A comparison between short-term sediment traps with filtered sea water and without during two contrasting periods with respect to Chl a and phytoplankton composition

Kaldfjorden is an ice-free fjord located in northern Norway (69.75°N 18.67°E). This study investigated (1) the difference between two methods of determining the vertical export with sediment traps; sediment traps deployed with filtered seawater and sediment traps deployed with unfiltered seawater. In addition, the study also looked at (2) how the concentration of chlorophyll a changed over the two periods and (3) a comparison between the distribution of phytoplankton in February and April in the fjord was made. The concentration of chlorophyll a increased considerably between February and April, correlating with the change in physical conditions of the fjord and the growth in phytoplankton community. This also affected the distribution of taxa where diatoms, and particularly pennate diatoms, were the most abundant in February, while centric, chain forming diatoms and Phaeocystis were the most abundant taxa in April. These findings correlated to the studies that have taken place in other fjords in northern Norway, such as Balsfjorden. A difference could also be seen between the two methods to deploy traps, where the concentrations of chlorophyll a was higher in the majority of samples in the sediment trap cylinders without filtered seawater than in the cylinders with filtered seawater. This might be explained by the barrier that is created from the increased salinity in the sediment traps with filtered seawater and the biomass already in the seawater that filled the traps when they were deployed. These results can be used to compare future studies that use different treatments of the sediment traps.