Seasonal changes in the viability of bacterial cells in the snowpack ecosystem of a High Arctic ice cap

Abstract We present an in-depth analysis of the proportions of potentially “viable” and “non-viable” bacterial cell populations within the different layers of a melting snowpack on a High Arctic ice cap, Foxfonna in Svalbard. To do so, we employed the SYBR-PI dual cell stain to both flow cytometry and epifluorescence microscopy for enumeration. Non-viable cells soon dominated on Foxfonna (2.5 ± 0.36 x 10 7 cells m − 2 ) during the June to early July period, when biological production is expected to be greatest. Moreover, non-viable cells also dominated total cell abundance within superimposed ice (223 ± 242 cells mL − 1 ) and glacial ice (695 ± 717 cells mL − 1 ) beneath the snow. As a result, bacterial production on the ice cap caused the proliferation of ‘potentially non-viable cells’ as early as mid-July. We propose that the rapid, early loss of cell viability was caused by abiotic and biotic factors, with UV damage and viral lysis being most plausible. Dead cell residue (necromass) therefore contributes to organic matter export, although in late July we also found a far more significant input from other detrital sources, most likely dust. The export of organic matter from ice caps as their snow cover is transformed into meltwater runoff is therefore derived from both autochthonous and allochthonous sources, but with limited viable bacteria.