Search

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.

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.

Habitat characterization provides predictive information about the distribution of species and is useful for as­sessing habitat quality and population stability. Larval abundance of six frequent and abundant demersal species and the relationship of each with the environment were analysed through generalized additive models to determine their preferential distribution and predictive response to the environmental variables in the southern part of the California Current (25-31°N) between two periods of data collection: 1997-2000 and 2006-2010. Essentially, the main associated variables governing the distribution patterns were related to common and oceanographic characteristics of the water column (temperature and salinity at 50 m depth, dynamic height and degree of water column stratification); however, the set of variables and their ranges are usually species-specific. Species of northern distribution, Sebastes sp. and Citharichtys stigmaeus, were recorded mainly in newly emerged, relatively unstratified waters characterized by a shallow mixed layer and low temperatures. Low dynamic height values were the most significant predictor of larval distribution for Merluccius productus. Citharichthys xanthostigma and Symphurus atricaudus were widespread, distributed across the study area mainly in autumn in unstratified or stratified waters and at a shallow mixed layer. Particularly C. Xanthostigma and S. Lucioceps were related to high dynamic height val­ues, likely influenced by a coastal flow towards the pole, as evidenced by counter-currents. La caracterización del hábitat proporciona información predictiva sobre la distribución de las especies y es útil para evaluar la calidad del hábitat y estabilidad de la población. La abundancia larval de seis especies demersales frecuentes y abundantes y de su relación con el medio ambiente se analizaron a través de modelos aditivos generalizados (GAM) para determinar su distribución preferencial y respuesta a las variables ambientales en la parte sur de la corriente de California (25-31°N) entre dos periodos de datos recolectados 1997-2000 y 2006-2010. Esencialmente, las principales variables aso­ciadas que rigen los patrones de distribución fueron en términos de las variables comunes y oceanográficas de la columna de agua (temperatura y salinidad a 50 m de profundidad, altura dinámica y grado de estratificación de la columna de agua), sin embargo, el conjunto de variables y los rangos suelen ser específicos de la especie. Especies con distribución norteña, Sebas­tes sp. y Citharichtys stigmaeus, se registraron principalmente en aguas de surgencia, identificadas por aguas relativamente no estratificadas, poca profundidad de capa mixta y menor temperatura; y menor altura dinámica, como el predictor más significativo de la distribución de larvas de Merluccius productus. Citharichthys xanthostigma y Symphurus atricaudus se distribuyeron ampliamente a lo largo del área de estudio preferentemente en otoño, en aguas no estratificadas o estratificadas y baja profundidad de la capa de mezcla, pero particularmente C. Xanthostigma y S. Lucioceps en valores altos de alturas dinámicas probablemente influenciadas por el flujo costero hacia el polo indicado por las contracorrientes.

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.

Ocean color is determined by the different components of seawater. Satellite ocean color data are commonly used to infer the inherent optical properties (IOPs) of seawater and concentration of chlorophyll $a$ (Chl- $a$ ). Many of the algorithms that relate satellite data to the components of seawater use global data to determine their parameters. Regionalizing the algorithms is recommended to improve the retrieval of IOPs from satellite data. In this article, we use the in situ and satellite data from the southern part of the California Current System (CCS) off the Baja California Peninsula during 1999 to test the Garver and Siegel IOPs’ inversion model (GSM). The strong seasonal variability observed in the data was not reproduced by this algorithm. Thus, we propose a new regional algorithm whose order and coefficient depend on seasonal variability. This algorithm includes the linear form of the GSM model but allows changes in two parameters according to the season. These two parameters are the magnitude and spectral shape of the relationship of the remote sensing reflectance with the ratio of the backscattering coefficient and the sum of backscattering and absorption coefficients. In this area, both parameters increase gradually from January to October. The new algorithm improves the retrieval of the IOPs’ ratio from an ${r}^{2}$ below 0.5 with the GSM model to an ${r}^{2}$ that ranges from 0.87 in April and October to 0.93 and 0.94 in January and August, respectively. Furthermore, Chl- $a$ data were used as a proxy to evaluate the new algorithm. Absorption data retrieved from remotely sensed data for 1999, 2008, and 2011 relate well to the in situ Chl- $a$ data.

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.

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 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.

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.

Anomalies occurring in the California Current System during 2013–2016 were examined using remote sensing data and in-situ measurements. Positive anomalies in sea surface temperature (SST, up to 4 °C) and absolute dynamic topography (ADT, up to 20 cm), as well as negative anomalies in satellite chlorophyll concentration (CHL, up to -3.0 mg m -3 ) were recorded. In-situ temperature anomalies in August 2014 increased equatorward, from 2°C along the northernmost line (CalCOFI hydrographic line 76.7) to 10 °C (below ~80 m depth) at the southernmost hydrographic line (off Baja California). In-situ negative Chlorophyll- a (Chl- a ) surface anomalies were similar in most of the lines examined (~ -1.5 mg m -3 ), but for the CalCOFI lines, larger anomalies (~ -3.5 mg m -3 ) were recorded. As a result of increased stratification, mirrored in the increase in mean monthly ADT and the upper water-column temperature, the 2003–2016 CHL time series showed a declining trend in phytoplankton production and biomass, which was particularly pronounced during the last four years in the central and southern zones of the California Current System. The mechanisms responsible for this trend seem to be related to a climate shift from cold to warm in the northeastern Pacific Ocean, as evidenced by large correlations between the CHL anomalies and the Pacific Decadal Oscillation, Multivariate ENSO Index, and Oceanic El Nino indices. Generalized additive models were used to explore the relationship between stratification and the decline in phytoplankton production. Two ADT ranges—characteristic of either highly dynamic or stratified environments—were defined, both of which led to a drop in primary production. The effects of these environments have been associated with the photo acclimation of phytoplankton to irradiance and nutrient availability regimes, by which primary production and biomass decrease due to the limitation of either of these factors. This study reveals some of the effects of the warm anomalies occurring from 2013 to 2016 in the California Current ecosystem, which will help to understand changes in higher trophic levels in this region.

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.

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.

