Temporal evolution of primary production in the central Barents Sea

Within the frame of the Study of the European Arctic Shelf (SEAS) programme, the central Barents Sea region was surveyed two times, in late June and late July, during the cruise ARK VIII-2, in order to describe the physical, chemical and biological evolution of the system and to provide estimates of primary production. Primary production daily rates are provided for a North–South section crossing the Polar Front, using a geochemical approach. Rates of primary production derived from the uptake of nitrate are regarded as new production, whereas rates based on production of oxygen are considered as net community production (NCP). They are compared, and estimates from oxygen are considered expression of the minimal rates of photosynthesis. NCP exhibited a decreasing trend from North to South: with moderate values (<1.0 g C m−2 day−1) at the northern end, lower (<0.4 g C m−2 day−1) at the central stations and dropping to the minimum (0.1 g C m−2 day−1) at the southernmost stations. New production showed a similar southward decreasing trend, ranging from 0.4 to 0.2 g C m−2 day−1 in the northern end and dropping to 0.0 g C m−2 day−1at the central and southern stations. Since both estimates exhibited the highest values in the North, the ecosystem there is regarded as still working under eutrophic conditions, considerably based on new production exerted mainly by diatoms and prymnesophityes. In the southern end, dropping to zero of new production and the lowest values of NCP both suggest that ecosystem has already reached oligotrophic conditions, mainly based on regenerated production, which corresponded to communities dominated by flagellates. All measured and calculated parameters indicate the shift from eutrophic to oligotrophic conditions as not strictly temporal but also spatial (latitudinal).