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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.

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.

Seasonal climatology of air–sea CO2 exchange was estimated from in situ sea surface CO2 partial pressure, temperature, salinity, and satellite wind data obtained from 2004 to 2011 in the southern region of the California Current, off the Baja California Peninsula (Mexico). The average annual CO2 flux indicates that the study area is a source of CO2 to the atmosphere (0.65 mmol m–2 d–1). It changes from being a source in summer (2.33 mmol m–2 d–1) and autumn (0.92 mmol m–2 d–1) to acting as a sink in winter (–0.26 mmol m–2 d–1) and spring (–0.37 mmol m–2 d–1). The area to the north of latitud 28oN (off Punta Eugenia) is a CO2 sink (–0.42 mmol m–2 d–1), whereas the area to the south of this latitude is a source of CO2 to the atmosphere (1.80 mmol m–2 d–1), mostly due to thermodynamic effects. The northern coastal zone is a permanent CO2 sink (–1.29 mmol m–2 d–1). During the 2004 El Nino event the whole area contributed 2.00 mmol m–2 d–1 of CO2 to the atmosphere, but during the 2011 La Nina the ocean absorbed 5.30 mmol m–2 d–1 as a result of physical and biological dynamics. The seasonal cycle is dominated by temperature rather than biological effects, except in the northern coastal area. It is necessary to continue with in situ measurements of the CO2 system to have solid foundations to estimate the effect of the long-term increase in dissolved inorganic carbon on marine organisms. Key words: CO2 fluxes, interannual variability, El Nino, La Nina, California Current. La climatologia estacional del flujo de CO2 entre el mar y la atmosfera en la region sur de la corriente de California, frente a la peninsula de Baja California, fue calculada con datos in situ de la presion parcial de CO2, temperatura y salinidad recolectados de 2004 a 2011. Segun el promedio anual del flujo de CO2 (0.65 mmol m–2 d–1), la zona de estudio es una fuente de CO2 a la atmosfera, y cambia de ser fuente en verano (2.33 mmol m–2 d–1) y otono (0.92 mmol m–2 d–1) a ser sumidero en invierno (–0.26 mmol m–2 d–1) y primavera (–0.37 mmol m–2 d–1). La zona al norte de la latitud 28oN (frente a punta Eugenia) presenta condiciones de sumidero de CO2 (–0.42 mmol m–2 d–1), mientras que la zona al sur de esta latitud se manifiesta como una fuente de CO2 a la atmosfera (1.80 mmol m–2 d–1), lo cual es atribuible mayormente al efecto termodinamico. La zona costera norte es un sumidero permanente de CO2 (–1.29 mmol m–2 d–1). Durante el evento de El Nino 2004 el oceano aporto 2.00 mmol m–2 d–1 de CO2 hacia la atmosfera, y durante el evento de La Nina 2011 el oceano incorporo 5.30 mmol m–2 d–1 debido a un efecto combinado de factores fisicos y biologicos. En el ciclo estacional predominaron los efectos de la temperatura en vez de los efectos biologicos, excepto en la zona costera norte. Es necesario continuar con las mediciones in situ del sistema del CO2 para contar con bases solidas que permitan estimar el efecto del aumento a largo plazo del carbono inorganico disuelto del oceano sobre los organismos.

Sebastian Vizcaino Bay (Baja California Peninsula, Mexico) presents hydrographic conditions and phytoplankton biomass corresponding to a temperate/subtropical transition zone affected by large-scale tropical and subtropical events and those events originating in the subpolar Pacific region. Conditions in the first 50 m depth of the bay are mostly temperate (average temperature: 15.5 oC; average salinity: 33.6) and mesotrophic (phytoplankton biomass: >1 mg m–3). During spring and summer the bay is heavily influenced by the water transported by the California Current and the coastal upwelling generated off Punta Canoas. During the rest of the year the hydrography and phytoplankton biomass are mostly associated with subtropical conditions. The ENSO events arising in the period 1997–2012 affected the bay’s water column. The extreme 1997–1998 El Nino generated increases of ~8 oC in temperature and ~0.8 in salinity. Local dynamic processes decreased the effects of moderate and weak El Nino events on phytoplankton biomass, with possible changes in the plankton functional groups. Due to the mostly temperate environment of the bay, the moderate 1998–2000 and 2010–2011 La Nina events did not generate a substantial change in the hydrography and phytoplankton biomass. However, the abundant subarctic water inflow in the period 2002–2006 abruptly decreased salinity and led to increased stratification of the water column and a reduction in phytoplankton chlorophyll. Bahia Sebastian Vizcaino (peninsula de Baja California, Mexico) presenta condiciones hidrograficas y biomasa del fitoplancton correspondientes a una zona transicional subtropical-templada, afectada por eventos tropicales y subtropicales de gran extension espacial y temporal, y por eventos originados en la region subpolar del Pacifico. En los primeros 50 m de profundidad de la bahia, el ambiente es mayormente templado (temperatura promedio: 15.5 oC; salinidad promedio: 33.6) y mesotrofico (biomasa del fitoplacton: >1 mg m–3). Durante primavera y verano la bahia esta fuertemente influenciada por el agua transportada por la corriente de California y por las surgencias costeras generadas frente a punta Canoas. Durante el resto del ano la hidrografia y biomasa del fitoplancton corresponden mayormente a condiciones sobtropicales. Los eventos de ENSO en el periodo 1997–2012 impactaron la columna de agua de la bahia. El Nino 1997–1998, que fue el de mayor magnitud, genero incrementos de ~8 oC en la temperatura y de ~0.8 en la salinidad de la columna de agua. Los procesos dinamicos locales disminuyeron los efectos de los eventos de El Nino moderados y debiles sobre la biomasa del fitoplancton, aunque posiblemente hubo efectos en los grupos funcionales del plancton. Debido al ambiente mayormente templado de la bahia, los eventos moderados de La Nina 1998–2000 y La Nina 2010–2011 no tuvieron un cambio sustancial en la hidrografia ni en la biomasa del fitoplancton. Sin embargo, el ingreso de agua subartica en el periodo 2002–2006 disminuyo abruptamente la salinidad, lo que resulto en mayor estratificacion de la columna de agua y reduccion de la clorofila del fitoplancton. Palabras clave: variabilidad de largo plazo, hidrografia, clorofila, ciclo ENSO, bahia Sebastian Vizcaino

