Researchers at the University of Toronto have identified the mechanism responsible for the formation of temperature and salinity “steps” in the Arctic Ocean, solving a mystery that has puzzled oceanographers and climatologists for more than half a century.
Understanding how these vertical structures work promises to shed more light on the causes and consequences of the rapid loss of Arctic sea ice amid climate change.
“Our discovery of a novel mechanism of hydrodynamic instability provides insight into the formation of trap-like structures as a result of the mixing of warm saltwater and cooler freshwater,” said Yuchen Ma, a Ph.D. candidate in the Department of Physics of the Faculty of Arts and Sciences and lead author of a study published in Physical Assessment Liquids describing the findings.
“These structures were first observed in the late 1960s, but the mechanism responsible for their existence has never been explained.”
These step-shaped variations in temperature and salt concentration, known as thermohaline steps, are common in many regions of the global ocean.
The findings reported in Physical Assessment Liquids– which have received significant positive responses from the research community – fully verify a previous analysis by the same authors published in the Journal of Fluid Mechanics in 2020 that documented the existence of this new hydrodynamic instability. The verification was achieved by designing a series of direct numerical simulations of turbulence in the Arctic Ocean to better understand global ocean circulation.
“The ocean is usually seen as a very chaotic and turbulent environment, so it’s striking to see such highly defined salt layers and heat in it,” Ma says.
The heat flow from the ocean to the overlying sea ice is greatly enhanced by the presence of thermohaline stairs. Thus, understanding the trapping process in the polar oceans is important for developing future projections of global warming and informing efforts to reduce sea ice loss.
“In this era of global warming, it is a widely recognized fact that the loss of the Arctic Ocean ice sheet is a critical aspect of this global process,” said university professor W. Richard Peltier, of the Department of Physics, a co-author of the study. author of the studies and Ma’s Ph.D. manager.
“While the extent to which trapping contributes to this loss has yet to be quantified, we can certainly say that the ocean component of the climate models used to make projections of global warming cannot resolve the trapping process.”
The research builds on previous work that focused on understanding global ocean circulation under glacial conditions from 30,000 to 70,000 years ago.
In the previously developed model of the glacial climate, it was shown that the rapid transitions from cold to warm weather were caused by a large “hole” in the sea ice cover of the North Atlantic as a result of heat flow from the ocean into the sea ice. . The magnitude of this heat flow was determined by the assumption that a staircase had formed in the ocean below.
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Yuchen Ma et al, Thermohaline turbulence instability and thermohaline trap formation in the polar oceans, Physical Assessment Liquids (2022). DOI: 10.1103/PhysRevFluids.7.083801
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