Reduced Meridional Sea Surface Temperature Gradients and Warmer Climates Produce Enrichment of Delta 18O in the Mid to High Latitudes

Abstract

The Pliocene is often seen as a potential analog for future climate change because of a similar configuration of continents and CO2 concentration as compared to the present day. A notable characteristic of the Pliocene is its weak mean east-west sea surface temperature (SST) gradient and meridional SST gradient in the Pacific. These reduced gradients could affect the global climate via the weakening of the Walker Circulation and of Hadley cells. In Burls and Fedorov 2014 (BF2014), by altering extra-tropical and tropical cloud albedo, these important characteristics were successfully reproduced using a global climate model (GCM). Here we take the resulting SST field from this Pliocene-like simulation, as well as other SST fields from the BF2014 study, and use them as a boundary parameter for another GCM, SPEEDY-IER. SPEEDY-IER is an atmospheric model that allows for the tracing of oxygen isotopes, namely O16 and O18. The ratio of these isotopes, d18O , has a known correlation with temperature and can be observed in the fossil record. Our results demonstrate the first-order control that temperature has on the d18O of precipitation in the mid- to high- latitudes, where experiments with a reduced meridional temperature gradient experience enrichment of d18O of precipitation in the high latitudes. In the future, d18O of precipitation derived from land-based fossil records can be used to verify our results.