New findings about ocean processes in the Antarctic show melting ice shelves and changes to sea ice could have catastrophic implications for the global climate.
A team of Australian researchers led by Dr David Gwyther at The University of Queensland has identified competing forces that control the formation of some of the coldest, densest – and most important – water on the planet.
“This very cold, salty water, called Antarctic Bottom Water, is formed by the freezing of the ocean surface in sea ice factories that we call polynyas,” Dr Gwyther said.
“This dense water sinks to the ocean floor where it flows northwards acting like a giant conveyor belt driving currents around the planet which influence the climate worldwide.
“Our study shows the formation of bottom water is a fine balance between strong coastal winds, sea-ice growth and the volume of fresh water released by melting ice shelves.
“The interaction between these processes determines how much dense water is formed and this balance could shift under climate change.
“Increased ice shelf melt, or reduced sea ice growth can weaken dense water production.
“Changes to dense water production might over time impact global ocean circulation and affect climate patterns such as rainfall in Africa or temperatures in Europe.”
Antarctic Bottom Water is formed at 4 known locations, and the research led by the School of the Environment focussed on Cape Darnley in East Antarctica, roughly 3,000 km from the Australian mainland.
“Until now we haven’t had a clear picture of what controls Antarctic Bottom Water formation at Cape Darnley,” Dr Gwyther said.
“We built an advanced regional ocean simulation that includes salinity, temperature, water currents, sea ice and wind data.
“We found 2 neighbouring systems played opposing and very delicately balanced roles in the production of bottom water.
“Meltwater flowing from beneath the Amery Ice Shelf freshens the water flowing northwards to Cape Darnley and suppresses dense water formation.
“Conversely, sea ice production in the nearby Mackenzie Polynya region between the Amery Ice Shelf and Cape Darnley increases salinity and strengthens dense water formation.
(Photo credit: The University of Queensland)
“These 2 systems influence Cape Darnley’s dense water formation in opposite directions.
“If the balance were to shift through more melting ice or a reduction in polynya activity, we could see major changes in how much dense water forms and flows into the global ocean.”
The team found that if Amery Ice Shelf melting doubles, dense water export decreases by about 7 per cent, while if sea ice production at Mackenzie Polynya shuts down, export decreases by around 36 per cent.
