Interannual climate variability exerts a strong control on the thermohaline structure of eastern boundary upwelling systems, particularly in transition zones where distinct water masses converge. Seasonal and interannual variability in temperature and salinity were examined in the southern California Current System for the period 2000–2015 using hydrographic observations and satellite altimetry, analyzed by season and ENSO phase. During El Niño, the upper 100 m exhibits positive temperature and salinity anomalies of 1–2 °C and ~0.1–0.2 g kg−1 associated with 50–80 m isopycnal deepening, reduced upwelling-induced ventilation, the expansion of subtropical waters onto the shelf, and enhanced poleward geostrophic transport. In contrast, La Niña conditions shoal isopycnals, enhances upper-layer stratification, and sustains equatorward flow throughout the year. Temperature and salinity anomalies extend below 100 m, suggesting a remote reorganization of the baroclinic structure at the shelf–ocean boundary. Salt fingering is inferred to be the dominant non-conventional mixing process in the region, with peak occurrence in autumn. These results highlight that ENSO confines thermohaline reorganization to the inner continental shelf (~150 km), modulates coastal–ocean density gradients, weakens equatorward geostrophic transport during El Niño, and alters coastal–ocean heat and salt exchanges within the southern CCS transition zone.

Hydrographic data from cruises of the Investigaciones Mexicanas de la Corriente de California (IMECOCAL) program since 1998 were used to assess the chemical conditions associated with carbon variables in the water column in the transect “Line 100.” Seasonal climatologies along the IMECOCAL line highlight the upwelling season, during which water with different chemical characteristics is transported to the surface. Additionally, interannual events influenced the amplitude and timing of wind‐driven coastal upwelling and the region's relative volumes of dominant water mass. Seasonal climatologies of pH, calcium carbonate saturation states, and dissolved inorganic carbon (DIC) concentration were estimated from hydrographic proxy variables. The strength of seasonal upwelling was reflected in the depth of the aragonite saturation horizon (ASH), which was variable nearshore: 90 m (±29 m) in spring and 133 m (±32 m) in winter. Offshore (>50 km), the effect of upwelling diminished, and the ASH was deeper and less variable (spring: 152 m ± 25 m; winter: 151 m ± 28 m). However, aragonite saturation values <1 were found at depths >250 m and were associated with Equatorial Subsurface Water (ESsW) dominance. At seasonal timescales, Subarctic Water (SAW) was found to modulate ASH depth. At interannual scales, ASH was found to be deeper (180 m) during periods of El Niño and shallower (120 m) during La Niña conditions. However, the impacts of El Niño and La Niña events give notable differences in the ASH depth.

The absorption or scattering of photosynthetically active radiation (PAR) in the ocean by its components is crucial in determining the extent of the euphotic zone. This stratum is the ocean's uppermost layer, where light availability governs primary productivity in marine ecosystems. This study aims to bio-optically categorize Gulf of Mexico oceanic waters based on regional differences in water transparency and the euphotic zone depth using remotely sensed diffuse attenuation coefficient data (Kd490) validated with in situ observations (KdPAR) from cruises conducted between May 2016 and June 2019. An overestimation of about 15 % of remotely sensed depths was found, which was significantly reduced using in-water records. A 22-year climatological analysis on the calibrated euphotic zone depths derived from satellite-based Kd identified three optical regions in the Gulf of Mexico (I, IA, and IB). Deeper euphotic zones were observed in Region I (in central waters), while Region IB (in the Bay of Campeche) had shallower euphotic zones. The differences in PAR light penetration were linked to variations in chlorophylla, which were modulated by mesoscale circulation and river discharges. Our findings support the extent of the euphotic zone down to 0.1 % of incident surface light, especially in Region I, where the large anticyclonic eddies detached from the Loop Current have the most influence in the oceanic waters of the Gulf of Mexico. This study contributes to understanding important optical variables that can be used to improve models for estimating primary productivity and carbon fluxes in oligotrophic surface layers.

Mathematical algorithms relate satellite data of ocean color with the surface Chlorophyll-a concentration (Chl-a), a proxy of phytoplankton biomass. These mathematical tools work best when they are adapted to the unique bio-optical properties of a particular oceanic province. Ocean color algorithms should also consider that there are significant differences between datasets derived from different sensors. Common solutions are to provide different parameters for each sensor or use merged satellite data. In this paper, we use satellite data from the Copernicus merged product suite and in situ data from the southernmost part of the California Current System to test two widely used global algorithms, OCx and CI, and a regional algorithm, CalCOFI2. The OCx algorithm yielded the most favorable results. Consequently, we regionalized it and conducted further testing, leading to significant improvements, especially in eutrophic and oligotrophic waters. The database was then separated according to (a) dynamic boundaries in the area, (b) bio-optical properties, and (c) climatic conditions (El Niño/La Niña). Regional algorithms were obtained and tested for each partition. The Chl-a retrievals for each model were tested and compared. The best fit for the data was for the regional algorithms that considered the climatic conditions (El Niño/La Niña). These results will allow for the construction of consistent regionally adapted time series and, therefore, will demonstrate the importance of El Niño/La Niña events on the bio-optical properties of the area.

