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Geochemical and stable isotope measurements in the anoxic marine zone (AMZ) off northern Chile during periods of contrasting oceanographic conditions indicate that microbial processes mediating sulfur and nitrogen cycling exert a significant control on the carbonate chemistry (pH, AT, DIC and pCO2) of this region. Here we show that in 2015, a large isotopic fractionation between DIC and POC, a DIC and N deficit in AMZ waters indicate the predominance of in situ dark carbon fixation by sulfur-driven autotrophic denitrification in addition to anammox. In 2018, however, the fractionation between DIC and POC was significantly lower, while the total alkalinity increased in the low-pH AMZ core, suggesting a predominance of heterotrophic processes. An isotope mass-balance model demonstrates that variations in the rates of sulfur- and nitrogen-mediated carbon fixation in AMZ waters contribute ~7-35% of the POC exported to deeper waters. Thus, dark carbon fixation should be included in assessments of future changes in carbon cycling and carbonate chemistry due to AMZ expansion.

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The Valdivia River estuary (VRE) located in south-central Chile is known as one of the largest estuarine ecosystems on the Pacific coast. This research aims to determine the intra-tidal and sub-tidal variability of saline intrusions into the VRE between November 2017 and March 2019 derived from salinity sensors located along the VRE. Complementary hydrographic measurements were conducted during flood and ebb conditions of the spring and neap tides for each of the four seasons of the year along the central axis of the VRE. The results of the salinity time series showed that saline intrusions (values greater than 0.5 Practical Salinity Units) occurred ~20 km from the estuary mouth, when the total flow of the Cruces and Calle-Calle rivers (main tributaries of the estuary) was low, around 280-300 m3 s-1. During the same period, the best co-variability was observed between the saline intrusions and the mixed-semidiurnal tide and the fortnightly and monthly periods of the tide. Regression analyses indicated that salinity intrusion length (L) is best correlated to discharge (D) with a fractional power model L α D-1/2.64 (R2 = 0.88). The decreasing discharge trend, found between 2008-2019, implies that saline water intrusions would negatively impact the Valdivia's main drinking water intake during the low rainfall season under future climate conditions.

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Abstract Zooplankton is an important component to understand oceanographic dynamics, they are considered good indicators of environmental variability, since most species are short-lived they can be tight coupling of climate and population dynamics, and some taxa are sensitive to variables such as temperature, quality and quantity of food, oxygenation and stratification. In the Colombian Caribbean two oceanographic cruises were carried out, in order to characterize and analyze the biodiversity of the continental margin, for the periods May-June 2008 and November-December 2009. The objective of this study was to determine which oceanographic variable was the most important in the distribution of zooplankton in the oceanic waters, and how the variables structure the community. In each cruise, zooplankton samples were obtained by vertical hauls with a 1 m2 diameter conical net (200 μm mesh size). The zooplankton community structure was studied by automated image analysis (ZooImage), which combined with abundance data, allowed to calculate the slope of size spectrum, and diversity indexes of taxa and sizes. The environmental variables included temperature, salinity, oxygen and chlorophyll a of the water column, and were used to calculate the stratification with the Brunt-Vaiisala frequency; this information was complemented by satellite images of temperature, surface chlorophyll, geostrophic currents and sea level, obtained from MODIS and AQUA products. The association between environmental variables and the zooplankton community structure was determined using Spearman's correlation ranges with the Bioenv routine and a stepwise regression model, and Principal component analysis (PCA). Our results showed spatial and temporal patterns in the oceanographic conditions of the study area, such as upwelling in the Northeast region, strong stratification in the Southwest, and mesoscale activity. The abundance of zooplankton exhibited differences between the two climatic seasons and zones. Temporal differences were also evident in the size and diversity of taxa (ANOVA 2-way p <0.05). These changes were related to the moderate upwelling and the activity of mesoscale eddies. Cyclonic and anticyclonic eddies of variable size can either transport or retain zooplankton over cross-shelf and oceanic areas, thus modifying the taxonomic structure of the community. According to the Bioenv analysis, the main variables that explained the abundance and composition of zooplankton were sea level and chlorophyll a (Spearman correlation = 0.49). The stepwise regression showed that stratification, oxygen and chlorophyll a were the most important predictors of zooplankton abundance and size. Rev. Biol. Trop. 66(2): 688-708. Epub 2018 June 01.

Resumen El zooplancton es un componente importante para entender la dinámica oceanográfica, es considerado un buen indicador de la variabilidad ambiental, ya que la mayoría de las especies tienen ciclos de vida cortos, por lo que puede haber un estrecho acoplamiento entre el clima y la dinámica de la población, algunos grupos son sensibles a variables como la temperatura, calidad y cantidad de alimento, oxigenación y estratificación. En el Caribe colombiano dos cruceros oceanográficos durante Mayo-Junio 2008 y Noviembre-Diciembre 2009 fueron realizados con el fin de caracterizar y analizar la biodiversidad del margen continental del Caribe colombiano. El objetivo de este estudio fue determinar qué variable oceanográfica es la más importante en la distribución del zooplancton en las aguas oceánicas del Caribe colombiano y de qué forma estas variables estructuran la comunidad. En cada crucero se obtuvieron muestras de zooplancton mediante arrastres verticales con una red cónica de 1 m de diámetro de boca y 200 µm de ojo de malla. La estructura comunitaria del zooplancton se estudió mediante el análisis automatizado de imágenes (ZooImage) el que combinado con datos de abundancia permitió calcular la pendiente del espectro de tamaño de la comunidad e índices de diversidad de taxa y tamaños. Las variables ambientales (temperatura, salinidad, oxígeno y clorofila a de la columna de agua) se obtuvieron desde los mismos cruceros y se utilizaron para calcular la estratificación mediante la frecuencia Brunt-Vaisala. Esta información in situ se complementó con imágenes satelitales de temperatura, clorofila superficial, corrientes geostróficas y nivel del mar, obtenidas de los productos MODIS y AQUA. La asociación entre variables ambientales y la estructura comunitaria del zooplancton se determinó mediante rangos de correlación de Spearman con la rutina Bioenv y un modelo de regresión paso a paso. El análisis de componentes principales (PCA) permitió observar patrones espaciales y temporales en las condiciones oceanográficas del área de estudio, tales como surgencia en la región Nororiental, fuerte estratificación en la Suroccidental y actividad de remolinos de mesoescala. La abundancia del zooplancton mostró diferencias entre las dos estaciones climáticas y entre las zonas. Diferencias temporales también fueron evidentes en el tamaño y diversidad de taxa (ANOVA 2-vías P < 0.05). Estos cambios se relacionaron con la surgencia moderada y la actividad de los remolinos de mesoescala. Los remolinos ciclónicos y anticiclónicos de tamaño variable pueden transportar o retener el zooplancton sobre áreas cruzadas y oceánicas, modificando así la estructura taxonómica de la comunidad. Según el análisis Bioenv las principales variables que explicaron la abundancia y composición del zooplancton fueron el nivel del mar y la clorofila a (correlación de Spearman = 0.49). El modelo de regresión paso a paso mostró que la estratificación, el oxígeno y la clorofila a son los predictores mas importantes para la abundancia y el tamaño del zooplancton.

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Contiene: Adaptación al castellano de un curso de hebreo a distancia. Tablas, vocabulario, listados

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