Seasonal variability of primary production in the Cap-Ferret Canyon area (Bay of Biscay) during the ECOFER cruises

Primary production measurements were carried out during the five ECOFER cru ises, in order to estimate the autochtonous contribution to particulate flu xes collected at two mooring sites, in the Cap-Ferret Canyon, from June 198 9 to August 1991. Primary production rates are reported in relation to leve ls of chlorophyll and nitrogenous nutrients in the euphotic zone. Except in early spring, the water column remains stratified until the beginning of a utumn surface-water cooling. During the stratified period, maximal chloroph yll concentrations were recorded at the bottom of the photic zone, near the 1% light depth, close to the nitracline; concentrations in some profiles w ere greater than those measured in surface waters during the early spring b loom. From June to October, a mean daily production of 0.4 g C m(-2) may be used to estimate particulate fluxes, because the recorded variability was low. During April and May, mean daily production rates can be about 3-4 tim es higher. Extrapolation of our data gives an estimate of yearly production from 145 to 170 g C m(-2) yr(-1). The possibility of greater production ra tes, under stratified conditions, is discussed taking into account the occu rrence of changes in the depth of the chlorophyll maximum during the day; s uch vertical movements could be caused by internal waves, particularly at t he shelf break. (C) 1999 Elsevier Science Ltd. All rights reserved.