Quantifying and identifying measurement error is an ongoing challenge for carbon cycle science to constrain measurable uncertainty related to the sources and sinks of CO2. One source of uncertainty in measurements is derived from random errors (e); thus, it is important to quantify their magnitude and their relationship to environmental variability in order to constrain local-to-global carbon budgets. We applied a paired-observation method to determine e associated with marine xCO2 in a coastal upwelling zone of an eastern boundary current. Continuous data (3-h resolution) from a mooring platform during upwelling and non-upwelling seasons was analyzed off of northern Baja California in the California Current. To test the rigor of the algorithm to calculate e we propose a method for determining daily mean time series values that may be affected by e. To do this we used either two or three variables in the function, but no significant differences for e mean values were found due to the large variability in e (−0.088 ± 27 ppm for two variables and −0.057 ± 28 ppm for three variables). Mean e values were centered on zero, with low values of e more frequent than greater values, and follow a double exponential distribution. Random error variability increased with higher magnitudes of xCO2, and in general, e variability increased in relation to upwelling conditions (up to ∼9% of measurements). Increased e during upwelling suggests the importance of meso-scale processes on e variability and could have a large influence seasonal to annual CO2 estimates. This approach could be extended and modified to other marine carbonate system variables as part of data quality assurance/quality control and to quantify uncertainty (due to e) from a wide variety of continuous oceanographic monitoring platforms.

espanolEn el periodo de la primavera de 2013 al verano de 2014 se llevaron a cabo 16 muestreos mensuales a 6.5 km al noroeste de la boca de bahia Magdalena (Mexico) con el proposito de estudiar la variabilidad temporal de la biomasa y las tasas de produccion primaria del fitoplancton y la respuesta del mismo a las caracteristicas hidrograficas predominantes. En cada muestreo se midieron la temperatura y salinidad en la columna de agua y se determinaron las concentraciones de nutrientes inorganicos (nitrato, fosfato y silicato) y el contenido de clorofila a (como proxy de la biomasa del fitoplancton); ademas, se hicieron incubaciones in situ para estimar la produccion primaria (PP) con el metodo de 14C. En primavera y principios de verano (marzo–julio), el sitio presento, en promedio, una columna de agua fria (14.4 oC a 80 m de profundidad y 17.7 oC en superficie) y mezclada con concentraciones de nutrientes altas en superficie (nitrato = 6.39 μM, fosfato = 0.91 μM y silicato = 11.87μM; valores caracteristicos de zonas de afloramiento intenso). Por el contrario, de agosto a febrero se observo una columna de agua estratificada (23.5 ± 3.2 oC arriba de la termoclina y 17.0 ± 1.7 oC a 80 m de profundidad) con menor contenido de nutrientes en superficie (nitrato = 3.90 μM, fosfato = 0.47 μM y silicato = 10.30 μM). La abundancia del fitoplancton, la concentracion de clorofila a y las tasas de PP en la zona eufotica fueron mayores en la temporada de surgencias, con densidad celular maxima de 1.7 × 106 cel·L–1 (fraccion del nanoplancton), contenido de clorofila a integrada de 231 mg·m–2 y tasa de produccion integrada de 553 mg C·m–2·h–1. Las abundancias de celulas EnglishSixteen monthly cruises were carried out at a station 6.5 km to the NW of the mouth of Magdalena Bay (Mexico) to study the temporal variability of phytoplankton biomass and primary production rates, and the response of phytoplankton to the prevailing hydrographic characteristics. During each cruise, temperature and salinity were measured in the water column, and discrete samples were collected to mea-sure inorganic nutrient concentrations (nitrate, phosphate, and silicate) and chlorophyll a content (as a proxy for phytoplankton biomass); in addition, in situ incubations were performed to estimate primary production (PP) rates using the 14C technique. During spring and early summer (March–July), the water column at the study site was cold (14.4 oC at 80 m depth and 17.7 oC at the surface) and well mixed, with high nutrient concentrations (nitrate = 6.39 μM, phosphate = 0.91 μM, and silicate = 11.87 μM) at the surface, typical of intense upwelling systems. On the contrary, from August to February the water column was stratified (23.5 ± 3.2 oC above the thermocline and 17.0 ± 1.7 oC at 80 m depth) and had low nutrient concentrations (nitrate = 3.90 μM, phosphate = 0.47 μM, and silicate = 10.30 μM) at the surface. Phytoplankton abun-dance, chlorophyll a concentration, and PP rates in the euphotic zone were higher during the upwelling season, with maximum cell density of 1.7 × 106 cells·L–1 (nanoplankton fraction), integrated chlorophyll a content of 231 mg·m–2, and integrated PP rates of 553 mg C·m–2·h–1). Abundance of cells