Experiments were carried out at a coastal upwelling site (ENSENADA station) off northern Baja California (Mexico) during autumn 2015 (OCT-15) and spring 2016 (APR-16) to estimate phytoplankton daily growth (μo) and mortality (m) rates and to assess microzooplankton grazing impact (m:μo) on the phytoplankton community and specific autotrophic groups. In accordance with regional seasonality and under an environmental warming scenario due to the El Nino 2015–2016 event, significant differences in both hydrographic conditions and the growth–mortality dynamics of the phytoplankton community were observed between the 2 study periods. The μo and m estimates were, respectively, 0.120 ± 0.012 d–1 and 1.145 ± 0.049 d–1 for OCT-15 and 1.186 ± 0.002 d–1 and 0.409 ± 0.086 d–1 for APR-16. The results of this study suggest that the effects of the anomalous warming on the phytoplankton community were more evident in OCT-15. During that period, growth of the larger autotrophic components (diatoms) was severely controlled by the environmental limitation of nutrients caused by the sinking of the thermocline that resulted from the entrance of warm water to the region. Furthermore, microzooplankton exerted active grazing pressure on phytoplankton biomass (72% of chlorophyll a [Chla]) and primary production (PP = 0.20 μg Chla·L–1·d–1), with grazing impact >100% of PP. In APR-16, when the ecosystem apparently started returning to the spring conditions, a high value for PP (3.73 μg Chla·L–1·d–1) was estimated, with only one third of it being consumed by microzooplankton (34% of PP). The results of this research evidence the high dynamism of multivorous food webs coupled to the seasonal and interannual variability of coastal upwelling systems. En un sitio de surgencia costera (estacion ENSENADA) frente a la region norte de Baja California (Mexico) se realizaron experimentos durante el otono de 2015 (OCT-15) y la primavera de 2016 (ABR-16) para estimar las tasas diarias de crecimiento (μo) y mortalidad (m) del fitoplancton, que permitieron evaluar el impacto (m:μo) que genera el pastoreo diario del microzooplancton sobre la comunidad de fitoplancton y grupos autotrofos especificos. Acorde con la estacionalidad de la region y bajo el escenario de un calentamiento ambiental debido al evento El Nino 2015–2016, se observaron notables diferencias en las condiciones hidrograficas y en la dinamica de crecimiento y mortalidad de la comunidad de fitoplancton entre los 2 periodos de estudio. Las estimaciones de μo y m fueron, respectivamente, 0.120 ± 0.012 d–1 y 1.145 ± 0.049 d–1 para OCT-15 y 1.186 ± 0.002 d–1 y 0.409 ± 0.086 d–1 para ABR-16. Los resultados de este estudio sugieren que los efectos del calentamiento anomalo sobre la comunidad del fitoplancton fueron mas evidentes durante OCT-15. En ese periodo, los componentes autotroficos mas grandes (diatomeas) estuvieron fuertemente restringidos en su crecimiento, posiblemente por una limitacion ambiental de nutrientes ocasionada por el hundimiento de la termoclina debido al mayor aporte de agua calida. Ademas, se estimo un activo consumo del microzooplancton sobre la biomasa (72% de clorofila a [Chla]) y produccion primaria (PP = 0.20 μg Chla·L–1·d–1) de fitoplancton (>100% de la PP). Para ABR-16, cuando aparentemente se empezaron a manifestar las condiciones propias de primavera en el ecosistema, se estimo una PP alta (3.73 g Chla·L–1·d–1) y solo una tercera parte de esta fue consumida por el microzooplancton (34% de la PP). Los resultados de esta investigacion revelan el alto dinamismo de las tramas troficas multivoras acoplado a la variabilidad estacional e interanual de los sistemas de surgencia costera.

A succession of interannual warm events occurred in the Pacific during the 2013–2016 period, when positive thermal anomalies were detected. A broad region with abnormally warm waters in the northeastern Pacific Ocean was observed in 2013, which by 2015 had reached waters off Baja California (Mexico). In addition to the ongoing warming effect, early evidence of an El Nino event was detected in 2015. This paper analyzes hydrographic data measured at Todos Santos Bay and environs, as well as satellite-derived sea-level data, to characterize changes in the hydrographic conditions during the 2013–2016 period. The highest positive temperature anomalies (~5 oC) were observed in September 2015, with a steep decline to neutral conditions in spring 2016. Records for the bay showed slight variations in hydrographic conditions during spring, highlighting the importance of local over remote forcings during this time of year. In autumn, by contrast, interannual signals prevailed over local processes. Satellite-derived sea-level data revealed an alongshore propagation of remote signals, identified as shallow coastal poleward flows. En el periodo 2013–2016 se presento en el Pacifico una sucesion de eventos calidos de escala interanual, durante los cuales se manifestaron anomalias termicas positivas. Durante 2013 se observo una region muy extensa de aguas anomalamente calidas, la cual se formo en el Pacifico nororiental y, para 2015, se extendio hacia aguas frente a Baja California (Mexico). Tambien en 2015, ademas del efecto de calentamiento ya existente, se registraron las primeras evidencias de un evento El Nino. En este trabajo se analizan los datos hidrograficos medidos en la bahia Todos Santos y sus alrededores, asi como datos satelitales del nivel del mar, para caracterizar los cambios en las condiciones hidrograficas durante el periodo 2013–2016. Las observaciones mostraron las maximas anomalias positivas de temperatura (~5 oC) durante septiembre de 2015 y un rapido decaimiento hacia condiciones neutras en la primavera de 2016. Los registros para la bahia mostraron cambios leves en las condiciones hidrograficas durante la primavera, lo cual evidencio la importancia de los forzamientos locales sobre los forzamientos remotos en esa epoca del ano. En contraste, en otono las senales interanuales dominaron sobre los procesos locales. El analisis de datos de altimetria sugirio una conectividad entre el norte y sur frente a la peninsula a traves de la propagacion de senales, identificadas como un flujo costero superficial hacia el polo.

The ocean off the Baja California Peninsula (Mexico) has been affected by interannual processes. Some of these processes have produced changes in oceanic circulation and the atmosphere, which have been reflected in the structure of the water column. Stratification, defined as the amount of energy needed to mix water throughout the water column, determines nutrient availability in the euphotic zone for phytoplankton growth. The aim of this study is to describe and relate the interannual variations of phytoplankton production and biomass with changes in the structure of the water column. To this end, we analyzed time series (1997–2016) for integrated Chlorophyll a, integrated primary production, pycnocline depth, mixed layer depth, and stratification indices along line 100 of the Investigaciones Mexicanas de la Corriente de California (IMECOCAL) program. The results showed 2 periods of high stratification and a decrease in phytoplankton production and biomass off Baja California, corresponding to the intrusion of subarctic water and El Nino 2015–2016. Finally, by using generalized additive models, we related 2 photosynthethic parameters-maximum photosynthetic rate and maximum light utilization coefficient-with water stratification. These relationships explained interannual variations in phytoplankton production in terms of water column stratification. The time series and the analysis reported here for IMECOCAL line 100 could be used to extrapolate the effects of interannual physical processes on phytoplankton in other zones off the Baja California peninsula. El oceano frente a las costas de la peninsula de Baja California ha sido afectado por diferentes procesos interanuales. Algunos de estos procesos han generado cambios en la circulacion oceanica y en la atmosfera que se han reflejado en la estratificacion de la columna de agua. La estratificacion, definida como la cantidad de energia necesaria para mezclar una columna de agua, determina la disponibilidad de nutrientes necesarios para el crecimiento del fitoplancton. El objetivo de este articulo es describir y relacionar las variaciones interanuales de la biomasa y produccion del fitoplancton con la estructura de la columna de agua. Para esto, se analizaron las series de tiempo (1997–2016) de clorofila a y produccion primaria integradas, profundidad de la picnoclina y de la capa de mezcla y los indices de estratificacion entre la superficie y los 100 y 200 m en la Linea 100 del programa Investigaciones Mexicanas de la Corriente de California (IMECOCAL). Los resultados mostraron que los periodos de mayor estratificacion en la columna de agua fueron durante la intrusion de agua subartica 2002–2007 y El Nino 2015–2016, los cuales trajeron como consecuencia el mayor declive en la biomasa del fitoplancton (en ambos periodos) y de produccion primaria (durante El Nino 2015–2016) en la zona norte frente a Baja California. Finalmente, se relacionaron la tasa fotosintetica maxima y el coeficiente de utilizacion maxima de la luz, con el indice de estratificacion por medio de modelos aditivos generalizados. Estas relaciones explicaron las variaciones interanuales en la produccion primaria en correspondencia con la estratificacion de la columna de agua. Las series de tiempo y el analisis presentado aqui para la linea 100 del IMECOCAL podran ser extrapoladas a otras zonas frente a la peninsula para entender la relacion entre los procesos fisicos con la biomasa y produccion primaria del fitoplancton. Palabras clave: fitoplancton, estratificacion, produccion primaria, Baja California, MECOCAL.

