A new applied mathematical theory could improve our understanding of how sea ice affects global climate, potentially enhancing the accuracy of climate predictions.
The authors of a new article published in the Proceedings of the Royal Society A offer fresh perspectives on how heat passes through sea ice, a crucial factor in regulating Earth’s polar climate.
Noa Kraitzman, a Chair Professor of Applied Mathematics at Macquarie University and the study’s lead author, states that the research addresses a fundamental gap in current climate modeling.
“Sea ice covers about 15% of the ocean surface during the coldest season, when it is at its greatest extent,” Kraitzman says. “It is a thin layer that separates the atmosphere and the ocean and is responsible for the transfer of heat between the two,” he adds.
Sea ice acts as an insulating blanket over the ocean, reflecting sunlight and moderating heat exchange. As global temperatures rise, understanding the behavior of sea ice will become increasingly important for predicting climate changes.
The study focuses on the thermal conductivity of sea ice, a critical parameter used in many global climate models. The movement of liquid brine inside the sea ice, which could potentially increase its heat transport, has not been accounted for in previous models.
Kraitzman says that the unique structure of sea ice, together with its sensitive dependence on temperature and salinity, means that it is a challenge to measure and predict its properties, specifically its thermal conductivity.
“When looking at sea ice on a small scale, what makes it interesting is its complex structure, because it is composed of ice, air bubbles and brine inclusions,” he explains.
“When the atmosphere above the ocean becomes extremely cold, below minus 30 degrees Celsius, while the ocean water remains around minus 2 degrees, this creates a large temperature difference and the water freezes from the top down,” he continues.
“As the water freezes rapidly, it pushes the salt out, creating a matrix of completely frozen water ice that traps air bubbles and pockets of very saline water, called brine inclusions, surrounded by almost pure ice,” he adds.
These dense brine inclusions are heavier than the ocean’s fresh water, which results in convective flow inside the ice, creating large “chimneys” through which liquid salt exits.
More accurate predictions of future conditions in polar regions
The research builds on earlier field work conducted by Trodahl in 1999, which first suggested that fluid flow within sea ice could increase its thermal conductivity. Kraitzman’s team now provides mathematical evidence of this phenomenon.
“Our mathematics definitely show that this increase should be expected when convective flow begins within sea ice,” he states.
The model also provides a way to relate the thermal properties of sea ice to its temperature and salinity, allowing theoretical results to be compared with measurements.
Specifically, it provides a tool to be used in large-scale climate models, potentially leading to more accurate predictions of future conditions in polar regions.
Arctic sea ice has been rapidly decreasing in recent decades. This loss can lead to a feedback cycle: as more dark ocean water is exposed, it absorbs more solar light, leading to more warming and further ice loss.
The loss of sea ice can affect weather patterns, ocean circulation, and marine ecosystems far beyond the polar regions.
Kraitzman states that understanding the thermal conductivity of sea ice is important for predicting its future.
The researchers note that, although their model provides a theoretical framework, more experimental work is needed to integrate these results into large-scale climate models.
The study was carried out by mathematicians from Macquarie University in Australia, the University of Utah, and Dartmouth College in New Hampshire, USA.
It was supported by funds from the United States National Science Foundation.