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;}

The Gulf of Ulloa, a highly productive area off the western coast of the Baja California Peninsula, is examined for five successive years (2003–2007) by using satellite data and seasonal net primary productivity (NPP) estimates obtained from a vertical generalised production model. The results identify that northwestern winds blow parallel to the coast throughout the year. However, highest NPP occurs from March to June. During this period, an equatorward coastal current transports water from neighbouring upwelling areas to the northern Gulf of Ulloa and in combination with local upwelling, which injects nutrients into the euphotic zone, produce the observed increase in NPP. The opposite situation occurs in late summer when a warm poleward current of tropical characteristics arrives and inhibits the productivity in the whole region and generates the yearly lowest NPP levels. Our findings reveal the importance of lateral advection in the modulation of the primary productivity in this subtropical upwelling region.

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.

8 pages, 5 figures, 2 tables, The continental shelf of Southern Baja California has been scarcely researched south of 25°N despite it being oceanographically necessary to gain a better understanding of the north-eastern Pacific transitional zone between middle and tropical latitudes. Therefore, the intra-annual patterns of the upwelling cycle and primary production were studied in a monitoring station (24.5°N, 112.1°W; 85 m depth) from August 2008 to December 2011. Monthly, thermohaline vertical profiles were recorded and seawater sampled at 100, 33, 10, 3 and 1% irradiance depth levels. Dissolved oxygen, nutrients and chlorophyll-a concentrations and net primary production (NPP, remote sensed and in situ) were determined. Two half-yearly recurrent periods (P < 0.001) were observed: an intense (cold) period from February to July and a faint (warm) period from August to January. In the euphotic layer, nitrate concentrations were inversely related to temperature, showing their dependence on upwelling. NPP was directly related to the upwelling process, with an annual average of 1.21 ± 0.81 gC m−2 d−1 in the triennium 2009–2011. Although the influence of La-Niña event was observed during the warm period of 2010 and the cold period of 2011, this change did not significantly affect NPP (P < 0.05)., This article was supported by the SIP Mexican projects (2005–2011) of the IPN in cooperation with the Spanish MINECO project CTM2011-28792-C02. Dr Cervantes-Duarte is grateful to COFAA-IPN, EDI program and CONACYT for financing his sabbatical study at IIM-CSIC.

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.

"Se realizaron muestreos durante diciembre 2005; mayo y agosto 2006; febrero, mayo y noviembre 2007 en Bahía de La Paz (Cuenca Alfonso). Se consideraron 7 niveles en la zona eufótica (Zeu), correspondientes al 100, 55, 33, 10, 3, 1 y 0,1% de la irradiancia superficial. Se estimaron las razones de asimilación con incubaciones in situ y se observaron 2 patrones básicos, uno con máximos subsuperficiales durante febrero y mayo de 2007 y otro con tendencia a incrementar sus valores hacia el límite inferior de la Zeu (diciembre 2005; mayo y agosto 2006 y noviembre 2007). Los mínimos se observaron en diciembre 2005 con una variación de 0,16 a 2,35 mg C (mg Cla)-1 h-1. En febrero 2007 se registró alta variabilidad con un rango de 3,3 a 22,4 mg C (mg Cla)-1 h-1. Durante diciembre 2005, mayo y agosto 2006 y noviembre 2007, se observó un incremento hacia el 0,1% de irradiancia superficial, llegando a 10,22 mg C (mg Cla)-1 h-1 en agosto de 2006. En mayo 2007, el máximo (13,23 mg C (mg Cla)-1h-1) se asoció con la profundidad de la capa de mezcla. Al integrar la producción primaria (PP), se obtuvo un valor superior a los 350 g C m-2 año-1, lo cual sugiere que la bahía es de carácter productivo alto. Se observó un incremento significativo en la PP al considerar el 0,1% de la irradiancia superficial como el límite inferior de la zona eufótica."

