ARCUS 15th Annual Meeting and Arctic Forum 2003

Microorganisms in Arctic sea-ice environments and their resilience and vulnerability to climate variations and change

Hajo Eicken¹, Christopher Krembs², Karen Junge³, Jody Deming⁴, Rolf Gradinger^5
1Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, 99775-7320, USA, hajo.eicken@gi.alaska.edu
²Applied Physics Lab and School of Oceanography, University of Washington, Seattle, WA, 98195, USA, christopher.krembs@apl.washington.edu
³School of Oceanography, University of Washington, Seattle, WA, 98195, USA, kjunge@ocean.washington.edu
⁴School of Oceanography, University of Washington, Seattle, WA, 98195, USA, jdeming@u.washington.edu
⁵Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK, 99775-7220, USA, gradinger@ims.uaf.edu

Microorganisms living within Arctic sea ice are subjected (on a seasonal basis) to what may qualify as the widest range of environmental conditions in any type of marine environment. Hence, the strategies of bacterial and microalgal assemblages in dealing with the adverse conditions encountered in the sea-ice habitat may help us obtain better insight into their resilience and vulnerability to impacts of global change on the Arctic Ocean's ice cover.

Recent studies have shown that microbial communities in polar terrestrial and marine environments are quite adept at dealing with the adverse, coupled effects of low temperatures and high salinities. In our work, we have demonstrated that bacteria thriving within the pore space of Arctic sea ice can remain active down to temperatures of at least -20 C. Based on optical microscopy and other methods characterizing distribution and activity of bacteria under very low in-situ temperatures, it appears as if the remarkable resilience of these bacterial assemblages is enhanced, if not controlled, by the presence of particulate surfaces. At the same time, some organisms are capable of mitigating the effects of low temperatures and high ambient brine salinities through the production of organic polymers. The latter may play a pivotal role in the mitigation of environmental stress associated with very low temperatures as well as in the interaction between organisms and their physical environment.

The other extreme in Arctic sea-ice environmental conditions is controlled by summer melt processes. Tracer studies have demonstrated that a substantial fraction of the sea-ice microbial habitat is being flushed by low-salinity meltwater during the summer months and that such freshwater immersion may be increasing in duration and extent due to enhanced ice and snow melt. While posing different physiological and ecological challenges to ice microbial communities, many of which are poorly understood, enhanced meltwater fluxes may have dramatic impacts on ice microbial communities as well as the sea-ice system as a whole.

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