Antarctica undergoes the acid test

UTS C3 scientists, Postdoctoral Fellow Dr Katherina Petrou and PhD candidate Ms Cristin Sheehan have spent their summer at Davis station, Antarctica. They are part of a science team lead by Dr Andrew Davidson (Australian Antarctic Division) studying the effects of elevated carbon dioxide on Antarctic marine microbial communities. Dr Petrou discusses the reasons for the long journey south:

Why are we here?:

The Antarctic marine ecosystem covers 20% of the global ocean and is fundamental to the Earth’s biogeochemical cycling and fisheries resources. Marine microbes are key organisms in the functioning of marine systems; forming the base of the food web and providing essential nutrient cycling. Elevated CO₂ concentrations potentially threaten the structure and function of marine ecosystems. In particular, Antarctic waters are amongst the most vulnerable, due to the high solubility of CO₂ in cold water. Atmospheric CO₂ concentrations continue to rise and have already reached values exceeding those experienced in the last million years. The CO₂ being released into our atmosphere, means that our oceans are becoming more acidic. Ocean acidity is expected to increase 300% by the end of this century yet the resulting physiological stresses on the Antarctic marine biota are poorly understood. Our study therefore, investigates the response of Antarctic marine microbes—both individual species and the whole community—to increased CO₂ concentrations with the aim to provide new knowledge on how future ocean food webs and productivity may be affected by increasing CO₂ levels.

Our journey to the South:

It was a long, rolling voyage from Hobart to Davis station on the RSV Aurora Australis. Fifteen days on the high seas of the Southern Ocean. The seas proved somewhat trying, however, we were duly rewarded with a spectacular approach to the continent through ‘Iceberg Ally”. Davis station is a coastal town overlooking small rocky islands and protected from harsh Antarctic weather by a spectacular backdrop of the Vestfold Hills. Unlike much of Antarctica, the weather at Davis is quite mild. So mild in fact, that it is also known as the "Riviera of the South" with pleasant spring days of anywhere between -5 and +4 degrees. At this time of year, the sun never really sets; it simply drops behind a few mountains only to pop up again an hour later.  

Acid test for Antarctic marine microbes:

It took us about a week to get things ready for our experiment; station inductions, unpacking our cargo, sorting out experimental protocols and testing our instruments. Eventually we were ready for receiving our seawater. However, at this time of year, Davis Station is surrounded by sea ice making access to the microbial community in the open ocean somewhat difficult. To obtain a representative oceanic community, we needed to use a helicopter to collect our seawater and airlift it to our holding tank at Davis Station ( www.antarctica.gov.au/news/2014/antarctic-marine-microbes-airdropped-into-science-experiment). Once we had obtained all 7000 litres of "airdropped" seawater, we were able to fill our six experimental tanks and slowly adjust dissolved CO₂ concentrations (ranging from 325-1500 parts per million) over 5 days.

We then spent the following 18 days sampling for community composition, growth, productivity, physiology and metagenomics, successfully accumulating a swathe of new information on the microbial community responses to CO₂ enrichment. Our next challenge is to understand the changes in community structure and function, the physiological responses that drive these changes, and deliver new information on the effects of CO₂ on marine biogeochemical cycling and Antarctic food webs.