This page on glacier ecosystems and life on ice was contributed by Dr Arwyn Edwards, a Lecturer in Biology at Aberystwyth University.
The secret life of glaciers
Where there is water, there is life. Glaciers are no exception. Research over the last thirty years supports the idea that we should rethink glacier ecosystems1. Indeed, since glaciers and ice-sheets lock up most of Earth’s freshwater, it could be argued that glaciers and ice-sheets are Earth’s largest freshwater ecosystems2 and that they form a distinct biome3. However, with the notable exception of Glaciers & Glaciation4, the textbook view is that life starts after the glaciers are gone. Let’s fix that by taking a look at the secret life of glaciers.
Life happens under the ice
The study of subglacial ecosystems is very topical for several reasons. Firstly, the search for life in Antarctica’s subglacial lakes has attracted substantial media attention, including media reports of novel microbes and microbial activity in Lakes Vostok and Whillans. Secondly, organic carbon trapped under the ice can be metabolized by microbes to form methane5, a potent greenhouse gas. Calculations suggest up to 21,000 petagrams of organic carbon (10 times the permafrost carbon stock) might be trapped under Antarctica’s ice and that microbial conversion of this carbon to methane could be a major feedback in climate change6. Thirdly, subglacial microbes seem to act as a “geochemical probiotic” by accelerating mineral weathering up to eight-fold7. Finally, recent work suggests moss plants can survive for centuries underneath glaciers, recolonizing the land as the ice retreats8.
Life happens in the ice. Slowly.
Life in ice is definitely stuck in the slow lane, but it does not grind to a halt. Temperatures far below zero do not present an absolute obstacle to microbial activity9,10, and three habitats have been suggested for microbes trapped in glacial ice.
The first en-glacial habitat is for rock-eating microbes living in thin films of water on the surface of debris entrained in the ice11, while other microbes can swim in the network of veins that form between individual ice crystals12. Finally, it’s thought that microbes can live inside solid ice crystals deep in ice-sheets13. To do so, microbes would have to survive by consuming and producing gases such as carbon dioxide or methane which small enough to diffuse through the ice at rates of a few thousand carbon atoms a year. Analyses of ice cores suggest metabolising gases in this way could explain some anomalies in greenhouse gas concentrations14 in ice core records.
Life happens on the ice
Glacier surfaces get plenty of sunlight, liquid water and direct contact with the atmosphere during summer, so life here is easy – some of the time. It could be said the story of life on the ice begins with making a single snowflake as some ice-nucleating bacteria can catalyze ice precipitation15. Moreover, as we are seeing the last of the dry, cold snow in the Northern hemisphere disappear at the peak of summer16, the potential for a massive bacterial bloom becomes apparent as microbes thrive in melting snowpacks. Microbes living at the interface between ice and the atmosphere are also important for the mass balance of glaciers as “biological darkening”17 by ice algae18 and aggregates of microbes bound to minerals called cryoconite19 accelerate surface melting rates. Finally, in summer, conditions can be gentle enough for some plants and animals to thrive on the ice surface, for example mosses (“glacier mice”20) or ice worms, thus increasing the complexity of the icy food chain. The photographs below show cryoconite holes on an Arctic glacier after a “rain kill”. The rest of the ice surface has ablated, melting out the cryoconite holes and making them even more obvious than usual.
In summary, it ought to be clear that glaciers and ice-sheets are not sterile landscapes but rather comprise several biodiverse habitats. Glacier ecosystems occur on the ice, in the ice and under the ice. We are starting to learn how these life forms interact with their icy homes and the consequences for both glaciers and climate. So perhaps it’s time to rewrite some of those textbooks.
About the author
@arwynedwards is a Lecturer in Biology at Aberystwyth University. He is at his happiest using DNA fingerprinting and sequencing to learn about the microbial life of glaciers and ice-sheets. See Arwyn’s personal webpage for more information.
- Carbon flux on glacier ice
- Subglacial lakes
- Glacier hydrology
- Aberystwyth Cryoconite Research Group blog
- Probing the Dark Side of life on Arctic Glaciers
- Arwyn Edwards personal webpage
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