Primary phytoplankton productivity has since 1985 been measured in the mouth

area of the Gullmar Fjord, as a part of the Swedish marine monitoring program.

Results from earlier evaluations of this primary production time series suggested

the presence of an indirect link between NAO, supply of nutrients, wind, and the

phytoplankton primary production and revealed the importance of climatic and

environmental forces among the factors responsible for the observed development

and fluctuations.

An analysis of five-year running means of the primary production time-series

from 1985 to 2008 revealed that the primary production in the Gullmar Fjord

increased and peaked during the five-year period 1992 – 1996, followed again by a

decrease in production. The increase in production, as calculated from the first

annual running mean and compared with the maximal mean, was 20 % and the

decrease of the last annual mean was 25 %. The total result was that the mean

annual primary production was 3.8 % lower when the difference between the first

and the last 5-year running means compared to the over-all mean production for the

whole period of time.

The present evaluation concludes that there is a direct link between primary

production and nitrate concentrations in the mouth area of the Gullmar Fjord.

Further, there is no influence from local runoff on the long term development of

the primary production. Any long-term co-variation in primary production of the

Gullmar Fjord and the adjacent Kattegat and Belt Sea areas is not evident,.

The overall results suggested that the primary production in the mouth area of

the Gullmar Fjord during 1985 – 2008 has been controlled by the coupling of large

climatic decadal patterns such as the NAO and the subsequent changes in the

nutrient regime at a regional scale including the Skagerrak. It may further be

concluded that the anomaly of an exceptional flux of nitrate-rich ocean water onto

the NW European shelf most likely extended its distribution also to the Swedish

west coast and the mouth area of the Gullmar Fjord, which in turn triggered the 19

% rise in annual primary production during the mid 1990s.