Warming trends and decadal variability in the Western Mediterranean shelf

Abstract

We analyse hydrographic, meteorological and sea level time series in the continental shelves of Málaga Bay and L'Estartit, in the South and North Western Mediterranean. We have detected an important reduction of the warming rates reported for the 90s decade, showing that the warming process of the Mediterranean is superimposed on several years lasting oscillations. These accelerations or interruptions, typically account for a fraction of the total trend, and therefore they are not able to obscure the warming detection if the time series are long enough. On the other hand, they can produce artificial results if the time series are short when compared with the length of these cycles. The warming of the shelf waters, its acceleration during the 90s and the reversal during the beginning of the XXI century, are also observed in air temperature time series along the Spanish Mediterranean. We have also checked the influence of the warming acceleration/disruption on the sea level rise. Mean sea level trends are around 1 mm/yr when long time series are analysed, but shorter time series can result in rising trends as large as 13 mm/yr, for accelerated warming periods, or even no sea level change for reversals of the warming trends. Another factor to study is the influence of the NAO on these warming/cooling periods as well as on the strength of upwelling favourable winds, which could have a great importance on shelf ecosystems