Underwater robot gives insight into ice shelf cracks

In recent years, the melting of Antarctica's ice has accelerated, and humans are facing a serious threat from rising sea levels. Because the state of the ocean at the bottom of the ice shelf and its interaction with the ice directly affect the stability of the ice shelf, in order to more accurately predict future trends, scientists urgently need to learn more about the bottom environment of the major Antarctic ice shelves.

Recently, a research team from Cornell University used an underwater robot called Icefin to deeply explore the submarine cracks at the bottom of the Ross Ice Shelf, the largest ice shelf in Antarctica, for the first time. They found that there are complex internal circulation patterns here, which provides a new perspective for us to understand the role of ice shelf cracks.

Importance of ice shelf cracks

Antarctica has 90% of the land-based ice. If all the ice in Antarctica melts, the sea level will rise by about 65-70 meters. Therefore, the stability of the Antarctic ice sheet is crucial to the global sea level.

There are a large number of cracks at the bottom of the ice shelf, which is the most active area of ​​ice-sea interaction. The cracks allow warm water to enter the bottom of the ice shelf, while also allowing cold water and meltwater from the ice layer to flow out. This exchange directly affects the melting and refreezing of the ice shelf.

However, directly observing the interior of the ice shelf cracks has always been a huge technical challenge. The cracks are narrow and tortuous, and the water depth can reach several thousand meters. Traditional underwater submersibles are difficult to enter. Scientists can only rely on numerical models for calculations, but the lack of direct verification will lead to low accuracy.

Icefin Robot

To overcome this limitation, the Cornell University research team chose a new type of slender underwater robot, Icefin, for direct detection.

Icefin is about 12 feet long and only 10 inches in diameter. It is equipped with thrusters, cameras, sonar and sensors to measure parameters such as water temperature, salinity and pressure.

In this experiment, the research team used hot water drilling to make a 1,900-foot-deep hole in the Ross Ice Shelf, near the intersection of the ice shelf and the Kambo Glacier. This is an ideal place for the research team to study the long-term effects of underwater conditions because the Ross Shelf is older than previously explored ice shelves, making it more representative of other ice shelves in Antarctica, while the Kambo Ice Stream is stagnant.

During three dives, Icefin was driven into a crevasse, down to a depth of 150 feet, to measure various hydrological parameters there. This was the first time that humans directly probed the environmental conditions inside an ice shelf crack.

Complex internal circulation

Through this direct measurement, the researchers found that there is a very complex water flow cycle inside the ice shelf cracks. In addition to the expected upwelling and downwelling flows, there are also strong lateral water jets entering the cracks. Cold water descends into the cracks from the lower side and circulates up inside the cracks.

They found that the melting and refreezing rates of ice layers on both sides of the cracks at different depths are also different, which is directly related to the complex movement of water flow. The strong lateral jet at the bottom of the crack brings in hot water, which accelerates the melting of the ice layer here. However, due to the desalination cooling effect, the ice layer refreezes faster at the top of the crack.

"We were surprised to see how complex and varied the patterns of water motion were in such a small space," said Peter Washam, a polar oceanographer and research scientist in Cornell's Department of Astronomy. "Each feature revealed a different type of circulation or relationship between ocean temperature and freezing."

Improving ice shelf stability prediction models

Traditional models of melting at the bottom of ice shelves are too simplified to reflect the complex hydrodynamic processes in reality. This direct observation confirmed the existence of complex three-dimensional circulation and uneven ice-sea interaction inside the cracks.

This research has broken through the long-standing technical barriers to directly detecting the internal environment of ice shelf cracks. The application of Icefin has opened up a new era in the study of the subglacial world. In the near future, we are expected to use various new underwater robots to directly observe the bottom cracks of Antarctic ice shelves on a large scale and establish a high-resolution three-dimensional observation network. This will greatly improve our ability to predict changes in Antarctic ice volume and sea level rise.

The IceFin team was led by Britney Schmidt, associate professor of astronomy, earth and atmospheric sciences and Cornell engineering and director of the Planetary Habitability and Technology Laboratory. The study also included members of a New Zealand research team led by Christina Hulbe, a professor at the University of Otago.

The research was funded by the RISE UP project (Ross Ice Shelf and Europa Underwater Explorer), part of NASA's Planetary Science and Technology for Analog Research program, with logistical support provided by the National Science Foundation through the U.S. Antarctic Program.