Below the ice: monitoring Antarctic ice shelves

A guest blog by Carolyn Branecky Begeman

Over 90% of the world’s freshwater and 200 feet of sea level rise are held in Antarctic ice sheets. Ice shelves, structures of floating ice that are at the fringes of the ice sheet, slow the flow of Antarctic ice into the sea. When ice shelves thin or break into icebergs, the ice behind them accelerates, leading to sea level rise.

The author (right) and colleagues on deck in Antarctica next to a half-mile-thick borehole through an Antarctic ice shelf.

The author (right) and colleagues on deck in Antarctica next to a half-mile-thick borehole through an Antarctic ice shelf.

Because ice shelves are so important to sea level rise, we have been monitoring them closely, at least from the surface. When an iceberg the size of Delaware broke away from the Larsen C Ice Shelf in Antarctica, scientists and the public knew about it almost immediately. Satellite images of the ice shelf were collected every 6 days by the European Space Agency, and these images made it easier to detect the changes that were happening. We watched as the crack at the surface of the ice shelf spread from 2010 to 2017. We could see ponds of water collect at the surface when air temperatures rose above freezing, and we could even see liquid water in snow cover on ice shelves with satellite microwave detection.

Antarctic ice shelves face an existential threat not only from above, due to atmospheric warming from climate change, but also from below. Approximately half of the ice that enters an ice shelf ends up breaking off as an iceberg. The rest melts off the base of the ice shelf, which touches the ocean water. Although satellite and radar technologies can measure with how fast this bottom melting is happening, the ocean conditions that cause ice shelves to melt often remain elusive.

In the Southern Ocean, circulation patterns and the temperature and salinity of water masses have been changing in recent decades due to climate changes. Scientists think it is becoming easier for warm water masses to flow beneath ice shelves, which could increase the rate at which ice shelves melt. However, ocean monitoring below ice shelves has been limited because it is incredibly difficult to sample below the ice. To do so, we need to create a hole in an ice shelf to lower an instrument to the ocean waters.

In January 2015, a group of scientists that I was a part of did just that – we melted away a narrow hole in half a mile of ice to access the farthest reaches of the largest ice shelf in Antarctica, the Ross Ice Shelf. I found that the temperature and salinity of the ocean water that we observed was different than it was when it first flowed underneath the ice shelf, which might give us clues about ice-shelf melting and future sea level rise. It’s hard to piece these clues together because there are only four observations below an ice shelf the size of Spain.

Only four observations of the ocean below the Ross Ice Shelf have been collected in the last 40 years. The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project drilled the most recent hole to the ocean cavity below the Ross Ice Shelf.  Right: an aerial photo of the WISSARD field camp.

Only four observations of the ocean below the Ross Ice Shelf have been collected in the last 40 years. The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project drilled the most recent hole to the ocean cavity below the Ross Ice Shelf.  Right: an aerial photo of the WISSARD field camp.

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Although the ocean waters beneath some ice-shelves have been sampled more frequently, in general, these environments remain woefully under-sampled. Exciting technology has emerged that would allow us to monitor much more of the waters below the ice-shelf at comparatively low cost. Small, remotely-operated submarines have been sent to explore beneath the ice shelf of Pine Island Glacier, where the most rapid ice loss in Antarctica has occurred. We need to do the same for other ice shelves to assess this second emerging threat from climate change, changes in the ocean water masses that flow beneath them. The international community should develop a monitoring program for ice shelves to capture melting from the surface and underside. This is a necessary step to improve sea level rise predictions.

Carolyn Branecky Begeman is a PhD candidate in Earth and Planetary Sciences at UCSC. She has spent two field seasons in Antarctica and one in Iceland. She collects observations in hard-to-reach places and uses computer models to milk the most knowledge from these observations. Learn more at carolynbegeman.weebly.com.