Ocean heat content in the Iberian–Biscay–Ireland regional seas

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Abstract. The ocean has the largest heat capacity of any single component of the climate system and plays a key dominant role in global heat content changes. To analyse ocean heat content (OHC) variability in the Iberia–Biscay–Ireland (IBI) region, several Copernicus Marine reanalysis and observational products are used together to provide multi-product estimations of OHC anomalies over the water column (at upper layers 150, 700, and 2000 m). This work provides a study of spatial and temporal variability of OHC in the northeastern Atlantic region through the analysis of area-averaged time series, trend maps, and trends linked with the main water masses found in the IBI region. The work states the key role that subsurface water masses play in the OHC trends in the IBI region. The study shows that, although no significant trends are detected for the surface water layers, the intermediate and deep water layers show significant trends (with rates of +0.40 W m−2). However, the high interannual variability of the subsurface water masses masks these trends. Two of the main water masses described in the region (i.e. Sub-Arctic Intermediate Water and Mediterranean Outflow Water) are found to explain more than 50 % of the OHC variability. Since the variability of both water masses is linked to the North Atlantic Oscillation, the work shows the mechanisms by which atmospheric forcing is able to affect the subsurface water layers without showing a signal in the surface.