Researchers at the University of Toronto have identified the mechanism responsible for the formation of temperature and salinity “ladders” in the Arctic Ocean, solving a mystery that has baffled 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 new hydrodynamic instability mechanism provides insight into the formation of ladder-like structures that result from the mixing of warm saltwater and cooler freshwater,” said Yuchen Ma, Ph.D. candidate in the physics department of the College of Arts and Sciences and lead author of a study published in Physical examination fluids describing the findings.
“These structures were first observed in the late 1960s, but the mechanism responsible for their existence has never been explained.”
Known as thermohaline ladders, these stepwise variations in temperature and salt concentration are common in a wide range of regions of the global ocean.
The findings reported in Physical examination fluids—which have attracted a significant positive response 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. 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 generally thought of as a highly chaotic and turbulent environment, so it is surprising to see such strongly defined layers of salt and heat within it,” says Ma.
The flow of heat out of the ocean into the overlying sea ice is strongly enhanced by the presence of thermohaline ladders. Therefore, understanding the process of ladder formation in the polar oceans is important for developing future global warming projections and informing efforts to mitigate sea ice loss.
“In this era of global warming, it is a well-recognized fact that the loss of Arctic Ocean sea ice is a critical aspect of this global process,” said University Professor W. Richard Peltier, of the department of physics who is a co-author of the studies and Ph.D. of Ma. supervisor.
“While the extent to which ladder formation contributes to this loss remains to be quantified, we can say with certainty that the oceanic component of climate models used to project global warming cannot resolve the ladder formation process.” .”
The research builds on previous work that focused on understanding global ocean circulation under ice age conditions from 30,000 to 70,000 years ago.
In the glacial climate model developed earlier, it was shown that rapid transitions from cold to warm weather are caused by an extensive “hole” in the North Atlantic Ocean sea ice as a result of heat flowing out of the ocean into the ocean. sea ice. . The magnitude of this heat flux was determined by the assumption that a ladder had formed in the ocean below.
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Yuchen Ma et al, Thermohaline Instability-Turbulence and Thermohaline Ladder Formation in the Polar Oceans, Physical examination fluids (2022). DOI: 10.1103/PhysRevFluids.7.083801
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