The thermohaline data of the first Brazilian hydrographiccruise to the northwestern Weddell Sea (AR XVIII) isdescribed. Favourable ice conditions allowed a dense stationcoverage of the area including the main pathways for WeddellSea deep and bottom waters. The results are compared withthe 1998-data of the German cruise ANT XV/4 and otherhistorical data. An interannual near-bottom variability wasdiscovered and related rather to fluctuations in theformation rate of cold bottom water in the western WeddellSea than to a long-term trend. The calculated fluctuationbased on the comparison agrees well with the formationvariance determined from mooring observations off the tipof the Antarctic Peninsula. The observed variability hasconsequences for the water mass export across the SouthScotia Ridge, as the absence of the colder/fresher/lighterWeddell Sea Bottom Water south of South Orkney Plateauduring AR XVIII might be related to a reduceed ventilationof the deep Scotia Sea. The results of this study supportongoing efforts to establish a long-term monitoring of thisregion with global importance.