Scientists Reconstruct Collapsed Antarctic Glaciers Using 1960s Aerial Photos
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Scientists Reconstruct Collapsed Antarctic Glaciers Using 1960s Aerial Photos

Scientists Reconstruct Collapsed Antarctic Glaciers Using 1960s Aerial Photos

The Larsen Ice Shelf in Antarctica has been breaking up for decades, but the collapse of Larsen B in 2002 was particularly dramatic. After at least 10,000 years of stability, much of the shelf collapsed, with consequences felt across the planet.

The extensive changes in Antarctica have been widely studied and publicized, but contextualizing and analyzing the impact of changing conditions in Antarctica on the rest of the world has been difficult. To address this, scientists used film footage from the 1960s to help understand how collapsing Antarctic glaciers affected global sea levels.

In a research article published in NatureRyan North and Timothy T. Barrows examine historical film images of Antarctica dating back to the 1940s and apply an advanced modern analytical technique called structure-from-motion (SfM) photogrammetry. The researchers say that “this technique creates digital elevation models (DEMs) by constructing 3D point clouds of matching features on overlapping images without the need for original camera positions or orientations.”

Satellite image showing mostly snow-covered land with visible dark waters and scattered icebergs. On the left side, darker patches of water are visible interspersed with white ice formations, while the right side of the image is dominated by a thick layer of clouds.
The collapse of the Larsen B ice shelf as seen from space on March 17, 2022 | NASA

As North and Barrows explain in their article on ConversationAn accurate understanding of the past is essential to predicting the future.

“To accurately predict how Antarctic glaciers will respond to future climate change, it is crucial to understand how they have responded in the past,” the researchers write.

Composite image showing different perspectives of Antarctic glaciers around the Larsen B Ice Shelf. Different maps in the panels show elevation changes, grounding lines, and glacier positions, highlighting areas such as the Melville, Crane, Mapple, Jorum, and Flask Glaciers.
Figure 1. Shows an example of superimposed historical aerial photographs from December 1968, 3D models derived from historical aerial photographs, and corresponding glacier outlines. The ice shelf outlines are from the SCAR Antarctic Digital Database.

A significant challenge is that Antarctica is remote, and collecting good data there is extremely expensive. While satellites are excellent for collecting data on much of the Earth’s surface, the Antarctic Peninsula is shrouded in clouds for most of the year. As a result, observations of the area are patchy and short-lived.

However, U.S. Navy cartographers took more than 300,000 aerial photographs of Antarctica, all of which are now freely available at the Polar Geospatial Center at the University of Minnesota as part of a large-scale mapping effort of the continent conducted between 1946 and 2000.

Large-format photos have extremely high resolution, so North and Barrows applied SfM photogrammetry to 871 specific photos from 1968 to create a historical record for the Larsen B region.

Selected images were taken on large 9×9 grayscale format on December 21, 23, and 27, 1968. The film was then scanned at 1000 DPI by the United States Geological Survey (USGS). 503 of the 867 images were used to construct data for the Jorum, Crane, Mapple, and Melville glaciers, and more than 360 were used to determine the elevation of the Flask Glacier. The images were also manually adjusted to reduce errors in the photogrammetric process, including changes in framing, exposure, contrast, and clarity.

“We use historical DEMs to precisely measure net surface elevation changes of the Larsen B (Jorum, Crane, Mapple, Melville, and Flask) glaciers between 1968 and 2021. For the same glaciers, we also calculate surface elevation differences between 1968 and 2001… Using accurate elevation differences, we provide new estimates of mass balance and sea level contribution spanning 53 years and discuss these measurements in the context of existing literature from before and after the collapse,” they explain.

The four-panel image shows satellite imagery of Crane Glacier, with boxes marked for areas of interest. Each panel gradually zooms in, culminating in a detailed view of surface debris and meltwater flow in the final panel.
Figure 2. Details of a high-spatial-resolution (1.6-meter pixel size) orthophoto mosaic covering the Larsen B region in December 1968. (A) Full extent of the orthophoto mosaic, (B) a magnified region on Crane Glacier, (C) a Crane Glacier tributary at even greater magnification, and (D) meter-sized surface debris and meltwater channels visible in the same Crane Glacier tributary.

As a result of their research, the duo pinpointed the precise elevation changes in distinct regions of Larsen B and detailed the remarkably small changes over the decades that ultimately led to the ice shelf collapse. They found that after Larsen B collapsed in 2002, the glaciers lost a staggering 35 billion tons of land ice. The largest glacier alone lost 28 billion tons, causing sea levels on Earth to rise by about 0.1 millimeters.

“That doesn’t sound like much,” the researchers admit. “But it’s the result of one glacier from one event. In other words, it’s the equivalent of every person on Earth pouring out a one-liter bottle of water every day for 10 years.”

A map showing the change in glacier surface elevation from 1968 to 2021 on the Antarctic Peninsula. Areas in red show significant elevation loss, particularly in the Mappie Glacier. Larsen B Inlet, Crane Glacier, and other landmarks are marked.
Figure 5. Shows the elevation change of Larsen B Glacier and its tributaries from 1968 to 2001. The net mass balance is labeled at the mouth of each tributary.

North and Barrow call the historical archive of aerial photographs “an invaluable resource waiting to be exploited,” and say the same process they used in this study could be used to analyze other ice shelves or glaciers, penguin colonies, vegetation expansion, and even direct human activity.

Antarctica’s ice shelves and glaciers will continue to evolve as climate change accelerates, affecting the rest of the planet. Of course, one of the most important steps toward solving this problem is understanding the problem itself.

Image sources: Unless otherwise noted, images in this article are from the Polar Geospatial Center and the United States Geological Survey. The study referenced is “High-resolution elevation models of Larsen B glaciers extracted from 1960s imagery” by Ryan North and Timothy T. Barrows.