Central water masses variability in the southern Bay of Biscay from early 90's The effect of the severe winter 2005

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A monthly hydrographical time series carried out by the Spanish Institute of Oceanography in the southern Bay of Biscay (eastern North Atlantic), covering the upper 1000 m, have shown local warming rates for the last 10-15 years that are much higher than the long-term ocean trend in the 20th century. At Mediterranean Water (MW) level this warming is linked to an effective modification of the termohaline properties but at the East North Atlantic Central Water (ENACW) levels the warming was mainly related to isopycnal sinking (heave) until winter 2005. The overall picture is consistent with the fact that climatic warming has accelerated over the last few decades. The anomalous winter of 2005 in south-western Europe (extremely cold and dry) caused the lowest temperature record of the time-series 1993-2005 for the surface waters in the southern Bay of Biscay, and the mixed layer reached unprecedented depths greater than 300 m. The isopycnal level σθ = 27.1 classically used to analyze ENACW variability disappeared (outcrops further south) and as a result the hydrographical structure of the upper layers of the ENACW was strongly modified remaining in summer 2006 completely different than what it was in the previous decade. However, the local warming trend was only disrupted down to 300-400 dbar but there is a noticeable increase in salinity much deeper.