Potential role of Atlantic Warm Pool-induced freshwater forcing in the Atlantic Meridional Overturning Circulation: ocean–sea ice model simulations Liping Zhang • Chunzai Wang • Sang-Ki Lee Received: 19 March 2013 / Accepted: 24 December 2013 / Published online: 7 January 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Recent studies have indicated that the multi- decadal variations of the Atlantic Warm Pool (AWP) can induce a significant freshwater change in the tropical North Atlantic Ocean. In this paper, the potential effect of the AWP-induced freshwater flux on the Atlantic Meridional Overturning Circulation (AMOC) is studied by performing a series of ocean–sea ice model experiments. Our model experiments demonstrate that ocean response to the anomalous AWP-induced freshwater flux is primarily dominated by the basin-scale gyre circulation adjustments with a time scale of about two decades. The positive (negative) freshwater anomaly leads to an anticyclonic (cyclonic) circulation overlapping the subtropical gyre. This strengthens (weakens) the Gulf Stream and the recirculation in the interior ocean, thus increases warm (cold) water advection to the north and decreases cold (warm) water advection to the south, producing an upper ocean temperature dipole in the midlatitude. As the fresh- water (salty water) is advected to the North Atlantic deep convection region, the AMOC and its associated northward heat transport gradually decreases (increases), which in turn lead to an inter-hemispheric SST seesaw. In the equilibrium state, a comma-shaped SST anomaly pattern develops in the extratropical region, with the largest amplitude over the subpolar region and an extension along the east side of the basin and into the subtropical North Atlantic. Based on our model experiments, we argue that the multidecadal AWP-induced freshwater flux can affect the AMOC, which plays a negative feedback role that acts to recover the AMOC after it is weakened or strengthened. The sensitivity of AMOC response to the AWP-induced freshwater forcing amplitude is also examined and discussed. Keywords Atlantic Warm Pool  Atlantic Meridional Overturning Circulation  Freshwater forcing 1 Introduction The Atlantic Meridional Overturning Circulation (AMOC) is a system of surface and deep currents encompassing the entire Atlantic basin. It carries an enormous amount of heat northward (Ganachaud and Wunsch 2000), thereby altering climates in North America and Europe substantially. Pre- vious studies suggested that the AMOC has large variations (e.g., te Raa and Dijkstra 2002; Lee and Wang 2010) and primarily varies on multidecadal timescales (e.g., Knight et al. 2005; Delworth and Mann 2000; Medhaug and Furevik 2011). It is also shown that the AMOC is a driving mechanism for the Atlantic Multidecadal Oscillation (AMO) (e.g., Delworth and Mann 2000; Knight et al. 2005; Dijkstra et al. 2006; Zhang et al. 2007), which is a climate mode wherein the North Atlantic sea surface temperature (SST) changes on the timescales of 30–80 years, with its largest variation centered in the high latitudes of the North Atlantic. The AMO variability is associated with changes in climate and extreme weather events such as rainfall and drought in North America and Atlantic hurricanes (e.g., Enfield et al. 2001; McCabe et al. 2004; Goldenberg et al. 2001; Bell and Chelliah 2006; Wang and Lee 2009; Wang et al. 2011). Thus, improving our understanding of the L. Zhang (&)  S.-K. Lee Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL, USA e-mail: ocean.climate.ping@gmail.com C. Wang  S.-K. Lee NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, FL, USA 123 Clim Dyn (2014) 43:553–574 DOI 10.1007/s00382-013-2034-z