Changes in ENACW observed in the Bay of Biscay over the period 1975–2010

Trends in Eastern North Atlantic Central Water (ENACW) were calculated in the Bay of Biscay over the period 1975–2010 using the Simple Ocean Data Assimilation (SODA) package. This approach, which reanalyzes data from different sources, allows obtaining information beneath the sea surface on a fine 0.5°×0.5° grid with 40 vertical layers, providing a complete view of the different hydrographic processes in the area. ENACW, which was associated to salinity and temperature values corresponding to the density interval 27.0–27.2 kg m−3, was observed to warm and salinificate in most of the area at a maximum rate of 0.11 °C per decade and 0.03 psu per decade, respectively. Trends are more intense in the middle part of the Bay and near the northeastern boundary. The origin of the changes in ENACW observed inside the Bay of Biscay is not due to local effects. Actually, trends seem to be related to changes in the subpolar mode of ENACW (ENACWsp), affecting a wider North Atlantic area. The highest trends (0.3 °C per decade in temperature and 0.05 psu per decade in salinity) were observed north of the bay, especially at the shallow area that stretches from Brest to Ireland, which is characterized by deep winter mixing. The dependence of changes in ENACW on the two main modes of variability over the North Atlantic (NAO and EA) was also analyzed. Trends in salinity and temperature showed to be consistent with changes observed in EA. In addition, air temperature and precipitation minus evaporation (P−E) balance showed to contribute to warming and salinification of ENACW.