Session: Warm Climates (Mid-Holocene, Last interglacial, Deep-time, Pliocene)
Author: David Hutchinson / email@example.com / Department of Geological Sciences, Stockholm University
Co-author: Agatha de Boer, Department of Geological Sciences, Stockholm University;
Helen Coxall, Department of Geological Sciences, Stockholm University;
Rodrigo Caballero, Department of Meteorology, Stockholm University;
Johan Nilsson, Department of Meteorology, Stockholm University;
Geological evidence suggests that North Atlantic Deep Water (NADW) first formed around the Eocene-Oligocene Transition (EOT; 34 Ma), coinciding with the large-scale glaciation of Antarctica. In earlier periods, deep water is thought to have formed in the Southern Ocean and possibly the North Pacific. Here we investigate possible causes of this reorganization of the deep circulation. We present novel EOT simulations using the coupled climate model GFDL CM2.1 adapted to late Eocene paleogeography. Using this paleogeography, we find that the North Atlantic becomes very fresh, which prevents NADW formation. Instead sinking occurs in the North Pacific and Southern Ocean in agreement with Eocene circulation proxies. We test the role of greenhouse forcing by varying the CO2 to values of 400, 800 and 1600 ppmv, but the cooling alone does not substantially alter the preferred sinking regions. We further test the effect of closing the Arctic-Atlantic gateway, in light of recent evidence that the Arctic Ocean became isolated at the EOT. The gateway closure shuts off freshwater export from the Arctic to the Atlantic. This change enables a strong salinification of the North Atlantic that triggers the onset of NADW production.