Effect of ice melting on bacterial carbon fluxes channelled by viruses and protists in the Arctic Ocean

During the last few years, extensive sea ice melting in the Arctic due to climate change has been detected, which could potentially modify the organic carbon fluxes in these waters. In this study, the effect of sea ice melting on bacterial carbon channelling by phages and protists has been evaluated in the northern Greenland Sea and Arctic Ocean. Grazing on bacteria by protists was evaluated using the FLB disappearance method. Lysis of bacteria due to viral infections was measured using the virus reduction approach. Losses of bacterial production caused by protists (PMM_BP) dominated losses caused by viruses (VMM_BP) throughout the study. Lysogenic viral production was detected in 7 out of 21 measurements and constituted from 33.9 to 100.0% of the total viral production. Significantly higher PMM_BP and lower VMM_BP were detected in waters affected by ice melting compared with unaffected waters. Consequently, significantly more bacterial carbon was channelled to the higher trophic levels in affected waters (13.05 ± 5.98 μgC l^-1 day^-1) than in unaffected waters (8.91 ± 8.33 μgC l^-1 day^-1). Viruses channelled 2.63 ± 2.45 μgC l^-1 day^-1 in affected waters and 4.27 ± 5.54 μgC l^-1 day^-1 in unaffected waters. We conclude that sea ice melting in the Arctic could modify the carbon flow through the microbial food web. This process may be especially important in the case of massive sea ice melting due to climate change.