Effect of Atlantic water inflow on timing of the phytoplankton spring bloom in a high Arctic fjord (Kongsfjorden, Svalbard)

The spring bloom in Kongsfjorden, Svalbard was followed during the years 2006–2008 to study the bloom dynamics in relation to environmental factors. Usual timing of the bloom in this normally ice-filled fjord has been May with few exceptions. But in 2006 the bloom occurred in April. This was the first of 3 consecutive spring seasons with no ice in the fjord. But even so the bloom was delayed until May both in 2007 and 2008. The 2006 bloom was characterized by high phytoplankton biomass and a mix of diatoms and Phaeocystis pouchetii. The 2007 and 2008 spring blooms were delayed until mid/late May, and the biomass and biodiversity were significantly reduced, with a more pronounced dominance of Phaeocystis relative to diatoms. The different bloom developments are discussed in relation to Atlantic water inflow, which varied between the years in question and seemed to be the main controlling factor of the spring blooms. Possible future bloom scenarios are also discussed.

► Timing of the phytoplankton spring bloom in Kongsfjorden is variable.
► Dependent on ice cover and Atlantic water inflow
► No ice and bottom inflow of AW with deep mixing gives an April bloom.
► Ice cover, or surface inflow of AW with reduced mixing in an ice-free fjord delays the bloom until May.
► Less diatoms and more Phaeocystis in a delayed bloom caused by disturbed mixing