Inter-Research
Marine Ecology Progress Series

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

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Published in MEPS Vol. 219 (2001) on September 10
Print ISSN: 0171-8630; Online ISSN: 1616-1599. Copyright © Inter-Research, Oldendorf/Luhe, 2001