Pine Island Glacier once sat on top of the ridge, which slowed the flow of the glacial ice into the sea. In recent decades, though, the glacier thinned and disconnected from the ridge, which allowed the ice to flow more rapidly from land to sea.
The separation from the ridge also let in warmer water "from deep down in the water masses that circulate around Antarctica [that] hasn't been in contact with the ocean surface for a long time," said Christian Schoof of the University of British Columbia in Canada, who was not a part of the team that studied the glacier.
The warm waters can flood over the ridge and into a widening cavity that now extends to an area of about 390 square miles (1,000 square kilometers) under the ice shelf. Those warm waters are causing the bottom of the ice shelf to melt, resulting in continuous thinning and acceleration of the glacier, which could cause more of the ice that is currently on land to melt into the sea and contribute more to sea level rise.
Connection to climate change?
What caused the initial separation of the glacier from the ridge is uncertain.
Researchers only began to closely study Pine Island Glacier in the 1990s, so there are no direct observations of the glacier before and during its separation from the ridge. To learn more about that process, scientists will need to use ice cores (long cylinders of ice drilled from glaciers that show the successive layers of ice that formed over the years) and computer modeling to figure exactly what happened, Jenkins said.