Threshold is defined as the point where small changes in an environmental driver produce large responses in the ecosystem. Generalized additive models (GAMs) were used to estimate the thresholds and contribution of key dynamic physical variables in terms of phytoplankton production and variations in biomass in the tropical-subtropical Pacific Ocean off Mexico. The statistical approach used here showed that thresholds were shallower for primary production than for phytoplankton biomass (pycnocline 0 cm d-1 vs. ADT 4 cm d-1). The relatively high productivity on seasonal (spring) and interannual (La Nina 2008) scales were linked to low ADT (45-60 cm), and shallow pycnocline depth (9-68 m), and mixed layer (8-40 m). Statistical estimations from satellite data indicated that the contribution of ocean circulation to phytoplankton variability was 18% (for phytoplankton biomass), and 46% (for phytoplankton production). Although the statistical contribution of models constructed with in-situ integrated chlorophyll-a and primary production data was lower than the one obtained with satellite data (11%), the fits were better for the former, based on the residual distribution. The results reported here suggest that estimated thresholds may reliably explain the spatial-temporal variations of phytoplankton in the tropical-subtropical Pacific Ocean off the coast of Mexico.

An analysis was conducted of the community structure variability of demersal fish larvae and its relationship with environmental forcing on the west coast of the Baja California Peninsula (25–31°N). The information comes from two data sets of oceanographic cruises in 1997–2000 and 2006–2010. From a total of 190 identified taxa, a high number of species (71) was shared throughout the peninsula. The spatiotemporal contrast in the community structure suggests the separation of two groups (northern and southern) whose boundary is located around Punta Eugenia. The northern group showed an alternate dominance of species with a subarctic-transitional faunistic affinity during the winter and spring and species of a subtropical affinity during summer–autumn. In contrast, the dominant taxa in the southern group have a tropical–subtropical affinity throughout the year, although some taxa of subarctic-transitional affinity also occur during winter–spring. In the spatiotemporal scale, these results suggest tha...

The hydrographic structure and circulation of the Southern Mexican Pacific, from August 31 to September 24 2004, when tropical atmospheric activity was at its peak, was analyzed based on AVISO absolute dynamic topography and an array of 106 CTD profiles, within an area of about 500 km×500 km between Punta Maldonado and Puerto Chiapas. The surveyed area was occupied by mesoscale anticyclonic and cyclonic eddies that determined the path of water with temperature and salinity characteristic of the Costa Rica Coastal Current. The origin of each eddy was investigated with respect to QuikSCAT wind conditions. The sequence of AVISO images and wind data showed that the largest anticyclonic eddies originated outside the Gulf of Tehuantepec through mechanisms distinct from local wind forcing, although two northerly wind events in the Gulf of Tehuantepec possibly had an influence on the smallest anticyclonic and cyclonic eddies. The relative position of each eddy allowed the flow of relatively low temperature and salinity water (the Costa Rica Coastal Current) into and throughout the Gulf of Tehuantepec, converging at about Puerto Angel with relatively high temperature and salinity water moving from the west.

The distribution of ichthyoplankton assemblages (summer 1999 and winter 2000) from the southern region of the California Current (CC) off the Baja California Peninsula were analyzed. Latitudinal and ocean-coast distribution limits of the assemblages were associated with the geostrophic flow, which showed the presence of cyclonic and anticyclonic eddies in the northern and central region of the Baja California Peninsula. The comparative analysis of distribution and abundance of the developmental stages (egg to preflexion, flexion, and postflexion larval stages), showed that each mesoscale eddy had a specific ichthyoplankton assemblage, and the ichthyogeographic regionalization of the study area was determined by the presence of eddies and fronts. Retention processes were observed on epipelagic and demersal species where the fish larvae were maintained near the coastal region. Normal 0 21 false false false ES X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabla normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri",sans-serif;}

13 pages, 11 figures, 2 tables, Sediment traps were deployed at two depths (300 m and 1200 m) off Monterey Bay (36°40′N and 122°25′W, Central California) for 7.3 years (1998–2005). The sediment trap data provided information about the quantity and quality of settling material, and allowed exploration of the relationship of the sinking material with the environmental conditions in this coastal upwelling region. The magnitude and composition of the settling material were highly variable over time. Organic carbon (Corg) fluxes ranged between 4–296 mg C m−2 day−1 and 0.1–142 mg C m−2 day−1 for shallow and deep sediment traps, respectively. The time series of Corg vertical flux was characterized by pulses of intense fluxes that were associated with peaks of primary production, generally during upwelling periods. Despite considerable variability, fluxes varied seasonally with highest values during the upwelling season and the lowest in winter. Attenuation of Corg vertical fluxes with depth (300 m vs. 1200 m) varied between 31% and 24% except for the late upwelling period, when there was an increase with depth likely due to resuspension of material from Monterey Canyon. Calculation of a seasonal vertical budget of organic carbon off Monterey Bay resulted in a transfer between 4.0% and 4.9% of the primary production to the deep ocean, suggesting that coastal upwelling efficiently sequestered CO2, The principal source of support for these measurements was the David and Lucile Packard Foundation. CGC was partially supported by a National Research Council Fellowship at the Naval Postgraduate School

Los peces pelagicos menores son importantes indicadores ecologicos del estado del Sistema de la Corriente de California, ya que su abundancia y distribucion se ven alteradas directamente en respuesta a los forzamientos climaticos. Estas especies forman cardumenes, consumen plancton y son forraje para niveles troficos superiores. En este trabajo se describen la s historias de vida y los patrones de distribucion de la sardina, anchoveta y dos especies de macarela que ocupan aguas del oceano Pacifico frente a la peninsula de Baja California (Mexico). Desde el punto de vista de las pesquerias (cuando la informacion esta disponible), se abordan temas relacionados con los forzamientos biofisicos que mantienen y estructuran la condicion del habitat de las especies, sus patrones de movimiento, su productividad y la estructura poblacional relativo a las subpoblaciones. A pesar de que la informacion basada en las pesquerias puede estar sesgada por la escala de operacion y las areas de disponibilidad de lo s peces, en este trabajo las capturas se utilizan como indicador es de la historia de vida de las diferentes subpoblaciones. Para evaluar la validez de varios paradigmas existentes en oceanografia pesquera, se utilizaron principalmente estudios basados en sardina. Por ultimo, con el objetivo de describir como el ambiente puede establecer la estructura poblacion al de los peces pelagicos, se discute la variabilidad espaciotemporal de las dos subpoblaciones, nortena y surena, de sardina ( Sardinops sagax ) y macarela ( Scomber japonicus ) de 2000 a 2014. En respuesta al enfriamiento re gional mantenido desde el inicio de este periodo, las subpoblaciones nortenas muestran una tendencia a contraerse hacia el sur del sistema, hasta aguas fre nte a bahia Magdalena. Estos cambios en distribucion y productividad de una poblacion parecen ser resultado de los efectos combinados de la pesca y el cambio en el clima del oceano que podrian alterar

