferous; Paleog. — Paleogene; Ng. — Neogene.

Vérard, C., and Veizer, J., 2019, On plate tectonics and ocean temperatures: Geology, v. 47, p. 881–885, https://doi.org/10.1130/G46376.1

Plate tectonics, the principal vehicle for dissipation of planetary energy, is believed to buffer the δ18O of seawater at its near-modern value of 0‰ SMOW because the hot/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 18O. The seawater δ18O is therefore a proxy for, rather than being buffered by, the intensity of plate tectonics. Detrending the Phanerozoic carbonate δ18Oc secular trend for its "tectonic" component yields a stationary time series that, interpreted as Phanerozoic climate, indicates low-latitude shallow ocean temperatures oscillating between 10 to 30°C around a baseline of 17°C; attributes comparable to modern counterparts.

August 29, 2019