Variability and seasonality of physical and biological fields at the Great Meteor Tablemount (subtropical NE Atlantic)

Abstract

Five oceanographic surveys were conducted at the Great Meteor Tablemount (subtropical NE Atlantic; 30.0ºN, 28.5ºW) throughout the 1992-1999 period to investigate temporal variability in the relationship between the physical structure of the water column associated with the seamount and phytoplankton biomass and/or production rates. Local increases in chlorophyll a, enhanced carbon incorporation rates and changes in phytoplankton species composition were associated with the seamount. These effects were subjected to a large degree of temporal and spatial variability both at seasonal and shorter time scales. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Résumé − Variabilité et caractéristiques saisonnières des champs physique et biologique du Mont sous-marin Great Meteor (Atlantique subtropical NE). Entre 1992 et 1999 cinq campagnes de recherche océanographique ont été réalisées (30,0ºN, 28,5ºO), pour étudier la variabilité temporelle du rapport entre la structure physique de la colonne d'eau associée aux abords du mont sous-marin d'une part, et la biomasse et les taux de production phytoplanctonique d'autre part. On observe une élévation locale de la teneur en chlorophylle a près du mont sous-marin ainsi que des taux élevés de production primaire et des changements de la composition spécifique du phytoplancton. Ces effets connaissent une variabilité spatiale et temporelle élevée, aussi bien à courte échelle de temps qu'à l'échelle saisonnière.

Biodiversity and species-environment relationships of the demersal fish assemblage at the Great Meteor Seamount (subtropical NE Atlantic), sampled by different trawls

“…marginal currents, upwelling as detected for the GMR by Meincke (1971) and Mourino et al (2001), and interception with the sound-scattering layer, stations were arranged into three types of habitat (see Fig. 1C): ''type a'' for plateau with mean soundings ranging from 285 to 310 m, ''type b'' for the inner margin of the plateau with a mean catching depth from 302 to 365 m, and an outer margin ''c'' with soundings from 358 to 470 m. The marginal habitats, type b and c, are assumed to be directly affected by processes at the border of the plateau.…”

“…Firstly, we consider enhancement of primary production by means of upwelling in the region influenced by the Taylor-column to be the driving force; this would explain the preference of marginal habitats for many fish species fairly well, but not the pronounced diurnal patterns. The failure to find persistently increased levels of primary production at GMR (Mourino et al 2001) further weakens the primary-production hypothesis.…”

“…Ehrich (1977) 1, 55, 56, 60, 64, 71, 77, 79, 80, 82, 83, 84 3, 4, 11, 12, 14, 16, 17, 18, 19, 20, 21 Net opening assessed according to the 5/8-of-head-rope rule (see Haedrich and Merrett 1988, equivalent to 2/3-rule, see Rijnsdorp et al 1996) The factor ''season'' accounts for potential changes of production as suggested by Ehrich (1977) and Mourino et al (2001) and weather conditions (Ehrich 1971). The latter are likely to affect catch efficiency.…”

“…Pelagic stocks were investigated by Kotthaus (1972). Recently, data on primary production and hydrography have further supplemented existing knowledge (Mourino et al 2001). The status of fisheries at GMR is unknown; however, it has at least been subject to exploratory fishing (e.g.…”

“…The seasonal cycle is weak, and the water column is almost permanently stratified (Jickells et al 1996). Chlorophyll distributions are characterised by a winter maximum and summer minima (Campbell and Aarup 1992;Mourino et al 2001).…”