Ocean currents and seabed shapes play a crucial role in the circulation of warm water beneath Antarctic ice shelves, contributing to their melting. A recent study by scientists at the University of East Anglia (UEA) has revealed this intricate relationship using an autonomous underwater vehicle to survey the Dotson Ice Shelf in the Amundsen Sea.
The research focused on the circulation of warm water and heat transport within ice shelf cavities, significant areas beneath ice shelves that were previously largely unknown. The team collected data from over 100 kilometers of dive tracks made by the underwater robot along the seabed in the Dotson cavity.
The findings, published in the journal Ocean Sciences, highlight that the upward transport of deep warm water to the shallower ice-ocean boundary in ice shelf cavities drives melting at the underside of the ice shelf. This melting makes the ice shelf thinner and less strong. Interestingly, the study revealed that most of the warm water under the Dotson Ice Shelf is not mixed upward but instead flows horizontally to the grounding line, where the glacier loses contact with the seabed and starts to float.
This horizontal flow means the water stays warm all the way to the grounding line, where it can directly melt the glacier. This process can cause the glacier to retreat, speed up, and lose more ice into the ocean, all of which contribute to global sea level rise.
During the mission, the researchers found warm, salty water below colder, fresher water. While it is known that warm water is transported upward by mixing, this study shows that the mixing and upward transport of warm water are strongest in the inflow areas to the east of the ice shelf, where the currents are faster and the seabed is steep, with a particularly significant gradient of the bedrock.
Current speeds recorded in this area by the Autosub Long Range (ALR) autonomous underwater vehicle, named Boaty McBoatface, were around 5-10 centimeters per second. The gradient was about 45 degrees in the steepest areas.
Dr. Maren Richter, the lead author, noted that the influence of current speed on mixing was expected to be higher than what was found. Instead, the shape of the seabed seems to be a critical factor. The study also revealed surprisingly warm water in the deepest part of the cavity, and researchers are now working to explain how and when it got there.
The data was collected over four missions in 2022, during which Boaty, equipped with sensors to measure water properties, traveled along the bottom of the ice shelf cavity, staying about 100 meters above the seabed for approximately 74 hours. These missions were challenging, especially with an instrument that can measure mixing, making this the first of its kind under the Dotson Ice Shelf.
Dr. Richter emphasized the value of these baseline measurements, which can now be compared to assumptions about mixing in regional and global models of ice shelf-ocean interactions. This will help scientists understand how these cavities are similar or different from each other.
Warm deep water that is mixed upward not only increases the temperature in the upper ocean but also transports nutrients and trace metals upward, which is vital for local algae blooms and the creatures that depend on them for food. While this study did not measure nutrient transport through mixing, the data can be used by other researchers to calculate the effects of mixing in the cavity.
The work was part of the International Thwaites Glacier Collaboration, a major five-year research program aimed at understanding ice loss causes and better predicting sea level rise contributions. It was funded by the UK's Natural Environment Research Council and the US National Science Foundation.
The paper, 'Observations of turbulent mixing in the Dotson Ice Shelf cavity,' by Maren Richter, Karen Heywood, Rob Hall, and Peter Davis, was published in Ocean Sciences on December 10, 2025.
