Sea Ice Microbial Ecosystems in the Rapidly Changing Arctic

点击翻译按钮获取中文摘要

Sea ice habitats are caught in the grip of climate change such that they are one of the most drastically changing environments on earth. Covering 10% of the global ocean, sea ice is currently in a period of transition with declining permanent `multiyear ice' being replaced with increasing amounts of transient `first year ice' that melts and refreezes annually. Microbial life in sea ice must therefore be adapted to extreme and rapidly changing conditions, yet very little is known about this microbiome. A complete picture of marine microbial ecology and biogeochemistry in the rapidly changing Arctic requires an improved understanding of the sea ice microbial communities, how they form, and what they do. In polar seas water begins to freeze when seawater temperatures drop below -2°C. During sea ice formation salts are expelled and brine channels form amidst the solid ice. At lower temperatures the salinity in the brine channels can be tenfold greater than seawater. Liquid brines are suitable habitats for certain microorganisms, and sea ice has been shown to contain surprisingly high numbers of bacteria - sometimes more than in surrounding seawater. Brine channel microbial community assembly is poorly understood, and likely involves environmental selection of seawater bacteria that are dormant or otherwise marginalized in that unfrozen setting, but that gain an advantage when they encounter colder and saltier conditions in winter sea ice brine channels. The longterm objective of the Geomicrobiology Group led by Dr. Hubert is to understand the distribution and ecophysiology of numerically rare organisms, some of them extremophiles, within microbial communities in the context of environmental change. In the face of environmental change, microbes are the first responders. The enormous microbial diversity present in natural environments is formed by many low abundance taxa, the so called `rare biosphere'. Rare organisms might be dormant yet they are poised to respond rapidly if environmental conditions change. The microbiome in first year sea ice offers an exciting and timely opportunity to examine the microbial response to rapid environmental change. The increasing prominence of dynamic first year ice brings microbial community assembly and `microbial seed bank' dynamics to the forefront of understanding marine microbial communities. Halopsychrophiles that may be rare and dormant in summer seawater become key players in winter ice brines as sub-zero temperatures and high salinity drive environmental selection.