Oceanologia (Sep 2006)
Development and dynamics of a coastal sub-surface phytoplankton bloom in the southwest Kattegat, Baltic Sea
Abstract
The study was based on CTD-casts performed on 5 consecutive daysat 7 positions along a shallow- to deep-water transect duringthe spring bloom in the southwest Kattegat. The development,dynamics and fate of the sub-surface chlorophyll maximum (SCM)are described. The SCM developed at a constant rate of1.4 mg chl a m-3 d-1,which is equal to a carbon fixation rate of49.0 mg C m-3 d-1. The SCM developed at 6 m depth at low irradiancelevels (10-43.0 µE m-2 s-1). Chl a concentrations reachedup to 23 mg chl a m-3 in the centre of the SCM. Growth ratesin the SCM were estimated at 0.82 d-1. The water column wasonly weakly stratified, with nutrients in excess in the wholeof the water column. The SCM was relocated vertically to depthsbelow the photic zone by wind-induced advection between the bayand the outer Kattegat. There were indications of a horizontalrelocation of the SCM by an internal standing wave. Applicationof high spatial and temporal resolution made it possible to estimatekey SCM parameters, such as growth rates [mg chl a m-3 d-1]and carbon fixation rate [mg C m-3 d-1],on the basis of chl a variations in time and space.
