Building a future ocean
Antarctic scientists are working to create a future ocean in an underwater ‘bio-dome’, 20 m beneath the sea ice off Casey station.
In a world-first experiment, marine scientists Dr Donna Roberts and Dr Jonny Stark, will assess the impact of ocean acidification – caused by increasing amounts of atmospheric carbon dioxide (CO2) dissolving in the ocean – on polar sea floor (‘benthic’) communities.
To do this Dr Roberts, an ocean acidification expert from the Antarctic Climate and Ecosystems Cooperative Research Centre and the University of Tasmania, will work with Australian Antarctic Division benthic ecologist, Dr Stark, and a team of Antarctic Division technicians, engineers and divers, to adapt ‘Free Ocean CO2 Enrichment’ (FOCE) technology for Antarctic deployment. These semi-enclosed underwater chambers allow scientists to vary the CO2 concentration in the water without changing light or nutrient conditions.
‘Basically we’re going to build a bio-dome on the sea floor with a future ocean inside it,’ Dr Roberts says.
‘We’ll do this by modifying a prototype FOCE system developed by Bill Kirkwood and his team at the Monterey Bay Aquarium Research Institute in California, to suit Antarctic conditions and the research questions we want to answer.’
Ocean acidification leads to a drop in the pH of seawater and affects the ability of some marine organisms, including corals, sea urchins, bivalves and some phytoplankton, to form shells and other hard, ‘calcareous’ structures.
The Intergovernmental Panel on Climate Change Fourth Assessment Report in 2007 found that since 1750 there has been an average decrease in ocean pH of 0.1 unit. Under a ‘business as usual’ CO2 emissions scenario, ocean pH is projected to decrease by another 0.3 to 0.4 units by 2100.
As cold waters absorb more CO2 than warmer waters, the effects of ocean acidification are expected to appear first in polar ecosystems.
While Dr Roberts and others have studied ocean acidification’s effects on individual organisms living in the open oceans, there has been little research on sea floor communities.
‘Polar sea floor communities contribute to fundamental ecological processes within the global marine ecosystem,’ Dr Roberts says.
‘They enhance sediment stability, recycle nutrients that support productivity, and provide habitat, shelter and nursery grounds for small invertebrates and fish, which in turn are food for fish, krill, seals, penguins and whales. So the effects of changing ocean chemistry on these sea floor communities will likely cause major ripple effects up the food chain.
‘This new technology will allow us to bring the laboratory to the sea floor and deliver urgently needed research on the community-scale effects of high CO2 waters.’
Since the prototype FOCE system was developed by the Monterey Bay Aquarium Research Institute in 2005, modified systems have been deployed in tropical and temperate waters to study the effect of high CO2 levels on deep sea marine communities, coral reefs and sea grasses.
The Antarctic FOCE system will consist of a coffee table-sized acrylic chamber (2m x 0.5 m x 0.5 m), anchored to the sea floor and sufficiently robust to withstand the -1.8°C water temperature and sea ice. A series of pipes and cables, linked to pumping, power and telecommunication equipment at the surface, will provide a constant flow of CO2 –enriched sea water through the chamber, and power to a range of instruments monitoring pH, conductivity, temperature, depth and oxygen concentration (see diagram below). Time lapse cameras will also record changes in the chamber over time.
Dr Stark, alongside other scientific divers, will deploy two experimental and two control FOCE chambers through the sea ice early in the 2014 Antarctic season, and retrieve them from open water about four months later.
‘The two control chambers will track natural fluctuations in pH, while the experimental chambers will be dosed with CO2 -enriched sea water at 0.4 pH units below the naturally fluctuating pH,’ Dr Stark says.
The CO2 -enriched sea water will be generated by pumping water piped from the environment through a CO2 supply installed at the surface and close to the shoreline at Casey station. This water will then be pumped back to the experimental chambers. Untreated seawater will be pumped through the control chambers.
Each FOCE chamber will be divided into four connected but distinct ‘zones’ (see figure). The first ‘bioturbation zone’ will look at changes in the recycling of nutrients by sediment-dwellers. The second ‘biodiversity zone’ will contain settling plates – like bath tiles – to provide habitat for non-sediment dwellers (other than predatory sea urchins) and microscopic larvae in the water column to colonize. In the third ‘biodiversity zone’ divers will extract small sediment cores to examine communities of sediment dwellers. The biodiversity zones will allow scientists to examine community composition and any changes in diversity and numbers in different habitats between the experimental and control chambers over time. The fourth zone will corral sea urchins and look at their behaviour and growth rate as the experiment progresses. Throughout the experiment time lapse cameras will also capture changes such as the rate of burrowing in sediment and the rate of community development on settling plates.
The team must now identify a study site that will accommodate four chambers, hosts a suitable sea floor community and can support the power and telecommunication infrastructure that needs to be installed.
It’s an ambitious project, but a critical one.
‘Southern Ocean communities are predicted to be among the first to respond to ocean acidification and this project will determine whether they have any resilience to these changes,’ Dr Roberts says.
‘This community level research will assist governments, scientists, modellers and society to understand the emerging impacts of ocean acidification on marine ecosystems and to ensure that the most relevant information underpins decisions to manage this threat.’
Australian Antarctic Division
Sea ice and fast ice pose one of the biggest challenges to the installation and success of the Free Ocean CO2 Enrichment (FOCE) experiment in Antarctica. Find out more about Making FOCE work.