Covariance between OHC and AMO and statistical forecast of subpolar OHC. (a) Pointwise covariance between the AMO and OHC over the period 1955–2013 (shading). Significant correlations are contoured at the 90% (black) level, where significance is calculated using the number of degrees of freedom determined by the integral timescale of decorrelation. The red box indicates the subpolar region used in the text. The map was created using Generic Mapping Toolbox v5.2.1 (gmt.soest.hawaii.edu/). (b) Time series of the AMO (black) and OHC anomaly (red) from the subpolar North Atlantic (red box in a). The AMO is the Trenberth and Shea19 definition, with 0–60°N Atlantic surface temperature minus the 60°S to 60°N average. The OHC anomaly is the NODC 0–700 m average for the subpolar region 45–70°N and 10–65°W.