Global warming: Oceans could absorb far more CO2
The ocean's plankton can suck up far more airborne carbon dioxide (CO2) than previously realised, although the marine ecoystem may suffer damage if this happens, a new study into global warming says.
The sea has soaked up nearly half of the CO2 that has been emitted by fossil fuels since the start of the Industrial Revolution. The gas dissolves into surface waters and is then transported around the oceans.
But a key role is played by plant micro-organisms called phytoplankton, which take in the dissolved gas at the ocean's sunlit surface as part of the process of photosynthesis. This plankton dies and eventually sinks to the ocean floor, thus storing the carbon for potentially millions of years.
One of the big questions is how much more of CO2 the sea can absorb. If, like a saturated sponge, the oceans cannot take up any more, atmospheric concentrations of CO2, the principal greenhouse gas, would sharply rise.
In an innovative experiment reported on Sunday in Nature, researchers closed off part of Raune fjord in southern Norway to see how plankton reacted to different levels of CO2.
They used nine large enclosed tanks of seawater that were exposed to CO2 concentrations likely to prevail over the next 150 years.
To feed the plankton, the researchers added nutrients to simulate food usually brought up by ocean currents and upwelling, and then monitored plankton levels over the next
24 days. The investigators found that, the higher the CO2 level, the more the plankton bloomed.
The organisms were able to gobble up to 39 per cent more dissolved carbon compared with today, but did not need any additional nutrients to achieve this.
The paper, though warns that algal blooms could inflict oxygen depletion in some parts of the ocean while rising carbon levels may cause imbalance in primary nutrients.