Southern Ocean clouds and currents focus of Australian research vessel investigating climate change

article-body

The Investigator research vessel has embarked on its longest voyage yet with the goal of understanding the impacts of future climate change.

The 60-day trip to the Southern Ocean and sea-ice edge is the longest the Investigator has undertaken since it became operational a decade ago.

Scientists from the CSIRO, Bureau of Meteorology and the Australian Program Partnership (APP) will use the journey – as far as 65 degrees south – to investigate why deep ocean currents near Antarctica are slowing, how clouds form over the Southern Ocean, and the extent to which the Southern Ocean will continue to absorb heat and carbon dioxide.

Dr Steve Rintoul, co-chief scientist of the research voyage known as Multidisciplinary Investigations of the Southern Ocean (MISO), explained that understanding the ways in which the Southern Ocean was sensitive to change would assist the team in anticipating how future climate and sea levels would change.

For example, he said the Southern Ocean acted as a sort of “handbrake on climate change” by taking up vast amounts of heat and carbon dioxide – meaning that these factors had a “profound influence” on global climate patterns.

“What’s amazing about the Southern Ocean is that everything is interconnected – we can’t hope to understand how the region influences climate unless we measure each piece and how it fits with the other parts of the system,” he said.

Climate change impacts are affected by any changes to the links between physics, biogeochemistry, plankton, aerosols, and clouds.

Rintoul added the investigation would explore between the deep ocean (as much as six kilometres below the water’s surface) and low-lying clouds (two kilometres above the atmosphere).

Co-chief scientist Dr Annie Foppert from the University of Tasmania said that the Southern Ocean acted as an absorber of more human-generated heat and carbon dioxide than any other earth latitude band. The study would consider what capacity the Southern Ocean head to continue acting as a “climate shock absorber”, she said.

“A key question is whether the Southern Ocean will continue to remove large amounts of our heat and carbon from the atmosphere, or will the Southern Ocean ‘sink’ become less effective as the climate warms,” Foppert said.

In terms of the ocean currents that control climate, scientists are also concerned about a reduction in dense water from the meltwater of the Antarctic Ice Sheet slowing those currents.

The Investigator research team will be deploying a dozen deep-diving robots to collect data that can be compared to earlier measurements and determine how climate and sea level rise will change as a result of this shift.

“These new floats, able to collect measurements down to six kilometres below the sea surface, will allow us to track how the ocean is changing for the next five years by profiling the full depth of the ocean,” Foppert said.

“Observing the deep ocean so regularly and over such large swaths was impossible before this new technology.”

The Investigator RV left Hobart last week and is sailing south to the edge of Antarctic ice before returning to Fremantle in early March.

The MISO voyage is possible thanks to a CSIRO Marine National Facility grant of sea time on the Investigator and supported by the national collaborative research infrastructure strategy (NCRIS).

The journey is supported by the AAPP, a 10-year program established in July 2019 and led by the University of Tasmania with core partner organisations including the CSIRO, the Australian Antarctic Division (AAD), and the Bureau of Meteorology.

The MISO team will also lead research to measure gasses and particles (also known as aerosols) released by phytoplankton, to examine the effect this phenomenon has on cloud formation.

The University of Tasmania’s Dr Marc Mallet said climate science and model projection had not yet deeply considered the effects of cloud formation in the southern hemisphere.

“This voyage will test the hypothesis that aerosols released by phytoplankton ’seed’ clouds and explain the unique properties of the Southern Ocean atmosphere,” he said.