Shifting fronts between temperate Atlantic and Arctic influences north and northwest of Iceland cause large interannual hydrographic variations where the relatively warm North Atlantic water may shift from being almost negligible to be the dominant surface layer water mass.  We present data on nutrients and hydrography from springtime surveys conducted from 1964 to 2022. The timing of the observations is from late May to early June each year. Temperature and salinity of the surface waters in spring have been highly variable in this period. The stoichiometry of N:P utilization has in general been close to 16 but the Si:N uptake ratio has varied. In years normally characterised by high Polar Water influence, nitrate and phosphate are nearly depleted whilst silicate remains near winter concentration. We relate the resultant anomalous Si:N ratios to the observed dominance of the non-silicious species <em>Phaeocystis pouchetii </em> in the phytoplankton assemblages. This trophic pathway has impact on the carbon cycling in the ecosystem and the microbial food web and could be an indication of future conditions in rapidly changing Arctic marginal areas in spring. Trophic responses to <em>phaeocystis</em> blooms have been shown to differ from those of diatom dominated blooms with possible food chain effects. We evaluate the interannual variability in the euphotic layer nutrient utilization and examine the variability in relation to the differing dominant water masses and hydrographic surface layer structure.

Primary Presenter: Solveig Olafsdottir, Marine and Freshwater Research Inst (solveig.rosa.olafsdottir@hafogvatn.is)

Authors:

Solveig Olafsdottir, Marine and Freshwater Research Institute  (solveig.rosa.olafsdottir@hafogvatn.is)

Jon Olafsson, Institute of Earth Sciences  (jo@hi.is)