Origin and fate of a bloom of Skeletonema costatum during a winter upwelling/downwelling sequence in the Ria de Vigo (NW Spain)

The onset, development and decay of a winter bloom of the marine diatom Skeletonema costatum was monitored during a 10 d period in the coastal upwelling system of the Ria de Vigo (NW Spain). The succession of upwelling, relaxation and downwelling-favorable coastal winds with a frequency of 10-20 d is a common feature of the NW Iberian shelf. The onset of the bloom occurred during an upwelling-favorable (1)/(2) wk period under winter thermal inversion conditions. The subsequent (1)/(2) wk coastal wind relaxation period allowed development of the bloom (gross primary production reached 8 g C m(-2) d(-1)) utilizing nutrients upwelled during the previous period. Finally, downwelling during the following (1)/(2) wk period forced the decay of the bloom through a combination of cell sinking and downward advection.