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 hydrophysical results obtained during six oceanographic cruises in 2011 (February, April, July, and October) and 2012 (February and April) over a 50-station sampling grid in front of the Magdalena-Almejas lagoon system (Mexico) are presented. MODIS-Aqua sensor data (1.1 km) of sea surface temperature (SST) and chlorophyll a, and geostrophic current fields were analyzed during the sampling periods. In the northern part of the study area the pattern of the thermohaline structure shows subsurface intrusion of modified subarctic water, especially during February and April of both years. To the south, in July and October 2011, evident indications of subtropical subsurface water were found. The geostrophic current fields in February and April show a surface southward flow along the coast, which changes direction towards the North Pole in July and October. In spring, the satellite-derived SST showed negative anomalies of up to 4.5 oC in the coastal zone, corresponding to cold upwelled water rising to the surface from a depth of 60–70 m. Based on the results, the study area can be considered the southern boundary of the transition zone between the subarctic and subtropical waters of the northeastern Pacific Ocean, with marked seasonality. Se presentan los resultados hidrofisicos obtenidos durante seis cruceros oceanograficos realizados durante 2011 (febrero, abril, julio y octubre) y 2012 (febrero y abril) en una red de 50 estaciones frente al complejo lagunar Magdalena-Almejas (Mexico). Se analizaron los datos de temperatura superficial del mar (TSM) y clorofila a del sensor MODIS-Aqua (1.1 km) y los campos de las corrientes geostroficas durante los periodos de muestreo. Al norte de la malla de muestreo, el patron de la estructura termohalina mostro intrusiones subsuperficiales de agua subartica modificada, especialmente durante febrero y abril de ambos anos. Al sur, en julio y octubre de 2011, se encontraron indicaciones de agua subtropical subsuperficial. Los campos de las corrientes geostroficas en febrero y abril mostraron un flujo superficial hacia el sur a lo largo de la costa, el cual cambio su direccion hacia el Polo Norte en julio y octubre. En primavera, la temperatura derivada de imagenes satelitales mostro anomalias negativas de hasta 4.5 oC en la zona adyacente a la costa, lo cual corresponde a las surgencias costeras que elevan agua hacia la superficie desde los 60–70 m de profundidad. Con base en los resultados, el area de estudio se puede considerar como el limite sur de la zona de transicion entre las aguas subarticas y subtropicales del oceano Pacifico nororiental, con una marcada estacionalidad.

[1] The study of air-sea CO2 fluxes (FCO2) in the coastal region is needed to better understand the processes that influence the direction and magnitude of FCO2 and to constrain the global carbon budget. We implemented a 1 year (January through December 2009) paired study to measure FCO2 in the intertidal zone (the coastline to 1.6 km offshore) and the near-shore (∼3 km offshore) off the north-western coast of Baja California (Mexico); a region influenced by year-round upwelling. FCO2 was determined in the intertidal zone via eddy covariance; while in the near-shore using mooring buoy sensors then calculated with the bulk method. The near-shore region was a weak annual net source of CO2 to the atmosphere (0.043 mol CO2 m−2 y−1); where 91% of the outgassed FCO2 was contributed during the upwelling season. Sea surface temperature (SST) and ΔpCO2 (from upwelling) showed the strongest relationship with FCO2 in the near-shore, suggesting the importance of meso-scale processes (upwelling). FCO2 in the intertidal zone were up to four orders of magnitude higher than FCO2 in the near-shore. Wind speed showed the strongest relationship with FCO2 in the intertidal zone, suggesting the relevance of micro-scale processes. Results show that there are substantial spatial and temporal differences in FCO2 between the near-shore and intertidal zone; likely a result of heterogeneity. We suggest that detailed spatial and temporal measurements are needed across the coastal oceans and continental margins to better understand the mechanisms which control FCO2, as well as reduce uncertainties and constrain regional and global ocean carbon balances.

We identify the dynamic northern boundary of the shallow Oxygen Minimum Zone (OMZ) in the eastern tropical Pacific off Mexico (ETPM; 16–23°N). Spatial and temporal variability of the upper limit of the OMZ (DO=9 μmol L −1 ) is studied analyzing the World Ocean Database 2009 (WOD09) and regional data collected during nine oceanographic surveys (2002–2010). The mean depth of the upper limit of the OMZ ranges from 300 to 400 m from 20° to 23°N, where the California Current induces the advection of oxygen-rich water. Further south (from 16° to 20°N), the shallow upper limit of the OMZ (∼60 m) results from the poleward transport of hypoxic Subtropical Subsurface Water (StSsW) near the surface layer (∼25.6 kg m −3 ). A transitional zone is located in the north (20–23°N), where the influence of StSsW disappears, and the top of the OMZ is forced deeper by eddies generating southward intrusion of California Current Water (CCW). This oxygen-rich water (50–150 μmol L −1 ), transported overlying the 18 °C isotherm, defines the northern boundary of the shallow OMZ in the ETPM. The mechanisms involved in the definition of the northward distribution of the shallow OMZ are associated with seasonal advection of CCW and StSsW as well as the intensification of regional mesoscale circulation. Regional and temporal dynamics of these two subsurface water masses largely determine the position of the northern boundary of the shallow OMZ in the ETPM.