The larval fish community in the southern region of the California Current (CC) was analyzed to test the hypothesis of a northward expansion of tropical species for the summer-fall seasons of La Niña (LN) 2010-2011, The Blob 2014, and El Niño (EN) 2015-2016. Interannual temperature anomalies (-5 to +2°C), as well as decreases in chlorophyll a (68%) and zooplankton density (71%), resulted in dramatic changes in the larval fish community, such as an 82% decline in larval fish density, unprecedented for the CC. Tropical species richness increased in the north by 46%, while temperate species decreased by 65% in the south. Mesopelagic species richness and relative abundance increased in the north by 53 and 92%, respectively. In the south, the species richness of the demersal component increased up to 39%, although demersal species were co-dominant with mesopelagic species, accounting for 47% of the relative abundance compared to 49% for the mesopelagic species. The magnitude of the changes in the community was unparalleled when compared with other warming events, such as EN 1983-1984 or EN 1997-1998. The differences were probably related to the presence of The Blob, which favored the transport of oceanic species into the neritic region of the CC. In both cold and warm years, fronts and mesoscale eddies in the middle part of the Baja California Peninsula represented barriers to the latitudinal distribution of species, even during intense tropicalization processes, since no latitudinal extensions in species distribution occurred.

The microbial plankton community is an integral part of the pelagic ecosystem. It hosts essential functional groups that play a vital role in organic carbon production, release, uptake, and degradation within open-ocean ecosystems. Given its significance, carbon biomass estimates are urgently needed, especially in oligotrophic regions, to provide and enhance our knowledge of biogenic carbon pools. They also aid in validating biogeochemical models that characterize the functioning of these extensive marine ecosystems within the global carbon cycle. This study addresses the temporal variability of microbial community biomass in two oceanic zones: the west-central (Perdido) and southern (Coatzacoalcos) areas of the Gulf of Mexico. During three seasonally contrasting periods (nortes, rainy, and dry seasons), seawater samples were collected from the euphotic zone in both regions to estimate the carbon biomass of different pico- (<2–3 µm), nano-, and microplankton groups (>3–200 µm). Carbon biomass assessments for the microbial groups were based on their abundance and carbon conversion factors. Overall, we found a significant contribution of pico-prokaryotic components (heterotrophic bacteria, Prochloroccocus, and Synechoccocus) to the total microbial carbon stock of the euphotic zone (84–89 % global estimates). The finding suggests these microorganisms are key functional groups that drive carbon production and fate in the Gulf of Mexico ecosystem. Pico-cyanobacteria, especially Prochloroccocus, were the dominant primary producers (68–82 % total autotrophic carbon), mainly in the upper layer of the oligotrophic euphotic zone. This vertical pattern implies that the deep chlorophyll-a maximum (DCM) depth level was unrelated to a net increase in phytoplankton biomass in the three study periods. The distribution of microbial carbon biomass exhibited striking differences associated with winter mixing (the nortes season), high river discharge accompanied by cross-shelf transport (the rainy season), and the dynamics of mesoscale structures. Ecological aspects, such as the habitat preference of the organisms and the seasonal complementary development of mixotrophic and heterotrophic grazers and their prey, were also essential drivers in regulating the microbial carbon pool of both oceanic regions. The microbial carbon assessments conducted in this study contribute to identifying and quantifying key planktonic functional groups involved in the biogeochemical carbon cycle in the Gulf of Mexico open-ocean ecosystem.

Depending on dimensions, orientation and topographic features, the circulation of semi-enclosed seas adjacent to regions of coastal upwelling are strongly influenced by their interaction with a shelf upwelling jet of adjacent waters. A special case are square bays, where opening is about the same size as length, and are bordered by headlands at the entrance. This study analyzed surface currents measured between 2009 and 2020 with high-frequency (HF) radar in Todos Santos Bay, a square bay located in northwestern México, to obtain mean and seasonal surface circulation patterns. HF radar measurements indicate that the average circulation pattern within the bay is cyclonic, with water of the California Current (CC) entering primarily as a coastal jet through the northern mouth of the bay. The similarity of monthly average maps with the long-term average suggests the cyclonic circulation persists year-round. Scale analysis demonstrates that given the size of the bay, only one eddy, primarily controlled by inertia, is dominantly formed inside. The mean cyclonic circulation defines the bay as an upwelling shadow.