The distribution of phyllosoma of California spiny lobster Panulirus interruptus was investigated in relation to the seasonal variability of hydrographic conditions off the west coast of the Baja California Peninsula between 2006 and 2008. Early larval stages were recorded mostly from summer to fall, immediately following the reproductive period. The duration of larval development in plankton is variable (8–12 months), and hence, larvae are found at different times of the year; thus, intermediate and late stages did not show a well-defined seasonal pattern. The highest phyllosoma density was associated with the relatively warm transitional water mass. However, the peak frequency of occurrence was observed in the colder subarctic water mass. A canonical correspondence analysis identified two distinct seasonal periods: (1) a warm period (summer–autumn), when the abundance of early and intermediate stages was highly correlated with a higher sea surface temperature, and (2) a cold period (winter–sprin...

Hydrographic data collected over the period 1997–2013 are analyzed to investigate the seasonality of hydrographic features and associated geostrophic flows off the Baja California peninsula. The upper ocean in the region was found to be homogeneous in winter and spring but subdivided into two regions in the summer and autumn. In the first case, the system typically shows relatively low-temperature and salinity waters, which give it a subarctic character. In the second, only the region north of Punta Eugenia (28°N) maintains subarctic characteristics, while the southern region receives an inflow of tropical and subtropical waters that results from the weakening of northwesterly winds, which allows the poleward advection of surface waters. Also during this period, a positive wind stress curl promotes the zonal advection of North Pacific's eastern edge waters into the coast and to the north as a surface coastal flow. Average seasonal patterns of geostrophic flow at 200 dbar revealed that the differentiation into provinces is also evident at that depth, with two clearly defined cyclonic structures in summer and autumn, both separated at the latitude of Punta Eugenia. The analyses conducted also showed a clear continuity of the California undercurrent along the shelf break, with more diffuse currents in the winter. Poleward flows were observed throughout the water column, especially in summer and autumn, although the origin of the surface flow does not necessarily involve a surfacing of the California Undercurrent.

The southern region of the California Current (CC) off Baja California represents a transitional environment, with the influence of low temperature and less saline CC water during spring and summer, and warm and salty tropical and subtropical conditions through the end of summer and autumn. From 2002 to 2006, an anomalous subarctic water (SAW) intrusion generated changes in the epipelagic ecosystem dynamics, affecting phytoplankton biomass and primary production. The goal of the present work is to show the effects of the SAW intrusion off Baja California in the phytoplankton production during the two contrasting years 2002 and 2005. Our results show that the minimum water salinity was associated with density levels of 24.6–25.5 kg m −3 in 2002 and 24.3–25.2 kg m −3 in 2005, indicating that the anomalous SAW intrusion was more pronounced in 2005. In 2005, the mean chlorophyll concentration was low ( −3 ) and associated with negative salinity anomalies ( −3 in 2002 and 2005, although in the coastal zone they were >1.0 mg m −3 in some months. CHL values were significantly different between the north and south zone and among months ( p B ) and maximum photosynthesis rate (P B m )) were one order of magnitude higher in 2005 compared to 2002 ( p −2 d −1 respectively), but similar in 2005 (750 and 1006 mgC m −2 d −1 respectively). The differences between models may be due to the diverse chlorophyll data used in the singular models ( in situ vs. satellite-derived), and to the weight of the phytoplankton photosynthetic parameters in each algorithm. We conclude that for the present data set the Herman and Platt model is more suitable. To assess the relative importance of physical variables, as well as bio-optical and physiological parameters in primary production, we conducted a principal component analysis (PCA). There was an apparent separation between the two years, while each year experienced a special structuring due to different physical variables (mainly salinity, but also temperature and K PAR in 2002, and temperature and water stability in 2005). No clear structuring is discernible in 2005, suggesting that the anomalous SAW intrusion homogenized the pelagic ecosystem. The decrease in primary production suggests a change in phytoplankton biomass as a result of a phytoplankton physiological acclimatization.

espanolEntre 1997 y 2016, en el programa de Investigaciones Mexicanas de la Corriente de California (IMECOCAL) se realizaron medi-ciones de clorofila a y produccion del fitoplancton frente a la peninsula de Baja California. En este trabajo se resumen los resultados del periodode observaciones. Se encontro que la productividad promedio fue alta en zonas de surgencias costeras, y en el giro ciclonico semipermanente frente a punta Eugenia. A escala estacional, la variacion de la produccion primaria fue diferente a la de la clorofila a integrada. La clorofila aintegrada presento maximos durante la epoca de surgencias costeras en primavera y verano, y minimos durante la influencia de agua calida de origen tropical-subtropical en la zona al sur de punta Eugenia en otono e invierno. Los mayores valores de produccion primaria integrada ocurrieron en primavera y verano al norte de punta Eugenia y en invierno y otono al sur de esta localidad. Esta variabilidad se relaciono con la presencia de fitoplancton de ciertos tamanos y sus tasas fotosinteticas maximas caracteristicas. A escala interanual, la menor productividad estuvo asociada con la mayor estratificacion durante los eventos de intrusion de agua subartica, y los eventos el “Blob” y El Nino entre 2015 y 2016. Los cambios en la productividad observados concuerdan con la variacion temporal del indice de la Oscilacion del Giro del Pacifico Norte. La variabilidad observada en ambas escalas contribuye a entender la variacion regional en niveles troficos superiores, dado que el fitoplancton es el principal componente de la cadena trofica marina. EnglishBetween 1997 and 2016, the Investigaciones Mexicanas de la Corriente de California (IMECOCAL, Mexican Investigations of the California Current) program conducted measurements of chlorophyll a and phytoplankton production off Baja California. Here, we summarize the main results obtained during the survey period. Long-term means indicated that high productivity occurred along the coastal zone where upwelling occurs, and in a semi-permanent cyclonic gyre off Punta Eugenia. At the seasonal scale, the variability of integrated primary production showed differences with respect to integrated chlorophyll a variability. Integrated chlorophyll a exhibited maximum values during the coastal upwelling season in spring and summer, while minimum values occurred during the inflow of tropical-subtropical waters south of Punta Eugenia in autumn and winter. In contrast, the highest values of integrated primary production occurred in spring and summer to the north of Punta Eugenia, whereas to the south of this location, the highest values occurred in winter and autumn. This seasonal variability was associated with phytoplankton size and maximum photosynthetic rates. At the interannual scale, low productivity was associated with increased stratification during the subarctic water intrusion events and the “Blob” and El Nino events in 2015–2016. Productivity time-series were in agreement with the seasonal variability of the north Pacific Gyre Oscillation index. Given that phytoplankton is the first level of the marine food web, this study contributes to the understanding of regional variations in higher trophic levels at the seasonal and interannual scales.