La variabilidad temporal de los datos hidrográficos, nutrientes, clorofila a del fitoplancton y la tasa de producción primaria fueron analizados en la Laguna de Cuyutlán (LC). La temperatura superficial mostró un patrón estacional con valores menores en diciembre y mayores en julio y octubre. La salinidad más baja fue observada en octubre debido a las lluvias estacionales que generaron características estuarinas dentro de la laguna. Las concentraciones de nutrientes (INSERTAR ECUACION) aumentó en febrero y junio como resultado de la remineralización de la materia orgánica, con altas concentraciones de silicato en octubre a causa de las escorrentías de agua dulce a la laguna. Durante los otros meses el silicato disuelto incrementó por la disolución del sílice biogénico. Usando la relación de Redfield como criterio para el balance estequiométrico de nutrientes, se observaron deficiencias de fosfato en LC debido a la asimilación del fitoplancton. La clorofila a aumentó por arriba de 2,0 mg m-3 como consecuencia de agua rica en nutrientes, produciendo una elevada biomasa del fitoplancton. La producción del fitoplancton promedio fue 1,26 g C m-3 d-1, indicando que la Laguna de Cuyutlán es ~ 40% más productiva en comparación con otras lagunas costeras subtropicales y templadas. La concentración de clorofila a fue utilizada como criterio para definir el nivel trófico de la LC la cual puede ser descrita como un ecosistema eutrófico. Las variables físicas, nutrientes inorgánicos disueltos y clorofila a mostraron variabilidad temporal en la laguna, sin tener relación con la circulación por la marea, excepto el oxígeno disuelto.

The eastern Pacific intermediate oxygen minimum layer (OML) is particularly well-developed and shoals close to the Mexican coast. We obtained hydrographic profiles including oxygen concentration [O], measured dissolved inorganic carbon (DIC), continuous surface pCO2 in water and air and took biological data south of the Gulf of California in March 2005. The core of the OML, with close to zero [O] was centered around 475 m with a thickness of the core varying between 80 m and 700 m and the upper limit of the core ranging from 500 m to 80 m. At the surface [O] was close to air-saturation and showed no relation with the depth of the OML contrary to DIC and pCO2 concentrations. Below 50-m depth the changes in DIC and Apparent Oxygen Utilization (AOU) yielding a molar ratio of dDIC 5 0.79 3 dAOU. When the OML shoaled, surface temperature, chlorophyll concentration [CHL], and depth-integrated zooplankton increased, resulting in positive correlations among plankton biomass, pCO2, and DIC in surface waters. When [CHL] is recalculated as particulate organic carbon (POC), a linear relationship with the sum of DIC and POC is observed as expected for concomitant transport of DIC and inorganic nutrients supporting POC formation. Neglecting ventilation of carbon into the atmosphere and the production of dissolved organic carbon, the results suggested that , 16% of the carbon transported up from the OML was present in surface waters in the form of POC and the rest in inorganic form.

Field data collected during June 2005 were used to determine the relationship between the second fluorescence maximum (FMax), the top of the oxygen minimum zone (OMZ), and physical processes (coastal currents, eddies, and upwelling) in the northern region of the Eastern Tropical Pacific off Mexico (ETPM). A recurrent second FMax was observed in the ETPM, which was formed only when the upper limit of the OMZ (9.0 µmol L–1) overlapped with the 1% downwelling blue irradiance depth (Ed490). The presence of the second FMax increased the total integrated water column chlorophyll from 20% to 40%. The second FMax was absent from areas where oxygenated California Current Water (CCW) deepened the upper limit of the OMZ below 1% Ed490. The poleward Mexican Coastal Current carried less oxygenated Subtropical Subsurface Water into the area, and enabled the formation of the second FMax. The variability of the second FMax driven by mesoscale physical processes was related to coastal upwelling and cyclonic eddies only in areas not influenced by CCW.

