Tides may be responsible for up to 69% of the melting of ice under the Antarctic ice shelf

Ice shelves – sea glaciers in the Antarctic ice sheet – are melting, and not only because of a warming atmosphere. In one fell swoop, Antarctica’s ice shelves are fighting a losing battle against rising temperatures on the surface and beneath their bodies.

Ocean heat and pressure contribute to this phenomenon, called basal melting, but tides may play a larger role than previously thought, according to a multi-institutional research collaboration based in China. Based on observational data in Breeds Bay, the first of the tidal currents and their role in basal melting, the researchers found that tidal currents from the third largest bay in Antarctica may be responsible for up to 69% of the basal melting in the Ameri. ice shelf.

The team published its findings on August 15 Ocean, Earth and Atmospheric Research.

Corresponding author Zhaomin Wang, Professor of Southern Marine Science and Engineering, said: “Tides play a major role in regulating circulation and water properties around Antarctica, yet tidal currents and corresponding effects in Breedes Bay have not been measured using observational datasets.” Guangdong Laboratory (Zhuhai) in China.

“The Amiri Ice Shelf Oceanographic Research Experiment and the Chinese Antarctic Expedition provide long-term hydrographic observations for ten anchorages over the continental shelf and six well sites drilled across the Amiri Ice Shelf.”

The moorings are anchored to the sea floor at Breed’s Bay. The measurements from the moorings and wells allowed the researchers to monitor the characteristics of tidal currents in the Gulf. They used these observations to inform two numerical modeling analyzes to quantify tidal contributions to shelf basal melting.

However, Wang noted that the observations did not include significant long-term information about velocity, so they used simulated velocity in the lower ice shelf cavity of the models, which may have distorted the true contribution of tidal currents to baseline melt.

Although Breed’s Bay is the third largest around Antarctica, the rise and fall of tides – tidal currents – are much weaker than the two larger bays, averaging only three centimeters per second.

“These weak tidal currents are not expected to play an important role in regulating the circulation and hydrographic characteristics of Breedes Bay,” said Chengyan Liu, first author. “However, the maximum observed tidal velocity of about 11 centimeters per second occurs at the front of the Amery Ice Shelf, and the maximum average tidal kinetic energy—the intensity with which the tides rise and fall—is about 31% of the total Kinetic Energy Over the Outer Continental Shelf”.

Liu added that at the well sites, a tidal-like temperature pulse was identified in the ocean layer adjacent to the core surface of the Amery Ice Shelf. Combined, these variables allowed the researchers to estimate the maximum tidal contribution to shelf basal melting at 69%.

“Because there are no long-term observations of velocity in the sub-ice shelf cavity, tidal-induced melting in this study may be overestimated due to uncertainty in the modeling results,” Liu said. “Our understanding of basal mass balance of the AIS could benefit from more long-term observations and advanced numerical modeling. However, this study still provides validation of criteria for sensitivity experiments and open parametric constraints in future modeling studies focused on Breed’s Bay.”

According to Wang, researchers will continue to collect more long-term observations in the Gulf to enrich their understanding of how much tidal currents contribute to the underlying melting of the Amiri Ice Shelf.