Radon in Groundwater of the Northeastern Gran Canaria Aquifer

[EN]Rn has been detected in 28 groundwater samples from the northeast of Gran Canaria (Canary Islands, Spain) utilizing a closed loop system consisting of an AlphaGUARD monitor that measures radon activity concentration in the air by means of an ionization chamber, and an AquaKIT set that transfers dissolved radon in the water samples to the air within the circuit. Radon concentration in the water samples studied varies between 0.3 and 76.9 Bq/L. Spanish radiological protection regulations limit the concentration of 222Rn for drinking water to 100 Bq/L, therefore the values obtained for all the analyzed samples are below this threshold. The hydrogeological study reveals a significant correspondence between the radon activity concentration and the material characteristics of the aquifer.

Radiación gamma natural en Gran Canaria

[ES]A raíz del accidente de Chernobyl en 1986 aumentó la preocupación por la vigilancia radIológica y se alentó el propósito de elaborar mapas de radiación gamma natural para poder evaluar los niveles de ral/iación y detectar así sus posibles incrementos. En España se ha piocedido a elaborar mapas de radiación gamma . . . natural. El presente trabajo contribuye a. completar dichos mapas, proporcionando datos s.obre la radiación natural en la isla deGran Canaria. Es Iruto de un convenio entre la Universidad de Las Palmas de . Gran Canaria, él Cabildo Insular de Gran Canaria Ji la Fundación Universitaria de Las Palmas. Se llevó a cabo en una campaña de medidas que se realizó desde el4 de mayo al10 de octubre de 1996, y aquí se presentan sus resultados

Identification, Abundance and Rearing of Mysids of Gran Canaria: aplication to laboratory and oceanographic respiratory metabolism studies

Programa de doctorado en Oceanografía

Scaling properties of rainfall and desert dust in the Canary Islands

[EN] Precipitation and desert dust event occurrence time series measured in the Canary Islands region are examined with the primary intention of exploring their scaling characteristics as well as their spatial variability in terms of the islands topography and geographical orientation. In particular, the desert dust intrusion regime in the islands is studied in terms of its relationship with visibility. Analysis of dust and rainfall events over the archipelago exhibits distributions in time that obey power laws. Results show that the rain process presents a high clustering and irregular pattern on short timescales and a more scattered structure for long ones. In contrast, dustiness presents a more uniform and dense structure and, consequently, a more persistent behaviour on short timescales. It was observed that the fractal dimension of rainfall events shows an important spatial variability, which increases with altitude, as well as towards northern latitudes and western longitudes.

Reconstruction of the aquifer history of Gran Canaria

[EN]A study on the recent history and current state of the aquifer in the Island of Gran Canaria (Canary Is., 28oN, 15oW) is performed. Though rainfall is scarce on the island, traditional agricultural practices and small population were able to keep the aquifer in a constant state for centuries. Nevertheless, at the beginning of the 20th Century, culture of several water-consuming species was introduced on a commercial basis due to the relative proximity of the Canaries to continental Europe and to the possibility of more than one yearly harvest. This led to generalised well digging (more than 300m deep in many cases) and to the appearance of a chronic hydraulic deficit, as well as to spoiling vastcoastal areas of the aquifer through intrusion of brackish water. In the mid 1960’s, coincident with the apex of agricultural exploitation, massive tourism appeared in the scene. This new activity soon became a susbstitute for Agriculture, but it attracted more new labour force to the island, and a fast growth of population was the main result. Moreover, new water use practices entered the scene. As a consequence, the main causes for the aquifer decline are population growth and extensive Agriculture practices in use during the last half of the 20th Century. Some remarks on sustainability issues in order to cope with Climate Change are also offered.

