Chemical resolution of a meddy emerging off southern Portugal

摘要

Cape St. Vincent and Portimao canyon, off southern Portugal, are known as sites of meddies formation. In September 1999 a meddy was identified centered at 35.91degreesN, 8.54degreesW, on the eastern flank of Portimao canyon. In this work we describe and analyse the chemical signature of the meddy and discuss its impact and admixture with surrounding waters. Meddy structure was clearly identifiable by nutrient dilution, being the vertical contours of nutrients and apparent oxygen utilization (AOU) as follows: 13 mumol kg(-1) of nitrate, 0.67 mumol kg(-1) of phosphate, 5.4 mumol kg(-1) of silicate and 64 mumol kg(-1) of AOU. The location of nutrient minima was visible mainly between 800 and 1400 m depth. Nevertheless, a pronounced extension of meddy chemical properties was perceptible further down the thermohaline fields, having an impact on the chemical characteristics of the surrounding intermediate and deep water masses. Horizontally the meddy chemical signature occupied similar to30-40 km, a characteristic scale of a meddy. This distribution points out to the meddy detachment from the slope, which is the main downstream route of the MW flow extending towards the west, following the topographic irregularities associated with Portimao canyon. (C) 2004 Elsevier Ltd. All rights reserved.