Intrusions of warm and salty waters onto the NW and N Iberian shelf in early spring and its relationship to climate variability

Abstract

Temperature and salinity data from a series of cruises carried out on the NW and N Iberian shelf, between 1987 and 2005 during early spring, were analysed to investigate the inter-annual variability of the intrusions of warm and salty waters into the Cantabrian Sea, and its relationship with the meridional sea surface temperature (SST) gradient in the NE Atlantic and the main modes of climate variability affecting the Northern Hemisphere. A sub-surface front, that separates warmer and saltier (i.e. spicy) waters in the westernmost part of the Iberian shelf from the colder and fresher waters, characteristic of the easternmost part of the southern Bay of Biscay, was observed in all the analysed years. The location of this sub-surface front, which defines the limit of the influence of the Subtropical mode of Eastern North Atlantic Central Water (ENACWst) advected by the Iberian Poleward Current (IPC), varied approximately between Finisterre Cape (43°N, 9°W) and Peñas Cape (43.5°N, 6°W), being located on average around the Ortegal Cape (43.5°N, 8°W). Its position, alongshore the Southern Bay of Biscay shelf, is displaced westward as the spring season progresses, and showed a positive correlation with the summer–autumn (July–October, JASO) meridional SST gradient (measured between 36°N 15°W and 46°N 15°W) of the previous year. This gradient was in turn correlated with the values of the Eastern Atlantic (EA) climate index for the same period.