Atmospheric Oxygen and Paleotemperature in the Paleozoic and Triassic

Abstract

δ13C in Triassic-to-modern plant resins has been used to derive estimates of atmospheric oxygen that are inversely linked to paleotemperature. Climate modelers have found comparable inverse oxygen - temperature relationships in the mid-Cretaceous, speculated on broader Phanerozoic analogues and argued for an under-appreciated climate forcing role of atmospheric oxygen. Other researchers working in the same mid-Cretaceous interval but with a different climate model, have found a (diametrically opposed) positive correlation between atmospheric oxygen and paleotemperature and suggest little or no forcing by oxygen. Here I test these opposing views by comparing much longer temporal profiles of Paleozoic and early Triassic atmospheric oxygen with profiles of coeval shallow-marine paleotemperature derived from oxygen isotopes. I confirm the postulated inverse relationship between pO2 and paleotemperature from the middle Ordovician to the early Triassic except for a short interval of earliest Permian time when a large step-like temperature increase accompanied modest pO2 increase. This inverse relationship thus characterizes a very large portion of the Phanerozoic. As in the earliest Permian, pO2 is directly proportional to temperature in the latest Cambrian-Early Ordovician and in the middle portion of the Triassic. Relationships in the late Triassic are indeterminate. Climate forcing by atmospheric oxygen, in the face of these changing and sometimes opposing relationships, can best be explained by bifurcations or bistability in the pO2/temperature relationship. (219 words)

Keywords: atmospheric oxygen, paleotemperature, Paleoclimate