Mertz Glacier under the microscope
Mertz Glacier under the microscope
Acting Chief Scientist Martin Riddle:
In January this year, 78 kilometres of the Mertz Glacier ice tongue broke off. Now this is a once in a lifetime event. What happened was a very large iceberg approached it from the eastern side, just gave it a little nudge and that sent it off ricocheting westwards.
The Mertz glacier is due south of Tasmania and it’s a very special place because adjacent to the Mertz glacier is the Mertz polynya. So most of the ocean around the Antarctic is covered in sea ice in winter, but polynyas are kept free of sea ice by the wind blowing the ice away from it. Paradoxically although they have no ice covering them, they are actually an ice factory, so they continually form sea ice and then it gets blown out and cleared.
The formation of sea ice creates heavy brine, heavy salt water, its heavy, its cold and so it sinks. In sinking it drives, pushes water in front of it and in fact the polynya areas that form Antarctic Bottom Water drive the ocean circulation.
The main purpose of the voyage this summer is to better understand what the ice tongues role is in the formation of the polynya and what its role is in driving the development of Antarctic Bottom Water. But it also provides an opportunity to better understand the effects on the biological systems in the region. So we’ll been using satellite remote sensing to see whether primary production is still high in the region.
We’ll also be using underwater videos to see what was living in the area that was previously covered by the ice tongue. We are expecting to see some very different communities. When the tongue was covering it, it was dark, it was very remote from open water. In those conditions very special biological communities develop, that are able to exist and thrive under what are very different conditions.
We’ll be visiting the areas where the ice tongue grounded and hit the continental shelf and getting a baseline that will provide us with a better understanding of how the seabed communities recover after a major disturbance. We are also going to revisit some cold water coral communities that we discovered during the International Polar Year. We want to understand just how common or rare these communities are.
This research is very important in understanding global ocean circulation patterns and the role of polynyas in driving those. More locally the work on the biological processes are important because they are very important areas of high biological productivity around the Antarctic.
The investigations of life under the glacier tongue, will inform our understanding of how life in the Antarctic has changed over time. It will also give us a better indication of what might change if we lose some of the ice shelves, the permanent ice shelves, around the Antarctic.
An array of underwater cameras, moorings and sensors will be deployed at the Mertz Glacier in east Antarctica this summer for the first time since a major iceberg calving event.
In January last year, 78 kilometres of the Mertz Glacier tongue broke off after being hit by another 97 kilometre-long iceberg.
A team of nearly 40 Australian and international scientists will depart Hobart today on the Aurora Australis for a month-long voyage to the glacier to measure the impacts of the calving event.
Voyage Leader and Oceanographer with the Antarctic Climate and Ecosystems Cooperative Research Centre, Dr Steve Rintoul, said the Mertz Glacier region is one of the few places in the ocean where dense, salty water forms at the surface and sinks 4 or 5 kilometres to the sea floor.
“This sinking of dense water near Antarctica is a key link in a network of ocean currents that influences global climate patterns,” Dr Rintoul said.
“One goal of the expedition is to see how the calving of the large ice tongue has affected the formation of dense bottom water in the region,” Dr Rintoul said.
The expedition will also measure how much carbon dioxide is being stored by the ocean.
“The ocean slows the rate of climate change by soaking up some of the carbon dioxide emitted by human activities, but this is gradually making the ocean more acidic affecting the ability of some organisms to form shells or other hard structures like reefs to develop,” Dr Rintoul said.
“Scientists on board will measure the impact of ocean acidification on phytoplankton, the base of the Southern Ocean food chain.”
The Australian Antarctic Division’s Acting Chief Scientist, Dr Martin Riddle, said the area around the glacier is also one of the ‘biological hotspots’ of the Antarctic and Southern Ocean ecosystem.
“Biological productivity is high in the region, attracting whales, penguins and seals to feed on plankton in one of the few areas not covered by ice in the Antarctic winter,” Dr Riddle said.
“On the voyage, underwater cameras will be deployed to explore the ocean floor in the area previously covered by the glacier tongue,” he said.
“I expect to see new and unusual animals on the sea-floor as the area has been covered by ice hundreds of metres thick for about 80 years – this is a once in a life-time opportunity to discover what lives in these inaccessible places under the ice.”
The expedition is the latest in a series begun in 1991 to assess how and why the Southern Ocean is changing.
“By comparing our new measurements to earlier observations, we will determine how the temperature, salinity and circulation of the Southern Ocean is changing,” said Dr Rintoul.
“This information will help us track how rapidly climate is changing and help us improve projections of future change.”
The Aurora Australis will return to Hobart in February.