Sea Ice Microbial Ecosystems in the Rapidly Changing Arctic

海冰栖息地受到气候变化的影响，因此它们是地球上变化最剧烈的环境之一。覆盖全球海洋10%的海冰目前正处于过渡期，不断减少的永久“多年冰”被数量不断增加的每年融化和重新冻结的瞬时“第一年冰”所取代。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群知之甚少。要全面了解快速变化的北极地区的海洋微生物生态和生物地球化学，需要更好地了解海冰微生物群落，它们是如何形成的，以及它们是做什么的。在极地海洋，当海水温度降至零下2摄氏度以下时，水开始结冰。在海冰形成期间，盐分被排出，卤水通道在固体冰中形成。在较低的温度下，盐水通道中的盐度可能比海水高十倍。液态卤水是某些微生物的适宜栖息地，海冰被证明含有惊人的细菌数量-有时比周围海水中的细菌更多。对卤水通道微生物群落组装的了解很少，可能涉及对海水细菌的环境选择，这些细菌在未冻结的环境中处于休眠或被边缘化，但当它们在冬季海冰卤水通道遇到更冷和更咸的环境条件时，它们会获得优势。休伯特博士领导的地球微生物学小组的长期目标是在环境变化的背景下了解微生物群落中数量稀有生物的分布和生态生理学，其中一些是极端微生物。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的生物分类群形成的，即所谓的“稀有生物圈”。稀有生物可能处于休眠状态，但如果环境和环境条件发生变化，它们将迅速做出反应。第一年海冰中的微生物群为进一步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。第一年冰的动态日益突出，将微生物群落组装和“微生物种子库”的动态带入了理解海洋微生物群落的前沿。嗜盐嗜盐菌在夏季海水中可能很罕见，并处于休眠状态，随着零下温度和高盐度推动环境选择，它们成为冬季冰盐的关键参与者。

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.