Over 300,000 images from the US Navy are crucial for Ryan North's research on collapsing ice shelves and glacial melt.
For more than fifty years, US Navy cartographers photographed Antarctica from the air, producing over 300,000 high-quality images on large format film, mapping nearly every part of the continent between 1946 and 2000.
Ryan North, a PhD candidate at the University of Wollongong's School of Earth, Atmospheric and Life Sciences, found this archive invaluable for studying Antarctica's landscape evolution and climate impacts.
A new research paper, co-authored by Professor Timothy Barrows of UNSW Sydney, titled "High-resolution elevation models of Larsen B glaciers extracted from 1960s imagery," was published on July 8 in Scientific Reports. It details Ryan's meticulous work on how ice shelf collapse and glacial melt contribute to rising sea levels.
Using the historical imagery, now freely available at the Polar Geospatial Center at the University of Minnesota, Ryan focused on the Larsen-B Ice Shelf's collapse in 2002, which spanned 3250 square kilometers, an area the size of Greater Sydney and Wollongong combined.
Ice shelves are thick, floating ice bodies attached to land that can remain stable for millennia under the right conditions. While their collapse doesn't directly cause sea-level rise, they act as barriers for glaciers, and their removal allows glaciers to release massive ice volumes into the ocean, leading to rising sea levels.
After an ice shelf collapses, tributary glaciers, which flow into an ice shelf, accelerate and thin without the ice shelf's protection.
Ryan used historical images to measure the ice in five glaciers 35 years before the Larsen-B ice shelf collapse. He constructed an accurate 3D model of the landscape using over 850 photos and found that the glaciers remained largely unchanged between 1968 and 2001, just before the collapse.
"After the collapse, I measured at least 35 billion tons of land-based ice lost to the ocean from five glaciers, with 28 billion tons from Crane Glacier alone. This is equivalent to every person on Earth pouring out a one-liter water bottle daily for 10 years," Ryan said.
Ryan, also an Associate Investigator in the Australia Research Council's Securing Antarctica’s Environmental Future research initiative, emphasized that understanding glacial melt helps predict future sea-level rise. However, long-term perspectives on Antarctica's landscape shifts have been difficult to obtain.
Since the 1970s, seven out of twelve ice shelves on the Antarctic Peninsula have rapidly collapsed or significantly retreated due to unusually warm temperatures. The Antarctic Peninsula is one of the fastest-warming regions on Earth, with an average annual air temperature increase of 2.5°C from the 1950s to the 2000s and substantial subsurface water warming.
Difficult field conditions, remote locations, and persistent cloud cover, which interfere with satellite measurements, make long-term observations rare. However, historical images like those taken by the US Navy can extend glacier records by decades. The 1960s imagery's high resolution rivals that of modern satellites.
Ryan said the US Navy's historical imagery is a treasure trove for researchers studying Antarctica's changes over the decades, particularly in light of climate change. The 850 images he used are just a fraction of the vast archive.
"The information in these images about such a remote and often inaccessible location is priceless. They can show sea ice extent, penguin colonies, moss growth, or freshwater lakes from up to 80 years ago. Archived data can be incredibly valuable, and there are another 299,000 images waiting to be analyzed."
The University of Wollongong is committed to the United Nations Sustainable Development Goals, aiming for a better and more sustainable future for all. This project addresses Goal 13, Climate Action, and Goal 14, Life Below Water.
