A Loop Current anticyclonic ring --•330 km in diameter and extending to a depth of > 1500 m was observed to collide in January of 1984 against the continental shelf slope of the western Gulf of Mexico between 21.5 ø and 23øN. The collision occurred precisely at the time we conducted our Argos 84-1 hydrographic cruise in the western gulf (26o00 ' to 19ø20'N) aboard the R/V Justo Sierra. The Caribbean Subtropical Underwater (SUW) was used as a tracer to identify the Loop Current anticyclonic ring within the western gulf. The collision was identified from temperature and salinity distributions and from the dynamic topography distribution relative to 500 m. The ring' s collision zone was identified by the presence of a horizontal baroclinic flow divergence, to the east of Tamiahua, that divides the surface circulation into northward and southward baroclinic currents parallel to the western gulf's continental shelf break, with speeds of 85 and 32 cm s -1, respectively. Horizontal divergence and vertical convergence (ring asymmetries) resulted at the focus of the anticyclonic ring's collision and originated the alongshore self advection and northward translation of the colliding anticyclone. Upon colliding the anticyclonic ring shed approximately one third of its volume (--•2 x 10 4 km3), mass, and transferred angular momentum to the south flanking water mass, thus generating a cyclonic ring to the south of the collision zone. The observed alongshelf southward current results from mass conservation and volume continuity requirements associated with the anticyclonic ring's volume shedding and most probably constitutes the colliding ring' s potential vorticity conservation mechanism. The weakening of the anticyclonic ring's relative vorticity due to the collision is most likely made up by gain of vorticity from lateral shear in the northward and southward current jets parallel to the continental shelf break. The core of both the anticyclonic and cyclonic rings had typical SUW salinity (>36.5%0) and temperature (--•22.5øC) values. The rings were separated by a 5 x 10 4 km 2 divergence zone occupied by Gulf Common Water (GCW). The SUW was absent within the collision zone to the east of Tampico (22.3øN, 97.8øW). The GCW within this divergence zone resulted from the convective mixing and dilution of the SUW with less saline (36.1 -< S -< 36.3%0) water from the uppermost layer of the thermocline. Hence the collision of Loop Current anticyclones against the western continental shelf slope of the gulf constitutes a primary mechanism by which 30 Sv of SUW are converted to GCW in the Gulf of Mexico. On the other hand, the coastal and continental shelf water temperature and salinity distributions that resulted from the ring's collision indicate that the offshore GCW mass intrudes the continental shelf to the east of Tamiahua and is diluted by low-salinity coastal water within the western continental shelf. This GCW mass intrusion most probably constitutes a principal and efficient exchange mechanism between the western gulf's cont...

During October‐November 1986 the baroclinic circulation of the central and western Gulf of Mexico was dominated by an anticyclonic ring that was being bisected by two north and south flanking cyclonic rings. The baroclinic circulation revealed a well‐defined cyclonic‐anticyclonic‐cyclonic triad system. The anticyclone's collision against the western gulf continental slope at 22.5°N, 97°W originated the north and south flanking cyclonic rings. The weakening of the anticyclone's relative vorticity, during the collision, was compensated by along‐shelf north (26 cm s−1) and south (58 cm s−1) jet currents and by the anticyclone's flanking water mass's gain of cyclonic vorticity from lateral shear contributed by east (56 cm s−1) and west (42 cm s−1) current jets with individual mass transports of ∼18 Sv. Within the 0–1000 and 0–500 dbar layers and across 96°W the magnitudes of the colliding westward transports were 17.80 and 8.59 Sv, respectively. These corresponding transports were 85 and 94% balanced by along‐shelf jet currents north and south of the anticyclone's collision zone. This indicates that only minor amounts (<15%) of the anticyclone's colliding westward transports might have flowed into the western gulf's continental shelf water mass or else they sank into deeper water along the continental slope during the anticyclone's collision event. The resultant effect of the coupled interaction between the anticyclone and the cyclonic pair was the surging of the water mass in the cyclones and its sinking in the anticyclone. This mechanism controlled the magnitude, direction, location of vertical advection, and transfer of kinetic energy from the upper to the deeper water layers. Our vertical transport estimates through the 1000‐m‐depth surface revealed a net vertical descending transport of 0.4 Sv for the ring triad system. This mass flux occurred primordially within the south central gulf region and most likely constituted a principal mechanism that propelled the gulf's deep horizontal circulation. The volume renewal time is ∼5 years for the ring triad system within 0–1000 dbar. The volume renewal time for the gulf's deep water layer (2000–3000 dbar), estimated as a function of its horizontal outflowing mass flux (1.96 Sv), is of the same order of magnitude and reveals that the deeper layer of the Gulf of Mexico is as well ventilated as its upper layer (0–1000 dbar). The ring triad's surface kinematic properties were derived from the sea surface baroclinic circulation field referenced to 500 dbar. Within this layer, individual ring geometries were conserved. Maximum tangential ring velocities were 60 and 58 cm s−1, for the north and south cyclones respectively, and 30 cm s−1 for the anticyclone. The corresponding periods of revolution were 16, 19, and 26 days, and vertical velocities calculated at the rings' peripheries, where maximum horizontal divergence was encountered, were 1.5, 1.0, and −1.0 m d−1.