Diatoms’ contribution to productivity and organic matter export are significant in high-latitude marine ecosystems.  

Unlike other abundant phytoplankton groups, diatoms have an obligate silicon requirement; therefore, silicon availability has the potential to regulate major high-latitude events like the spring bloom.  Waters in the high-latitude sector of the Atlantic (e.g. coastal Greenland, Faroe Islands, Barents Sea, Svalbard) have lower silicic acid concentrations than nitrate.  Given diatoms require Si and N near unity, the deplete Si relative to N sets a potential control on diatom productivity in this system, such that Si could limit diatom biomass yield in a bloom.  

Recent publications have reported declining silicic acid concentrations between ~60 – 75 °N latitude in the Atlantic.   Despite the clear changes in Si availability, there are no reported data for the magnitude of diatom Si uptake and whether ambient silicic acid limits Si uptake or diatom growth.  

Here I report data from the Atlantic sector of the Arctic in the Svalbard archipelago and the sub-Arctic West Greenlandic Nuup Kangerlua fjord.  In both systems, we quantified biogenic silica production and the kinetics of Si uptake (to diagnose limitation).  In Svalbard, we assessed spatial variability in waters fed by the North Atlantic, glacial fjords and the high-Arctic, whereas in Kangerlua fjord we quantified the development of the spring bloom over two months at a single site influenced by the subpolar mode water, Greenland coastal water and early-season glacial melt water.  

In both systems, the ambient silicic acid chronically limited the rate of Si uptake by diatoms and, at times, may have limited their growth rate.  Therefore, we present the first direct evidence that silicon availability plays an important role in the bloom phenology (e.g. termination) of the high-latitude Atlantic.