The in situ primary productivity (PP) and phytoplankton biomass (chlorophyll a concentration, Chla) of the Cabo Corrientes region, in the eastern tropical Pacific off Mexico, were studied using data from three oceanographic cruises (May and November 2002, and June 2003). The coastal region ( 2 mg m–3), when the mean PP was 361 mgC m–2 d–1. The highest PP values were recorded in June 2003, with a mean value of 447 mgC m–2 d–1, and the lowest in November 2002, with a mean value of 200 mgC m–2 d–1. Satellite ocean color images, supported by our field data, suggest that the area off Cabo Corrientes can be characterized by three periods: (1) a relatively intense upwelling period, with high Chla and PP (spring); (2) an upwelling relaxation period, when the highest PP values of the year were recorded (late spring-early summer); and (3) a summer-fall period, with strong stratification and lowest Chla and PP values. The high PP registered for the region off Cabo Corrientes during the spring season leads us to conclude that this is an area of high fertility, similar to other rich regions in the Pacific Ocean off Mexico. Se estudio la productividad primaria (PP) in situ y la biomasa del fitoplancton (concentracion de clorofila a, Cla) en la region de Cabo Corrientes, en el Pacifico oriental tropical frente a Mexico, durante tres cruceros oceanograficos (mayo y noviembre de 2002 y junio de 2003). La region costera ( 2 mg m–3), con un promedio de PP de 361 mgC m–2 d–1. Los valores mas altos de PP se registraron en junio de 2003, con un promedio de 447 mgC m–2 d–1, mientras que los valores mas bajos se registraron en noviembre de 2002, con un promedio de 200 mgC m–2 d–1. Imagenes satelitales del color del oceano, apoyadas por datos de campo, sugieren que el area frente a Cabo Corrientes puede caracterizarse por tres periodos: (1) un periodo de surgencia relativamente intensa, el cual presento valores altos de Cla y altas tasas de PP (primavera); (2) un periodo de relajamiento de la surgencia, con los mayores valores de PP durante el estudio (finales de primavera-inicios de verano); y (3) el periodo de verano otono, con fuerte estratificacion de la columna de agua y los menores valores de Cla y PP. Las altas tasas de PP registradas en primavera para la region frente a Cabo Corrientes nos permitieron concluir que esta es un area de gran fertilidad, similar a otras regiones ricas del Oceano Pacifico frente a Mexico.

"Se presenta la serie de tiempo de la producción ??toplanctónica nueva (Pnueva) frente a la Península de Baja California de 1970 a 2008, calculada por modelos estadísticos de la relación temperatura-nitrato en diez grupos de estaciones costeras y oceánicas de las Líneas 90, 107, 120, 137 y 157 de la red CalCOFI-IMECOCAL. La Pnueva se calculó a partir de la razón-ƒ y la producción primaria total (Ptotal). Espacialmente las zonas más productivas fueron las oceánicas de las Líneas 90, 120 y 157. La Pnueva en las Líneas 107 y 137 presentó valores bajos y se comportó como un parte-aguas entre las regiones norte y sur. Estacionalmente la Pnueva fue alta en la transición primavera-verano; disminuyó en el verano y el otoño, con aumento en invierno. La Pnueva se relacionó con el índice de surgencias costeras y se concluye que para un índice de surgencias costeras menor a 200 m3/s/100 m, la Pnueva aumenta y el máximo se produce en el mismo período que las surgencias costeras. Para un índice superior a 200 m3/s/100 m la Pnueva disminuye y ambas series se desfasan temporalmente."

"Se propone una regionalización oceánica y costera dinámica del Pacífico Norte mexicano frente a la Península de Baja California a partir de un modelo de temperatura y producción primaria nueva (Pnueva). La Pnueva se calculó con base en imágenes de temperatura del AVHRR; clorofila y PAR del sensor SaeWiFS y se multiplicó por la producción fitoplanctónica total (PPZ) y la razón-fz para cada profundidad. Se confeccionaron mapas mensuales de temperatura y Pnueva para profundidades de 0, 10, 30, 50, 75 y 100 m. Esta es la primera regionalización marina con el concepto de “regionalización territorial”. Los resultados muestran la dinámica oceanográfica frente a la Península de Baja California; ésta varió de la costa al océano y de forma latitudinal. Para la regionalización del Pacífico Norte mexicano, se propone nueve Unidades de Gestión Ambiental (UGA): tres oceánicas y seis costeras. La UGA oceánica VIII y las vecinas costeras IV y V son consideradas “zona de transición” entre las condiciones norteñas (agua subártica) y las sureñas (agua subtropical). En particular, la región de Isla Navidad se destaca como divisoria entre el agua fría al norte y cálida al sur. En primavera, el efecto de las surgencias costeras de las UGAs I y II se distingue desde la superficie hasta 100 m, con zonas eutróficas en las UGAS costeras IV y V en 30-50 m. En otoño el área de estudio es oligotrófica."

Forty-two species of dinoflagellate motile cells and 18 species of organic-walled dinoflagellate resting cysts were identified in samples collected at Todos Santos Bay, Baja California, Mexico, from September 1999 to June 2000. These temperate to cool-temperate species belong mainly to the families Gonyaulacaceae and Protoperidiniaceae. Lingulodinium polyedrum (Stein, 1883) Dodge 1989 was the dominant species both in the sediments and water column. During this period we observed planktonic motile cells, temporary cysts with cellulose walls, and resting cysts with resistant dinosporin walls. Two dinoflagellate blooms occurred in the spring to summer of 2000 allowing us to observe the timing of cyst production. The temporary cysts appeared between these blooms and also in the summer, whereas the resting cysts appeared during the preceding fall and winter. Resting cysts appeared in colder conditions, whereas the temporary cysts were produced within a particular thermal window and under nutrient depletion. Resting cysts were concentrated in discrete areas at depths of less than 25 m, and associated with sediments ranging from silt to fine sand. These cysts were abundant in the surface sediments during summer, fall and winter, whereas the motile cells dominated during the spring and summer, when the two L. polyedrum blooms were observed. The abundance of cells in the plankton, comprising motile cells and temporary cysts, appears to be inversely proportional to the concentration of resting cysts of the same species in the surface sediments.