Short-term variability and trophic interactions within planktonic community in subtropical waters of he Canary Islands (Northeast atlantic)

ES]Los giros subtropicales abarcan grandes áreas del océano donde la productividad del ecosistema se sostiene a través del reciclado de materia y energía. En estas aguas, la interacción entre la disponibilidad de recursos y la presión de los niveles tróficos superiores determina la dinámica de la comunidad planctónica. Sin embargo, en aguas subtropicales, el conocimiento de la variabilidad temporal o el papel de los diferentes componentes de la comunidad dentro de la red trófica es bastante limitado. En esta tesis se evalúa la variabilidad a corto plazo de los diferentes componentes de la comunidad planctónica. El picoplancton dominó la comunidad salvo durante la época productiva, en la que los organismos autótrofos de mayor tamaño desempeñaron un papel destacado. Nuestros resultados muestran como la variabilidad estacional está relacionada con fuerzas “bottom-up”, mientras que los procesos “top-down” dominan a una escala de tiempo más corta. Encontramos que el microzooplancton ejerce un gran impacto sobre la comunidad microbiana, en organismos tanto autótrofos como heterótrofos. Además, observamos un acoplamiento muy estrecho entre estos consumidores y sus presas. Otro mecanismo que regula la estructura planctónica es la depredación de los migradores verticales sobre el zooplancton. Así, la variabilidad del mesozooplancton epipelágico está controlada por un ciclo de depredación vinculado a la iluminación de la luna. En este trabajo realizamos una simulación de esta variabilidad con la que se obtuvieron valores de mortalidad comunitaria de los que derivamos el flujo de carbono activo hacia la zona mesopelágica. Estos valores calculados de transporte activo de carbono son del mismo orden de magnitud que el flujo gravitacional en aguas subtropicales. En el Atlántico noreste la comunidad marina también podría estar influenciada por las tormentas de polvo sahariano que ocurren con gran frecuencia en la zona. En este sentido, se estudió la respuesta de la comunidad planctónica en un período de deposición de polvo atmosférico de gran intensidad, en el año 2010, sin observar una clara respuesta en términos de producción primaria. Por el contrario, la biomasa de diatomeas y mesozooplancton sí se vio aumentada en gran medida tras el paso de una fuerte tormenta de polvo del Sáhara, mientras que los organismos autótrofos de menor tamaño se vieron afectados negativamente. Los resultados de esta tesis suponen una contribución importante para entender la dinámica planctónica tan compleja en los ecosistemas subtropicales, y además, pone de manifiesto la necesidad de llevar a cabo muestreos oceanográficos a escalas de tiempo más cortas.

An Overview of Geodetic Volcano Research in the Canary Islands

The Canary Islands are mostly characterized by diffuse and scattered volcanism affecting a large area, with only one active stratovolcano, the Teide?Pico Viejo complex (Tenerife). More than 2 million people live and work in the 7,447 km2 of the archipelago, resulting in an average population density three times greater than the rest of Spain. This fact, together with the growth of exposure during the past 40 years, increases volcanic risk with respect previous eruptions, as witnessed during the recent 2011?2012 El Hierro submarine eruption. Therefore, in addition to purely scientific reasons there are economic and population-security reasons for developing and maintaining an efficient volcano monitoring system. In this scenario geodetic monitoring represents an important part of the monitoring system. We describe volcano geodetic monitoring research carried out in the Canary Islands and the results obtained. We consider for each epoch the two main existing constraints: the level of volcanic activity in the archipelago, and the limitations of the techniques available at the time. Theoretical and observational aspects are considered, as well as the implications for operational volcano surveillance. Current challenges of and future perspectives in geodetic volcano monitoring in the Canaries are also presented.

3D Attenuation Tomography of the Volcanic Island of Tenerife (Canary Islands)

Peer reviewed

3D Attenuation Tomography of the Volcanic Island of Tenerife (Canary Islands)

Peer reviewed

3D Attenuation Tomography of the Volcanic Island of Tenerife (Canary Islands)

Peer reviewed

Petrology and geochemistry of the Quaternary Caldera-forming, Phonolitic Granadilla Eruption, Tenerife (Canary Islands)

