Session: Last Millennium & Past2K
Author: Eduardo Moreno-Chamarro / email@example.com / Massachusetts Institute of Technology. Cambridge. USA
Co-author: Davide Zanchettin, Venice University. Venice. Italy;
Katja Lohmann, Max Planck Institute for Meteorology. Hamburg. Germany;
Jürg Luterbacher, Justus Liebig University of Giessen. Giessen, Germany;
Johann H. Jungclaus, Max Planck Institute for Meteorology. Hamburg. Germany;
Climate reconstructions reveal a strong winter amplification of the cooling over central and northern continental Europe during the Little Ice Age (LIA; here defined as c. 16th–18th centuries), via persistent, blocked atmospheric conditions. Although several potential drivers have been suggested to explain the European LIA cooling, including solar minima and/or volcanic eruptions, together with a persistent negative phase of the North Atlantic Oscillation (NAO) and/or a weakening of the Atlantic meridional overturning circulation (AMOC), no coherent mechanism has yet been proposed for the seasonal contrast in the European LIA cooling. Here we demonstrate that such exceptional wintertime conditions arose from sea ice expansion and reduced ocean heat losses in the Nordic and Barents seas, driven by a multicentennial reduction in the northward heat transport by the subpolar gyre (SPG). However, these anomalous oceanic conditions were largely decoupled from the European atmospheric variability in summer. We reject previous hypotheses that linked the European LIA cooling with a weakened AMOC or with a persistent negative NAO. Our novel dynamical explanation is derived from analysis of an ensemble of last millennium climate simulations, performed with Max Planck Institute Earth System Model, and is further supported by reconstructions of European temperature and atmospheric circulation variability and North Atlantic/Arctic paleoceanographic conditions. We conclude that SPG-related internal climate feedbacks related were responsible of the European LIA winer cooling amplification. Thus, characterization of SPG dynamics is essential for understanding multicentennial seasonal variability in the European/North Atlantic sector.