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A Place Where Icebergs Go to Die

September 23, 2018

Today’s story is the answer to the October 2018 puzzler.

This could be a scene out of a spooky movie. But the reality is just as morbid for this coffin-shaped iceberg. After 18 years at sea, B-15T has entered a region where Antarctic icebergs go to die.

On September 23, 2018, when an astronaut on the International Space Station shot this photograph, iceberg B-15T had already left the Southern Ocean. It was spotted in the South Atlantic between South Georgia and the South Sandwich Islands. The second image shows a wide view, acquired the same day by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Icebergs like this are known to melt rapidly as they make their way north into warmer waters.

September 23, 2018
September 23, 2018                                                                                                                               JPEG


B-15T’s journey to this iceberg graveyard has been a long one. Its parent berg (B-15) first broke away from the Ross Ice Shelf in March 2000. It fractured over time into smaller bergs, many of which continued riding the Antarctic Coastal Current (counter-clockwise) around Antarctica.

By late 2017, the Weddell Sea gyre had redirected B-15T from its near circumnavigation and sent the berg drifting north. This third image was acquired in October 2017 by MODIS on NASA’s Aqua satellite. It shows the iceberg when it was near Elephant Island, an icy bit of rock located a few hundred kilometers north-northeast from the tip of the Antarctic Peninsula.

October 20, 2017
October 20, 2017                                                                                                                                      JPEG

The Antarctic Circumpolar Current, which funnels through the Drake Passage, then steered the iceberg toward the east and its current location. Water at this latitude—about 54 degrees South—is generally warmer than the Southern Ocean and deadly for icebergs. NASA/UMBC glaciologist Chris Shuman noted that Southern Hemisphere winter was just ending when the astronaut spotted the berg, so the return of abundant sunlight could further warm the water around it. The lack of sea ice in the vicinity of B-15T implies that the water was above the freezing point.

The spooky shape of B-15T was acquired long before it moved into this iceberg graveyard. For more than a decade, B-15 had numerous collisions—smashing back into the Ross Ice Shelf where it originated, hitting bedrock along the coast, and bumping into other tabular icebergs. Such collisions can be strong enough to abruptly fracture the crystalline ice and produce linear edges—similar to the rectangular iceberg that debuted this month near the Larsen C ice shelf and iceberg A-68. That iceberg is visible in the photograph below, acquired October 16 during an Operation IceBridge science flight.

October 16, 2018
October 16, 2018                                                                                                                                      JPEG

“This fracturing is akin to ‘cleaving’ a mineral crystal with a sharp tap of hammer,” Shuman said. Of course, the edges are not always so linear. Other bergs have edges that are curved. Some become jagged when the pull of gravity or the cutting action of waves causes ice to irregularly splinter.

“The coffin shape is accident of time and space, given the approximately 18.5-year voyage of B-15T,” Shuman said. “We can only guess at the forces that have acted on this remnant of B-15 along the long way around Antarctica.”

Astronaut photograph ISS056-E-195042 was acquired on September 23, 2018, with a Nikon D5 digital camera using a 800 millimeter lens and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 56 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. NASA Earth Observatory images by Lauren Dauphin and Jeff Schmaltz, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Airborne photograph by NASA/Jeremy Harbeck. Story by Kathryn Hansen.