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.

In recent years, experts of optical hydrology have shown great interest in the variability of the specific absorption coefficient of light byphytoplankton ( a � ). This parameter is important and necessaryfor comparing in situ bio-optical and satellite optical measurements. Such comparisons are needed for detecting primaryproductivityat a mesoscale level. At present, however, the parameters used in algorithms for predicting productivityare global averages. To avoid this bias, we measured the spatial-temporal variabilityof aas part of the Jan-01 Investigaciones Mexicanas de la Corriente de California cruise along the southern California Current. We observed median values of 0.041 m 2 (mg chlorophyll a (Chl a)) � 1 at 440 nm and 0.015 at 674 nm, with significant differences between inshore and offshore stations. In general, the stations located in the area of Bahia Vizcaino, with oceanographic conditions favorable for the growth of phytoplankton, showed lower values of the a �. The nano-microphytoplankton (45mm) community comprised of 26 diatom genera with mean abundance values of the 19.5 � 10 3 cells l � 1 . Nitzschia closterium, a pennate diatom, was almost uniform throughout the studyregion. Flow cy tometrymeasurements indicated that the picoplankton (o5mm) communityconsisted of two prokary otes, Prochlorococcus (mean 3.6 � 10 6 cells l � 1 ) and Synechococcus (mean 10.4 � 10 6 cells l � 1 ), and a mixture of picoeukaryotes (mean 6.5 � 10 6 cells l � 1 ). Analyses of Chl and carotenoid pigments determined byhigh-performance liquid chromatographic confirmed the presence of the divinyl Chl a characteristic of Prochlorococcus. The nano-micro- and picoplankton were 82% and 18% of total phytoplankton ARTICLE IN PRESS

To estimate ocean primary production at large space and time scales, it is necessary to use models combined with ocean-color satellite data. Detailed estimates of primary production are typically done at only a few representative stations. To get survey-scale estimates of primary production, one must introduce routinely measured Chlorophyll-a (Chl-a) into models. For best precision, models should be based on accurate parameterizations developed from optical and photosynthesis data collected in the region of interest. To develop regional model parameterizations 14 Cbicarbonate was used to estimate in situ primary production and photosynthetic parameters ða � ; P �, and Ek) derived from photosynthesis–irradiance (P–E) experiments from IMECOCAL cruises to the southern California Current during July and October 1998. The P–E experiments were done for samples collected from the 50% surface light depth for which we also determined particle and phytoplankton absorption coefficients (ap, af, and a �Þ. *

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.

The IMECOCAL Program began in 1997, with the objective of sampling plankton systematically in the Mexican region of the California Current. We present results of chlorophyll a concentrations and zooplankton displacement volumes for the eight cruises from September 1997 to October 1999. The abundance of 22 zooplankton groups was also analyzed for the first four cruises. The response of plankton to the 1997–1998 El Nino was atypical. From September 1997 to January 1998, chlorophyll a and zooplankton volume were at typical values (median integrated chlorophyll was 27 mg/m 2 and zooplankton 100 ml/1000 m 3 in 9801/02). After the peak of El Nino, the system shifted to cooler conditions. Integrated chlorophyll gradually increased to a median of 77 mg/m 2 in April 1999. In contrast, zooplankton volumes decreased from October 1998 onward, despite favorable phytoplankton availability in 1999. Zooplankton structure was dominated by copepods and chaetognaths through the ENSO cycle, but interannual changes were evident. In the fall of 1997 there was a higher proportion of copepods, chaetognaths, and other minor groups, while the fall of 1998 zooplankton was richer in salps and ostracods. Historical data from previous Baja California CalCOFI cruises indicated that zooplankton volumes measured during the IMECOCAL cruises were above the long-term mean for the period 1951–1984. This suggests a differential response of plankton to the El Nino of 1997–1998 compared to the El Nino of 1957–1959. Regional differences in zooplankton volumes were also found, with central Baja California having 41% higher biomass than northern Baja California. Volumes from both regions were larger than those recorded by CalCOFI off southern California during 1997–1998, but the situation was reversed in 1999. The higher biomasses in the 1997–1998 El Nino can be attributed to high abundance of salps, which showed an affinity with warm, saline water.

