On 24th May I spoke to the Biodiversity Festival – it was moderated over a Zoom call and live streamed to Youtube. You can watch HERE. I was talking about an often overlooked aspect of glacier melting that ties in very tightly with the theme of biodiversity. Here’s a transcript:
We do not usually think of snow and ice as being rich in biodiversity. If you imagine being in the heart of the melting zone on the Greenland Ice Sheet, or on the ocean-facing glaciers on the Antarctic Peninsula, or on the remote, high altitude ice on Kilimanjaro, or the snow fields of Alaska, you probably picture a barren, frigid, white landscape without many hints of life.
And indeed, that is how scientists and explorers have traditionally thought about snow and ice – sure there are large mammals like polar bear that migrate across the snow and reindeer that feed around the edges, and musk ox that live on the tundra. There are hares and foxes there too, and the polar oceans are full of life – from corals to tiny krill right through to the giant humpbacks, blue whales and orca. But the glacier surface and the snow themselves do not seem like obvious habitats. These hostile environments do not offer much in the way of food, or shelter.
But if we look closely, and consider creatures that are too small to see with our naked eyes, we discover a hidden universe – a microscopic frozen rainforest on the ice surface. While these creatures are too small to see, their impact is too large to ignore. In this talk, we will explore this hidden ecosystem and discover why ice is alive and why we should care.
Let’s rewind back to the late 1800s, at the very start of the heroic age of polar exploration, when people were first beginning to attempt crossing of the major ice sheets and discovering unmapped, frozen worlds. Adolf Nordenskiold had sailed to Greenland to make an attempt at an ice sheet crossing. His diaries contain detailed, vivid accounts of his experiences, of all the struggles and hardship and the discoveries made along the way. On reaching the edge of the ice sheet, he wrote in his diaries about a strange, dark off-grey colour to the ice, which surprised him as he expected the ice to be shades of white and blue. As he started to make his crossing, he wrote about the trouble caused by millions of strange, bucket-like holes in the ice with a thin layer of black sediment on their floors, some tiny and some meters across and meters deep – so many in fact that he was unable to find anywhere to set down his sleeping bag at night, and often found himself suddenly knee-deep in frigid glacier water from accidentally stepping or tripping into these holes. Being a curious scientists, Nordenskiold was intrigued by these two features – the darkness of the ice and the existence of millions of these ponds in the ice, so he studied them. Astonishingly, especially at the time, Nordenskiold realised that these two phenomena, were biological. Under the microscope, he saw clearly that the material giving the ice its dark grey colour was a type of algae, and much of the material at the bottom of these holes was microbiologial too.
His colleague, Dr Berggren, was quick to document the various species they found on the ice, and named them Ancylonema Nordenskioldii and Mesotaenium Bergrenni. Nordenskiold diaries from the time clearly demonstrate that he saw the significance of this discovery at the time, describing the algae as the “greatest enemy of the mass of ice” because they change the colour of the ice from bright white and blue to dark greyish-purple. Darker materials warm up in the sun, and Nordenskiold realised that this darkening effect would cause the ice sheet to melt much faster.
In the image on the screen you can see this darkening effect in a photo I took from a drone at a field camp on the Greenland Ice Sheet, not far from where Nordenskiold made his observations in 1875. The dark colour of the ice is the result of algae growing on the ice surface. We all know that dark things heat up in the sun if you have ever walked barefoot on black tarmac or worn a black tshirt on a sunny day- the ice is melting faster because of this biological staining than it would if it was clean and bright. However, at the time Nordenskiold made this discovery, climate change and sea level rise were not issues in the public conscioussness – this was before the industrial revolution began to pollute the skies with emissions and humans really started to rapidly warm the planet. But now, with climate change being arguably the most pressing issue facig humans now and in the coming decades, we have remembered Nordenskiold’s discovery and are examining it in a new light – with a new focus on exploring and documenting the biodiversity of glacier and ice sheets and understanding at a deep level their effects on glacier melting and sea level rise – right now we do not account for this biological darkening process in our predictions for the future, which probably means we are systematically underestimating the rate of ice sheet melting.
So, I have spent the past decade studying this process, from early studies that documented what lives where and what processes the glacier microbes perform right through to recent studies blending drone and satellite remote sensing with artificial intelligence and complex field work aiming to measure the microbial effects on sea level rise. So I’m going to share with you some of what I’ve learned along the way, acting as your guide on a virtual safari through the microscopic frozen rainforest so you too can see what lives on our glaciers and ice sheets.
Earlier I mentioned the bucket-like ponds that Nordenskiold wrote about in his diaries. Those are called “cryoconite holes”, a name which comes from Greek meaning “cold dust”. Let’s take a dive into one of these holes now (video below).