The southern Mexican Pacific Ocean presents seasonal changes related to the rainy season and Tehuano winds, which generate mesoscale processes affecting biological productivity and marine biodiversity. Size distributions of squid paralarvae collected in this region during the rainy season (July 2007 and May-June 2008) were analyzed in relation to regional oceanography. Samples were collected through oblique hauls, and CTD casts were used to determine the structure of the water column. Between surveyed periods, there were no significant changes in the water temperature at 10 m, but there were significant variations in the mixed layer depth (MLD). The number of taxa, community composition and total abundance of paralarvae were similar between periods. However, in July paralarvae ≤2.0 mm were distributed along the margins of cyclonic and anticyclonic eddies associated with high temperatures. In May-June, the MLD and high concentrations of chlorophyll a (Chl- a ) determined the presence of a group of oceanic paralarvae and another of coastal paralarvae, separated by an upwelling front. The percentage of recently spawned paralarvae (≤2.0) nearly doubled during this period as a result of increased coastal sampling and high concentrations of Chl- a , indicating a coupling of adult reproduction with regional productivity. In the absence of winds, the mesoscale oceanographic complexity generates gradients and a differential effect on the distribution, transport and survival of cephalopod paralarvae. Normal 0 21 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabla normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri",sans-serif; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} Normal 0 21 false false false EN-US X-NONE X-NONE

The response of primary producers to seasonal and interannual variabilities in the hydrographic conditions observed between 1997 and 2012 is analyzed for the southern portion of the California Current System (CCS). The analysis uses the optimum rate of primary productivity (PP) normalized by units of chlorophyll (Chla) in the water column (PBopt) and Chla concentration. In situ PP estimations using the 14C method were obtained as part of the seasonal cruises conducted by the Investigaciones Mexicanas de la Corriente de California program. Supplementary data included sea surface temperature (SST) as measured by the AVHRR sensor from 1985–2009. We found the mean value of PBopt to be at 5.1 ± 3.3 mg C·(mg Chla)–1·h–1, with maximum ranges of 0.5 and 17.5 mg C·(mg Chla)–1·h–1. The relationship between PBopt and SST suggested a phytoplankton community change at around 19 oC, which characterized the transitional nature of the southern portion of the CCS. SST data suggested, on the one hand, that on average the 19 oC isotherm is located in the vicinity of Punta Eugenia and, on the other, that its spatial variability defined the alternating cool–warm conditions. At the seasonal scale, this isotherm showed a marked latitudinal displacement (from 24oN to 32oN), which was observed to be even out of this range during interannual events associated with El Nino/La Nina. Under both cool-warm hydrographic conditions, the phytoplanktonic community showed large PBopt rates (~6 mg C·(mg Chla)–1·h–1). At the interannual scale, changes were associated to changes in the abundance and composition of nano-microphytoplankton. Additionally, data suggested that high PP rates during warm periods could be attributed to an enhanced picoplankton contribution. Se analizo la respuesta de los productores primarios a la variabilidad estacional e interanual de las condiciones hidrograficas en la region sur del Sistema de la Corriente de California (SCC) entre 1997 y 2012. El analisis se basa en la tasa optima de productividad primaria (PP) normalizada por unidad de clorofila (Chla) en la columna de agua (PBopt) y en la concentracion de Chla. Como parte del monitoreo que realiza el programa de Investigaciones Mexicanas de la Corriente de California, se obtuvieron para cada estacion del ano datos de PP in situ con la tecnica de 14C. La informacion se complemento con datos de la temperatura superficial del mar (TSM) medida por el sensor AVHRR de 1985 a 2009. El analisis de los datos de TSM demostro que, en el promedio de largo periodo, la isoterma de 19 oC se ubico en las inmediaciones de punta Eugenia y que su variabilidad espacial permite seguir la alternancia del cambio entre las condiciones frias y calidas. En la escala estacional, esta isoterma presento un marcado desplazamiento latitudinal (de 24oN a 32oN), y se extiendio aun mas durante eventos interanuales asociados a El Nino/La Nina. El valor promedio del PBopt fue de 5.1 ± 3.3 mg C·(mg Chla)–1·h–1 y vario de 0.5 a 17.5 mg C· (mg Chla)–1·h–1. La relacion entre el PBopt y la TSM sugiere un cambio en la comunidad del fitoplancton a los 19 oC, lo que se considero como una respuesta al caracter transicional del SCC. La comunidad fitoplanctonica mantuvo altas tasas promedio de PBopt (~6 mg C·(mg Chla)–1·h–1) en ambas condiciones hidrograficas (frio/calido). Las variaciones en la escala estacional e interanual del PBopt estuvieron asociados a cambios en la composicion y abundancia del nano-microfitoplancton. Los datos sugieren que las altas tasas PP en periodos calidos pueden atribuirse a la contribucion del picoplancton.

Fetch-limited wave grow th was analyzed using high spatial and temporal resolution measurements obt ained with high-frequency (HF) radars. To calculate the wave spectrum, the second-order echo ( S 2 N ) was extracted from the Doppler spectrum and mapped to the wave frequency domain. The conversion of S 2 N to the wave frequency spectrum was carried out us ing a linear parametric model dependent on wind speed. Wave growth, represented by the dime nsionless energy and peak frequency as a f unction of dimensionles s fetch, was determ ined from the spectra calculated for 25 cells (~400 km 2 ) in the vicinity of a moored AirSea Interacti on Spar buoy. The buoy data were used as reference and to provide the wind informa tion required for the wave growth analysis. The simultaneous data from the buoy and HF radars sh owed a suitable agreement with the wave growth curves. The analysis of the 25 cells showed an adequate agreement and certain dispersio n around the growth curves. Possible causes of this disp ersion are related to errors in the est imation of the frequency spectrum and fetch, and the assumption of homogeneous wind conditions. Fr om the limited data set used, it was not possible to prove any impact of swell on wave growth ; however, it is possible that analysis over a wider range of swell heights may provide this evidence. Neverthe less, the results suggest that the linear parametric model is able to re produce fetch-limited wave growth. This work represents th e first effort focu sed on fetch-limited wave growth using HF radars.

