Sub glacial ecosystems: life between a rock and a hard place. The author and collaborator Prof. Birgit Sattler sampling under Gaisbergferner in the Austrian Alps.
Glacier ecosystems: Life inside the bergschrund of an Alpine glacier is dark, cold and very little organic matter to consume. Microbes can live on the surface of debris entrained in ice, or in solid ice. The discovery of viable photosynthesising microbes inside this glacier recently featured in an episode of BBC TV’s Horizon
Bio diverse microbes live in different habitats on the ice surface
Most life in glacial environments is invisible. Microscopic view of glacial melt water stained with a dye that fluoresces green when bound to DNA. The bigger bugs are bacteria, while the tiny pin-pricks of light are viruses which infect those bacteria
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 ecosystems. 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 ecosystems and that they form a
distinct biome. However, the textbook view is that life starts, after the
glaciers are gone.
LIFE UNDER THE ICE The study of sub glacial 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 methane, 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
change. Thirdly, subglacial microbes seem to act as a “geochemical probiotic”
by accelerating mineral weathering up to eight-fold. Finally, recent work
suggests moss plants can survive for centuries underneath glaciers, recolonizing
the land as the ice retreats.
LIFE IN THE ICE 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 activity 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 ice, while other microbes can swim in the network of veins
that form between individual ice crystals. Finally, it’s thought that microbes
can live inside solid ice crystals deep in ice-sheets. 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. Analysis of ice cores suggest metabolising gases in this way could explain some anomalies in greenhouse gas
concentrations 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 precipitation. Moreover, as we are seeing the last of the dry,
cold snow in the Northern hemisphere disappear at the peak of summer, the
potential for a massive bacterial bloom becomes apparent as microbes thrive in
melting snowpack’s. Microbes living at the interface between ice and the
atmosphere are also important for the mass balance of glaciers as “biological
darkening” by ice algae and aggregates of microbes bound to minerals called cryoconite 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”) or ice worms, thus increasing the complexity of the icy
food chain.