Plankton blooms devour carbon in dust storm aftermath

Australia’s recent extreme dust storms, a likely indicator of climate change, might ironically also have produced a would-be solution to global warming in the form of ocean life-based carbon capture.

The dust storms seem to have provided an unexpected benefit to the environment in Sydney Harbour and the Tasman Sea, according to scientists from the University of Sydney’s Ocean Technology Group at the Faculty of Engineering.

“Nutrient rich topsoil, like the three million tonnes dumped on Sydney at the end of September, contains up to one per cent as nutrients such as nitrogen and phosphates,” said Ian Jones, head of the Ocean Technology Group. “After the dust is deposited on the sea surface, the nutrients dissolve in the sunlit region of the ocean and are used by the phytoplankton to multiply.”

Measurements taken following the dust storm found a tripling of phytoplankton populations in Sydney Harbour and in areas 10 kilometres offshore.

“We estimate that as a consequence of this, the extra phytoplankton in the Tasman Sea will be capable of capturing eight million tonnes of carbon dioxide, about the equivalent of a year’s CO2 emissions from a coal-fired one gigawatt power station, or a month’s worth of emissions for the Munmorah Power Station on the Central Coast,” Jones said.

Jones said this carbon will slowly be exported to the deep ocean in the form of an additional two million tonnes of phytoplankton. As the phytoplankton moves through the food chain, this will in turn grow extra fish, thus benefiting the fishing industry.

Previous studies led by Jones have established that adding fertiliser nutrients to the sea promotes the growth of naturally occurring phytoplankton near the surface of the ocean. The quantity of phytoplankton is limited only by the shortage of nitrogen in the ocean.

For some time now, the Ocean Technology Group has been planning an experiment that replicates the dust deposition in the Tasman Sea.

“Our intention is to inject 2.5 tonnes of nitrogen (in the form of urea) into the upper ocean in order to increase the amount of phytoplankton in a controlled patch away from shore near the edge of the continental shelf,” said Rob Wheen, an associate professor in civil engineering. “Satellite remote sensing will be used to monitor the patch of enriched water. This sensing can detect the chlorophyll in phytoplankton. We want to demonstrate safe and practical ways of broadcasting the nutrients. We see this as a precursor to larger scientific experiments in the ocean.”