The aim of this work was to determine if the variation patterns in the abundance of dominant species of fish larvae in the transition zone off Bahia Sebastian Vizcaino, Mexico, could be used as indicators of interannual environmental variability, and how larval fish assemblages respond to this environmental variability during the period 1997–2013. With the 16 years of plankton data in the southern region of the California Current System, anomaly curves of larval abundance were calculated, from which the temporal abundance patterns of the dominant fish larvae of the mesopelagic, epipelagic and demersal environments were obtained. Classification and ordination analyses were carried out to obtain the larval fish assemblages as well as their relations with environmental variables (sea surface temperature, surface salinity, concentration of Chlorophyll-a and zooplanktonic volume) and climatic indexes (ONI, MEI, PDO and NPGO). Results showed a high positive correlation between the mesopelagic abundance with MEI and PDO indices, demonstrating their affinity with warm oceanic waters, while there were not statistically significant correlation between the climatic indexes and the epipelagic (Sardinops sagax and Engraulis mordax) or demersal species (Synodus lucioceps). The interannual variability of the abundance of three dominant mesopelagic species (Vinciguerria lucetia, Diogenichthys laternatus and Cyclothone signata) show that these species had a clearer response to environmental variability than epipelagic and demersal species. Trends in the abundance of mesopelagic species larvae and their high correlation values with the environmental variables used, demonstrate their potential as indicators of environmental change of the pelagic ecosystem in the transitional area off Bahia Sebastian Vizcaino.

Linear array antennas and beamforming techniques offer some advantages compared to direction finding using squared arrays. The azimuthal resolution depends on the number of antenna elements and their spacing. Assuming an ideal beam pattern and no amplitude taper across the aperture, 16 antennas in a linear array spaced at half the electromagnetic wavelength theoretically provide a beam resolution of 3.5° normal to the array, and up to twice that when the beam is steered within an azimuthal range of 60° from the direction normal to the array. However, miscalibrated phases among antenna elements, cables, and receivers (e.g., caused by service activities without recalibration) can cause errors in the beam-steering direction and distortions of the beam pattern, resulting in unreliable ocean surface current and wave estimations. The present work uses opportunistic ship echoes randomly received by oceanographic high-frequency radars to correct an unusual case of severe phase differences between receiver channels, leading to a dramatic improvement of the surface current patterns. The method proposed allows for simplified calibrations of phases to account for hardware-related changes without the need to conduct the regular calibration procedure and can be applied during postprocessing of datasets acquired with insufficient calibration.

We conducted a study from January 2002 to February 2008 on silicoflagellate fluxes in Alfonso Basin at the entrance to the Gulf of California. Thirteen taxa were identified in sediment trap samples, with Octactis pulchra as the dominant species. Total flux climatology reached a maximum value of 5×106 skeletons m-2 day-1 in December and then sharply decreased to a minimum value in February (2.3×103 skeletons m-2 day-1) concurrently with the climatological sea surface temperature (SST) minimum. Subsequently, there was a positive trend with a second relative maximum of 1.6×106 skeletons m-2 day-1 in September coincident with a maximum in climatological SST. During this period, there was a similar increase to 1.4×106 skeletons m-2 day-1 in May. Factor analysis identified three patterns of variation: “subtropical oceanic,” “subarctic,” and “equatorial El Niño.” Factors had reasonable correlations with the Pacific decadal oscillation (PDO), North Pacific Gyre oscillation (NPGO), and El Niño Modoki indices (r=0.53, 0.67, and 0.63, respectively). The first and second modes were apparently linked to decadal climatic conditions correlated to PDO and NPGO, as suggested by the silicoflagellate species Dictyocha messanensis forma messanensis and the assemblage of D. epiodon and Distephanus speculum, respectively; the third mode was related to the presence of warm equatorial-oceanic waters identified by D. messanensis forma spinosa, which defines El Niño influence. These results demonstrate the importance of the region where there is a confluence of the low-frequency, high-latitude PDO, NPGO, and high-frequency El Niño signals.

The role of coastal lagoons and estuaries as sources or sinks of inorganic carbon in upwelling areas has not been fully understood. During the months of May–July, 2005, we studied the dissolved inorganic carbon system in a coastal lagoon of northwestern Mexico during the strongest period of upwelling events. Along the bay, different scenarios were observed for the distributions of pH, dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) as a result of different combinations of upwelling intensity and tidal amplitude. DIC concentrations in the outer part of the bay were controlled by mixing processes. At the inner part of the bay DIC was as low as 1800 μmol kg −1 , most likely due to high water residence times and seagrass CO 2 uptake. It is estimated that 85% of San Quintin Bay, at the oceanic end, acted as a source of CO 2 to the atmosphere due to the inflow of CO 2 -rich upwelled waters from the neighboring ocean with high positive fluxes higher than 30 mmol C m −2 d −1 . In contrast, there was a net uptake of CO 2 and HCO 3 − by the seagrass bed Zostera marina in the inner part of the bay, so the p CO 2 in this zone was below the equilibrium value and slightly negative CO 2 fluxes of −6 mmol C m −2 d −1 . Our positive NEP and ΔDIC values indicate that Bahia San Quintin was a net autotrophic system during the upwelling season during 2005.

Using high-frequency radars, ocean surface currents were mapped every hour over an area of ≈5000 km2 in the inner Gulf of Tehuantepec (Mexico). The coastal circulation patterns (≈100 km offshore) were studied during spring, summer, and autumn 2006. The spring circulation was similar to the typical winter circulation, when the circulation is forced by outbursts of northerly winds (>8 m s–1) known locally as Tehuanos. Although Tehuano events are less common in spring than in winter, they are perfectly capable of modifying the sea surface by triggering cyclonic and anticyclonic eddies (≈50–200 km in diameter). Under moderate wind conditions, the ocean circulation showed a quasipermanent westward coastal current (≈50 cm s–1). Though the Tehuano winds were absent in summer, cyclonic eddies were observed and likely linked to the westward coastal current. Autumn was influenced by steady northerly winds with speeds of ≈12 m s–1 that remained over the region for almost 15 days. These conditions allowed us to study the competition between the wind-induced circulation and the more intense (≈100 cm s–1) westward coastal current during this period. The origin of this coastal current could be related to a warm coastal-trapped flow, composed of tropical low-salinity waters. The northwestward excursion of the observed coastal current is discussed, and the three-dimensional implications of surface current fields are studied by the Ekman theory and vorticity conservation. Se obtuvieron datos de corrientes superficiales mediante radares de alta frecuencia en un area de ≈5000 km2 dentro del golfo de Tehuantepec (Mexico). Los patrones de circulacion costera (≈100 km desde la costa) se estudiaron durante la primavera, el verano y el otono de 2006. La circulacion de primavera fue similar a la circulacion tipica de invierno, que esta influenciada por chorros de viento intenso del norte (>8 m s–1) conocidos localmente como tehuanos. Aunque menos comunes que en invierno, los tehuanos de primavera pueden modificar la superficie oceanica al generar grandes remolinos (≈50–200 km de diametro) ciclonicos y anticiclonicos. En ausencia de vientos tehuanos, la circulacion oceanica revelo una corriente costera (≈50 cm s–1) casi permanete con direccion al oeste. No se observaron eventos tehuanos en verano, aunque si remolinos ciclonicos que pudieran estar relacionados con la corriente costera que fluye hacia el oeste. Durante el otono se observo un evento de viento del norte que, aunque no supero los ≈12 m s–1 de magnitud, fue continuo y persistente durante casi 15 dias. Estas condiciones de otono permitieron observar una competencia continua entre la circulacion inducida por el viento y la corriente costera hacia el oeste en su etapa mas intensa (≈100 cm s–1). El origen de esta corriente costera podria estar relacionado con un flujo de agua calida y ligera, atrapado a la costa y compuesto por aguas tropicales. Se discute la excursion de la corriente costera hacia el noroeste del golfo, y se estudian las implicaciones tridimensionales de los campos de corriente superficial mediante los criterios clasicos de Ekman y conservacion de vorticidad.