The Granadilla eruption at 600 ka was one of the largest phonolitic explosive eruptions from the Las Cañadas volcano on Tenerife, producing a classical plinian eruptive sequence of a widespread pumice fall deposit overlain by an ignimbrite. The eruption resulted in a major phase of caldera collapse that probably destroyed the shallow-level magma chamber system. Granadilla pumices contain a diverse phenocryst assemblage of alkali feldspar + biotite + sodian diopside to aegirine–augite + titanomagnetite + ilmenite + nosean/haüyne + titanite + apatite; alkali feldspar is the dominant phenocryst and biotite is the main ferromagnesian phase. Kaersutite and partially resorbed plagioclase (oligoclase to sodic andesine) are present in some eruptive units, particularly in pumice erupted during the early plinian phase, and in the Granadilla ignimbrite at the top of the sequence. Associated with the kaersutite and plagioclase are small clots of microlitic plagioclase and kaersutite interpreted as quenched blebs of tephriphonolitic magma within the phonolite pumice. The Granadilla Member has previously been recognized as an example of reverse-then-normal compositional zonation, where the zonation is primarily expressed in terms of substantial variations in trace element abundances with limited major element variation (cryptic zonation). Evidence for cryptic zonation is also provided by the chemistry of the phenocryst phases, and corresponding changes in intensive parameters (e.g. T, f O2, f  H2O). Geothermometry estimates indicate that the main body of phonolite magma had a temperature gradient from 860 °C to ∼790 °C, with hotter magma (≥900 °C) tapped at the onset and terminal phases of the eruption. The reverse-then-normal chemical and thermal zonation reflects the initial tapping of a partially hybridized magma (mixing of phonolite and tephriphonolite), followed by the more sequential tapping of a zoned and relatively large body of highly evolved phonolite at a new vent and during the main plinian phase. This suggests that the different magma types within the main holding chamber could have been laterally juxtaposed, as well as in a density-stratified arrangement. Correlations between the presence of mixed phenocryst populations (i.e. presence of plagioclase and kaersutite) and coarser pumice fall layers suggest that increased eruption vigour led to the tapping of hybridized and/or less evolved magma probably from greater depths in the chamber. New oxygen isotope data for glass and mineral separates preclude syn-eruptive interaction between the vesiculating magma and hydrothermal fluids as the cause of the Sr isotope disequilibrium identified previously for the deposit. Enrichment in radiogenic Sr in the pumice glass has more likely been due to low-temperature exchange with meteoric water that was enriched in 87Sr by sea spray, which may be a common process affecting porous and glassy pyroclastic deposits on oceanic islands.

Annual westward propagating anomalies near 26 degrees N and eddy generation south of the Canary Islands: remote sensing (altimeter/SeaWIFS) and in situ measurement

Seasonal changes in altimeter data are derived for the North Atlantic Ocean. Altimeter data are then used to examine annually propagating structure along 26 degree N. By averaging the altimeter data into monthly values or by Fourier analysis, a positive anomaly can be followed from 17 degree W to similar to 50 degree W along similar to 26 degree N. The methods give a westward travel speed of 1 degree of longitude a month and a half-life of one year for the average decaying structure. At similar to 50 degree W 26 degree N, the average structure is about 2.8 years old with an elevation signal of similar to 1 cm, having gravelled similar to 3300 km westward. The mean positive anomaly results from the formation of anticyclonic eddies which are generally formed annually south of the Canary Islands by late summer and which then travel westward near 26 degree N. Individual eddy structure along 26 degree N is examined and related to in situ measurements and anomalies in the annual seasonal concentration cycle of SeaWiFS chlorophyll-a.

Breves notas sobre plantas y comunidades de Gran Canaria

En este artículo se describen varias comunidades de plantas en Gran Canaria, especialmente las procedentes de playas y otros lugares de la zona SE de la isla. También se hacen comentarios sobre la presencia reciente de alguna especie hasta el momento no registrada en el territorio recorrido, como Limnoniastrum monopetalum. Se estudian algunas asociaciones nitrófilas y otras de los depósitos arenosos de la desembocadura de la rambla de Jinamar. También la expansión de alguna especie de acacias en las dunas de Maspalomas. Se da a conocer una nueva asociación cerca de la playa de San Agustín: A triplici-Amaranthetum gracilis, muy extendida por la zona estudiada.