Underwater mapping reveals insights into melting of Antarctica’s ice shelves

Underwater mapping reveals insights into melting of Antarctica’s ice shelves

Subject: Geo

Sec: Climatology

Context:

New research documents never-seen-before shapes formed at the base of a West Antarctic ice shelf. An autonomous underwater vehicle found these features — including tear-shaped indents — exclusively in areas with higher melting rates by underlying warm ocean water.

Ice shelf:

• An ice shelf is a mass of glacial ice, fed from land by tributary glaciers, that floats in the sea above an ice shelf cavity.
  • An ice sheet, such as theWest Antarctic ice sheet, covers vast land areas, holding a substantial amount of freshwater
  • The two major ice sheets in the world, Greenland and Antarctica,collectively possess around two-thirds of the Earth’s freshwater.
• When ice sheets gain or lose mass, they respectively contribute to a fall or rise in global mean sea levels.

Dotson Ice Shelf:

• Dotson Ice Shelf is part of the West Antarctic ice sheet and next to Thwaites Glacier, which is considered to have a potentially large impact on future sea level rise due to its size and location.
• Brought to the Amundsen Sea through ocean circulation, warm salty water is a significant driver of ice melt and, thus, sea level rise.
• This bottom-up melting, called basal melt, thins and hollows out cavities at the base of floating ice shelves, reducing or eliminating structural support for grounded ice that flows into them.
• The physical dynamics of basal melt have been poorly understood because the process occurs in deep water under ice — an environment best explored by autonomous vehicles.
• Basal melt patterns at the base of the Dotson Ice Shelf (DIS) located in West Antarctica’s Amundsen Sea.

Findings:

• From January to March 2022, the team sent an AUV with multibeam sonar up to 17 km into a basal melt cavity to chart its topography over 140 sq. km.
• They found some things as expected, for example the glacier melts faster where strong underwater currents erode its base.
• Using the submersible, they were able to measure the currents below the glacier for the first time and prove why the western part of Dotson Ice Shelf melts so fast. They also found evidence of very high melt at vertical fractures that extend through the glacier.
• During the expedition, the vehicle also recorded data about the salinity, temperature, and currents of the water below the ice shelf.
• Overall, the findings indicate that previously unquantified basal melt mechanisms are happening beneath Dotson Ice Shelf and likely other ice shelves.