Ghost Ice Shelves
Nick Frearson, Gravimeter Instrument Team, Lamont-Doherty Earth Observatory:
PUNTA ARENAS, Chile–Not all rides in the DC-8 are smooth and effortless. Our flight down the Thwaites Glacier was a race against weather, with the stomach-churning quality of a carnival ride. Both the Thwaites and Pine Island glaciers flow into the Amundsen Sea. This section of Antarctica, along the western coastline just below the continent’s peninsular arm, has been an intense focus of the ICE Bridge mission.
Icebergs that have broken off Thwaites Glacier might look like stepping stones in this image, but up close these icebergs loom approximately 100 feet above the water. The open water around the icebergs can remain open throughout austral summer, yet just beyond, the sea ice remains as far as you can see.
Mt. Murphy was visible as we flew over Pine Island Glacier and its grounding line, the point where the glacier transitions from land to sea. We flew just inland of the grounding line to measure the glacier’s ice surface elevation with the ATM laser and the ice depth with the radar. These measurements will tell us how much ice is crossing the grounding line.
We had been given old area maps for guidance as we flew over the ice. It was startling to see bays with floating ice-shelves on the map now appear as open water. One bay over from Pine Island, an ice shelf appeared to have almost completely disappeared; what had once jutted prominently into the sea was now a thin ribbon of bright white glued tightly to the coastline. The wind had long since blown away any vestige of the old ice-shelf . Flying over this ‘ghost’ ice shelf is a reminder of the rapid changes taking place here.