Extreme experiment under the Antarctic ice
A team of researchers diving under the Antarctic ice braved minus-two degree water temperatures and curious Weddell seals to complete the world’s first seafloor ocean acidification experiment in Antarctica.
The team of 15 people have returned to Hobart after studying the impact of ocean acidification on marine and seafloor communities at Australia’s Casey station over summer.
Australian Antarctic Division Project Leader, Dr Jonny Stark, said it was a challenging experiment in such an extreme environment.
“During the twelve weeks of the study we did over 200 dives, spending about 200 hours in almost minus 2 degree water,” Dr Stark said.
“The human body can only take those sort of temperatures for about an hour, so we had to continually rotate divers, and ensure they could be warmed up quickly once out of the water.”
The study mimicked future ocean conditions, predicted to be two and half times more acidic by 2100.
The research team of scientific and commercial divers, dive supervisors, engineers and technicians and PhD students, drilled holes through the sea ice to deploy four acrylic two-metre long chambers onto the seafloor.
Carbon dioxide-enriched seawater was then pumped into two of the chambers through a series of 40m long ducts or ‘slinkies’. Regular seawater was pumped through the other two chambers for comparison.
“The four chambers were fitted with underwater flow meters, thrusters, pH and temperature sensors and time-lapse cameras to record all the changes in the carbon dioxide-enriched environment, including the growth and behaviour of seafloor invertebrates and marine-plants.
“We took over 1200 samples of the various components of the ecosystem and while we don’t have any conclusive results yet, initial indications are that the photosynthesis of some of the tiny marine plants changed in response to the more acidic seawater and they may have migrated deeper into the sediment.”
Currently the Southern Ocean absorbs 40% of the global ocean uptake of carbon dioxide and polar waters are acidifying at twice the rate of tropical waters.
“The rate and scale of the changes we are seeing in the Southern Ocean are unprecedented, so it’s critical that we are able to get a clearer picture of how ocean acidification will impact the marine ecosystems into the future.”
The ocean acidification research was supported under Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership. The final results of the study are not expected to be known for several months.
The experiment was one of 28 research projects conducted in Antarctica and on sub Antarctic Macquarie Island over summer.
There were 84 ship days dedicated to marine science including a voyage to the Totten and Mertz glaciers, work off Australia’s Davis and Mawson stations looking at the foraging habitat of Antarctic seals and penguins, and a blue whales voyage.
This season 482 expeditioners and scientists went south with the Australian Antarctic program.
The Aurora Australis returned to Hobart yesterday after its final voyage of the season to Macquarie Island.
Extreme experiment under the Antarctic ice
Dr Jonny Stark – Chief Investigator
The aim of the project is to create a future ocean scenario that we might expect to see by about the end of this century. So as we’re increasing the carbon dioxide concentration in the atmosphere about 1/3 of the carbon dioxide is being absorbed by the ocean. That increase in carbon dioxide in the ocean, causes a chemical change in the ocean and basically l makes it more acidic. It’s this process which is known as ocean acidification.
So aim of this experiment was to get some idea of how Southern Ocean communities, and in particular animals living on the sea floor might respond, what sort of changes we might expect to see by the end of this century under business as usual emissions scenario, which means we keep emitting more or less what we are now.
We are expecting an atmospheric concentration of about 1000ppm. It’s currently around 400. It’s only a 0.4pH change, but it is actually a very big change in pH and would have very serious implications for a lot of marine life. For example, it can affect everything from the reproduction, to the growth and development of many marine organisms.
So we were looking at everything from the very, very small so the microbial forms of life and bacteria, up to the macro, the larger invertebrates that you find on the seabed things like starfish, sea anemones, and those sorts of things.
The experiment ran for an eight week period. The basic experimental design was specially designed chambers. So these were placed on the seabed and they were acidified to a level that we expect to see by the end of this century, so roughly 2.5 times more acidic or a 0.4 pH change.
We had four chambers in total; two of those were acidified and two of those were control. So we could compare the acidified ones and see what kind of changes might have occurred in those communities living in the chambers.
Dr Glenn Johnstone – Project Leader
Every aspect of what we did with this project was something that we’ve not really come up against before. We were modifying and inventing ways to do this and it was really gratifying when they worked. It was really great to work with a team of people and use all their different skills to try and come up with a method to make sure that this all worked.
We use dry suits, we use surface supply and AGA masks. So unlike the normal half masks that you’d be used to, this covers your entire face. It allows a space that we can have a microphone, so we have communications and earpieces, we can talk to the other diver and we can also talk to the surface.
So underneath that dry suit, we’ve got a layer of thermals, then a fleece layer and then an even thicker fleece layer. And you’re probably wearing two gloves, two pairs of socks, each person just depends is a bit different, and we have three fingered gloves – you’ve got to learn to manipulate things underwater with three fingered gloves on. A dive at the depths we were at, which was about 12–14 m, would last 50 mins. Water is always about −1.8 and under the sea ice there in that Bay it doesn’t vary over the year.
When we first got there, there was good visibility. The first dive that we did we had probably about 80–100 m worth of visibility, which is remarkable anywhere in world. Then slowly over the season that decreases when you have the algal bloom. At the end of the season it was much less than when we started but wasn’t particularly dark – it can be if you’ve got a lot of snowfall. Though we had plenty of wind, which tends to clear the snow off the ice. So even though the ice was 2.2 metres thick there was plenty of light down there.
We were visited many times by Weddell seals and on one occasion in particular we were visited by one that had a fish in its mouth, which is not something any of us had ever seen before and proceeded to eat it right in front of us in the dive hole which was really special to see that.