Fig. 4: Historical contributions of the North Atlantic source regions to full water column ΔOHC at 25°N and their future projections.
From: The redistribution of anthropogenic excess heat is a key driver of warming in the North Atlantic
a Time series of NAO index45. b Times series of the ΔSST (blue, right y-axis) and of the full depth ΔOHC response at 25°N (black, left y-axis), both relative to 1850, for the NEA SubP source region defined in Fig. 3a. The ΔOHC is extrapolated in latitude over 10 degrees as in Fig. 2. The ΔSST are regionally averaged over 5° × 5° patches, each patch being weighted by its contribution to the full water column at 25°N. The ΔSST are low-passed filtered using a 10-year moving mean. The ΔSST time axis is shifted backward in time by the modal age to highlight the correspondence between ΔSST and ΔOHC. The Green’s functions potential to infer the interior signal from past ΔSST is also used to project ΔOHC in the future over a time span equal to the modal age (yellow dotted line). The grey shading represents the one standard deviation of the time series estimated as in Fig. 2. c–f. Same as for (b) but for Lab-Irm, Nordic, NA SubT, Med-Sea. Note the different y-axis scales. The six climatic epochs identified in Fig. 2a are indicated by numbers as follows: 1. Late-nineteenth-century cooling (1879–1919), 2. Early-twentieth-century warming (1923–1943), 3. Mid-twentieth-century cooling, (1943–1970), 4. Late-twentieth-century warming (1975–2007), 5. Early-twenty-first-century slowdown (2007–2012), and 6. Early-twenty-first-century acceleration (2012–2018). Horizontal bars indicate NAO+ (orange), NAO− (blue) when it lasted for more than 5 consecutive years, and cooling (black) and warming (white) corresponding to the six climatic epochs.
