Scientists set sail south in search of climate evidence

Glen Paul: G'day, and welcome to CSIROpod, I'm Glen Paul. The Aurora Australis is Australia's Antarctic Flagship, designed as a multi-purpose research and resupply ship. On New Year's Eve the Aurora is once again setting sail for the Southern Ocean, taking with it a team of scientists to investigate how the Southern Ocean is changing, and to discover what impact those changes will have on climate, sea level, and marine life.

The month long voyage will see the research team retrieve current metre moorings, and deploy deep diving robots, known as Argos, beneath the Antarctic's Ross Sea winter sea ice.

CSIRO's Dr Steve Rintoul will be leading the scientific mission aboard the Aurora Australis, and joins me on the phone. Firstly Steve, I must say as much as I dislike the cold I'm extremely envious of you. This of course isn't your first trip to the Antarctic, but how will this trip differ from those of the past?

Dr Rintoul: Well there are a few things that are different and exciting about this particular voyage. Among other things we’ll be recovering some current metre moorings that we deployed two years ago, and so these have been measuring the speed of the ocean currents, as well as temperature and salinity for the last two years, and they’re in a particularly interesting part of the Antarctic where what we call a boundary current, a strong deep flow down four kilometres below the sea surface, is carrying dense water that forms around the edge of Antarctica and out into the rest of the ocean, and that’s an important part of a system of ocean currents called the overturning circulation – it influences the climate of the earth.

Glen Paul: And what sort of information are you expecting to retrieve from them?

Dr Rintoul: Well one of the things that’s really cool about these moorings – this is a joint experiment with some U.S. scientists – at the bottom of each of the moorings is an instrument that measures temperature and salinity, but it crawls up and down the mooring wire once or twice a day, and collects continuous profiles of the temperature and salinity in the lower 500 metres of the water column.

Now why that’s interesting is that we’ve never had that sort of information before that goes through a whole seasonal cycle and extends over a couple of years. And so in the past we’ve always had very brief snapshots – we go down with a ship and we measure what the conditions were at that particular time – but we don’t have a continuous record of what’s happening, so that will be something new.

These instruments, we only get the data back if we can recover the instrument. They’re anchored to the sea floor with a pile of railway wheels, and they’re held onto that with an instrument that has an acoustic transducer, and we can send a coded sound pulse and say OK, it’s time to let go, and it let’s go and all the instruments float up to the surface, and we gather them in. But it’s always a little bit hairy because it’s a lot of gear, and a lot of valuable data that we can only get back if we do that part successfully.

Glen Paul: OK. So it’s been a long two years then in waiting to get your hands on this information. So you’re also deploying Argos – are these the standard type, or are you using a modified version for this job?

Dr Rintoul: We’re deploying some of the standard type, but also three modified versions. We want to study a region called a polyna – it’s a Russian word that refers to an area within the sea ice that stays open water, stays free of ice throughout the winter. They’re kind of unusual, but they are a number of those around the Antarctic coast, and they’re very important for the climate system.

It's very difficult to make measurements of those regions during winter when ships are usually not there, and traditional, the regular garden variety Argo floats don’t work well in the ice zone either, but these polar profiling floats are designed to rise and fall like regular profiling floats, but they have a special way of communicating using the Iridium Phone Satellite system, and so they can bump into the ice without being damaged, and they can pop up into very small holes between the ice flows and send the data back to us of the temperature and salinity that they’ve measured. And then they sink down and they’ll sit on the sea floor and stay in one location until ten days later when they’ll bob up again and send us some more information.

So we hope that for the first time we’ll get a continuous measurement right through the winter season, of what happens in these important polyna regions.

Glen Paul: Absolutely. And I understand these robots replaced the role of helpful seals that acquired data whilst swimming around fitted with acoustic tags.

