The role of local-ice meltwater in the triggering of an under-ice phytoplankton bloom in an Arctic fjord

Abstract

We combined records from moorings, profilers, and CTD transects obtained in an Arctic fjord (Young Sound, Greenland) to assess the effects of local meltwater input at the beginning of ice melt while the fjord was still covered by ice. Results indicate that light penetrated below the ice and was available throughout the sampling period. Melting began at the mouth, where the ice and snow layers were thinner. At the mouth, meltwater triggered stratification and the onset of an under-ice phytoplankton bloom, as shown by an increase in chlorophyll-a (chl-a), fluorescence-CDOM, and oxygen saturation. Chl-a was highly correlated with salinity (−0.84) and temperature (0.88), indicating a strong association with the input of meltwater, while the maximums in chl-a and oxygen matched the distribution of the meltwater. At the mouth, in the area where the meltwater occurred, average chl-a increased from 0.27 mg m−3 to 0.40 mg m−3, and by the end of the record, it was three times greater than the surrounding waters. In the area of the patch of meltwater on 26–28 May, averaged oxygen increased by 4%–5% during the sampling period. Inside the fjord, patches of meltwater occurred and were advected from the mouth by an in-fjord flow. Within these patches of meltwater, chl-a and oxygen saturation increased, and by the end of the record, they were two times and 5% higher than the surrounding waters, respectively. This study shows that meltwater and stratification were more important than light for the onset of the under-ice bloom and suggests a significant portion of pelagic primary productivity occurs before ice breakup.