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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...

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In situ observations of submarine hydrothermal activity have been conducted in Punta Banda, Baja California, Mexico, approximately 400 m from the coast and at a seawater depth of 30 m. The hydrothermal activity occurs within the Agua Bianca Fault, a major transverse structure of Northern Baja California. Hot springwater samples have been collected and analyzed. Marked differences exist between the submarine hot springwater, local land hot springwaters, groundwater, and local seawater. SiO2, HCO3−, Ca, K, Li, B, Ba, Rb, Fe, Mn, As, and Zn are enriched in the submarine hot springwater, while Cl, Na, SO42−, Mg, Cu, Ni, Cd, Cr, and perhaps Pb are depleted in relation to average and local seawater values. Very high temperatures, at the hydrothermal vents, have been recorded (102°C at 4‐atm pressure). Visible gaseous emanations rich in CH4 and N2 coexist with the hydrothermal solutions. Metalliferous deposits, pyrite, have been encountered with high concentrations of Fe, S, Si, Al, Mn, Ca, and the volatile elements As, Hg, Sb, and Tl. X ray dispersive spectrometry (1500‐ppm detection limit), X ray diffraction, and scanning electron microscopy of the isolated metalliferous precipitates indicate that the principal products of precipitation are pyrite and gypsum accompanied by minor amounts of amorphous material containing Si and Al. Chemical analyses and XRD of the reference control rocks of the locality (volcanics) versus the hydrothermally altered rocks indicate that high‐temperature and high‐pressure water‐rock interactions can in part explain the water chemistry characteristics of the submarine hydrothermal waters. Tritium dating of the hydrothermal solutions places them in the prebomb period of 1953 with an undetermined old age. Their long residence time, the occurrence of an extensive marine sedimentary formation, their association with CH4, and their similarities with connate waters of oil and gas fields suggest that another component of their genesis could be in cation exchange reactions within deeply buried sediments of marine origin. The approximate volume discharge of the hydrothermal system has been measured (330,000 m3/yr), and the overall convective heat flux over the mapped submarine hydrothermal area has been calculated, the value of which exceeds 105 times the reported average conductive flux through the sea floor. Our data and observations indicate that metal‐rich marine sediments and marine ore‐forming processes are a concurrent reality and that ores are being formed today in submarine areas of high convective heat flow where hydrothermal activity is the precursor for their occurrence. At the same time the results of our investigations have demonstrated that submarine hydrothermal activity and submarine hot springs exist in the ocean in regions characterized by relative quiescence and that technically ‘active’ ridge environments are not an exclusive prerequisite for their existence.

A geochemical model of the Punta Banda submarine hydrothermal system (PBSHS) and Ensenada quadrangle subaerial hot springs is developed using 18O/16O, D/H, 34S/32S, 3H, water and gas chemistry. The PBSHS water is a primary high temperature, acid, reducing fluid of old seawater origin which has been titrated by cold, alkaline groundwater of meteoric origin. The final exiting solutions represent a 1 : 1 mixture of the two primary mixing components. In contrast, the subaerial hot spring waters are of unmixed meteoric origin. The subaerial hot spring gas is predominantly atmospheric N2, while the PBSHS contains large amounts of CH4 and N2 derived from trapped marine sediments of Cretaceous age; δS34 values of sampled hydrothermal waters are similar to Cretaceous marine sulfate values and suggest that the waters contacted Cretaceous marine sedimentary strata. The presence of the Alisitos and Rosario marine sedimentary formations of Cretaceous age within the Ensenada‐Punta Banda quadrangle renders support to the above hypothesis. The data also demonstrate that pyrite mineralization and deposition in submarine hydrothermal environments result from the complexing of ferrous iron with elemental sulfur and sulfide and that submarine hydrothermal activity acts as a major source of silica, Ca2+, and trace metals and as a major sink for seawater Mg2+ and SO42−.