The Gulf of Tehuantepec air–sea interaction experiment (intOA) took place from February to April 2005, under the Programme for the Study of the Gulf of Tehuantepec (PEGoT, Spanish acronym for Programa para el Estudio del Golfo de Tehuantepec). PEGoT is underway aiming for better knowledge of the effect of strong and persistent offshore winds on coastal waters and their natural resources, as well as performing advanced numerical modelling of the wave and surface current fields. One of the goals of the intOA experiment is to improve our knowledge on air–sea interaction processes with particular emphasis on the effect of surface waves on the momentum flux for the characteristic and unique conditions that occur when strong Tehuano winds blow offshore against the Pacific Ocean long period swell. For the field campaign, an air–sea interaction spar (ASIS) buoy was deployed in the Gulf of Tehuantepec to measure surface waves and the momentum flux between the ocean and the atmosphere. High frequency radar systems (phase array type) were in operation from two coastal sites and three acoustic Doppler current profilers were deployed near-shore. Synthetic aperture radar images were also acquired as part of the remote sensing component of the experiment. The present paper provides the main results on the wave and wind fields, addressing the direct calculation of the momentum flux and the drag coefficient, and gives an overview of the intOA experiment. Although the effect of swell has been described in recent studies, this is the first time for the very specific conditions encountered, such as swell persistently opposing offshore winds and locally generated waves, to show a clear evidence of the influence on the wind stress of the significant steepness of swell waves.

The temporal variability of the physical and chemical conditions of coastal waters off Ensenada, Baja California (Mexico) was characterized. A historical analysis was made based on 11 years (1998–2008) of temperature and salinity data records measured quarterly by IMECOCAL, along a transect perpendicular to the coast (CalCOFI line 100). Moreover, the physical and chemical conditions at a coastal monitoring observatory called station ENSENADA were described using a 2-year data series (October 2006–November 2008) obtained with improved temporal resolution. The historical analysis of line 100 showed marked seasonal variability in the thermohaline conditions associated with fluctuations in the flow of the equatorward California Current and the poleward California Undercurrent, as well as with coastal upwelling events whose magnitude and frequency increase towards spring–summer. Interannual variability was also observed, related to warm and/or cold ENSO phases that modify the characteristics of the water column in this coastal region. The most striking characteristics of the interannual variability at station ENSENADA were La Nina conditions recorded from summer 2007 to mid 2008. During this cold ENSO phase, temperature, salinity, dissolved oxygen, density, and dissolved inorganic carbon data revealed the anomalous presence of subsurface water at the surface layers in spring 2008. Results suggest that the coastal observatory is sensitive to the temporal variability of hydrographic conditions on shelf coastal waters (

Temperature and salinity anomalies derived from observations obtained in the period 1997–2008 are used to study the changes in physical properties off the Baja California west coast (24–31 N). Near surface anomalies were used to characterize four periods of distinctive variability: (1) a warm and saline phase of El Nino 1997–1998, (2) a saline period from 1999 to 2002, (3) fresh subarctic water in 2002–2006, and (4) a saline-fresh (El Nino-La Nina) phase in late 2006 to early 2008. Subsurface (200 m) salinity anomalies depicted a trend towards saltier conditions (ΔS ∼ 0.1) from 2001 onwards, and did not show the four periods discernible near surface. EOF analysis of sea surface wind stress and wind stress curl suggested that after the intense westerly winds in late 2001, freshening during late 2002–2006 was due to the weakening (strengthening) of the North Pacific Current (Aleutian Low), and to a decrease of wind stress curl produced upwelling. Data also showed differences in the timing and magnitude of anomalies observed between the north (poleward of 28 N) and the south (equatorward of 28 N). Subsurface geostrophic currents demonstrated the existence of two large scale cyclonic gyres, one associated with a subarctic domain in the northern region, and another having tropical characteristics. The likely role of subsurface cyclonic pairs in the definition of a provincial boundary, and the importance in influencing the CCS ecosystem, are discussed.

Observations of residual exchange flows at the entrance to four subtropical estuaries, two of them semiarid, indicate that these flows are mainly tidally driven, as they compare favorably with theoretical patterns of tidal residual flows. In every estuary examined, the tidal behavior was that of a standing or near-standing wave, i.e., tidal elevation and tidal currents were nearly in quadrature. The pattern of exchange flow that persisted at every estuary exhibited inflow in the channel and outflow over the shoals. Curiously, but also fortuitously, this pattern coincides with the exchange pattern driven by density gradients in other estuaries. The tidal stresses and the residual elevation slopes should be the dominant mechanisms that drive such tidal residual pattern because the Stokes transport mechanism is negligible for standing or near-standing waves. Time series measurements from the semiarid estuaries showed fortnightly modulation of the residual flow by tidal forcing in such a way that the strongest net exchange flows developed with the largest tidal distortions, i.e., during spring tides. This modulation is opposite to the modulation that typically results in temperate estuaries, where the strongest net exchange flows tend to develop during neap tides. The fortnightly modulation on tidal residual currents could be inferred from previous theoretical results because residual currents arise from tidal distortions but is made explicit in this study. The findings advanced herein should allow the drawing of generalities about exchange flow patterns in subtropical estuaries where residual flows are mainly driven by tides.

The hydrodynamics of a relatively small semi-enclosed bay influenced by the California Coastal Current were studied by means of sea surface current measurements obtained with two HF radars and by data recorded with sea surface drifters. Results showed that fine-scale tidal and subtidal circulation in the inner bay depends on two mesoscale processes, the California Coastal Current (CCC) and the synoptic variability of the wind field. On the one hand, a fringe or margin of convergence–divergence produced by the impinging CCC over the inner waters of the bay developed a barrier, which restrained surface particles, hence waters, inside the bay. On the other hand, the mountain chain around the bay apparently modifies the synoptic wind field, by means of developing a shadow-like zone inside the bay where the drifters tend to accumulate. This may be explained by slightly sea surface set up, hence, water convergence due to the fine-scale atmospheric pressure field.

