Predictability in the Atlantic Multidecadal Variability and its Connection with the Atlantic Meridional Overturning Circulation and the Mixed Layer Depth

Abstract

The fluctuation of sea surface temperature in the Northern Atlantic on a multi-decadal time scale, referred to as Atlantic multidecadal variability (AMV), is a key driver of climate variability in surrounding regions. The scientific community is still unsure of the main cause and drivers for the AMV. In order to get a better understanding of the AMV, we analyzed the differences in the predictability of the AMV over two centuries (years 2645-2744 and 2856-2955) within a 3000-year long climate model simulation. These two centuries were chosen because the 2645-2744 century has an AMV that is more predictable than the 2856-2955 century. To understand the cause of these changes in predictability from one century to the next, we investigated the connection between the AMV, simulated mixed layer depth (MLD), Atlantic Meridional Overturning Circulation (AMOC) The MLD is the depth in the Ocean to where the temperature remains relatively similar to the surface temperature, while the AMOC is the large system of ocean currents which transports heat northward into the Atlantic. The century with a more predictable AMV (2645-2744) has deeper MLDs on average, therefore increased heat storage appears to be a plausible mechanism for why this century is more predictable. Looking at the differences in the AMOC, we have also concluded that this century had a stronger AMOC in the subtropics but weaker in the subpolar region. Therefore we concluded that the AMOC was not the most precise tool to measure the AMV. Our results suggest that a deeper MLD within a given century can allow for a more predictable AMV.