As we get closer to the floor we begin to see individual granule of soil-like material that is full of microbial life. The pig-shaped creatures are called Tardigrades and they are the apex predator – the equivalent of the tigers or polar bear in the macroscopic world. There are algae and fungi and lots of bacteria, and the long stringy cells are a particular type of microbe called cyanobacteria.
This is a real microscope image of some cryoconite from Greenland. You can see those same microbes in this still image. It is the stringy cyanobacteria that act as the architects of cryoconite holes. Because they are long and ropelike, they can act like fishing nets on the ice surface, trapping bits of dust and debris that washes over the ice and bundling it all up into granules. These cyanobacteria also produce a kind of biological cement as a by-product of their photosynthesis that glues the granule together – these granules are then heavy enough to settle on the ice surface rather than being washed away, and because they are dark they warm up and melt downwards into the ice, scuplting cryoconite holes. This carves out a comfortable environment for microbes to thrive in – they could not live on the ice surface but they can enjoy a stable, sheltered life on the hole floor with just the right amount of sunlight, and many other microbes can live there too, feeding on the carbon produced by the cyanobacteria as they photosynthesise. So these cyanobacteria are the architects of the ice surface and they enable glaciers to have a rich biodoversity. We refer to creatures that perform that function as ecosystem engineers.
What is really fascinating about cryoconite holes is that they naturally expand to make sure the granules on the floors do not stack up on top of one another which would prevent some from receving enough sunlight – instead, when more material washes into cryoconite holes the hole walls expand and the granules spread over the new, larger floor area, making sure the maximum amount of photosynthesis always occurs. Even more incredible than that is that the holes themselves can migrate across the ice surface away from shady slopes and towards more evenly lit, flatter areas, maintaining the biological activity and promoting the biodiversity of the ice surface. As they migrate they take on all kinds of complicated and interesting shapes like the examples on the screen.
On the ice surface between the cryoconite holes there exists another different habitat – algae can grow in very thin films of water around the surface of melting ice grains, forming a blanket covering across the ice surface. These algae are special because they produce a pigment that is unique to those particular algae that acts as a natural sunscreen, allowing these algae to survive in the intense 24 hour daylight at the ice surface. This is crucial because these algae bake in the sun 24 hours a day in mid-summer and the ice is very reflective so they get lit from all angles, not just from above. This sunscreen pigment they produce has a dark purplish grey colour. Because there are so many trillions of the algae, this turns the colour of the ice itself dark purplish-grey, explaining Nordenskiold’s observations of the dark ice from 1875.
This is not something that happens over a small area of the ice, it is so widespread that it is clearly visible from space, particularly in Greenland where the biological stain can be seen as a distinctive dark stripe running along the western coast of the ice sheet – sometimes covering more than 10,000 km2. This stripe has generally been growing over the past decade, and a major question is whether it will continue to grow and accelerate Greenland’s melting in the future, and whether in a warming world the great “sleeping giant” ice sheets of Antarctica will start to show this behaviour too. Using drone and satellite remote sensing data and detailed field work, my team and I conservatively estimated that up to 13% of all the melting from the south-western sector of the Greenland Ice Sheet could be attributed to the growth of these algae in summers 2016 and 2017.
Far from being a lifeless place, we have found life everywhere we have looked on glaciers – and we have looked in some very unlikely places. In the summer, when the ice sheet is melting huge volumes of meltwater are generated, and as it flows towards the sea it carves out enormous vertical pipes in the ice that act as a kind of glacial plumbing system for flushing that water out to sea. In winter 2017 and 2018, when the water was all frozen, a team of cavers and I abseiled hundreds of meters into these pipes in search of signs of life.
Hanging from the ropes, I gathered samples of ice that was hundreds or even thousands of years old and my colleagues were able to extract DNA from these samples on site on the ice sheet. We were surprised to find that even here, locked away in ancient frozen ice in the dark, an active microbial system. Even in the most extreme corners of the ice sheet, the ice is alive. It is fascinating to wonder, if life can persist in dark, frozen pockets of ice like this on Earth, whether the same might be true on ice elsewhere in the solar system like underground caves on Mars or the ice of Jupiter’s moon Europa.
The current state of the science is that we have confirmed that the hidden biodiversity of glaciers and ice sheets is causing them to melt faster. In Greenland this is having a significant accelerating effect on global sea level rise. We have gathered field measurements to show that the dark stripe on the Greenland Ice Sheet really is caused by algal growth, developed mathematical models to describe the process at the local scale and methods for detecting these algae from the air and from space. The next frontier is to build these processes into the big scale climate models and start to predict the effects of the hidden glacier biodiversity on future sea level rise.