Secrets beneath the ice
It’s an odd thing to consider — but we know less about the oceans beneath the Antarctic ice shelves than we do about the surface of Mars.
Covering just under half of the continent’s coastline, these shelves hide the least-measured ocean water on Earth, and few observations have been taken in the pristine waters beneath them.
There is an obvious reason — these giant floating glaciers are hundreds of metres thick, making it very hard to get under them. But the need to do so is increasingly urgent.
Amid the warming of climate change, measurements of ocean temperatures are a crucial part of climate research.
Almost all the excess heat we’ve pumped into the atmosphere — 96 per cent — has gone into oceans.
The Southern Ocean has absorbed more than half — a vast, cold but ultimately temporary buffer against rising land temperatures.
“The most challenging problem facing Southern Ocean oceanographers and engineers is a lack of instruments specifically designed to make measurements of deep ocean properties beneath floating glaciers and ice shelves,” Otago University’s Dr Inga Smith explained.
Sensors are designed for broad use in temperate and tropical waters — but not for the extremes of Antarctica.
A fascinating innovation is being developed by Smith and colleagues, however.
A study in the McMurdo Sound in the 2020/21 summer aims to understand how to overcome two features of the ice shelves — small, freefloating ice crystals known as frazil, and what’s called “supercooled water”.
Beneath the Antarctic sea ice and ice shelves, the water is often colder than freezing point — yet manages to stay in liquid form.
Smith wants to learn more about frazil, and the snap-freezing of super-cooled water, as both are stopping scientists from getting highprecision measurements of some of the key ocean parameters needed for climate models.
With collaborators Dr Britney Schmidt from Georgia Tech in the United States, Professor Lars Smedsrud from the University of Bergen in Norway, and Dr Greg Leonard from the University of Otago, Smith’s team will design a high precision supercooling measurement instrument, or HiPSMI.
This pumped system, fitted with sensors, will take measurements very close to where ice meets water, and capture factors such as salinity and temperature to calculate supercooling.
Smith said the HiPSMI will then be installed into an underwater robot, the Icefin.
“By pushing ocean engineering to extreme limits, we will determine the influence of frazil crystals on measurements of in situ supercooling,” she said.
It will revolutionise the understanding of supercooled waters by providing an indicator for future climate observations.
The research is supported with a $954,000 grant from the Marsden Fund.
Jamie Morton will travel to Antarctica in early January. He’ll be regularly filing articles from the ice and over the coming weeks.