Dr Rintoul: That’s right. So in the past then – this is continuing really – the Biologists that we work with have been putting instruments, miniaturised oceanographic sensors attached to the fur of seals to study where the seals go and where they feed, and try to understand the dynamics of the seal populations that way. But we get a valuable bonus, which is that the seals also collect oceanographic information, and from regions that are very difficult for us to measure using regular tools, like satellites, floats, or ships, and that’s deep within the sea ice zone in winter

So these new floats that we’re deploying, combined with the information that we get from the seals, will help us really understand what’s happening to the ocean right around the edge of Antarctica, and that’s important because where the ocean contacts the ice that flows off the Antarctic continent and into the sea, if the water warms up it will melt that ice more rapidly. As that ice melts and thins, and starts to break up that allows more ice to flow off the continent and into the ocean, and that has the potential to raise sea levels.

So at the moment our biggest uncertainty in terms of what future sea levels might be is related to the response of the ice sheets in Antarctica and Greenland, and that in turn is much more tightly liked to what happens in the ocean than we once thought.

Glen Paul: I see. So there certainly is call for more information to be made available. How long do you think it will take to profile the Southern Ocean with the Argos?

Dr Rintoul: So it would take a very long time if we did it everywhere continuously, and so what we need to do is target the most important regions, and so there’s particular locations where we know from satellite measurements that the ice is thinning more rapidly than in other locations, so those are the key places to look first to see how the ocean might be affecting the ice sheet.

Glen Paul: Hmm, and that would require quite a few ships too. Who do you call upon to deploy the Argos for you?

Dr Rintoul: So we use lots of different ships. We deploy them from research vessels like CSIRO’s Southern Surveyor, and from the Aurora Australis. We deploy them off merchant vessels that are running along the regular shipping routes, and sometimes we charter vessels to go into parts of the ocean where it's very difficult to get any other way. And our New Zealand colleagues, for example, have a small ship that has deployed more Argo floats than any other vessel in the world, and in particular in parts of the South Pacific and the Southern Ocean, and the southern Indian Ocean, where very few other ships go.

Glen Paul: OK, hats off to the Kiwi’s for that one. So is there somewhere that a shipping owner or operator can go to sign on to offer assistance?

Dr Rintoul: Yeah. And so we do work very closely with the shipping agencies, but people that are interested in contributing, there’s a website for Argo, which is A R G O, and there’s a deployment stage on there where people can find more information about how to contribute.

Glen Paul: Is the data from Argos freely available to anyone wanting to access it?

Dr Rintoul: Yes it is, so that’s one of the features of the Argo program that’s been the case from the start, which is that this data will be most valuable if everybody can use it. So even if you’re not deploying floats yourself, if you had an interest in what’s happening in the ocean, you can get onto the Argo website and download whatever data you want, and use it for whatever you like.

Glen Paul: Now you've got a month long trip ahead of you, what's your itinerary? Can you lay that out for us?

Dr Rintoul: So we steam south from Hobart and head to Commonwealth Bay, and one of the first things we’ll do is it’s the 100th anniversary of Mawson’s Australian Antarctic Expedition, so when he built his hut in Commonwealth Bay, so there’s a visit to the hut to celebrate the Centenary of Mawson’s expedition, and we’ll hopefully repeat some measurements that Mawson made in 1911. So there are very few places in the ocean where we have records that go back a hundred years, so we hope to revisit that site and collect some measurements there.

Then we head west along the Antarctic coast to close to the Antarctic base, Australia’s base at Casey, which is pretty much due south of Perth. And we’ll pick up the moorings there and then start heading north to Fremantle, and as we head north we’ll collect measurements of a wide variety of ocean properties, from the sea surface down to the sea floor, down to depths of up to five kilometres.

Glen Paul: OK. Well look, as I say, I’m very envious of you. I’ll give you a call on the satellite phone towards the end of January and check in, see how the trip’s progressing, and how the celebrations went, so in the meantime bon voyage Steve, and thank you very much for discussing the trip with us today.

Dr Rintoul: Thanks very much.

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.