Pelagic ecosystem dynamics between late autumn and the post spring bloom in a sub-Arctic fjord

Marine ecosystems, and particularly fjords, are experiencing an increasing level of human activity on a year-round basis, including the poorly studied winter period. To improve knowledge base for environmentally sustainable management in all seasons, this study provides hydrographic biological baseline data sub-Arctic fjord Kaldfjorden, Northern Norway (69.7° N, 18.7° E), between autumn 2017 spring 2018. Field observations integrated with results numerical ocean model simulation, illustrating how pelagic biomass, represented by chlorophyll (Chl a), particulate organic carbon (POC), zooplankton, is affected stratification circulation from October to May. We observed unusually warm that likely delayed onset cooling may have supported high abundances holoplankton meroplankton (5768 individuals m–3). With winter, water column cooled became vertically mixed, while suspended Chl concentrations declined rapidly (< 0.12 mg In January February, POC downward flux were elevated near seafloor. The hydrodynamic indicate strongest currents at depth occurred these months, potentially inducing resuspension events close (April), peak biomass (6.9–7.2 m–3 5–15 m; 9952 zooplankton ind. 0–100 m), field suggest Atlantic origin probably advected into Kaldfjorden. During investigated simulation suggests complex pattern, even such small fjord, which can implications environmental fjord. conclude system Kaldfjorden changes continually must be seen as dynamic period, not season where ecosystem ‘at rest’.