MEPS 219:41-49 (2001)  -  doi:10.3354/meps219041

ABSTRACT: Primary production and uptake rates of ammonium, nitrate and silicic acid were measured during the 1996 spring bloom in the Oslofjord, southern Norway, using isotope methodology (¹⁴C, ¹⁵N and ³²Si). Chlorophyll a (chl a) standing stock peaked at 38 mg chl a m^-3. Diatoms, especially Thalassiosira nordenskioeldii, dominated the plankton community. The diatom bloom followed a sigmoid growth pattern until it abruptly declined. Both nitrate and silicic acid were depleted from the surface layer during the bloom. Nitrate was the major nitrogen-source for phytoplankton growth, the f-ratio was >0.9 until the bloom declined. Virtually all the silicic acid was converted into diatom frustules (biogenic silica), and silicon controlled the primary production during the bloom.

KEY WORDS: Diatoms · Thalassiosira nordenskioeldii · Spring · Silicic acid · Coagulation · Fjords