CHISELLED, grey rock walls loom on all sides, brought to life by the faint beam of my headlamp. Tiny rivulets of groundwater form a tangle of silver threads around me. As I inhale, I smell the heavy scent of cold, damp, stale air, which clings to my face like an invisible cloth. Slowly, I drag my welly-clad feet along the seemingly endless dirt track towards the eye of the tunnel ahead and the guts of the glacier.
I have never had much of a proclivity for caves, but here I was living in a labyrinth of tunnels beneath the Norwegian glacier Engabreen of the Svartisen ice cap. I spent two weeks here in the winter of 2006, coming to visit its tantalisingly named “subglacial laboratory”, where you could access the glacier bed thanks to tunnels originally bored through the mountain to tap the copious meltwater for hydroelectric power.
The laboratory was equipped with an ingenious means of getting to the inhospitable glacier bed. You would open up a shaft (with a door made of iron girders) to reveal the dirty, basal layer of the glacier topped by a translucent, 200-metre-thick mass of slowly moving ice and then melt your way in with a hot-water drill. My reason for being there was a grand hunt for microbial life and one of its troublesome by-products, methane.
Methane is a potent greenhouse gas: it has around 80 times the warming power of carbon dioxide over 20 years. Some of the places most notorious for its production are rice paddies, landfill sites, wetlands and even the stomachs of cows, but, increasingly, it seems like glaciers could be hotspots too.
That is because one type of microbe that thrives in the oxygen-starved conditions beneath a glacier is a methanogen, or “methane maker”. Its carbon supply comes from ancient soils, lake sediments and marine muds that were entombed by the glacier when it grew. Remarkably, some methanogens may be fed by hydrogen produced as the glacier grinds over its rocky base.
If it were possible to venture deep into the vast basins of sediment buried beneath ice sheets in geothermically active zones, we think you would find methane forming without the input of life through the slow heating of carbon in these sediments.
My toils beneath Engabreen enabled me to obtain mud from the glacier’s bed, which I added to our burgeoning collection sampled by chainsaw from the edges of other glaciers around the world. We recreated the glacier bed in the lab using simple experiments with glacial mud and meltwater. Two years later, measurable biological methane had been produced in all glacier samples, save those from Engabreen. Here, there was just hard rock and not enough carbon for microbes.
Since then, the evidence for glaciers as methane producers has exploded. In 2015, we found that rivers issuing from the margin of the Greenland ice sheet were supersaturated with the gas. High concentrations have also been found in other glacier rivers, a subglacial lake in West Antarctica and even the dirty layers of ice cores. In deep parts of ice sheets, we worry that methane might be stored in its solid form, methane hydrate. As climate change thins ice sheets, this could be released as gas.
Research by Norway’s Centre for Arctic Gas Hydrate, Environment and Climate indicates that this happened to methane beneath former European ice sheets around 10,000 years ago as they collapsed after the last glaciation. Might this occur to current ice sheets in a warming world?
The jury is still out on whether glacier methane is a whiff of something small or something world-changing for our climate, but, regardless, we need to find out if we are going to halt global warming.
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