The ocean is characterized by a circulation dominated by vortex of different sizes; the vortex play a very important role in the oceanic climate as they transport energy, mass and organisms. Their study is therefore of first importance to understand the different processes that occurring in the seas at different time-space scales. The Bay of Campeche, in the southern Gulf of Mexico, is characterized by a cyclonic circulation. With the aim of identifying the origin and the formation of the cyclonic vortex, data of currents registered in an oceanographic survey and data of sea altimetry obtained with remote sensors were analyzed. From the results, the formation of the cyclonic vortex of the Bay of Campeche depends mainly on the conservation of the potential vorticity.

We used a two-year dataset (1998-1999) of monthly temperature profiles from Lake Alchichica, Mexico to estimate values of the vertical coefficient of eddy diffusivity. This lake is located in a tropical region at high altitude and shows considerable seasonal variations (i.e., rainy and dry seasons). It has an area of 2.3 km2 and a mean depth of 40.9 m. Alchichica is a warm monomictic lake, which annually becomes isothermal near the end of December or early January at the onset of the dry season and remains stratified for the rest of the year (from late March or early April to early December) during the warm-rainy season. Mathematical models of the spatial and temporal variation of passive substances in lakes and oceans require a quantitative formulation of the vertical transport. Vertical mixing is generally a function of the density profile, which, in lakes, can be directly related to the temperature profile. A widely used method to estimate the vertical diffusion coefficients in lakes from temperature data is the flux-gradient method. In the present study, we applied a simple approach to calculate the eddy diffusivity coefficient (Kz) based on the solution of the vertical component of the modeled temperature equation. We characterized the eddy diffusivity coefficient (Kz) in Lake Alchichica as a dynamic coefficient that changes during the year, between years, and with depth, ranging from 10-10 to 10-6 m2 s-1, whereas typical values of Kz in thermally stratified lakes range from 10-9 to 10-2 m2 s-1. As expected, we found the lowest values in the deeper regions of the lake, and that the temporal variation of temperature with depth showed a quasi-bimodal shape from one year to the next. We also found a structure of alternating peaks and troughs in the vertical Kz, which indicates a response to oscillating vertical mixing. We concluded that the solution of the vertical component of the temperature equation could be a useful tool to estimate the eddy diffusivity in lakes. The major advantage of this method is its simplicity. We also conclude that the differences observed in the estimations of eddy diffusivity coefficients in other lakes are attributable to the differences in local characteristics of the thermal conditions in each lake.

Se presenta el análisis de un conjunto de datos de temperatura, salinidad y sigma-t, obtenidos en los cruceros oceanográficos OGMEX I, IT, III y V, realizados en el sur de la Bahia de Campeche en febrero-marzo, julio-agosto, noviembre-diciembre de 1987 y agosto de 1988, respectivamente. De la distribución de parámetros hidrográficos, promediados en el tiempo, de las cuatro campañias, se observa el efecto de los rfos formando frentes semi-permanentes inducidos por la descarga de aguas de menor temperatura y salinidad. Mediante el uso de un modelo inverso lineal en diferencias finitas, aplicado a los datos hidrográficos promediados en el tiempo, se determina el campo de velocidad a 3 profundidades diferentes 0, 10 y 20m. Los resultados del modelo inverso confirman la existencia de un giro ciclónico en la zona de estudio.

This study evaluated the ingestion of microplastics (MP) by copepods in Terminos Lagoon (TL), a RAMSAR-listed site in the southern Gulf of Mexico. The evaluation was carried out in two contrasting seasons of 2022, as follows: the dry (April) and the rainy (October). Copepods were collected using a conical plankton net (mesh size of 200 μm). In the laboratory, a pool of all pelagic adult copepod taxa was picked, and the MP inside the organisms were extracted, classified, and photographed using traditional optical and scanning electron microscopy. A total of 268 MP particles were extracted from the interior of copepods; among them, 149 and 119 corresponded to the dry and rainy seasons, respectively. The ingestion rate in the dry season was 0.14, while in the rainy season, it was 0.11. In addition, fibers, plastic fragments, and microspheres with different colors (blue, red, black, green, transparent, and multicolored), sizes, forms (angular, round, triangular, and twisted), and textures were also detected. Fibers were the most abundant MP found in a proportion of more than 85%. In addition, in some sampling sites, microspheres were observed with high relative abundance values (80%). In some sites, fragments reach 20% of the total abundance. Significant differences were observed between the two seasons. The sites closest to the urban area adjacent to TL observed high diversity and abundance of MP. The higher abundance of MP in the dry season is due to lower river discharge, on the other hand. Thus, MP particles accumulate and become available for consumption by copepods. This is the first study that has revealed that the MP was ingested by the copepods in TL. Furthermore, this study provides a baseline information for future research on the abundance of MP in the Gulf of Mexico region.