The first Antarctic ocean acidification experiment using four specially designed underwater chambers, was successfully conducted under the sea ice at Casey for eight weeks this summer, according to Project Chief Investigator Dr Johnny Stark.
Two of the four semi-enclosed chambers were used to mimic future ocean conditions under a ‘business as usual’ carbon dioxide emissions scenario, to examine the impact of ocean acidification on marine and sediment communities. The other two chambers acted as ‘controls’ for comparison.
‘The aim of the Antarctic Free Ocean Carbon Enrichment (AntFOCE) experiment was to create ocean conditions that we might expect to see by the end of this century if we continue to emit carbon dioxide into the atmosphere at the current rate,’ Dr Stark said.
‘This carbon dioxide dissolves in the ocean and causes chemical changes that make seawater more acidic, with profound implications for marine life. So we wanted to look at how these chemical changes might affect the community of plants and animals living on the Antarctic sea floor.’
For the past two years the AntFOCE team has been developing and testing the design of the underwater chambers for Antarctic conditions (Australian Antarctic Magazine 27: 4–5, 2014). The chambers were adapted from a prototype developed by the Monterey Bay Aquarium Research Institute in California that has been used in temperate, tropical and sub-tropical waters.
‘The scientists and science technical support team at the Australian Antarctic Division did a lot of work to modify the system for the rigours of Antarctica, such as the sea ice and cold water and air temperatures,’ Dr Stark said.
‘We also had to identify a suitable site close to the shore, so we could set up shore-based infrastructure to power and monitor the experiment. The site also needed to retain sea ice over the summer to provide a platform for us to work on.’
In November 2014 the team finally got the chance to put all their hard work, planning and design to the test. Project Manager, Dr Glenn Johnstone, was amongst the first of the 15-strong team to arrive at Casey and begin the process of deploying the chambers in O’Brien Bay.
The team — which included scientific and commercial divers, dive supervisors, engineers and technicians — began by drilling holes in the sea ice to deploy their chambers and four 40m-long ducts or ‘slinkies’ that would carry the carbon dioxide-enriched and untreated seawater to the experimental and control chambers.
‘On the shore we had our “silver chalet” containing all the sensing equipment to monitor the experiment, such as oxygen and pH sensors, as well as computer equipment to relay this information back to the station,’ Dr Johnstone explained.
‘We also had a generator van for power, cage pallets of gas cylinders full of carbon dioxide, and pumps for pumping water up and down.
‘All this was connected across the intertidal zone and tide cracks by a big umbilical cable and a float, which took power, data and water between the surface and under the ice.’
To deploy the chambers on the sea floor the team used lift bags and ropes to gently lower them and avoid disturbing the fine layer of sea floor silt. Similarly, a complicated rope and pulley system was rigged to carefully deploy and connect the ducts to the chambers.
‘Equipment like this has never been deployed in Antarctica,’ Dr Johnstone said.
‘However, our team had a lot of different expertise and experience, and we were able to combine mountaineering and climbing experience with commercial diving experience to rig up a system that would suspend the ducts and allow us to control their descent and connection.’
Once the chambers and ducts were in place and teething problems ironed out, the experiments required very little maintenance.
‘We didn’t disturb the chambers during the experiment. They ran for eight weeks and we sampled them at the end,’ Dr Stark said.
‘We ran a constant flow of carbon dioxide-enriched seawater through the two experimental chambers, keeping the pH at 0.4 pH units below the naturally fluctuating pH of the seawater. To put this in perspective, in the past 25 million years the pH of seawater hasn’t changed by more than 0.1 or 0.2 pH units, but by 2100, under a business as usual carbon emissions scenario, we’re expecting a 0.4 unit change. On an evolutionary time scale, that doesn’t give animals much time to adapt.’
Over the coming months the team will examine their samples for, among other things, changes in the biodiversity and composition of the seafloor invertebrate community and the bacteria and diatom (single-celled marine plants) communities, changes in sediment nutrient cycling, and changes in the growth of diatoms and other tiny marine plants.
During the main experiment the team also deployed two mini-chambers, which were designed to investigate specific questions over 24 to 48 hours. Here the team looked at the respiration rates in sea urchins under controlled and acidic conditions, and changes in photosynthesis in marine microalgae growing on the sea floor.
‘It appears that acidification induced a response from these microalgae communities, possibly making them migrate deeper into the sediment than in the control treatments, but more work is needed to confirm this preliminary result,’ Dr Stark said.
‘However, it is an encouraging sign for the rest of the experiment in terms of detecting the potential effects of acidification.’
Unfortunately, issues with weather meant the team couldn’t run the experiments for as long as they’d hoped. Any future experiments would ideally run for three to 12 months.
‘Despite the challenges the project was an outstanding success, and we now have many months of sample processing ahead,’ Dr Stark said.
‘Every aspect of the project was new to us, but our team was able to modify and invent ways to do the work, and it all came together over many frozen sandwiches and blocks of chocolate.’
Australian Antarctic Division
This research was funded by the Australian Antarctic Division, the Antarctic Climate and Ecosystems Cooperative Research Centre and the Australian Research Council’s Special Research Initiative for Antarctic Gateway Partnership.