3 The ice time machine
Snowfall differs depending on whether it falls in summer (when snow is comparatively warm and moist) or winter (when snow is cold and dry). These differences mean that when snow turns into ice, on the surfaces of glaciers and ice sheets, it is possible to see distinct annual layers. The layers are in a sense similar to tree rings: thick annual layers mean high snowfall, and thin annual layers mean low snowfall.
The accumulation of snowfall on the Greenland and Antarctic ice sheets – and most importantly what is trapped within the crystals as it turns to ice – can provide a record of the past. Digging down into the ice cap is equivalent to going back in time through the snowfall of previous years and you have to dig down a long way (equivalent perhaps to 300 years of snowfall) before reaching the ice.
To make the digging back in time easier, a drilling rig that extracts ice cores about 13 cm in diameter is used to get to very deep levels (Figure 10(a)). Once extracted, the annual layers in the cores are clear (Figure 10(b)).
Figure 10 (a) The NEEM (North Greenland Eemian Ice Drilling, where Eemian is the name of the last interglacial period) ice camp on the summit of the Greenland ice cap being dragged nearly 500 km to a new location to become EastGRIP (East Greenland Ice-core Project).
Figure 10(b) Annual layers in a model of a Greenland ice core. Light bands represent summer and dark bands represent winter.
The British Antarctic Survey (BAS) is world renowned for its polar research, including analysis of ice cores. Video 3 visits the BAS research laboratories in Cambridge, UK where Liz Thomas, head of ice core research at BAS, explains how ice cores can provide a time capsule of past snow falls that record what past atmosphere and climates were like.
Download this video clip.Video player: Video 3
Transcript: Video 3 British Antarctic Survey (BAS) and its polar research
TAMSIN EDWARDS:
Climate science is a global endeavour involving scientists of every kind from every nation. The British have a long history of polar exploration and science, and much of it is carried out at the British Antarctic Survey.
Hello, I'm Dr. Tamsin Edwards. I'm a lecturer in environmental sciences at the Open University. And I'm a modeller. I use computer models to study environmental change in the past and the future.
Today I'd like to explore how it is we know what we know about climate change. How do we do scientific research? How do we use the data that we collect? So I've come here to the British Antarctic Survey, which is one of the institutes that has really key research into climate change to find that more.
LIZ THOMAS:
Here at the British Antarctic Survey, we conduct a range of research centred around climate change. So we investigate the atmosphere-- looking at the air-- and we investigate oceans-- oceanography. And we also look at the ice. In this country, when it snows, if you're lucky, you get to make a snowman. And then it melts.
But in Antarctica you don't get that. So each year, the snow will build up. Year on year, you'll get it. And so you build up with these huge, great ice sheets.
And what we can then do is we drill the ice core through this. And it's like going back in time. So we get a time capsule which can actually record what the Earth's atmosphere and what the climate was like at the time when that snow fell.
And we can do this over years. We can drill down just shallow cores. Or we can actually drill back hundreds, thousands, and even close to a million years.
So one of the things that we particularly focus on here is actually looking at the chemistry of the ice cores. The chemistry can actually give us indications of what's happening in the sea ice, can tell us about the atmosphere, so we can see how the atmosphere gets dustier during the winter, as there's more storms, and less dusty during the summer periods.
And we can also look at the bubbles trapped in the ice. And this is particularly interesting, because that catches records of the Earth's atmosphere, particularly things like greenhouse gases-- carbon dioxide and methane. And we can not only see what the atmosphere was like at the time the snow fell, we can then take that backwards in time nearly a million years.
So we're now in the Ice Core Labs, kept at minus 20. And this is where we see the majority of our work. When we bring the cores back from Antarctica or from the Arctic, we actually cut and subsample the ice here.
So what I've got over here is actually one of the cores that we've drilled. And this is from a particularly deep core that we retrieved. And this is actually the bottom core. And we estimate that the age down at the bottom is 140,000 years.
TAMSIN EDWARDS:
So what have you over here then?
LIZ THOMAS:
So one of the really interesting things and really valuable things in terms of the ice core research is that we can actually get a record of volcanic eruption. So what we can see here, if you look up, we've got a sort of dark band, a grey mark. That's actually the volcanic eruption. So that's actually physically the ash from the volcano.
And the really useful thing about that is that it allows us to date the core, because some of these big volcanic eruptions, we actually have historical records from the time that they erupted. And we can use this to not only provide the date of the core that we're drilling, potentially in Antarctica, but also some of these very big volcanic eruptions, the same volcanic signal will show in Antartica core as it would all the way up in Greenland.
TAMSIN EDWARDS:
And I see you've got some spare bits.
LIZ THOMAS:
These are just some offcuts. So as we come back and we process the core and we divide it up for samples, these are some of the chippings and some of the offcuts. And what I really want to see here is that you can actually look. And these tiny little white dots are actually the bubbles. So this you can see, visually, how the ice has been trapped into these bubbles.
So when we talk about being able to look at how the atmosphere of the earth has changed, particularly these big important gases-- the greenhouse gases-- what we actually mean is we take this section of ice, you melt it, the air comes out of those bubbles. And then we have a record of what the atmosphere was like.
TAMSIN EDWARDS:
So you literally just melt the ice, and the bubbles come out, almost just like a fizzy drink.
LIZ THOMAS:
Exactly. Just like a fizzy drink. And actually we were standing outside, you'd start to hear them now, very much fizzing and crackling as air that's potentially been trapped in here for thousands of years becomes reintroduced to the Earth's atmosphere again.
TAMSIN EDWARDS:
We've heard about how ice cores provide a really amazing record of the past of our planet. I'd like to talk now to my colleague Mark Brandon about the present. Mark, you're a polar oceanographer. I know you go out into the field to difficult environments. Tell me the kinds of things that you're measuring.
MARK BRANDON:
So as a polar oceanographer, I'm interested in how the ocean is interacting with what I call the cryosphere. That's the frozen parts of our planet. So I've been out on ships and working on the frozen oceans in the Arctic and the Antarctic and making measurements around the continents.
TAMSIN EDWARDS:
So I'm a computer modeller. I use data like use in my work. I study Antarctica. This is a model of the bedrock underneath Antarctica. And I know that one of the areas you've worked in is down here in the Amundsen Sea area.
MARK BRANDON:
So I was on a ship that was working down at the edge of the ice front in the Amundsen Sea. And we were working out on decking conditions of about minus 20. And we were deploying this equipment, which measured the temperature and salinity of the ocean from the surface right the way down to the seabed. And what about enabled us to do is to work out how much heat is in the ocean, and how much of the heat is flowing towards Antarctica.
And what we found was the heat from the ocean is responsible for melting about 10 metres a year. That's one of parts of Antarctica that's melting the most rapidly at the moment.
TAMSIN EDWARDS:
Now 10 metres a year might not sound like that much, but of course it all adds up. And I think the key to thinking about how science works is we put all of this information together. We have different kinds of data from around the world and different kinds of scientists.
And we feed that into computer models-- like I use-- to try and make predictions. And what I'm particularly interested in is the uncertainty in those predictions. It's a huge scientific effort to put all this information together and try and work out the range of possible futures that we face.
Video 3 British Antarctic Survey (BAS) and its polar research
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The next section shows you how ice cores are extracted and illustrates how data from ice core analyses can be used to help develop our understanding of past atmospheric conditions.