Glen Paul: G'day, and welcome to CSIROpod, I'm Glen Paul. Early in the New Year, Australia's Antarctic flagship, the Aurora Australis, set out from Hobart on a mission of discovery and celebration on the 100th anniversary of Mawson's Australian Antarctic expedition.
Led by CSIRO's Dr Steve Rintoul, the complement of 50 scientists and support staff investigated how the Southern Ocean is changing under climate change.
To find out how the trip went, and what the findings were, I've got Steve on the phone, and by now Steve, you should well and truly have your land legs back. But how was the trip weather wise; did you experience any rough seas?
Dr Rintoul: It was actually one of the smoother trips I've done. I've been down – I think this was my 12th trip down to Antarctica, and this might have been the smoothest of them all actually.
Glen Paul: And what about ice flows, did they hinder progress at all?
Dr Rintoul: Well it did, and a large iceberg which had drifted into Commonwealth Bay, which is the area where Mawson's hut is located, caused lots of sea ice to form between the iceberg and the coast, and that made it difficult to get people to shore to carry out the celebrations of Mawson's Centenary, but they did get there eventually. So that ice slowed us down a bit, but didn’t really prohibit us from doing too much.
Glen Paul: So how was Mawson's 100th anniversary celebrated and commemorated?
Dr Rintoul: Well the group went ashore and had a trip through Mawson's hut, which is truly an incredible place to see, because it really does look as if they just picked up and walked out the door, and you can see the place really as it was a hundred years ago, and imagine them on the incredible voyage and adventure that they were on at that time. It’s amazing to see it a hundred years on.
There was a ceremony and plaque installed, and some words said by Tom Griffiths, who's a historian at ANU, an expert in Antarctic history, who was fascinating to talk to in order to get a feeling for the place of Mawson and his expedition in Australian history.
Glen Paul: Absolutely. And I’m sure we’re all very envious of those who got to participate in the ceremony there. Now of course the main reason for the journey was scientific, and you were to deploy some Argos and retrieve some current meter moorings – how did all that go?
Dr Rintoul: Well it went really well. And usually when I go to sea I pray for good weather. In a sense I was hoping for some bad weather, because if we got some bad weather before we got to Mawson’s hut, I might be able to steal a bit of time and steer the ship over to a place where we could take some opportunistic oceanographic samples.
And that’s how it turned out, we had weather that was too bad for flying the helicopters, so we had some time to wait, and so we brought the ship over to the area of the Mertz Glacier. In February of 2010 a large of piece of this glacier broke off, about 80 km by 30 km chunk of ice drifted away, and that’s really changed the oceanography in that region, and so this summer we got a chance to go back and see how things are evolving there, and how the ocean's changing.
Glen Paul: And how are things evolving and changing?
Dr Rintoul: Well what we found was that – we were there a summer before that as well – and what we found is once this big chunk of ice broke off from the edge of Antarctica it meant that the dense water that’s formed around Antarctica became much fresher and less dense than it has been in the past. And that’s important because the water sinking around Antarctica is part of a global pattern of ocean currents that plays a big role in regulating the climate by determining how much heat and carbon dioxide the ocean can absorb from the atmosphere.
So the region’s important, and these changes are big. The first thing that we saw after the calving of the glacier tongue was the equivalent of about 50 years of the freshening trend we’d seen since 1950. So we saw as much freshening in the last year, than the first year after the calving of the glacier, than we had in the previous 50.
And so it’s a reminder to us that the system around Antarctica and in the southern ocean is pretty delicately poised, and if we change something, like the arrangement of chunks of ice in grounded icebergs and glacier tongues and so on, we can have a significant impact on the oceanographic conditions.
Glen Paul: And of course it wasn't just about making physical observations, you had the current meter moorings to retrieve. Did you get all of those successfully, and have you had a chance to analyse the data?
Dr Rintoul: We did collect all the moorings, and that was a little tricky. There was sea ice around one of the sites, and a very small hole in the ice, so we had to make a decision whether we waited another year or went for it – and so we went for it, and we got it back, so it looks like a very sound decision. If we’d lost it, I wouldn’t be looking so good.
And we then made a series of measurements from the surface down to the sea floor, all the way from Antarctica back to Australia, and that’s allowing us to see how the amount of carbon, and heat, and salt in the ocean is evolving with time. And what we found is that this dense layer that occupies about the lower 1 km of the ocean around Antarctica is shrinking. So it’s a water mass that we call Antarctic bottom water, it is water that sinks around the edge of Antarctica and then spreads out throughout the rest of the world ocean along the sea floor.
And what we found is that that layer use to be about a thousand metres thick in 1970, and it’s only about 300 m thick now. And so what it tells us is that the dense water sinking around Antarctica is becoming less dense over time, and there’s less of it.
It wasn’t too long ago, maybe ten or 15 years ago, that we use to think of the deepest parts of the ocean as pretty static, that things didn’t change much with time, and these measurements we’ve been making in the southern ocean make it very clear that the deep ocean is a very dynamic place, and responds very rapidly to changes in the surface climate for whatever reason, whether it’s natural effects like an iceberg calving, or due to human factors like emitting CO2, and also as a result of the ozone hole.
Both of those human activities are also having an imprint on the ocean, and the measurements we were making this summer allow us to track the evolution of those ocean changes.
Glen Paul: Well that’s certainly not the kind of news that we like to hear. So what happens now with the information? You’ve probably still got some analysing to do, but obviously it’s very important information, where does it go now; who do you hand it on to?
Dr Rintoul: We're madly working it up, and writing it up. One of the places it will go is, if it’s published soon enough, some of the evidence will go into the Inter-Governmental Panel on Climate Change report on ocean changes as part of the fifth assessment report.
That process is important because it’s one of the main ways that policy makers get a summary, a regular summary of the state of the art of our understanding of climate science, and so these observations we’ve been making are one small contribution to that much larger report.
Glen Paul: Okay. And will there be a trip 13 to gather more information next summer?
Dr Rintoul: I do have a trip going next summer, but I'm going to sit this one out and stay home, and send the rest of the team. I’ve been the last two summers, so it’s time for a summer at home.
Glen Paul: Well I’ll take that berth if you don’t mind.
Dr Rintoul: I might take you up on that.
Glen Paul: Well I don't have to be asked twice, Steve, so I might just take you up on it as well, so sounds good to me. Anyway, thank you very much for discussing the trip with us today; it certainly seems like quite an adventure.
Dr Rintoul: Thanks.
Glen Paul: Dr Steve Rintoul. For more information find us online at www.csiro.au. You can like us on Facebook, or follow us on Twitter at CSIROnews.