Increasing ozone depletion in the Arctic and the 24-hour sunlight of its summer days have a surprising effect on plankton activity, new research suggests.
Instead of reducing plankton photosynthesis, as in the Atlantic, Mediterranean and Southern Ocean regions, researchers have found that UV-B solar radiation in the Arctic gives plankton communities a boost. This means greater CO2 uptake and a potential offset against the effects of warming Arctic waters on climate change in future.
University of Western Australia Oceans Institute Professor Susana Agusti says night is the key to this process. "In other environments, UV-B reduces plankton photosynthesis more than the activity of bacteria," she says.
"But our work has shown that without darkness, Arctic bacteria do not have time to recover from the damage they suffer from solar radiation. This decreases heterotrophic [carbon-emitting] activity, namely respiration, while allowing for the greater production of plankton, which serves to sequester carbon."
The predominant Arctic plankton species, Phaeocystis pouchetti, doesn't suffer the same UV-B damage as bacteria thanks to a mucus-like secretion that acts as a natural sunscreen.
Lead author Dr Lara Silvia Garcia-Corral says the findings could impact the 'five-degree threshold'. "When water temperatures reach five degrees Celsius, bacterial and biological activities in plankton alter, leading to communities switching from being CO2 sinks to CO2 sources," she says.
"But the possible effect of increased UV-B radiation has not been considered as yet and may partially compensate for the negative effects of warming on plankton communities in waters where significant levels of UV-B penetrate."
The study's surprising results support the value of in-situ testing.
"Previous research has been experimental in that it was hampered by the use of plastics or glass, which blocks UV-B radiation, or was conducted in laboratories using artificially-added UV," Agusti says. "Our research is the real product of the Arctic—of authentic conditions."
UV-B radiation in the Arctic has become an area of increasing interest in recent years due to an 11 per cent/decade decrease in the region's stratospheric ozone over the past two decades. This peaked in the spring of 2011 when data suggested the first signs of a hole in the ozone layer.