Hektoria Glacier in Antarctica experienced a rapid retreat of over 8km in two months in late 2022, and a total retreat of about 25km between January 2022 and March 2023. A new study proposes this event could be the first modern observation of a glacier front resting on the seabed rapidly destabilising, retreating significantly faster than previously recorded grounded glaciers. However, other scientists contest this interpretation, suggesting the affected section of the glacier may have been floating, which would make the event less unusual. The disagreement centres on the precise location of the glacier's grounding line.
Hektoria Glacier Retreat
Satellite data indicates that Hektoria Glacier's front retreated by approximately 25km (16 miles) between January 2022 and March 2023. During a two-month period in late 2022, the glacier retreated by 8.2km. This rate of retreat is noted by the study authors as potentially nearly ten times faster than any previously recorded grounded glacier.
The Study's Findings and Hypothesis
Lead author Naomi Ochwat and her team suggest that the rapid retreat in late 2022 occurred while the glacier's front was "grounded," meaning it was resting on the seabed rather than floating. They propose this rapid change could be attributed to an "ice plain," a relatively flat area of bedrock where the glacier rests lightly. The hypothesis suggests that upward forces from ocean water could "lift" the thinning ice, leading to icebergs breaking off and a swift retreat of the glacier. The authors note that while this process has not been observed in modern times, markings on the seafloor suggest similar rapid ice loss events occurred in Earth's past.
Co-author Adrian Luckman stated that while the circumstances might be specific, this rapid retreat indicates what could occur in other areas of Antarctica where glaciers are lightly grounded and sea-ice influence diminishes. Dr. Ochwat added that understanding such processes is important for assessing potential impacts on sea-level rise, especially for larger glaciers like Thwaites, which holds enough ice to raise global sea-levels by 65cm (26in).
Historical Context of Hektoria Glacier
The region where Hektoria Glacier is located underwent significant changes starting in 2002 with the collapse of the Larsen B ice shelf in the eastern Antarctic Peninsula. This event involved the loss of approximately 3250 sq km (1250 sq miles) of ice shelf. Larsen B had previously acted to restrain Hektoria Glacier. Following its collapse, Hektoria Glacier's movement accelerated, and it thinned. The bay left by the ice shelf was subsequently filled with sea-ice fastened to the seabed, which provided some stabilisation for Hektoria. This stabilisation ceased in early 2022 when the sea-ice broke up, leading to further loss of floating ice from Hektoria's front through iceberg calving.
Scientific Disagreement
Other researchers have expressed differing views on the study's interpretation. The primary point of contention revolves around the precise location of the "grounding line," the point where a glacier transitions from resting on the seabed to floating in the ocean.
Dr. Frazer Christie, a glaciologist, noted that there is significant disagreement within the glaciological community regarding Hektoria Glacier's grounding line location due to challenges in obtaining accurate radar satellite data in the fast-flowing region. Dr. Christine Batchelor stated that if the affected section of the ice sheet was indeed floating, the event would represent iceberg calving from an ice shelf, which is considered a more common behaviour. She added that while the proposed mechanism and retreat rate are plausible in certain ice plain settings, uncertainty about the grounding zone's location at Hektoria leads to a lack of full conviction regarding this specific observation.
Broader Consensus on Antarctic Change
Despite the debate over the specific processes at Hektoria Glacier, there is scientific agreement that changes in the polar regions are occurring rapidly. Professor Anna Hogg emphasised that while there is disagreement about the process driving the change at Hektoria, there is consensus that changes in polar regions are rapid. She highlighted the importance of collecting more satellite data to better monitor and understand these changes and their implications for sea-level rise. Floating glacier tongues, known as ice shelves, are understood to be more susceptible to breaking up than grounded glacier fronts, largely due to erosion by warm ocean water from beneath.