Oxygen isotope values from high-latitudes: Clues for Permian sea-surface temperature gradients and Late Palaeozoic deglaciation

The Permian was a period of waning large-scale continental glaciations in the southern Hemisphere. The waning of these ice sheets during the Early Permian led to discharge of 18O-depleted ice–melt water into the oceans. This, coupled with rising seawater temperatures, resulted in a concomitant decline of about 2.5‰ in the δ18O of seawater, as recorded by brachiopod shells from low-latitude (< 30°) habitats. The transition from ice- to greenhouse conditions is reflected also in the oxygen isotope data of unaltered brachiopods and bivalves from high high-latitudes. Moreover, the high-latitude specimens have consistently more positive δ18O, by about 2.5‰, than their coeval low-latitude counterparts, suggesting a Permian sea-surface temperature (SST) gradient of about 9 to 12 °C between tropical–subtropical (< 30°) and high southern (55 ±10°) latitude localities, apparently irrespective of whether in a greenhouse or an icehouse mode. This Permian SST gradient is comparable to the modern SST gradient of about 14 °C. The δ18O seawater records suggest that the global warming that resulted in the waning of the Permo-Carboniferous ice sheets during the Sakmarian was followed by another cooling during the late Kungurian and by renewed warming during the Mid- and Late Permian.