Researchers have investigated how increased levels of ocean acidity and carbon dioxide concentrations have resulted in unexpected changes in marine biological production of organic gases that affect the Earth’s climate.
The study sheds light on several chemical processes that regularly occur throughout the world’s oceans and which may have the potential to help regulate the Earth’s climate and slow down global warming.
New Mexico Tech chemistry professor Oliver W Wingenter and his research colleagues have determined that by increasing atmospheric mixing ratios of carbon dioxide, the scientists were then able to make ocean surface waters three times more acidic than normal.
Other recent scientific studies have shown that ocean acidity is rising at a rate of about 100 times faster than at any known time, Wingenter said, but this newly published study links the effect of increasing ocean acidity to changes in phytoplankton ecosystems that consume and produce carbon dioxide and other organic “greenhouse gases.”
“Pronounced physiological changes in some phytoplankton have been observed during previous CO2 perturbation experiments,” said Wingenter. “And although the changes in ocean acidity can be predicted, the consequences for marine organisms, their ecosystems, and climate-relevant organic gas emissions are largely unknown.”
In their month-long field experiment, conducted in 2005, Wingenter and his research team used three sets of three large plastic bags – two metres in diameter, and filled to a depth of 10 metres with seawater – to simulate present-day carbon dioxide concentrations and ocean acidity, as well as CO2 levels that are expected to be found at the end of this century and the middle of the next one.
During the study, concentrations of dimethyl sulphide (DMS) and chloroiodomethane, which are produced by phytoplankton in the ocean water, were analysed, measured and recorded.
Wingenter found that marine micro-organisms produce DMS, which is a radiatively important gas. “In the atmosphere, DMS is rapidly oxidised to sulphur dioxide, which can form sulphate aerosols. As a result, emissions of DMS are a major source of cloud condensation nuclei in the clean marine atmosphere,” he said.
“In addition, chloroiodomethane and other iodocarbons produced by phytoplankton quickly react with sunlight in the atmosphere and end up releasing iodine that can destroy ozone and lead to aerosol nucleation,” Wingenter said.
The marked increases in the climate-relevant gases and ocean acidity observed in the study may be directly attributable to changes the phytoplankton’s environment brought on by adding more carbon dioxide, the researchers explained.
Wingenter pointed out that enhanced future production of these gases may contribute to planetary cooling and may eventually slow down global warming.
Said Wingenter: “This experimental study points to the need for similar work to determine the changes in other phytoplankton communities in response to future CO2 concentrations and any resultant changes in organic gas production.
“Combining future experimental and modelling efforts will lead to a better understanding of the feedback systems between the atmosphere and ocean in the future,” he added.
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