High frequency radars (HFR) are systems that allow us to monitor some oceanographic variables through the backscatter signal from the ocean surface. Typically, they provide us with a relatively high space-time resolution of surface currents and the wave field, very important local information to be used for maritime operation applications, such as search and rescue, safety at sea and transportation, and marine energy resources assessment. Although the main product from HFR is ocean surface currents, they can in addition, provide useful information to derive important characteristics of the wave field, such as significant wave height (Hs) and even the directional spectrum. We, nevertheless, focus our attention in this work in the wave field, and specifically Hs values. A HFR (WERA system) is in operation in Todos Santos Bay, Ensenada, Mexico, since March 2021. Maps of significant wave height are estimated every hour over an area of approximately 250 km2 with spatial resolution of 800 m. These measurements have been compared with wave data derived from three moored instruments (ADCP), the results yielded correlations greater than 0.7 and RMSE values less than 40 cm. In the last two decades this technology has been implemented throughout the world, although there is very limited detail on calibration and validation of the instrument with local ocean wave conditions, especially with respect to the presence of swell. In this study, an empirical calibration is performed using an algorithm provided by the manufacturer in which a correction parameter is obtained according to the operating frequency of the radar, in particular a WERA system. This study takes into consideration some particular characteristics of the area of interest and the performance of the correction parameter is determined as a function of the wave height and direction of travel relative to the radial direction from the WERA site.

Vinciguerria lucetia is a mesopelagic fish whose larvae show an almost permanent presence in the southern portion of the California Current System. Due to its sensitivity to environmental changes, the species has been considered an indicator of water masses and interannual variability. Fish larvae abundance registered from 1997 to 2015 by the program Investigaciones Mexicanas de la Corriente de California was used to predict the abundance distribution of V. lucetia larvae under two extreme thermal conditions (2000 La Nin similar to a and 2015 El Nin similar to o), utilizing the novel machine learning algorithm eXtreme Gradient Boosting (XGBOOST). The data were segmented into COLD and WARM groups based on the mean sea surface temperature recorded at each station and contrasted with an undivided TOTAL group. Models were generated using 12 environmental and biological predictor features. Root-mean-squared logarithm error (RMSLE) was used as a prediction performance metric for both internal and external validation. The COLD model showed the best performance for the internal validation with a lower RMSLE value, while the TOTAL model for both the coldest and warmest external validation presented the lowest RMSLE values. The external validation demonstrated models that accurately predicted the spatial distribution; however, none of the models were able to accurately predict the same abundance magnitude observed in both extreme thermal conditions. Nevertheless, XGBOOST shows promise for describing the future distribution traits of V. lucetia.

Oceanographic features acting on different spatial-temporal scales influence the variation in the partial pressure of CO2 (pCO2) and ocean-atmosphere CO2 flux (FCO2). In this work, we regionally characterize regions of variability in the Mexican Pacific (MP) based on these chemical properties. We also evaluate the seasonal and interannual changes of each region: in the California Current System (CCS), Cabo Corrientes (CC), and Gulf of Tehuantepec (GT) regions. Sea surface temperature (SST), salinity, wind, pCO2, and FCO2 data from 1993 to 2018 were analyzed. Bayesian t-tests (95% credibility intervals) determined showed that the three regions had high probabilities of being different. Typical FCO2 values in the CCS were higher (- 27.6-29.8 mmol C m- 2 d-1) than those of the CC and GT regions (- 19.9-25.8 and - 11.8-12.5 mmol C m- 2 d-1, respectively). The highest positive seasonal variation of FCO2 (mean +/- standard deviation) was found in the CCS and CC (-4.6 +/- 4.2 mmol C m-2 d- 1) regions during spring, and in the GT region (1.2 +/- 2 mmol C m- 2 d-1) in autumn due to the strong northerly winds. It was found that during ENSO conditions the MP was a source (4.0 and 3.9 mol C m- 2 y-1 for El Nin similar to o and La Nin similar to a, respectively), although on average over the last 25 years included in the study the MP acted as a slight-CO2 sink (-10.9 +/- 0.005 mol C m-2).

