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Marine Ecology Progress Series

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

Spring bloom nutrient dynamics in the Oslofjord

Svein Kristiansen*, Tove Farbrot, Lars-Johan Naustvoll

Department of Biology, University of Oslo, PO Box 1069 Blindern, 0316 Oslo, Norway
*Present address: Norwegian College of Fishery Science (NFH), University of Tromsø, Breivika, 9037 Tromsø, Norway. E-mail:

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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