"The hydrophysical results obtained during six oceanographic cruises in 2011 (February, April, July, and October) and 2012 (February and April) over a 50-station samp ling grid in front of the Magdalena-Almeja s lagoon system (Mexico) are presented. MO DIS-Aqua sensor data (1.1 km) of sea surfa ce temperature (SST) and chlorophyll a , and geostrophic current fields we re analyzed during the sampling periods. In the northern part of the study area the pattern of the thermohaline structure shows subsurface intrusion of modifie d subarctic water, especially during February and April of both years. To the south, in July and Octobe r 2011, evident indications of subtropical subsurface water were found. The geostrophic current fields in February and April show a surface southward flow along the coast, which changes d irection towards the North Pole in July and October. In spring, the sate llite-derived SST showed negative anomalies of up to 4.5 ºC in th e coastal zone, corresponding to cold upwelled wa ter rising to the surface from a depth of 60–70 m. Based on the re sults, the study area can be considered the southern boundary of the transition zone betw een the subarctic and subtropi cal waters of the northeast ern Pacific Ocean, with m arked seasonality."

Spatial and temporal size-fractionated phytoplankton chlorophyll-a (Chl-a) variability as pico-nanoplankton (PN, 0.4- 8.0 μm) and nano-microplankton (NM, 8.0 μm) off Baja California is shown. Chl-a samples from the upper 200 m were obtained from nearshore, offshore, and intermediate locations during winter, spring, and summer 2008. PN-Chl-a contribution to phytoplankton biomass was ~4 times higher than NM fraction. Chl-a PN/NM ratio increased toward offshore, while total Chl-a (PN + NM) decreased. Seasonally, offshore phytoplankton cells abundance had a comparable contribution for both size-fractions, without an apparent change by the integrated water-column total Chl-a (60 mg m2). Vertical Chl-a profiles were similar for winter and summer seasons. The highest Chl-a concentration and phytoplankton- cells abundance arose in spring, predominantly for NM at nearshore locations, reaching from 2.7-fold (nearshore: middle) to 4.2-fold (middle: offshore) ratios. Phytoplankton Chl-a increased from winter to spring (5.4 times), with maximum contribution of NM (6.6 times) at nearshore zones. Water-column integrated phytoplankton abundance was 5-fold higher in spring than winter, and 2-fold over summer. Using optical microscopy, dinoflagellate cells were the most abundant and variable phytoplankton recognizable group at intermediate zone. Smaller phytoplankton cells sustained approximately continuous biomass off Baja California. The spatial and temporal phytoplankton biomass variability was mainly influenced by an increase of larger cells as result of spring coastal upwelling events.

The hydrophysical results obtained during six oceanographic cruises in 2011 (February, April, July, and October) and 2012 (February and April) over a 50-station samp ling grid in front of the Magdalena-Almeja s lagoon system (Mexico) are presented. MO DIS-Aqua sensor data (1.1 km) of sea surfa ce temperature (SST) and chlorophyll a , and geostrophic current fields we re analyzed during the sampling periods. In the northern part of the study area the pattern of the thermohaline structure shows subsurface intrusion of modifie d subarctic water, especially during February and April of both years. To the south, in July and Octobe r 2011, evident indications of subtropical subsurface water were found. The geostrophic current fields in February and April show a surface southward flow along the coast, which changes d irection towards the North Pole in July and October. In spring, the sate llite-derived SST showed negative anomalies of up to 4.5 ºC in th e coastal zone, corresponding to cold upwelled wa ter rising to the surface from a depth of 6070 m. Based on the re sults, the study area can be considered the southern boundary of the transition zone betw een the subarctic and subtropi cal waters of the northeast ern Pacific Ocean, with m arked seasonality.

The seasonal variability of dissolved inorganic nutrients (phosphates, PO–3 4; nitrates, NO– 3; nitrites, NO– 2) and chlorophyll a was studied during fiv...

Spatial variability of the central Gulf of California (CGC) phytoplankton biomass and photosynthetic parameters in relation to physical forcing was studied. Sampling was carried out in November, and the surface T°C range was 20-27.5°C. Strong tidal mixing in the midrift islands region injects relatively cool, nutrient-rich waters to the euphotic zone. Some of this water is transported via jets and cool filaments throughout the Gulf. In general, chlorophyll a (Chl) of small phytoplankton ( 2.5 mg m -3 ) was higher than that of large phytoplankton. Highest values of phyto- plankton assimilation numbers (P B m) (3.17 mg C (mg Chl a) -1 h -1 ), and photosynthetic efficiency (a B ) (0.23 mg C (mg Chl a)-1 h-1 (W m-2)-1) were determined for the large phytoplankton cells (>8 µm). Our hypothesis that PBm values increase from cooler to warmer waters is not supported by the data. We found a 27-fold spatial difference of Chl, compared with a 10-fold difference of PBm and a 6-fold difference of aB. Thus, in our study area, the major source of variability for primary productivity (PP) comes from Chl, and not from PBm and aB. Therefore, we propose that it is possible to estimate late- fall PP for the CGC using average photosynthetic parameters. Average values for PBm and aB of total phytoplankton were 0.72 mg C (mg Chl a)-1 h-1 and 0.12 mg C (mg Chl a)-1 h-1 (W m-2)-1, with standard errors of 0.07 and 0.03, respectively.