Marine heatwaves (MHWs) can have detrimental effects on seagrasses, but knowledge about the impacts on their ecosystem services remains scarce. This work evaluated Phyllospadix scouleri (surgrass) as a biofilter for wastewater discharges, and how warming associated with MHW may affect this ecological function. The nitrogen uptake kinetics and assimilation abilities for ammonium, nitrate, and urea were examined under two different warming scenarios (single and repeated events) simulated in a mesocosm. N-uptake kinetics were related to urban sewage discharges close to surfgrass meadows. Our results revealed that surfgrasses can serve as effective biofilters because of their high nitrogen uptake rates and above-average canopy biomass. Nonetheless, exposure to both experimental warmings resulted in a significant decline in their ability to incorporate and assimilate nitrogen. Consequently, MHWs may reduce the capacity of surfgrasses to function as nitrogen sinks and green filters for sewage waters, jeopardizing their role as Blue Nitrogen systems.

In the ocean, nitrogen availability is an important control of primary production and influences the amount of energy flowing through food webs. Mesoscale eddies play important roles in modulating the spatial distributions of physical and biogeochemical properties in the Gulf of Mexico (GM), including the availability of nitrate + nitrite (NN). In this study, we explore an oceanographic station classification based on the integrated NN stock that we have named the “nitracentric classification” and a classification based on hydrographic variables that we call the Best Fit Variables (BFVs), such as the depth of the 20°C isotherm and the depth of the 26 kg m-3 isopycnal, to identify stations under the influence of mesoscale eddies. We analyzed hydrographic profiles of CTD data and the NN concentrations in discrete samples collected in June 2016 during the oceanographic campaign XIXIMI-5, which was conducted in the deep-water region of the GM. The best station separation was produced when the NN concentration was integrated between the surface and 200 m depth, which was supported by the station classification based on the BFVs. Our classification system produces a better separation between station groups when compared to other classifications that rely on the use of altimetric variables and hydrographic criteria that have been previously employed to study biogeochemical and physical processes in the GM. We obtained parameterizations that accurately predicted the NN profiles between 100–500 m of stations sampled under stratified conditions in two other XIXIMI cruises in the gulf, although the parameterization has to be adapted to obtain accurate predictions under winter mixing conditions. Our results can be used to predict nitrate stocks and profiles based on a single BFV value obtained from the existing hydrographic databases of the GM as well as from CTD data at the time of sampling. The analysis of the CLIVAR Section A22 in the Caribbean Sea indicates that the nitracentric and hydrographic classification methodology developed in this study can also be applied to other oligotrophic basins where mesoscale eddies play important roles in controlling the distributions of hydrographic and biogeochemical properties.

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-4x10-9 to-1x10-9 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.

High Frequency Surface Wave Radars (HFRSW) are used as a technological alternative to sense oceanographic variables in a remote and non-intrusive manner. Currently, a great variety of companies commercialize these products, but at high cost. Seeking higher flexibility and lower economic and computational cost, many researchers propose the inclusion of Software Defined Radio (SDR) in schemes and developments on these devices. The inclusion of SDR has resulted in more compact systems, with lower energy consumption, and more flexibility configuration for each work mode, among other advantages. In this paper we implement the Gurgel methodology to obtain the Doppler Spectrum. We perform a comparison between our own implementation (LaQuinta) and Wera (WERADesk) to identify the applicability and limitations of LaQuinta. We also used LaQuinta to learn a set of LimeSDR-USB skills. We conclude that we need to know the calibration functions in LaQuinta and develop a Front-end RF before the A/D process to improve the measures when using low-cost SDR and own implementation.

Los remolinos son estructuras transitorias que influyen en gran medida en la circulación promedio del océano. Modifican la distribución de masa y propiedades como calor, sal, clorofila y partículas inertes. La capacidad que tienen los remolinos para transportar propiedades o partículas depende de su capacidad de retención. En este estudio se identificaron y caracterizaron los remolinos de mesoescala del noroeste del golfo de México (NOGM) a través de un método lagrangiano que permite evaluar el tiempo de retención y la fracción de masa que pueden retener y transportar. Para el análisis, se utilizaron datos diarios de altimetría de 1993 a 2016. En el periodo de estudio se detectaron un total de 254 remolinos, 73 anticiclones y 181 ciclones. Se identificó una región (94.75º W, 26.75º N) donde ocurren ~30% del total de los remolinos ciclónicos detectados entre las isóbatas de 1,000 y 2,500 m. En promedio, el radio de los remolinos fue de ~40 km para la isobata <1,000 m y ~70 km para la isobata >2,500 m. Los remolinos de mesoescala del NOGM pueden trasportar ~60% de la masa que contenían al momento de ser detectados. En promedio, el transporte de masa ocurrió por 33 d para los ciclones y por 26 d para los anticiclones. Rara vez ocurrió por 60 d o más.

