Cecilia Chapa-Balcorta

The Mexican Tropical Pacific (MTP) is a key component of the Eastern Tropical North Pacific Oxygen Minimum Zone, yet its carbonate system variability remains poorly constrained. This study examines wind-driven circulation effects on dissolved oxygen (DO) and the carbonate system —dissolved inorganic carbon (DIC), total alkalinity (TA), total-scale pH (pH_T), partial pressure of CO₂ in seawater (pCO_2w) and air–sea CO₂ fluxes (FCO₂)— in the Gulf of Tehuantepec (GT) and Tehuantepec Bowl (TB). Hydrographic data and discrete water samples were collected at 50 oceanographic stations during March 2020. Principal Component Analysis (PCA) identifies wind-driven circulation as the primary control of biogeochemical variability. Tehuano wind events and mesoscale eddies promoted upwelling of low-oxygen (DO < 20 µmol kg⁻¹) and high-DIC (>2200 µmol kg⁻¹) waters to 50 m depth in the central GT, while downwelling conditions prevailed in the TB. Stoichiometric analysis revealed DIC-DO coupling (slope = −1.39). Overall, the MTP acted as CO₂ source (FCO₂ ranging from −1.92 to 24.11 mmol m⁻² d⁻¹), with enhanced emissions linked to eddy-induced upwelling. This study provides the first integrated characterization of the carbonate system across both the GT and TB.

We hypothesized that mesoscale physical processes, specifically anticyclonic eddies and coastal upwelling, generate distinct vertical phytoplankton community structures at the chlorophyll maximum in the southern Gulf of California. From November 5th to 21st, 2020, an oceanographic cruise was carried out aboard the RV "Dr. Jorge Carranza Fraser" of the Instituto Mexicano de Investigación en Pesca y Acuacultura Sustentable, in the southern Gulf of California. Temperature, salinity, dissolved oxygen, and chlorophyll variables were measured at 54 stations using a conductivity, temperature and depth instrument. We identified the depth of the chlorophyll maximum and obtained an aliquot of water was obtained for phytoplankton identification. We processed satellite images of sea surface temperature and chlorophyll, obtained with the MODIS Aqua sensor (L3 level) with a five-day resolution and 1 km per pixel. Images of geostrophic flux and absolute sea level height were obtained to identify the mesoscale physical processes present in the study area that influence the structure of the phytoplankton community. We analyzed phytoplankton diversity and abundance using standard ecological indices, evaluating the influence of mesoscale features on community structure. We observed surface chlorophyll maxima (less than 10 m) and high abundances of Thalassiosira , Thalassionema , and Chaetoceros at upwelling-influenced coastal stations. Meanwhile, we observed deeper maxima (more than 40 m) and the dominance of Thalassionema and Chaetoceros in oceanic anticyclonic eddies. These niche differentiations of the dominant phytoplankton species provide essential fundamental for applying predictive models of fishery productivity under mesoscale regimes in changing ocean environments due to global warming.

Providing reliable instrumentation that enables collection of high-​quality, comparable data is one of the most challenging aspects of establishing ocean acidification monitoring programs. This is especially true for under-resourced countries, where such data are mostly unavailable. In 2016, The Ocean Foundation (TOF) worked with international bodies, including the International Atomic Energy Agency’s Ocean Acidification International Coordination Centre and the Global Ocean Acidification Observing Network (GOA-ON), and subject matter experts to develop a set of equipment known as the “GOA-ON in a Box” kit (The Ocean Foundation, 2017). This comprehensive kit provides researchers with everything needed—down to specialized rubber bands—to obtain weather-quality carbonate system measurements as defined by GOA-ON (Newton et al., 2015). Data are generated from spectrophotometric measurements of pHT and manual titrations for total alkalinity from discrete samples as well as in situ sensors, the iSAMI-pH and a CTD. The kit’s modular design, composed of nearly 100 unique items, makes it much less expensive than comparable integrated systems and allows for easier troubleshooting and replacement of supplied spare components.

