Svein Kristiansen

• Norwegian University of Science and Technology

A review of silicon, with emphasis on its forms, uptake, dissolution and role in marine primary production, is given. The importance of silicon in marine food webs is discussed, as well as the concentrations of silicon in various areas and the importance of changing N:Si:P ratios. The methodology for measuring silicate transformations has recently...

Denitrification was studied in the water column in the Bunnefjord, inner part of the Oslofjord in southern Norway, using a 15N-technique (the isotope pairing method). The fjord is 150 m deep and during our surveys in September–December 1998 hydrogen sulphide was present in the deep water below 80 m. No significant denitrification was found in water...

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 (C-14, N-15 and Si-32), Chlorophyll a (chl a) standing stock peaked at 38 mg chl a m(-3). Diatoms, especially Thalassiosira nordenskioeldii, dominated the plankton communit...

The radioactive isotope 32Si was used to measure Si uptake during a spring bloom dominated by the diatom Thalassiosira nordenskioeldii. The diatoms converted virtually all dissolved silicic acid in the surface layer into biogenic silica. The rate of Si uptake was unsaturated in all the experiments conducted during the bloom. The half-saturation con...

In June/July 1994 a study was made of a small bloom of the coccolithophorid Emiliania huxleyi in an area of the North Sea to the east of the Shetland Islands. Observations on the hydrography of the study area indicated the bloom was associated with Atlantic water and was confined to an area in which a stable shallow mixed layer had formed. There wa...

An infiltration community was the dominating ice algal community in pack-ice off Queen Maud Land, Southern Ocean, in January 1993. The community was dominated by autotrophic processes, and the most common species were the prymnesiophyte Phaeocystis antarctica and the diatoms Chaetoceros neglectus and Fragilariopsis cylindrus. The concentration of c...

An extraordinary flood event occurred in SouthernNorway in May–June 1995. The impact of fresh waterdischarge from the river Glomma on phytoplanktonspecies composition and on primary production duringthe flood was studied. The phytoplankton community wasdominated by species usually found in the fjord, thediatom Skeletonema costatum dominated thecomm...

Blooms of the coccolithophorid Emiliania huxleyi were monitored in two land-locked fjords, Fauskangerpollen and Nordasvannet (Western Norway), in May 1993. The chemical composition of particulate matter, size-fractionated photosynthesis, calcification, nitrogen uptake rates and the patterns of macromolecular synthesis were examined during the peak...

At the Oceans'95 conference the authors presented a paper entitled “Applications of remotely controlled equipment in Norwegian marine archaeology”. That paper discussed the use of remotely controlled equipment in Norwegian marine archaeology, and more specifically a project that studies the wreck of a Russian navy ship which sank in 1760 off the co...

The uptake rates of nitrate, ammonium, and urea were measured with a ¹⁵ N technique during seven cruises in the marginal ice zone (MIZ) in the Barents Sea in 1984–1988. The results from all the cruises were pooled to obtain means for the prebloom, bloom, transition, and postbloom periods. New production—nitrate uptake as percent of total uptake—was...

Samnangerfjorden is a narrow and sheltered fjord with a pronounced low salinity phosphate- depleted surface layer. The coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler bloomed in a nitrate-depleted intermediate layer below the phosphate-depleted surface layer in the inner part of the fjord in May 1992. Maximum cell density was 7 × 106 cel...

Ice algae in infiltration assemblages were the dominating primary producers in the northwestern Weddell Sea during the austral spring 1988. Band and sub-ice assemblages were encountered at a few stations only. Maximum ice algal biomass measured was 424 g Chl. a I–1 compared to less than 0.4, g Chl. a I–1 in the water column. Biomass and nutrient co...

Uptake rates of ammonium, nitrate and urea were measured during the EPOS leg 1 cruise to the Weddell Sea in October–November 1988 using the isotope 15N. Nitrate was the most important nitrogen source both for ice algae (f-ratio 0.88) and for phytoplankton in the water column (f-ratio 0.85). Indications of a gradual decrease in % new production with...

Micromonas pusilla (Butcher) Manton & Parke appears to be a prominent member of the Barents Sea picoplankton community as revealed by the serial dilution culture method. Cell numbers frequently exceeded 107 cells 1−1, though they usually varied between 103and 106 cells l−1. A number of other identified and unidentified taxa were recorded and quanti...

Uptake rates of NH4+, NO3− and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a 15N-technique. NO3− was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in sit...

Uptake rates of NH4+, NO3? and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a 15N-technique. NO3? was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in sit...

Micromonas pusilla (Butcher) Manton & Parke appears to be a prominent member of the Barents Sea picoplankton community as revealed by the serial dilution culture method. Cell numbers frequently exceeded 107 cells 1?1, though they usually varied between 103and 106 cells l?1. A number of other identified and unidentified taxa were recorded and quanti...

Uptake of ammonium, nitrate and urea by phytoplankton in the Barents Sea was measured in May–June and in August 1984 by a 15N-technique. Ammonium was the most important nitrogen source for the phytoplankton. Nitrate was an important nitrogen source in water with large phytoplankton biomass but was of no importance in water with small phytoplankton...

The nanoplankton communities were studied by means of a serial dilution culture method to reveal the presence of viable species during a 100 tonnes offshore oil spill experiment. The nanoplankton was dominated by the coccoid chrysophycean species Pelagococcus subviridis with cell numbers up to 107 cells per litre. Other important species were Emili...

The safety of commercial shipping is regulated by the International Maritime Organisation (IMO) which is an United Nations agency. The maritime safety regulation is basically prescriptive and therefore not in line with current practices in comparable transport sectors and industries. It should also be kept in mind that shipping is a true internatio...

Techniques from Artificial Intelligence and Knowledge Based Systems are well suited for analysis and diagnosis of complex relationships. Especially powerful are the Neural Networks (NN) that have the ability to identify any underlying functional relationships. This paper is based on a study of how management and organisational factors influence the...

An approach for assessing the effect safety controls on the policy level is proposed, outlined and demonstrated with a limited set of empirical data. Focusing on impact accidents the probability of loss of navigational control may be taken as a safety level criteria. The paper describes how this criteria can be estimated on the basis of direct and...