Nested central volcanism related to rift development and giant landsliding in oceanic islands

Centro Superior de Investigaciones Científicas, Museo Nacional de Ciencias Naturales, Estación Volcanológica de Canarias

Horizontal distribution of invertebrate larvae around the oceanic island of Gran Canaria: the effect of mesoscale variability

In October 1991, the horizontal distribution of invertebrate larvae was studied in the waters surrounding the island of Gran Canaria (Canary Islands). The cruise was typified by the presence of three recurrent mesoscale hydrographic structures: a cyclonic eddy southwest of the island, a warm lee region downstream of the island and the offshore boundary of an upwelling filament from the African coast reaching the southeast of the island. Decapod larvae were the most abundant group. In general, a rather high spatial variability was found. The horizontal distribution of the invertebrate larvae groups showed that the highest values of abundance occurred in an elongated zone around the island oriented in the overall direction of flow, leeward and windward of the island, while the lowest values occurred off the eastern and western flanks of the islands. On the other hand, Stomatopoda and Mollusca larvae showed a distribution associated with the boundary of the upwelling filament and decapod larvae of pelagic species were distributed around the eddy structure. Our results suggest specific retention mechanisms for the larvae of neritic invertebrate populations that are related to the particular physical oceanography around Gran Canaria. Se estudió la distribución horizontal de las larvas de invertebrados alrededor de la isla de Gran Canaria (Islas Canarias) en octubre de 1991. La campaña se caracterizó por la presencia de tres fenómenos oceanográficos de mesoescala recurrentes: un remolino ciclónico al suroeste de la isla, la estela cálida a sotavento de la misma y el borde de un filamento proveniente del afloramiento africano situado al sureste de Gran Canaria. Las larvas de crustáceos decápodos fueron las más abundantes. En general, las larvas de los diferentes taxa estudiados mostraron una gran variabilidad en cuanto a su distribución espacial. La distribución horizontal de las larvas de los diferentes grupos de invertebrados mostró que las densidades más altas se registraban alrededor de la isla en la banda cercana y orientada hacia el suroeste, en la dirección del flujo, mientras que los valores más bajos se encontraron en el norte y en los flancos este y oeste de la isla. Por otro lado, las larvas de estomatópodos y moluscos presentaron una distribución asociada al frente del filamento, mientras que las larvas de decápodos pelágicos se distribuyeron en torno al remolino ciclónico. Los resultados obtenidos sugieren la existencia de mecanismos de retención específicos para el mantenimiento de las poblaciones insulares, relacionados con los procesos físicos de mesoescala predominantes

High-resolution modelling of the Canary Basin oceanic circulation

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Is the GDH/RNH4+ ratio in the mesozooplankton constant through different oceanic systems?

[EN] Nitrogen (N) is essential for life, but its availability is frequently limited in ocean ecosystems. Among all the compounds which influence the N pool, ammonium (NH4+) represents the major source of N for autotrophs. This NH4+ is provided by bacterial remineralization and heterotrophic grazers, with the mesozooplankton responsible for 12% to 33% of the total NH4+ recycled.  Quantifying the excretion physiology of zooplankton is then, necessary to understand the basis of an aquatic ecosystem’s productivity.
The measurement of glutamate dehydrogenase (GDH) activity has been widely used to assess the NH4+ excretion rates in planktonic communities. However, its relationship with the physiology varies with temperature and the nutritional status of the organisms, among other variables. Here we compare the GDH/RNH4+ ratio between oceanic regions with different trophic conditions.  Strengthening our knowledge of the relationship between GDH activities and the NH4+ excretion rates will lead to more meaningful interpretations of the mesoscale variations in planktonic NH4+ excretion.

Is the GDH/RNH4+ ratio in the mesozooplankton constant through different oceanic systems?

[EN]Nitrogen (N) is essential for life, but its availability is frequently limited in ocean ecosystems. Among all the compounds which influence the N pool, ammonium (NH4+) represents the major source of N for autotrophs. This NH4+ is provided by bacterial remineralization and heterotrophic grazers, with the mesozooplankton responsible for 12% to 33% of the total NH4+ recycled. Quantifying the excretion physiology of zooplankton is then, necessary to understand the basis of an aquatic ecosystem?s productivity. The measurement of glutamate dehydrogenase (GDH) activity has been widely used to assess the NH4+ excretion rates in planktonic communities. However, its relationship with the physiology varies with temperature and the nutritional status of the organisms, among other variables. Here we compare the GDH/RNH4+ ratio between oceanic regions with different trophic conditions. Strengthening our knowledge of the relationship between GDH activities and the NH4+ excretion rates will lead to more meaningful interpretations of the mesoscale variations in planktonic NH4+ excretion.

An observational study of oceanic eddy generation mechanisms by tall deep-water islands (Gran Canaria)

[EN]Oceanic eddy generation by tall deep-water islands is common phenomenon. It is recognized that these eddies may have a significant impact on the marine system and related biogeochemical fluxes. Hence, it is important to establish favourable conditions for their generation. With this objective, we present an observational study on eddy generation mechanisms by tall deep-water islands, using as a case study the island of Gran Canaria. Observations show that the main generation mechanism is topographic forcing, which leads to eddy generation when the incident oceanic flow is sufficiently intense. Wind shear at the island wake may acts only as an additional eddy-generation trigger mechanism when the impinging oceanic flow is not sufficiently intense. For the case of the island of Gran Canaria we have observed a mean of ten generated cyclonic eddies per year. Eddies are more frequently generated in summer coinciding with intense Trade winds and Canary Current.