En este trabajo se hace un análisis de la información existente sobre acidificación del océano en el Pacífico mexicano (pM) obtenida mediante campañas oceanográficas, para identificar las condiciones generales en las distintas regiones, así como para identificar las zonas con vacíos de conocimiento y determinar las necesidades de investigación. La distribución espacial del pH, carbono inorgánico disuelto (cid), temperatura, salinidad y dirección de la corriente superficial, se muestran en un perfil tipo de las regiones norte, centro y sur del pM; además, se hace un análisis de los efectos de la acidificación del océano (ao) en especies marinas de importancia comercial y para el sector pesquero. El resultado de este análisis indica que las cuatro regiones del pM (Baja California [BC], Golfo de California [GC], Pacífico tropical mexicano [pMt] y Golfo de Tehuantepec [gt]) se han medido al menos una vez. En mar abierto la región más estudiada es frente a las costas de Baja California, estudiada en el programa Investigaciones Mexicanas de la Corriente de California (Imecocal). En contraste, existen vacíos de información alrededor de las Islas Revillagigedo y la región exterior de la Zona Económica Exclusiva (zee). El iMipaS ha contribuido con el 28.45% de las colectas de agua de mar realizadas a la fecha para el estudio de la acidificación del océano. En cuanto a la columna de agua, se desconoce totalmente la magnitud, distribución espacial y variabilidad del pH y dic a profundidades mayores a 500 m. De las cinco masas de agua que se distribuyen en el pM entre 0 y 500 m de profundidad, el agua subsuperficial subtropical (ASsSt) presenta una mayor concentración de cid (> 2200 μmol kg-1), así como valores mínimos de pH (7.2-7.7), cuya distribución espacial está en función de la dinámica física y biogeoquímica de cada región. En el pM se distribuyen especies de importancia pesquera y ecológica que son sensibles a estos intervalos de pH. Por lo anterior, es esencial seguir realizando estudios de AO e impulsar políticas y estrategias de manejo que ayuden a identificar umbrales óptimos para las especies y regiones con mayor vulnerabilidad y/o establecer umbrales con valores donde se requiere implementar medidas para contribuir a incrementar la resiliencia de los ecosistemas marinos ante la acidificación del océano asociado al cambio climático.

El golfo de California (GC) presenta diversos procesos oceanográficos. Tiene comunicación con el océano Pacífico mediante un flujo de salida de agua superficial (0–200 m) con valores relativamente bajos de carbono inorgánico disuelto (CID) y un flujo de entrada de agua (200–600 m) con valores altos de CID. Los datos sobre el sistema de carbono marino en el GC son escasos, y la mayoría proviene de la región de las islas grandes, en el centro del golfo. Se exploraron los posibles agentes forzantes que controlan la variabilidad del flujo de CO2 océano-atmósfera (fCO2) en 5 zonas costeras del GC. Se realizaron 6 cruceros oceanográficos en 5 regiones: frente al norte de Sinaloa en septiembre de 2016 (NAV2016) y marzo de 2017 (NAV2017), en la cuenca de Guaymas (centro del golfo) en septiembre de 2016 (GUA2016), en bahía Concepción (Baja California Sur) en julio de 2017 (BC2017), en Mulegé (Baja California Sur) en julio de 2017 (MUL2017) y frente a Mazatlán (golfo sur) en julio de 2017 (MAZ2017). Se midió la temperatura y la salinidad, se estimó el CID y la alcalinidad total y se calculó la presión parcial de CO2 superficial y el fCO2. Se utilizaron imágenes de satélite para generar compuestos de la anomalía del nivel del mar con flujo geostrófico, la temperatura superficial del mar y la concentración de clorofila en los días de muestreo. La temperatura más baja, el CID más alto y el fCO2 negativo se registraron en NAV2017. NAV2016, GUA2016 y BC2017 registraron las temperaturas más altas, y MUL2017 y MAZ2017, temperaturas intermedias. Los mayores contrastes de fCO2 ocurrieron en GUA2017 (0.56 ± 0.46 mmol C· m–2·d–1) y MAZ2017 (–2.26 ± 1.85 mmol C· m–2·d–1). En general, el fCO2 está determinado por las condiciones oceanográficas de cada zona de estudio.

