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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.

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 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 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 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.

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 (

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.

Hydrographic data collected along the West Coast of North America between January 1997 and January 1999 have been compiled into a web-based Atlas of the 1997–8 El Nino event. This paper discusses the organization of the Atlas, describes the data that were incorporated into the Atlas and explains how vertical and horizontal distributions for the different properties were constructed. Examples of figures from the Atlas are shown.

ARGOS drifters deployed in the Northern Gulf of California in September 1995 showed the presence of a cyclonic gyre, while a second deployment in March 1996 revealed an anticyclonic gyre. A circulation pattern consisting of a seasonally reversing gyre had been proposed before on the basis of satellite images, geostrophic calculations, and numerical models, but so far no direct observations have been made to test its existence. In September the gyre was cyclonic, baroclinic, very well defined, stable, and strong; its mean speed and rotation time were 0.3 m s−1 and ∼7 days. In March the gyre had the same mean speed, but it was anticyclonic and displaced to the northwest of the summer position. The March gyre has barotopic and baroclinic characteristics, but the observed speeds are stronger than in numerical simulations. These data and a data bank analysis suggest that the summer gyre is a persistent summer feature, but the winter–spring situation remains ill-defined and requires further research.

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

The freshwater discharge of the Colorado River into the Gulf of California has been reduced to negligible quantities since the construction of the Hoover Dam in 1935. These radical anthropogenic changes in the hydrography of the Colorado River Delta had striking repercussions on both physical and biological processes. Using historical river discharge data, the changes in the flow dynamics and hydrographic patterns before and after the drastic freshwater reduction are studied numerically, using a three-dimensional nonlinear shelf model. The results are applied to assess the environmental impact of the reduction of river discharge on the area. Satellite imagery is also used to compare our results with observed fronts.