Oceanographic studies off Baja California: the IMECOCAL program.

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A numerical study of the ex-ROFI of the Colorado River

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

Temporal variability of downward fluxes of organic carbon off Monterey Bay

17 USC 105 interim-entered record; under review.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.

Seasonal variation of the temperature and salinity at the entrance to the Gulf of California, Mexico

The article of record as published may be found at http://dx.doi.org/10.7773/cm.v26i4.621Se describe la variabilidad estacional en la entrada al Golfo de California utilizando datos de CTD en una sección a través de la entrada al golfo, la cual fue ocupada en ocho ocasiones entre 1992 y 1998. Se encontró que la variabilidad decrece rápidamente debajo de los 100 dbar; las desviaciones estándar mayores que 0.5ºC y 0.05 para temperatura y salinidad, respectivamente, fueron confinadas a la capa superior de 150 dbar. El campo medio de salinidad fue asimétrico, con aguas de menor salinidad (S 34.8) arriba de 50 dbar y entre 100 y 150 dbar cerca de Baja California. En la capa superior de 50 dbar se observó una termoclina estacional sobre la cual las temperaturas superficiales cambiaron de 21ºC en febrero a 31ºC en agosto. Debajo de los 100 dbar, la temperatura a una presión dada fue típicamente más fría en el centro de la sección, indicando flujo ciclónico (flujo de entrada al golfo cerca de Sinaloa y de salida del golfo cerca de Baja California). El enfriamiento subsuperficial en la mitad de la sección del golfo (flujo ciclónico) fue más fuerte durante el invierno y la primavera, época cuando el intercambio de calor entre el golfo y el Océano Pacífico es mayor. No se observó el calentamiento subsuperficial en la parte media de la sección que corresponde a un flujo anticiclónico. La distribución temporal y espacial de las masas de agua de mayor salinidad sugieren que los intercambios de calor se dan por la alternancia de flujos de entrada y salida de masas de agua de mayor temperatura (superficial) y menor temperatura (subsuperficial). Durante el evento de El Niño 1997–1998 se observó un hundimiento de 50 dbar en la termoclina en noviembre de 1997, así como una disminución de 0.1 a 0.2 de la salinidad de las aguas arriba de la termoclina.Seasonal variability at the entrance to the Gulf of California is described using high resolution CTD data from a section across the entrance to the gulf that was occupied eight times between 1992 and 1998. Variability decreased rapidly below 100 dbar, so that standard deviations exceeding 0.5ºC and 0.05 for temperature and salinity, respectively, were confined to the upper 150 dbar. The mean salinity field wasasymmetric, with fresher waters (S < 34.6) between 25 and 75 dbar next to Sinaloa and saltier waters (S > 34.8) above 50 dbar and between 100 and 150 dbar near Baja California. A seasonal thermocline developed in the upper 50 dbar, increasing from 21ºC in February surface temperatures to 31ºC in August. Below 100 dbar, temperature at a given pressure was typically colder in the center of the section, indicating cyclonic flow (flow into the gulf next to Sinaloa and out of the gulf next to Baja California). The subsurface mid-gulf cooling (cyclonic flow) was strongest during winter and spring when the exchange of heat between the gulf and the Pacific Ocean is large. Subsurface mid-gulf heating (corresponding to anticyclonic flow) was not observed. Temporal and spatial distribution of saline water masses suggests that heat exchanges take place by alternating the inflow and outflow of warm (surface) and cold (subsurface) water masses. The 1997–1998 El Niño resulted in a 50 dbar deepening of the thermocline in November 1997, as well as a freshening of 0.1 to 0.2 of waters above the thermocline.CONACYTUABCOceanographer of the Navy (US)Naval Postgraduate SchoolSecretaría de MarinaUNAM (Mexico)26653-T4271P-T9601400940151076-T920

Modelos predictivos de la distribución preferencial de larvas de peces demersales en la parte sur de la corriente de California

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

Phytoplankton size-fractionated chlorophyll-a off Baja California during winter, spring, and summer 2008

Spatial and temporal size-fractionated phytoplankton chlorophyll-a (Chl-a) variability as pico-nanoplankton (PN, 0.4- 8.0 µm) and nano-microplankton (NM, &gt;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 m?2). 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 Making of a Productivity Hotspot in the Coastal Ocean