Coastal pollution levels in Todos Santos Bay (TSB) recreational beaches have increased in recent years due to the uncontrolled disposal of wastewater and pollutants to the coast by human activities (urbanization and tourism). In this work, the concentration of water quality parameters along the coast of TSB was evaluated from February 2012 to January 2013. Sampling was carried out at monthly intervals on 29 beach locations. Results showed that the maximum values of all parameters were always found close to the treated wastewater discharge area at Arroyo El Gallo station. Temporally, both nutrients and biochemical oxygen demand reached notably high levels in winter-spring and close to wastewater discharges. During summer, maximum counts of total coliforms and parasite eggs were detected close to wastewater discharges. Overall, our study provides a diagnostic approach on the spatiotemporal variability of water quality parameters for future studies along the coastal waters of TSB.

This study proposes a method to detect ocean fronts from in situ temperature and density glider measurements. This method is applied to data collected along the CalCOFI Line 90, south of the California Current System (CCS), over the 2006–2013 period. It is based on image-processing techniques commonly applied to sea surface temperature (SST) satellite data. Front detection results using glider data are consistent with those obtained in other studies carried out in the CCS. SST images of the Multi-scale Ultra-high Resolution (MUR) dataset were also used to compare the probability of occurrence or front frequency (FF) obtained with the two datasets. Glider and MUR temperatures are highly correlated. Along Line 90, frontal frequency exhibited the same maxima near the transition zone (~130 km offshore) as derived from MUR and glider datasets. However, marked differences were found in the bimonthly FF probability with high (low) front frequency in spring-summer for glider (MUR) data. Methodological differences explaining these contrasting results are investigated. Thermohaline-compensated fronts are more abundant towards the oceanic zone, although most fronts are detected using both temperature and density criteria, indicating a significant contribution of temperature to density in this region.

We report the seasonal variability of temperature, nutrients, and total and size-fractionated chlorophyll-a (Chl-a) in nearshore waters off northern Baja California (nBC), under conditions of the marine heatwave and El Nino that occurred in the northeastern Pacific during 2014-2015. Compared with the mean annual cycle (2008-2015), our study period was characterized by warmer waters, nitrate-impoverished, and with very low Chl-a concentration, which was closely associated with strong stratification and reduced upwelling conditions off nBC. Temperature anomalies were >2.0 degrees C by the end of 2014 when the marine heatwave prevailed, decreased during the spring-early summer upwelling season of 2015, and returned to >2.5 degrees C by the end of 2015 when El Nino appeared along the coast of nBC. As in 2008-2012 and closely coupled with upwelling, a seasonal cycle of total Chl-a was recorded under these abnormally warm conditions. However, relative to the mean annual cycle, total Chl-a and nitrate concentrations were significantly reduced (19%-55% and 40%-81%, respectively), with negative anomalies throughout the study period. Moreover, the seasonal evolution of the size-fractionated Chl-a concentration showed that smaller cells (<5 mu m) systematically contributed with the largest fraction (>60%) of the total Chl-a. Our findings indicate that the sequential occurrence of the marine heatwave in 2014 and El Nino in 2015 had a significant and sustained impact limiting the nitrate supply and reducing the total Chl-a in nearshore waters off nBC. In conclusion, our data reveal that a shift toward an oligotrophic state occurred in coastal waters off nBC during the warm period of 2014-2015.

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 similar to 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.

Atlantids are holoplanktonic gastropods present in tropical to sub-polar waters, and have gained an increasing interest due to their potential use as biological indicators of climate change and ocean acidification. However, there is a lack of information regarding their distribution for large areas of some oceans, particularly in the California Current System (CCS), which has been used as a model for many acidification studies and where intense warming events occur. The distribution patterns of 18 species of Atlantidae off the west coast of the Baja California Peninsula, Mexico, representing 90% of the atlantid species registered for the Pacific Ocean, were analyzed during a period of warm anomalies associated with the El Niño of 2015-2016 and the 2014-2016 marine heat wave (MHW). The species distribution showed 3 groups: 2 in the north (coastal and oceanic) and 1 in the south. The limit of distribution between these 3 groups was found in the vicinity of Punta Eugenia (PE). The southernmost community of atlantids was characterized by tropical and subtropical species that were transported northward due to coastal advection of warm waters associated with the El Niño of 2015-2016. North of PE, the warm-water affinity oceanic speciesAtlanta roseaandA. fragiliswere found, evidencing the entrance of water from the Central Pacific related to MHW which affected the oceanic region off the coast of PE. The response of the distribution patterns proves that atlantids can be used as biological indicators, as they reflect the effect of environmental anomalies in the southern CCS.