The influence of Great Meteor Seamount on the distribution of coccolithophorids

Abstract

During a multidisciplinary research cruise to the Great Meteor Seamount (GMS) (30°N 28.5°W) in September 1998 we studied the distribution of phytoplankton around and above this prominent topographic feature (min. depth 290 m) and its influence on the distribution of coccolithophorids in particular. Observations of the hydrographic conditions and the currents combined with a numerical model lead to the result that the dominant process at GMS was tidal forcing originating internal wave generation, trapped waves, flow rectification and a system of closed, horizontal and vertical circulation cells. These led apparently to an isolation of the phytoplankton community above the GMS summit as indicated by the distribution of various parameters, e.g. chlorophyll a and other phytopigments as well as cell numbers obtained by direct counting and flow cytometry. The distribution of the coccolithophorids showed an overall similar trend with an isolated patch above the seamount plateau with maximum cell numbers (47000 l-1) and maximum concentrations of the markerpigment 19’-Hexanoyloxyfucoxanthin. The max. concentrations of this phytopigment, typical for Prymnesiophyceae, were detected in the lower photic zone coinciding roughly with physico-chemical gradients such as the thermocline and nutricline. This could be also confirmed by the species assemblage which was mainly dominated by Florisphaera profunda and Gephyrocapsa ericsonii. The identification of ca. 80 different taxa confirms the high diversity of coccolithophorids in oligotrophic waters such as those around GMS.