Deep-Sea Research I 46 (1999) 1109 } 1136 Some aspects of time variability of the Mediterranean Water o! south Portugal I. Ambar*, L. Armi, A. Bower, T. Ferreira Instituto de Oceanograxa, University of Lisbon, 1700 Lisbon, Portugal Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA, USA Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA, USA Received 28 October 1997; received in revised form 2 July 1998; accepted 3 September 1998 Abstract Mediterranean Water contributes signi"cantly to the hydrological properties and circulation of the intermediate layers of the North Atlantic, yet the temporal variability of the Mediterra- nean Undercurrent is still not well understood, even at intra-annual time scales. The present study addresses the evolution of the temperature "eld in the layers of Mediterranean Water o! south Portugal during one year (July 1993 }July 1994), obtained with an almost weekly repetition of a high-resolution expendable bathythermograph (XBT) section in the vicinity of Portima  o Canyon, during the AMUSE experiment. The information obtained with this set of data was complemented by velocity observations of the Mediterranean Undercurrent with RAFOS #oats launched simultaneously with the XBT lines. The typical structure of the Mediterranean Undercurrent along the slope of the Gulf of Cadiz, consisting of a westward jet associated with the cores of the thermohaline structure, was observed in almost 60% of the 24 repetitions of the XBT section. The results show that this typical structure in the velocity was not always accompanied by a typical thermal structure. Anomalous behaviour of the Undercur- rent } southward or southwestward #ow or local recirculation } occurred only in winter and corresponded to some anomalies in the thermal "eld associated with the Mediterranean Water. The occurrence of warm features o!shore of and separated from the main body of warm water found against the slope o! south Portugal seemed to be connected with episodes of changes in direction and speed of the Undercurrent. Several scales of time variability within the Mediterra- nean Water layers were identi"ed ranging from a week to a month. A possible seasonal trend in the temperature of these layers was apparent in the XBT data and seemed also to be found in time series obtained with moored current meters.  1999 Elsevier Science Ltd. All rights reserved. * Corresponding author. Fax: 00351 1 7500009; e-mail: iambar@fc.ul.pt 0967-0637/99/$ } see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 - 0 6 3 7 ( 9 8 ) 0 0 0 0 6 - 0