Data from seven oceanographic cruises in the southern Gulf of California from 1997 to 2002 are used to describe the thermohaline variability and the geostrophic circulation. Baroclinic patterns exhibited spatial and temporal variability. A deepening of isotherms at the center of the section was evident in February 1999, suggesting anticyclonic flow. In May 1998 and November 1997, cyclonic flow was suggested by shoaling of isotherms at the center of the section. Other cruises showed alternating cores of flow into and out of the Gulf (August 1998, September 1997 and October 2002). Neither a seasonal nor a spatial pattern in geostrophic flows was apparent, suggesting that the exchange of waters between the cyclonic flow of Pescadero basin and the interior of the Gulf is complex. Relatively high salinities were recorded during most of the cruises indicating that Gulf of California Water (GCW) was present most of the year. Higher salinities were observed during winter and spring, although during summer, relatively high and low salinities were both observed as surface and subsurface cores. Temperature and salinity characteristics of California Current waters were observed only in August 1995 when they reached as far north as Cerralvo Island at ∼50 dbar. During El Nino conditions in November 1997, a mixed layer (∼70 dbar) and deepening of the thermocline (∼50 dbar) characterized anomalous conditions; during this cruise an asymmetric salinity pattern was observed with low salinities characteristic of Tropical Surface waters at the center and east of the section, while maximum salinities (34.9

The effect of Santa Ana winds on bio-optical properties (absorption coefficients of particles, detritus and phytoplankton) off Baja California (Mexico) was evaluated using data obtained during four cruises in January, April, August and October 1999. Meteorological data from a station at Todos Santos Bay and satellite-derived wind data indicated three Santa Ana events during October 1999, with low relative humidity, high air temperature and persistent ENE winds. The absorption coefficient of detritus (adT) in surface samples was ten-fold higher in October because of the inorganic material wind-driven by the Santa Ana events that occurred from 9 to 11 and from 17 to 20 October, 1999. The absorption coefficients of particles (ap) and phytoplankton (aɸ) in the euphotic zone were higher in the April survey as a result of higher phytoplankton abundance. The ap, a and Kd values in the euphotic zone were fitted to chlorophyll using a power function, with an explained variance of 37%, 72% and 16%, respectively. On excluding the October adT surface values, chlorophyll explained 82% of the changes in the absorption coefficients (ap and aɸ), and 87% of the Kd variability. Approximately 80% of the chlorophyll concentration can be explained by the water column spectral reflectance relationship: Rrs(443)/Rrs(555). According to our results, regional chlorophyll estimates from water column bio-optical information were not greatly affected by wind-borne dust transported during the October 1999 Santa Ana events.

Oceanographic conditions in the Pacific waters off Baja California are described for the period 2002–2003. Anomalies in the temperature-salinity relationships were observed from October 2002 to April 2003, with a clear contribution of low salinity and low temperature subarctic water in the upper 100 m of the water column. Below 100 m, physical data suggested weak El Niño conditions. Weakened or poleward winds were not observed. The pelagic ecosystem during the intrusion of subarctic waters showed strong seasonal changes, with localized centers of high chlorophyll and zooplankton in July 2002, followed by a strong decrease in the following autumn and winter seasons. Both chlorophyll and zooplankton rebounded in April 2003, but zooplankton showed a stronger onshore-offshore gradient. There was no strong biological signal. The zooplankton taxa that showed an increase during El Niño 2002–2003 were salps and chaetognaths. The increase of salps did not appear to be related to this event, due to their seasonal occurrence limited to the northern region. In contrast the increase of chaetognaths presented a similar pattern to that observed in El Niño 1997–1998.

We present geostrophic velocities obtained using hydrographic-altimeter data and direct measurements of currents from 11 cruises offshore of Baja California from January 2000 to July 2002. The study area was dominated by meanders and eddies in geostrophic balance. Two mechanisms of eddy generation were observed; the first associated with the geometry of the coastline, and the second a product of the cooling of the California Current and the California Undercurrent from the South. There were two persistent eddies observed during the study. The first eddy was offshore of Bahia Vizcaino and had an anticyclonic circulation. Situated in the southern region, the rotation of the second eddy was dependant on which current was first to enter the transition zone along the coast. Spring was a transition period characterized by the formation of meanders. The summer brought a period of eddy generation along the coast. Autumn and winter were marked by a separation of eddies from the coast and their subsequent drift towards the west. The phase velocity of the mesoscale eddies was in accordance with the theory of the linear propagation of a Rossby wave.

Nine years of data (1992–2000) were used to study the evolution of the sea–surface temperature (SST) over the eastern south Pacific. Our analysis shows that the variability in the SST on the interannual scale is attributed mainly to the equatorial El Nino-La Nina events while cooling, associated with the wind-Ekman drift, is an important component of the annual cycle. The anomalies at the interannual scale show up as a front that parallels the coast. At the seasonal scale, anomalous warming and cooling of coastal waters is strongly altered by the local effect of the wind-driven Ekman transport. This latter effect is especially significant along the Peruvian and Northern Chilean coast where wind induced upwelling and cooling is out-of-phase with other important annual forcings (i.e radiation and annual Kelvin waves). These local wind effects show up in the time-latitude plots as a thinning of the warm-water bands along the Peruvian coast (∼10°S y 17°S) and a thickening of the bands further south (∼18°S y 22°S). Three anomalous events that stand out clearly at the interannual scale are El Nino 92–93, La Nina 96 and El Nino 97–98. Their individual evolutions over time and along the coast are very different. Though the least intense of the three, the 92–93 event had the longest duration. The 96 event was the shortest in duration and its strongest anomaly occurred around the Peruvian coast, similar to the warm event of 92–93. The strongest event for the period occurred in 97–98, its warm anomaly showing strongly along the whole latitudinal extent of the study area. Contrary to what occurs at the seasonal scale, the increase on east/west Ekman transport on the interannual scale seems to be in phase with other relevant cooling and warming mechanisms. The interannual Ekman anomalous transports are at their maximum near the Peruvian-northern Chilean coast; however, they do not seem to alter the SST in a significant way. A similar situation has been described for sea-level data in the California Current System, i.e. interannual variability being associated mostly with variability of equatorial origin while seasonal variability is associated to both wind-forced local variability and remotely forced variability (J. Geophys. Res. 94 (1989) 3159)

This paper examines the oceanic response off Baja California, Mexico, to the 1997–1998 El Nino and the transition to La Nina conditions. The data presented were gathered during seven cruises over a grid based on the CalCOFI station plan, from lines 100–130, out to station 80. T–S diagrams with data obtained during the peak phase of El Nino, demonstrate that warmer and saltier (spicier) than normal conditions prevailed in the upper 600 m over this region. Temperature and salinity anomalies calculated for CalCOFI line 120 revealed waters near the coast at 50 m depth to be up to 8.7 °C warmer and S=0.8 saltier than the climatology during October 1997. These large anomalies persisted through January 1998, with some slight diminution in the magnitudes near the surface. This study suggests that anomalously warm and salty waters were fed from a source of spicy water to the southwest, identified as Subtropical Surface Water (StSW), and that low-salinity Tropical surface waters (TSW) were blocked to the southeast in the vicinity of the tip of the Peninsula. Subsurface waters associated with the California undercurrent (CU), fed from the Eastern Tropical Pacific (ETP), were also warmer and saltier than normal, and indicate a significant expansion in volume of the CU, presumably a result of intensification of poleward flow at depth. We postulate that the well defined near-surface and deep poleward flows in the study area reflect anomalous large-scale cyclonic circulation affecting the flow in the southeastern region of the North Pacific subtropical gyre east of 125°W. Following the El Nino event, warm and salty upper waters retreated to latitudes south of Punta Eugenia. With the return to normal and cooler conditions, equatorward flow over the sampling grid predominated with an increased meandering and mesoscale activity. Transition to La Nina conditions would have been associated with re-establishment of normal anticyclonic flow in the southeastern quadrant of the Pacific subtropical gyre.