ROTTEN ICE: STRUCTURAL AND BIOLOGICAL CHANGES IN FIRST-YEAR ARCTIC SEA ICE DURING ADVANCED SUMMER MELT

As summer melt seasons in the Arctic continue to lengthen, more Arctic sea ice will be subjected to advanced stages of melt. The final stage of melt, so-called “rotten” ice, is poorly-understood. Here, we present results of an interdisciplinary effort to characterize the physical properties of rotten first-year ice and track the changes in sea ice microbial community as ice progresses through summer melt, from samples collected near Barrow, Alaska in May-July of 2015. Rotten ice is approximately isothermal, largely drained of brine, and is characterized by the presence of large multi-cm-scale brine channels that contribute to its very high permeability and low structural integrity. Significant changes in microbial community were also observed during the evolution of late-season ice. After the loss of the ice-bottom algal bloom community that dominates the sea ice biomass earlier in the season, it appears that a much lower number of algae remain embedded in or attached to the ice throughout the full depth of ice, and bacterial counts increase dramatically in the upper horizons of ice. In addition, patterns of chemistry are suggestive of a biogeochemical environment within the rotten sea ice that is distinct from that of prior months and also distinct from the underlying seawater. Results from SSU rRNA amplicon sequencing will also be presented. This study represents the first geomicrobiological characterization of this unique microbial habitat that will become increasingly significant in the future warmer Arctic.