Seasonal variations of the CO₂ system in seawater for coral reefs are often controlled by both chemical‐biological processes and by regional oceanographic features in combination with the residence time of adjacent water. This study reports the seasonal variability of the CO₂ system along a year though dissolved inorganic carbon and pH measurements in Cabo Pulmo, a fringing reef from the Mexican Pacific. Two conditions were found on the reef: summer with the presence of Tropical Surface Water (TSW), characterized by high temperature, lower DIC levels, and a higher aragonite saturation (Ω_arag); and winter with Gulf of California Water (GCW), when the opposite occurred. This seasonal variation was due to the horizontal advection of two surface water masses: Gulf of California water during winter and Tropical Surface Water the rest of the year as a result of the ocean circulation at the entrance of the Gulf of California. Therefore, the reef is significantly influenced by open ocean waters, where the depth is less than 20 m. The seasonal variability in Ω_arag between months with the presence of GCW and TSW is one of the largest ranges reported in coral reefs (ΔΩ_arag = 0.5 units). Our results suggest that the reef community cannot modify the aragonite or pH of incoming ocean water. This might be the case in other fringing reefs, where the use of ocean acidification forecast models is suitable.

Global warming and ocean acidification affect coral calcification. Nevertheless, there is not enough information regarding the growth parameters of the main reef-building coral species in marginal growth areas such as the Pacific coast of southern Mexico. In order to fill this gap, coral growth parameters of 8 hermatypic coral species (massive species: Porites panamensis, Porites lobata, Pavona gigantea, and Pavona varians; branching species: Pocillopora meandrina, Pocillopora damicornis, Pocillopora verrucosa, and Pocillopora capitata) were estimated in 2 areas of the southern Mexican Pacific. Branching coral species had a higher calcification rate (2.99–5.23 g CaCO3 cm–2 yr–1) than massive species (0.34–1.13 g CaCO3 cm–2 yr–1). A significant relation between sea surface temperature (SST) and skeletal density was observed in all massive coral species. Also, 2 massive species (P. gigantea and P. varians) showed a significant relation between SST and calcification rate. Upwelling in the Gulf of Tehuantepec transports deep water with low pH and low aragonite saturation, and may be affecting the calcification rate of stony corals in the studied area.

This investigation reports, for the first time, results of CO₂ system variables in the Gulf of Tehuantepec, located in the Mexican tropical Pacific. We quantified the post‐Tehuano concentration of dissolved inorganic carbon (DIC) and pH (April 2013). These values were used to calculate pCO2, aragonite saturation (Ω_Ar), and air‐sea CO₂ fluxes (FCO₂). The intense vertical stratification was found to contribute to the biogeochemical processes in surface waters (−1), as well as low Ω_Ar (∼1.1) and pH (∼7.5), remain in surface waters for a few days after Tehuano winds have weakened. We identified four oceanographic areas: (a) a highly mixed region due to previous Tehuano events; (b) coastal upwelling in the western region; (c) mesoscale eddies; (d) a poleward surface coastal current. The first three promoted the influence of Subtropical Subsurface Water in the chemistry of surface waters, whereas the coastal current contributed to the horizontal advection of DIC. The calculated CO₂ fluxes ranged from −2.3 mmol m⁻² d⁻¹ in areas with stratified waters to over 25 mmol m⁻² d⁻¹ for mixed areas. Positive values indicate an ocean‐to‐atmosphere flux. Our findings suggest that the Gulf of Tehuantepec is a major source of CO₂ into the atmosphere.

In the Midriff Islands region (MIR) of the Gulf of California (Mexico), tidal mixing plays a very important role in the distribution of chemical properties. Although the temporal variability of the water masses is linked to the ocean dynamics of this region, its importance has not been considered. This work estimates the effect of water mass dynamics on the spatial distribution and seasonal variation of dissolved inorganic carbon (DIC) in the region, with special emphasis on the Ballenas Channel, during winter 2002, spring 2003, and summer 2004. Gulf of California Water (GCW) was found throughout the area in the first 100 m. Below, Subtropical Subsurface Water (SSW) filled the Delfín, Salsipuedes, and Tiburón basins, while to the southeast it was found between 150 and 350 m. Pacific Intermediate Water did not cross the sills. SSW enriches the surface water of the MIR with DIC when it increases in volume and when mixed with GCW by tidal effects. This contribution decreases towards summertime, when SSW sinks and the volume of GCW increases. In winter, GCW had three water types associated with oceanographic mixing processes and in combination with the presence of SSW. There was a strong DIC vs temperature relationship, which can be applied to analyze the carbon dynamics in the MIR, both at the surface using satellite imagery and vertically to simulate physical processes.