Low-frequency transport components in Mona Passage (Caribbean Sea).

摘要

Two bottom-mounted acoustic Doppler current profilers (ADCP; RDI—75khz) and one S4 current meter were deployed in the Mona Passage, along the ridge that runs from the western end of Puerto Rico up to the northeastern end of Dominican Republic. Data collected span the period from September 1997 to May 1999 although not continuously.; Using the vertical profile of Brunt-Väisälä frequency, dynamic normal modes were computed for each deployment for the low frequency currents. The first baroclinic Rossby radius of deformation was 26.94km. The low frequency currents were decomposed into the barotropic and baroclinic modes using the dynamic normal modes estimated for the deployment of ADCP I and ADCP II. For ADCP I the 94 percent of the observed variance can be accounted for by the linear combination of the first two modes at the center region of the Mona Passage, while for the ADCP II 80 percent is needed. Hence, the barotropic and first baroclinic modes represent the low frequency currents in the Mona Passage. The results obtained by the method of empirical orthogonal function showed that the first empirical mode explain more than 88 percent of the recorded variance.; The vertical profile of the mean meridional transport is characterized by a two-layer structure, (baroclinic structure). The upper layer lies above 300 meters depth with the upper water masses, the Caribbean Surface Water, Subtropical Underwater and Sargasso Sea Water entering the Caribbean from the Atlantic Ocean. Below this layer the Tropical Central Water exits toward the Atlantic Ocean.; The vertical structure of the mean meridional transport has a maximum peak at 100 meters. The maximum values for the mean meridional total transport through Mona Passage occurred during December 1997, July 1998 and January 1999 with values of −4.50 Sv, −4.25 Sv, and −4.7 Sv into the Caribbean Sea, respectively. The minimum values occurred during June 1998 and August 1998 with values of 0.74 Sv out of the Caribbean and −0.66Sv into the Caribbean.; The spectral analysis shows that the bulk of the kinetic energy is contained in three sharp peaks at the inertial, diurnal and semi-diurnal tidal frequencies, and a broad peak in the low frequency. The dominant peak is that of the semi-diurnal tidal frequency component. The structure and generation mechanisms of low frequency currents in the Mona Passage are discussed as well as the local and remote forcing.