Ice Acidification: effect of elevated pCO2 on Antarctic Sea Ice Communities

Chair: Jean-Pierre Gattuso

Andrew McMinn (1)* Andrew Martin (1), Marius Muller (2)

1 University of Tasmania, Hobart, Tasmania, 7050, Australia
2 University of Sao Paulo, Sao Paulo, Brazil

Background
Sea ice is recognized as one of the most extreme habitable environments on earth where organisms can be exposed to temperatures of below -20°C and salinities greater than 200 for extended periods of time. They also endure long periods of darkness and extremes in nutrient concentration, dissolved gases (O2, CO2) and experience a natural pH range from 7 to 12. In spite of this some sea ice habitats are very productive and often support dense microbial biomasses.

Methods
Sea ice brine was collected at Scott Base and in the pack ice adjacent to the Mertz Glacier in 2012, 2013 and 2014. The carbonate chemistry of the natural communities was manipulated chemically and the samples were returned to the ice from where they were taken and incubated in situ for up to 8 days.

Findings
Antarctic spring and summer sea ice brine communities tolerated a wide range of pH conditions (7-9) with only small, non significant, decreases in growth rate above 8.5 and below 7.5. Photosystem II parameters (Fv/Fm, rETRmax) were unaffected by pH. Separate in situ experiments that held pH constant but used high pCO2 showed no growth impairment.

Conclusions
Ice algae are naturally exposed to a wide range of pH and pCO2. Manipulating these parameters well above predicted end of century levels had little effect.