Sea Ice Microbial Ecosystems in the Rapidly Changing Arctic

海冰栖息地受到气候变化的影响，成为地球上变化最剧烈的环境之一。海冰覆盖了全球海洋的10%，目前正处于一个过渡时期，永久性的“多年冰”正在减少，取而代之的是每年融化和重新冻结的短暂的“一年冰”。因此，海冰中的微生物生命必须适应极端和快速变化的条件，但人们对这种微生物组知之甚少。在快速变化的北极地区，海洋微生物生态学和海洋地球化学的完整图景需要更好地了解海冰微生物群落，它们是如何形成的，以及它们的作用。在极地海洋中，当海水温度降至-2 ° C以下时，水开始结冰。在海冰形成过程中，盐被排出，在固体冰中形成盐水通道。在较低的温度下，盐水通道中的盐度可以是海水的十倍。液态盐水是某些微生物的合适栖息地，海冰已被证明含有数量惊人的细菌-有时比周围的海水还多。盐水通道微生物群落组装知之甚少，可能涉及在解冻环境中休眠或以其他方式被边缘化的海水细菌的环境选择，但当它们在冬季海冰盐水通道中遇到更冷和更咸的条件时，它们会获得优势。由休伯特博士领导的地球微生物学小组的长期目标是了解环境变化背景下微生物群落中数量稀少的生物（其中一些是极端微生物）的分布和生态生理学。面对环境变化，微生物是第一反应者。自然环境中存在的巨大微生物多样性是由许多低丰度分类群形成的，即所谓的“稀有生物圈”。稀有生物可能处于休眠状态，但如果环境条件发生变化，它们会迅速做出反应。第一年海冰中的微生物组为研究微生物对快速环境变化的反应提供了一个令人兴奋和及时的机会。第一年动态冰的日益突出，使微生物群落组合和“微生物种子库”动态成为了解海洋微生物群落的最前沿。在夏季海水中可能很罕见并处于休眠状态的嗜盐嗜冷菌，由于零度以下的温度和高盐度推动了环境选择，成为冬季冰盐水的关键参与者。

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.