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Submesoscale eddies (1-10 km diameter) were identified using surface velocity observations obtained from a high-frequency radar system (HFR) operated in Todos Santos Bay (TSB), Baja California, Mexico. Eddies were detected through a special case of the Okubo-Weiss parameter for divergent flows in the form of eigenvalues of the Jacobian matrix. The detection method, applied for a surface velocity grid, shows encouraging results in the recognition and tracking of submesoscale features in TSB. The detection method is rapid and efficient. Results show the formation and persistence of an eddy structure inside the Bay in December 6, 2010, displaying a trajectory from NE to SW until disappearing at the center of the Bay. The eddy is approximately 4 km in diameter with a frequency of ~0.1f (f is the Coriolis parameter). The real part of the Okubo-Weiss parameter ranged between − 4 × 10 − 9 to − 1 × 10 − 9 s − 2, and outlined the eddy for approximately 9 hours. Although it is difficult to identify the origin of the detected submesoscale eddy, its appearance coincided with a drop in relative atmospheric humidity suggesting land-ocean Santa Ana winds as a possible generating mechanism.

The influence of easterly and northeasterly dry and warm Santa Ana winds (SAw) on the surface circulation of Todos Santos Bay, Mexico, is studied from surface currents and wind data measured during the most extreme periods of activity (autumn-winter season). Sea surface currents were measured using a system of coastally-based HF radar stations between 2009 and 2015. Winter-mean surface circulation showed a cyclonic tendency. Atmospheric variables allowed the grouping of ~122 SAw events, 23% of which caused a noticeable change in the background circulation. Event-mean current patterns showed dissimilar responses to the acting winds, with some SAw events driving weak offshore currents, another that developed an eddy-pair circulation inside the bay, and one rather intense (winds of 8-10 m s–1) that developed a clockwise circulation overturning the cyclonic long-term winter-mean. In general, changes in the circulation were related to an offshore transport of surface waters into the open ocean.

In this work we present the exchange flows between a semi-enclosed Bay and the adjacent ocean as measured by a real-time coastal observing system in Baja California, Mexico. Several sources of information as numerical modeling, currents profile data, high frequency radar observations and drifters tracking, all together show an interesting three-dimensional structure to the exchange flows. The northern entrance (relatively shallow, ∼40 m at its deepest portion) showed an estuarine-like exchange pattern, with a net outflow at the shallow parts and inflow at the deepest, suggesting that the frictional effect is more important than the earth's rotation, as typically observed in relatively small bodies of water like estuaries and coastal lagoons. On the other hand, the southern entrance (with a ∼400 m deep canyon) is more complex, with recurrent anticyclonic exchange pattern with inflows at the western limit and outflows at the east. We suggest that the vertical structure of this circulation may be sustained by the deep canyon which lowers the thermocline, but further investigation is needed.

Climatological data indicate that Gulf of California (GC) waters are warmed in spring by the exchange of waters with the Pacific Ocean. To better understand this exchange, hydrographic observations were collected across the entrance to the GC during 19–21 April 2013. Results indicated an anticyclonic exchange with the Pacific Ocean. Strong outflow of Gulf of California Water (GCW) occurred over the outer continental shelf and slope of Sinaloa with maximum velocities of 0.5 m·s–1 at ~60 m depth and reaching ~500 m depth. Inflow close to the Baja California Peninsula was weaker (0.1–0.2 m·s–1) and transported both California Current Water and GCW. Satellite altimeter data indicated a possible reason for this flow pattern at the entrance to the GC: a couple of eddies to the east blocked the usual path of California Current flow toward Sinaloa. Horizontal transports integrated across the gulf were calculated with observed velocity and geostrophic balance. Transports were greatest in the upper 200 m, with outflow above 500 m depth, implying a net cooling of these upper layer waters in the gulf. Observations were compared with data collected in early May 1992. April 2013 exhibited much greater thermohaline variability in the upper ocean than May 1992, when a well developed cyclonic flow was observed at the entrance to the GC. The transports estimated with Pegasus for April–May 1992 were very different from those estimated for April 2013, when inflow (and heat gain) dominated above 500 m depth. The contrast between the 2013 and 1992 measurements is an example of how mesoscale eddies can reverse normal seasonal exchanges at the entrance to the GC.

Microplastics (MPs) are ubiquitous and a threat to marine and freshwater environments. Effluent waters from secondary wastewater treatment plants (WWTPs) into Todos Santos Bay (TSB) were investigated as sources of MPs. MPs were detected in all analyzed matrices and presented variable morphologies. MPs from surface water samples (n = 18) varied from 0.01 to 0.70 plastic particles/m3 (pp/m3). Fragments (47 ± 23%) and fibers (47 ± 23%) were the most abundant particles found in the surface water samples. In sediment samples (n = 11), MPs varied from 85 to 2494 pp/0.1 m2. Sediment samples showed fragments of 70 ± 19%, fibers 28 ± 18% in mean. The range of MP values from WWTP effluents (n = 24) was 81 to 1556 pp/m3, and fibers (65 ± 28%) were the most abundant MP particles. Several synthetic polymers (polypropylene, polyethylene, polyethylene-propylene, polyvinyl chloride, cellophane), and natural fibers (cotton and wood) were identified. The surface currents and the parameters that modulate them, are the main factors that dominate the distribution of MPs in surface waters. While in the sediments the parameters such as bathymetry and grain size distribution have more influence on their distribution in the marine environment, where the effluent waters from WWTPs only contributes MPs to the TSB.

