Wilkinson Basin area water masses: a revisit with EOFs

摘要

Hydrographic data sets from the Brooks (J. Geophys. Res. 90 (1985) 4687) survey are used for the initial study of water mass characteristics and distributions of the Wilkinson Basin area in the northwest corner of the Gulf of Maine. Parameters of Maine Surface, Intermediate, Bottom, and Slope waters are derived from the available conductivity-temperature-depth (CTD) casts and developed using cluster analysis with a distribution function for cluster point differences in temperature, salinity and depth. The cluster analysis yields two distinct surface water masses, one of which is warmer and less salty. This warmer water mass could be a result of the transport of fresher water into the western Wilkinson basin area by a branch of the Maine Coastal Current and subsequent solar heating.A variance-based empirical orthogonal functions (EOF) analysis associated with water masses in the Wilkinson Basin area is simultaneously undertaken for the advancement of feature models. The cloud of points representing each water mass in terms of temperature, salinity, and depth are derived through cluster analysis and identified as matrix elements in the singular-value-decomposition (SVD) and covariance analysis. Covariance and correlation statistics of the water masses are analyzed. The vertical temperature and salinity is reconstructed through an EOF decomposition of each water mass cloud of points and a summation of all of them for the resultant vertical distribution. This constitutes the basis for a water mass-based feature model with latest-measurement update capability.The percentage of the water volume occupied by each of the five water masses is derived and expressed as a function of depth and CTD cast location. The means, standard deviations, and ranges of the water masses are extracted in the temperature-salinity-depth space. The origin and formation of the water masses is considered together with the controlling physical processes. The prevalent dynamics is related to the water mass structure and characteristics. It is shown that slope water arrives into the Wilkinson Basin area from the Northeast Channel. (C) 2004 Elsevier Ltd. All rights reserved.