Warm ocean water melts largest glacier in East Antarctica
Warm ocean water melts largest glacier in East Antarctica
Dr Steve Rintoul – Voyage Science Leader
The Totten glacier has remained a secret, has remained unobserved for so long because its so difficult to get to.
We were extremely lucky on this voyage. When we left Casey and started heading to the Totten I thought it was very unlikely that we were going to be able to reach the Totten itself because we had about 100 km of heavy sea ice to traverse to get to the front of the Totten. And we were very lucky we got just the right weather conditions, just the right wind conditions that allowed us to take advantage of a crack in the ice that opened up that extended all the way to the front of the Totten.
The Totten glacier flows off Antarctica and starts to float and the floating part of the glacier is about 120 km long. Out at the front of the glacier where we made our measurements the ice is about 200 metres thick. It then gets thicker as it goes back towards the Antarctica continent and the grounding line, the place where the glacier leaves the bedrock and starts to float is 2 km below sea level.
The surface of the glacier is sinking, it’s thinning. The question is why? It could be related to the dynamics of the ice itself or it could be because the ocean is melting the glacier from below. The Aurora Australis voyage that we just completed was aimed at testing that second idea – is there any evidence that warm ocean water reaches the glacier capable of driving melt of the floating glacier?
What we found is evidence that exactly that is happening. That warm water does reach the Totten glacier. The temperatures that we measured at the front of the Totten are about 3 degrees warmer than the freezing point at the grounding line and so that’s a measure of how much heat is available to melt the ice.
We can detect melting of glacial ice a few different ways. One is just from the temperature. If we see temperatures that are minus two degrees, we know that must have happened at great depth below the floating ice shelf. That’s the only way you can produce temperatures that cold. As the glacial ice melts, it also leaves a signature in the water, that we can detect using different chemical elements and isotopes.
One of the spectacular successes of the voyage were recovery of oceanographic moorings. One year ago the US ship Nathaniel B Palmer deployed Australian and US moorings near the Totten. So we were able to recover all six of those. Those are important because it will provide a year round record of what’s happening near the Totten.
I’ve been going down south for almost 30 years now. I’ve done 15 trips, 12 of them to Antarctica and I’d have to say that this is probably the most successful trip that I’ve been part of that entire time.
Warm ocean water is melting the largest glacier in East Antarctica from below, according to new Australian Antarctic research.
The team of 23 scientists and technicians from the Australian Antarctic Division (AAD), the Antarctic Climate and Ecosystems CRC (ACE CRC), the University of Tasmania’s Institute for Marine and Antarctic Studies and CSIRO Oceans and Atmosphere Flagship, returned to Hobart today on Australia’s icebreaker Aurora Australis, after taking the first water samples ever collected alongside the Totten Glacier.
Voyage Chief Scientist Dr Steve Rintoul, from the ACE CRC, said that until this voyage no oceanographic measurements had been made within 50 kilometres of the glacier.
“At 120km long and more than 30 km wide the Totten Glacier is one of the world’s largest and least understood glacial systems,” Dr Rintoul said.
“It drains 538,000 square kilometres of East Antarctica, an area more than twice the size of Victoria. 70 billion tonnes of ice flow out of it every year, enough to fill Sydney Harbour every two and a half days.”
“It was thought that glaciers on the East Antarctic ice sheet were relatively immune to the kind of melting taking place on the much smaller West Antarctic ice sheet.”
“But satellite data show that the Totten has been thinning faster than other glaciers in East Antarctica and until now we have not known why.”
The researchers used new instruments, such as autonomous floats and gliders, designed to sample the ocean beneath sea ice and traditional oceanographic tools like Conductivity, Temperature and Depth (CTD) profilers lowered from the ship.
“We also measured chemical tracers of glacial melt water that we will use to assess how fast the glacier is melting.”
“We will use the data gathered from these instruments at the Totten Glacier to assess how much ocean heat is available to melt the base of the Totten Glacier.”
As warm ocean waters melt the Totten and other floating glaciers around the edge of Antarctica, more glacial ice can flow into the ocean, raising sea level.
“This study will help address one of the biggest questions concerning future sea level rise: how will warming of the ocean affect the Antarctic ice sheet?”
The Totten Glacier alone contains an amount of ice equivalent to 6 metres of global sea level rise.
Glaciers grounded on bedrock below sea level, like the Totten, are particularly vulnerable to changes in ocean temperature and currents, because the ocean can penetrate deep under the glacier.
A key part of the voyage was the recovery of US and Australian instruments moored on the sea bed for up to two years at six different locations adjacent to the Totten glacier. The Australian instruments are part of the national Integrated Marine Observing System (IMOS).
The instruments were deployed by the US icebreaker Nathaniel B. Palmer and recovered by the Australian icebreaker Aurora Australis as part of an ongoing international collaboration.
“The mooring records will provide the first ocean measurements spanning the full year in this area, giving us an idea of what happens during the long cold winter months when access to the region is impossible,” Dr Rintoul said.
The seven week marine science voyage was funded through the Australian Research Council’s Special Research Initiative for Antarctic Gateway Partnership, the AAD, the ACE CRC, CSIRO and IMOS.