Highly productive hotspots in the ocean often occur where complex physical forcing mechanisms lead to aggregation of primary and secondary producers. Understanding how hotspots persist, however, requires combining knowledge of the spatio-temporal linkages between geomorphology, physical forcing, and biological responses with the physiological requirements and movement of top predators.) off the Baja California peninsula, Mexico.We have identified the set of conditions that lead to a persistent top predator hotspot, which increases our understanding of how highly migratory species exploit productive regions of the ocean. These results will aid in the development of spatially and environmentally explicit management strategies for marine species of conservation concern

State of the California Current 2014-15: Impacts of the Warm-Water "Blob"

In 2014, the California Current (~28˚–48˚N) saw average, or below average, coastal upwelling and relatively low productivity in most locations, except from 38˚–43˚N during June and July. Chlorophyll-a levels were low throughout spring and summer at most locations, except in a small region around 39˚N. Catches of juvenile rockfish (an indicator of upwelling-related fish species) remained high throughout the area surveyed (32˚–43˚N). In the fall of 2014, as upwelling ceased, many locations saw an unprecedented increase in sea surface temperatures (anomalies as large as 4˚C), particularly at 45˚N due to the coastal intrusion of an extremely anomalous pool of warm water. This warm surface anomaly had been building offshore in the Gulf of Alaska since the fall of 2013, and has been referred to as the “blob.” Values of the Pacific Decadal Oscillation index (PDO) continued to climb during 2014, indicative of the increase in warm coastal surface waters, whereas the North Pacific Gyre Oscillation index (NPGO) saw a slight rebound to more neutral values (indicative of average productivity levels) during 2014. During spring 2015, the upwelling index was slightly higher than average for locations in the central and northern region, but remained below average at latitudes south of 35˚N. Chlorophyll a levels were slightly higher than average in ~0.5˚ latitude patches north of 35˚N, whereas productivity and phytoplankton biomass were low south of Pt. Conception. Catches of rockfish remained high along most of the coast, however, market squid remained high only within the central coast (36˚–38˚N), and euphausiid abundance decreased everywhere, as compared to the previous year. Sardine and anchovy were nearly absent from the southern portion of the California Current system (CCS), whereas their larvae were found off the coast of Oregon and Washington during winter for the first time in many years. Waters warmed dramatically in the southern California region due to a change in wind patterns similar to that giving rise to the blob in the broader northeast Pacific. For most of the coast, there were intrusions of species never found before or found at much higher abundances than usual, including fish, crustaceans, tunicates and other gelatinous zooplankton, along with other species often indicative of an El Niño. Thus species richness was high in many areas given the close juxtaposition of coastal upwelling-related species with the offshore warm-water intrusive or El Niño-typical taxa. Thus the California Current by 2015 appears to have transitioned to a very different state than previous observations

Effects of ocean climate on life cycles and distribution of small pelagic fishes in the California Current System off Baja California

Due to their sensitivity to climate forcing that may alter their abundance and distribution, small pelagic fish are important ecological indicators of the state of the California Current System. They are schooling, planktivorous fish that provide forage for higher trophic levels. We describe the life cycle histories and patterns of distribution of sardine, anchovy, and mackerel species occupying the waters along the west coast of the Baja California Peninsula (Mexico). The links between the physical and biological forcing and the structure and condition of their habitats, their patterns of movement, productivity, and stock structure (where information is available) are described in relation to the fisheries. We have used the catches as a proxy for the history of the different stocks, while recognizing that fisheries-derived information is biased by the operational scale and only covers areas where fish are available. We have relied mainly on studies of sardines to evaluate the validity of the principal paradigms in fisheries oceanography. We describe how the environment can structure a population by relating an example given by the spatiotemporal variability of the northern and southern stocks of Pacific sardine (Sardinops sagax) and Pacific mackerel (Scomber japonicus) from 2000 to 2014. During this period, the northern stocks showed a marked tendency to contract southwards, as far south as Magdalena Bay, in response to the regional cooling that began in the previous decade. It appears that the combined effects of fishing and climate change may sufficiently alter habitat characteristics so that both the distribution and productivity of a population are shifted.