Variation of the tidal properties around Gran Canaria

Abstract

Analysis of water level and current meter series from different locations on the island shelf of Gran Canaria reveals strong variations in tidal properties. Semidiurnal sea level amplitudes agree with the results obtained from global tidal models for this region only on the northern coast of the island, while they decrease towards the southwest (10 cm difference for the M2 constituent). Semidiurnal currents present maxima at the southeastern and northwestern extremities of the island (30-40 cm s-' for MJ and minima in the north-northeast and southwest (3-6 cm s-' for M,), showing simultaneous strong changes in the phase. Diurnal levels and currents display smaller variations than the semidiurnal band. The behaviour of semidiumal constituents is studied with the help of analytical and numerical solutions, in which the incident wave is modelled by a barotropic M2 Kelvin wave. The results show that the insular shelf could be a source of differences in level amplitudes around the island and could be also responsible for the enhancement of currents in the southeast and northwest. They also show that the variation of the current phases is due to the amplification of the standing character of the wave at the northeastern and southwestern parts of the shelf. 0 Elsevier, Paris / Ifremer / Cnrs / Ird tide / tidal current / island / numerical modelling / Canary Islands R&urn6-Variation des propriCtCs de la mar& dans les eaux de la Grande Canarie. L'analyse de series chronologiques du niveau de la mer et de la courantometrie, en plusieurs points du plateau continental de la Grande Canarie, revele de grandes variations dans les proprietes de la maree. Les amplitudes des variations semi-diumes du niveau de la mer sont en accord avec le modble global de maree au nord de l'ile, mais elles diminuent au sud-ouest (de 10 cm pour la composante MJ. Le courant semi-diume presente un maximum au sud-est et au nord-ouest de l'ile (de 30 a 40 cm s-l pour M,) et un minimum au nord-nord-est et au sud-ouest (de 3 a 6 cm s-' pour M,) avec, simultanement, une forte variation de phase. Les variations de periode diume des niveaux et des courants sont plus faibles que celles de periode semi-diurne. Les composantes semi-diumes sont Ctudiees par des methodes analytiques et numeriques, en considerant que I'onde incidente est une onde barotrope de Kelvin. Les resultats indiquent que le plateau continental est probablement a l'origine des differences observees dans les variations du niveau de la mer autour de l'ile et dans le renforcement des courants au sud-est et au nord-ouest. 11s montrent Cgalement que la variation de phase du courant est due a l'amplification du caractere stationnaire de l'onde sur le plateau continental, au nord-est et au sud-ouest de l'ile.

Fish larvae from the Canary region in autumn

“…In fact, the two stations with the greatest concentration of gobid larvae and a smaller percentage of oceanic larvae were two coastal stations sampled during the second leg of this cruise with one located to the north and the other to the south of this island. These two stations, because of particular conditions of water circulation around Gran Canaria (Van Camp et al, 1991;Hernández-Guerra et al, 1993;Arístegui et al, 1994Arístegui et al, , 1997Barton et al, 1998;Martínez et al, 1999;Rodríguez et al, unpublished data) would have been those that presented more neritic characteristics. …”

A new ocean tide loading model in the Canary Islands region

“…The tides are dominated by the semidiurnal constituents (Martínez et al, 1999) and, therefore, the cotidal chart for the O1 wave (Fig. 3) shows smaller variations than M2.…”

“…Gran Canaria island is characterized by a narrow shelf that rises sharply from 2000 to 3000 m depth. Martínez et al (1999) showed that the island shelf and, therefore, the effect of the shallower waters are responsible for the amplitude variation around this island. The maximum difference between the models (10-12 cm) found at the South of Gran Canaria reveals that the fine resolution of CIAM1 is better to represent this tide variation in contrast with the global ocean tide model.…”

“…From the tidal time series analysis they found that the tidal currents in this area are dominated by the barotropic mode (i.e., depth-independent) (Martínez et al, 1999). Therefore, the basic equations of the hydrodynamic model used are the two-dimensional depth-integrated barotropic shallow water equations (SWE).…”