During the winter phase from November to February, there is low diversity and low production, with chlorophyll concentrations close to zero. The lowest levels are found in the ice free areas in the northern parts. During this period there are sufficient nutrients for growth, but the absent of clear stratification and light prevent large production. The species that are present are cosmopolitan representatives of dinoflagellates (Dinophyceae), large armed forms as Protoperidinium, Ceratium, Dinophysis (Protoperidinium depressum, Ceratium longipes, Ceratium tripos, Dinophysis norvegica) and athecate forms from the genus Gymnodinium and Gyrodinium and occasionally diatoms (Bacillariophyceae).
The spatial distribution of the phytoplankton in this period shows maximal abundance near the edge of ice formation in the open waters of the Barents Sea ( Ryzhov, 1985). This fact has been causing debates among the specialists regarding the reasons for such distribution. This question has an important theoretical meaning for the explanation of so called “edge bloom” of microalgae.
The spring phase, from March to late May (early June), could be divided into two periods. In the early spring (March) the water masses is still mixed; there are adequate levels of nutrients, and enough light penetration for primary production. The main bloom does not appear, however, before the water shows some degree of stratification. Stratification of water masses in different parts of the Barents Sea occurs in different ways and will appear at different times. During this early period there is an increase in the phytoplankton population, dominated by neritic diatoms in the open areas of the Barents Sea.
Back in the end of the 19th century, the first Arctic researchers observed a high concentration of pelagic microalgae near the ice edge and under the ice. That fact led to the multiple hypotheses on the “ice-edge” bloom and processes that take place in this particular biotope, as well as the “start” of the spring bloom of phytoplankton in the northern seas. The earliest activity of phytoplankton occurs near the border of the ice cover, in stratified water masses. However, this link between the mass development of microalgae and ice edge is not always the case and is not observed in all areas of the Barents Sea. The early phytoplankton production could also take place in the polar front zone and in coastal and estuarine areas.
There has been some attention paid to the so-called ice algae – a specific community of microalgae, living within the layer of sea ice and possibly playing an important role in bioproductivity processes in the Arctic marine ecosystems (Alexander, 1974; Melnikov, 1989). However, there has been some discussion about the overall significant of this production in the Barents Sea. Most likely this communities are important on small scales, where as their contribution to the overall primary production is low (Kuznetzov and Shoshina, 2003). Hegseth (1998) estimated the ice algal production to comprise 16-22% of the total annual primary production in the ice-covered regions of the Barents Sea.
A stronger stratification of the water masses result in a rapid increase in the phytoplankton biomass in the surface water – spring bloom or spring maximum period. This period is characteristic by high abundance of phytoplankton, both as chlorophyll a and numbers of cells, and large diversity in the phytoplankton. The point in time of the spring bloom will vary considerable within the Barents Sea and between years. In some areas and years it could start as early as early April other years as late as early June. Species, forming the first peak of the spring bloom, are Thalassiosira cf.gravida, Т. nordenskioeldii , Chaetoceros socialis , C. furcellatus, Navicula vanhoeffenii. In addition, during this period there is often an intensive bloom of the golden algae Phaeocystis pouchetii , and it can reach high quantity and biomass, being a important part of the spring maximum (highest recorded quantity and biomass – 8 mln cell/l and 1.7 mg/l respectively) (Druzhkov and Makarevich, 1989). In some years and areas the first spring peak could be followed up by a second peak. This shows lower density as is composite by other species of diatoms, often from the genus Thalassiosira and Chaetoceros, in additions to Phaeocystis pouchetii, taking please late in May.
The summer phase, from June to the end of August, is characterized by low to moderate density of phytoplankton. The typical spring species disappear and summer community of diatoms and dinoflagellates takes over (Protoperidinium depressum, Ceratium arcticum, C. fusus, Leptocylindrus danicus, Leptocylindrus minimum, Skeletonema costatum, Chaetoceros decipens, and Chaetoceros laciniosus). This composition starts with diatoms and is gradually taken over by the dinoflagellates. During the summer phase, smaller blooms of flagellates and diatoms could be observed. In the later years blooms of the Coccolithophyceae Emiliania huxleyi has been observed in blooming concentration in the open areas. The phytoplankton shows biomass and distribution in a mosaic pattern during the summer period, with the highest abundance and diversity is observed in coastal waters and inn front system.
In august- September the biological summer is ended and the phytoplankton community goes into an autumn phase that could last until mid November. The biomass and diversity of phytoplankton will gradually decrease during this period, until it reaches a winter level in November. The community is a mix of diatoms (Thalassiosira, Chaetoceros, Rhizosolenia, Nitzschia, Rhizosolenia) and dinoflagellates (Protoperidinium, Gyrodinium, Dinophysis, Ceratium). Dinoflagellates will gradually become more abundant. In some years high abundance of smaller flagellates is registered late in this period.
