Ocean heatwave 2011. Photo: CSIRO
Australian and Indian scientists have teamed up to identify the causes and impacts of so-called marine heatwaves such as the devastating pulse of warm water that swept down the West Australian coastline in 2011.
During that event, water temperatures soared to 5 degrees above long-term seasonal averages for a two-week period – and were more than 3 degrees higher for an extended time – triggering large-scale fish kills and coral bleaching.
To study the interplay of biology and physics in the Indian Ocean, including how circulation is changing as the planet warms, CSIRO has joined India’s National Institute of Oceanography and the Indian National Centre for Ocean Information Services to launch 15 sophisticated robot floats in mid-2014.
Coral bleaching can devastate reef life, as seen here off Queensland. Photo: Supplied
Australia and other nations already operate more than 3600 of the Argo floats to collect data on temperature and salinity in the world’s oceans. The pilot scheme, which has the potential to double in size, involves floats equipped with extra sensors to gather a wider range of information on levels of oxygen, chlorophyll and dissolved organic matter.
“We’ll probably have more data from these floats in a decade’s time than we have in the whole past century from ships,” said Tom Trull, a professor at the University of Tasmania and a senior principal research scientist at CSIRO.
Oxygen changes will be one focus, with levels in the deep ocean apparently decreasing over the last century as temperatures rise and circulation alters. Regions off north-west India and in the Bay of Bengal have large patches of ocean with little or no oxygen.
More than 3600 Argo buoys have been deployed globally.
By adding oxygen sensors, “we can figure out what those changes in circulation mean for the health of the deep sea”, Professor Trull said.
Other sensors will detect levels of phytoplankton, microscopic plants that form the basis of the aquatic food chain, and the zooplankton that feed on them.
“It will probably give us an idea of which year, in which place, we’re likely to get strong amounts of fish production,” Professor Trull said.
How Argo floats work. Photo: CSIRO
Changes in sea-surface temperatures in the Indian Ocean, the world’s third-largest, can have a big influence on the Australia’s weather. Warmer-than-normal waters off north-western Australia, as seen last winter, typically trigger increased flows of moisture over the continent and above-average rains over south-eastern states.
Australian scientists are keen to understand more about the “Ningaloo Nino”, named after the Ningaloo Reef off Coral Bay in WA, when waters in the region are unusually warm. It serves as a counterpart to the El Nino-Southern Oscillation – the main climate driver over the Pacific Ocean.
While Australia’s wheat production can be correlated to an El Nino phase, which typically results in reduced rainfall over eastern Australia, relatively little is known about how ocean ecosystems including fisheries are affected by changing weather patterns, Professor Trull said.
“We don’t understand what the links might be,” he said. “These kinds of sensors may get us that kind of data.”
Each specially equipped Argo buoy costs about $50,000 and can collect data down to 2000 metres below the surface as they drift on the ocean currents. Depending on the task, the buoys surface between four times a day to once every 10 days to transmit information to satellites.
Each “profile” sent costs about $50, far cheaper than ship surveys. Sending a vessel might take 100 readings in a month but cost $50,000-80,000 per day, Professor Trull said.