Seasonality of vertical flux and sinking particle characteristics in an ice-free high arctic fjord—Different from subarctic fjords?

Abstract

The arctic Adventfjorden (78°N, 15°E, Svalbard) used to be seasonally ice-covered but has mostly been ice-free since 2007. We used this ice-free arctic fjord as a model area to investigate (1) how the vertical fl ux of biomass (chlorophyll a and particulate organic carbon, POC) follows the seasonality of suspended material, (2) how sink- ing particle characteristics change seasonally and affect the vertical fl ux, and (3) if the vertical fl ux in the ice-free arctic fjord with glacial runoff resembles the fl ux in subarctic ice-free fjords. During seven fi eld investigations (December 2011 – September 2012), suspended biomass was determined (5, 15, 25, and 60 m), and short-term sediment traps were deployed (20, 30, 40, and 60 m), partly modi fi ed with gel- fi lled jars to study the size and frequency distribution of sinking particles. During winter, resuspension from the sea fl oor resulted in large, detrital sinking particles. Intense sedimentation of fresh biomass occurred during the spring bloom. The highest POC fl ux was found during autumn (770 – 1530 mg POC m − 2 d − 1 ), associated with sediment-loaded glacial runoff and high pteropod abundances. The vertical biomass fl ux in the ice-free arctic Adventfjorden thus resem- bled that in subarctic fjords during winter and spring, but a higher POC sedimentation was observed during autumn.