What lies beneath the Antarctic ice?
Chris - First, an expedition to tap into a lake buried 3 kilometres beneath the Antarctic ice sheet kicks off next month, after 16 years of planning. Scientists will be looking for the chemical hallmarks of life, as well as bacteria and other microbes in the lake water, which has been cut off from the outside world for tens of thousands, if not millions of years. Chris Hill from the British Antarctic Survey in Cambridge has the unenviable task of being in-charge of the operation and actually drilling into the lake. So what is this lake known as Lake Ellsworth and what are the conditions like there?
Chris H. - Lake Ellsworth is a liquid body of water underneath approximately 3.2 kilometres of ice sheet. It's a fairly sizeable lake. It's probably about the size of Lake Windermere and it's been cut off for, as you say, many 10s or possibly hundreds of thousands of years from our biosphere. The basic premise is that where there's water there's life, we see that all over our planet, and there's a very special relationship between water and life. But because of the extreme conditions of Lake Ellsworth, the dark, the high pressure, the apparent lack of energy transfer, we really wonder what that life might look like. It's a fascinating exploration to find something new.
Chris - What keeps it as water under all the ice?
Chris H. - Well, that's a very good question and it's actually quite an easy answer. The Earth is relatively quite a hot body. There's a lot of geothermal heating effects underneath the Earth and ice, for all it's cold, is actually quite a good insulator. So if you get a thick enough layer of ice over a hot body, it's inevitable that you're going to get pockets of water.
Chris - And we think that water has been there for a very long time.
Chris H. - Again, it's quite difficult to say until we can actually access the lake and get a sediment core to find out when that ice sheet last collapsed, but the hypothesis is, it's many hundreds of thousands of years, possibly as many as a million.
Chris - Wow! That's quite some time, isn't it? What about on the surface? What are the conditions that you've got to work in like? What's it like up there?
Chris H. - It's not pleasant. We're on the top of a very open ice plateau. It's very cold, so even in the middle of summer, we were looking at temperatures of minus 25 degrees Celsius with average wind speeds of 25 knots. So, it's not pleasant. There's no shelter, there's nothing anywhere near us for about 200 kilometres, there's no mountains. So, we really are exposed, we have to take everything in. There's nothing there already, so we have to take all our equipment in, all our living accommodation and everything with us. We'll be living in tents. We'll be wearing probably the thickest clothing you've ever seen.
Chris - Michelin Man positive.
Chris H. - Completely.
Chris - So, how will you access the water in the lake because it's under 3 kilometres of ice? It's a long way down.
Chris H. - That's right. There's many ways we could do this. There's a lot of techniques for drilling into ice and scientists have been doing this for many years. But by far, the cleanest and quickest is hot water drilling. Essentially, it's the same as a jet wash that you might use on your car. We're going to take some water from the melted snow, the ice on the surface and we're going to heat it, we're going to clean it, and we're going to pump it up to a very high pressure and push it through a very long hose. It's a very quick, efficient, and very clean way of drilling.
Chris - So, this will start at the surface and slowly melt its way down towards the lake.
Chris H. - Exactly and not so slowly actually. At 3.2 kilometres, we will probably get through from the surface to the lake in about 60 hours or 2 ½ days.
Chris - Really? And you've got a 3-kilometre long hose pipe.
Chris H. - We've 3 ½ kilometres and that's another interesting thing actually because the number of engineering challenges we faced to get this far are huge. Even simple things, like you wouldn't think it will be difficult to get a 3 ½-kilometre hose made. It actually is. We only found 2 companies in the world that could produce a hose to our specification. So, I mean, just the hose itself, just a simple piece of tubing was a real phenomenal engineering achievement.
Chris - So, the hot water goes down a hose, this melts the ice in front of it. How do you stop introducing the very molecules that you're going to go hunting for into the lake by dissolving them out of the ice and pushing them with this very high temperature?
Chris H. - Yeah, so that's quite a good question. The preservation of the lake has been paramount in our minds right from day 1. For two reasons, one obviously, we have an environmental responsibility to keep the lake pristine, but probably more selfishly, we actually want to preserve our samples. We don't want to be measuring anything that we've put into the lake accidentally. So, it's two-fold. Firstly, the water we're using to drill is taken from the background ice. So, there's nothing that we're going to use that wouldn't come into the contact of the lake at some point anyway. But more than that, the drill has been designed so that as we fire hot water out of the nozzle, the actual melted ice that's in the way will actually flush back up the borehole to the surface, keeping it away from the lake. So, the only water that will actually reach the lake in the end is the water that's already gone through our filtration system, has been pumped down at high pressure.
Chris - So you're filtering all the water that you're using for the melting.
Chris H. - Absolutely. Every stage of this program has a cleaning protocol and for the water, we filter to beyond pharmaceutical levels.
Chris - So that means screening up bugs and things like that.
Chris H. - Completely.
Chris - So, how will you know when you've actually got through the last bit of slush and you're now in the lake?
Chris H. - There's two ways. We'll know when we're close because the radio-echo sound and seismic data has given us a really accurate distance to the surface of the lake, and we obviously will know how much hose we've paid out and we will know the stretch of our hose. So we'll know when we're within a few meters. But then what we have is a suite of pressure sensors that will allow us to monitor the change in water levels at the top of the borehole. So, we anticipate and as we breakthrough to the lake, we won't fully have accurately equalised the pressure of the lake. So, as soon as we do breakthrough, there'll be a pressure change in the borehole, and we'll be able to sense that, and that will give us the indication beneath the lake.
Chris - Like the Coke bottle that when you take the top off and it fizzes up a bit, you'll see a little pressure change.
Chris H. - Yeah, definitely. We'll see a pressure change and we should be able to measure that, and that will be accurate indication of breaking through.
Chris - And then you'll drop in some probes to measure things in the lake.
Chris H. - That's exactly right. So, when we finish drilling, we need to recover the drill hose because we can't put two things down the borehole at the same time. So we recover the drill hose and then because we're not using any anti-freeze to keep the hole open, we have just 24 hours to deploy 2 instruments. The first instrument is a sampling probe which will take water samples and will also flush through some of the filtrate, the background filtrate in the lake and we'll take a small amount of mud from the bottom of the lake. We then recover that and we deploy a sediment core which we hope to get a 3-metre core sediment from the base of the lake which could give us a really good time record of what's happened in the West Antarctic ice sheet in years gone by.