Water bacteriological qualities of 22 recreational beaches in Ensenada Bay, Baja California, Mexico were analyzed during the summer and winter of 2008. Total and fecal coliforms as well as enterococci bacteria were used as pollution indicators. Results showed that bacteria concentrations were higher in winter than summer, associated with Southern California rainy season. Bacteria loads in winter exceeded both the daily and monthly standards showing a clear effect of storm water runoff in the quality of Todos Santos Bay recreational beaches. Statistical analysis showed significant differences between bacteria concentration during summer and winter. The general behavior of the indicators based on daily and monthly standards from high to low was enterococci > FC > TC> total/fecal ratio. Water discharged from 3 sewage treatment plants were responsible for the pollution observed at stations, when the uptake capacity of plants exceeded the storage. During summer pollution was due to non-programmed discharges from sewage treatment plants.

Closely spaced XBT and CTD data were used to study the sub-surface structure of features observed in satellite AVHRR sea-surface temperature (SST) images of the Gulf of California (GC), such as fronts, jets and gyres. The lowest SSTs in the GC are found around the midriff islands, and especially over the sills, because of strong mixing from tidal currents and breaking internal waves. This minimum SST area is limited to the south and north by sharp SST fronts, which frequently show convolutions, gyres, and filaments. A vertical section of temperature along the Gulf length shows that about 300 km south of the sills, the isotherms begin to spread out in the vertical, reducing stratification. The thermocline isotherms begin surfacing about 100 km south of the sill, forming the SST minimum area, which has a maximum temperature difference of ∼6 °C with waters to the south and a horizontal SST gradient of ∼0.05 °C km −1 . The evolution and subsurface structure of a cool filament, apparently originated as an instability of the SST front, was intensely sampled. Satellite images show that its head advanced due south at about 0.5 ms −1 , along the edge of a pool of warm surface water about 110 km in diameter. The thermocline below the warm pool was raised at its edge, and some isotherms reached the surface, producing the cool filament. The tilt of the temperature, salinity and density isolines at the edge of the warm pool produced a geostrophic jet, adjacent to the cool filament and just inside the warm pool, with maximum speed ∼0.5 ms −1 and extending down to ∼80 m. The filament lasted about 10 days, its width was ∼30 km and it reached a maximum length of ∼120 km.The volume transport of the jet in the top 100 m was around 0.7 Sv.

Fernández-Barajas et al. (1994) reportan los resultados de mediciones hidrográficas realizadas en la entrada del Golfo de California en agosto de 1992. Durante ese crucero, el CTD se encontraba calibrado inadecuadamente, teniendo como resultado mediciones anómalas de altas temperaturas y bajas salinidades. Fernández-Barajas et al. (1994) incorrectamente atribuyeron estas condiciones anómalas al fenómeno El Niño de 1991- 1993 y a la tormenta tropical Lester. Fernández-Barajas et al. (1994) report results of hydrographic measurements at the entrance to the Gulf of California in August 1992. During this cruise, the CTD was improperly calibrated, and this resulted in anomalously high (low) near-surface temperatures (salinities) being reported. Fernández-Barajas et al. (1994) incorrectly attribute these anomalous surface conditions to the 1991-1993 El Niño and tropical storm Lester.

Fernández-Barajas et al. (1994) report results of hydrographic measurements at the entrance to the Gulf of California m August 1992. During this cruise, the CTD was improperly calibrated, and this resulted in anomalously high (low) near-surface temperatures (salinities) being reported. Fernández- Bara,jas et al. (1994) incorrectly attribute these anomalous surface conditions to the 1991-1993 El Niño and tropical storm Lester.

Mediante observaciones directas (XBT, CTD y radioflotadores) se realizó la primera descripción detallada de la estructura interna y del campo de corrientes de algunas de las manifestaciones térmicas que regularmente aparecen en las imágenes infrarrojas del Golfo de California, tales como filamentos y giros de baja temperatura. La estructura interna de estas estructuras reveló la ausencia de la capa mezclada (que es de 40 m en los alrededores) y un levantamiento de las isotermas, detectable hasta ≈ 200 m. El agua superficial es más fría y salina (y por tanto más densa) que los alrededores. Entre las estructuras estudiadas destaca un filamento frío; el cual originándose en la zona de intensa mezcla del umbral sur del sistema de canales Ballenas-Salsipuedes, siguió una trayectoria anticiclónica por el eje del golfo y terminó frente a Punta Concepción. El filamento presentó dos fases de evolución; una impulsiva con altas velocidades (.5 m/s) y de dos días de duración, y otra estable de casi una semana. La circulación superficial coincide, en términos generales, con el patrón inferido por la distribución de temperatura: tanto las corrientes geostróficas como las radioboyas indican que hay una intensa corriente (60 cm/s) en el interior del chorro y corrientes de retorno (opuestas) más débiles en sus alrededores. El transporte de este filamento de 40 km de ancho (0.5 a 1 Sv) es muy importante, pues es del mismo orden que el promedio de una sección a través del Golfo. Por otro lado se investigó un intenso evento de surgencia costera frente a la bahía de Guaymas: las isolíneas se levantaban hacia la costa, originando corrientes de hasta 70 cm/s y temperaturas y salinidades superficiales (19˚C y 35.25 ups) típicas de una profundidad de ≈ 50 m, con la consecuente inyección de nutrientes a la zona eufótica. A pesar de la intensa corriente, las imágenes de satélite no revelan la formación de un chorro frío. Se analizó una estructura vórtice dipolo, también llamada en forma de hongo, detectada tanto con imágenes infrarrojas como por los datos directos de XBT y CTD. El vórtice presentó características radicalmente diferentes a las estructuras frías, mostrándo aguas templadas, salinas y boyantes, i.e. agua de origen superficial. El análisis de datos sugiere que esta formación es el resultado de una inestabilidad superficial en la interfase de un frente térmico de las aguas calientes de la cuenca del Carmen con las aguas frías de la cuenca de Guaymas. N/E