Marginal Detachment Zones: The Fracture Factories of Ice Shelves?

• Published in: Journal of geophysical research. Earth surface 2023-06, Vol.128 (6), p.n/a
• Main Authors: Miele, Chris, Bartholomaus, Timothy C., Enderlin, Ellyn M.
• Format: Article
• Language: English
• Subjects: Antarctica; Decoupling; Fjords; Floating ice; Fractures; Greenland; Ice; Ice calving; Ice shelves; Iceberg calving; Icebergs; Land ice; Rifting; Stresses; Vulnerability
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1029/2022JF006959

Along the lateral margins of floating ice shelves in Greenland and Antarctica, ice flow past confining margins and pinning points is often accompanied by extensive rifting. Rifts in zones of marginal decoupling (“detachment zones”) typically propagate inward from the margins and result in many of Earth's largest calving events. Velocity maps of detachment zones indicate that flow through these regions is spatially transitioning from confined to unconfined ice shelf flow. We employ the software package icepack to demonstrate that longitudinally decreasing marginal resistance reproduces observed transitions in flow regime, and we show that these spatial transitions are accompanied by near‐margin tension sufficient to explain full‐thickness rifts. Thus, we suggest that zones of progressive decoupling are a primary control on ice shelf calving. The steadiness of detachment zone positions may be a good indicator of ice shelf vulnerability, with migratory or thinning detachment zones indicating shelves at risk of dynamic speedup and increased fracture. Plain Language Summary The massive icebergs released from the ice shelves of Greenland and Antarctica all originate from fractures in the ice. Fracture occurs where extensional stresses are great enough to break the ice. We observe that zones of extensive fracture tend to coincide with regions where shelf ice flows just beyond lateral confinements such as fjord walls or islands, and that the fractures accrued through such zones often result in icebergs. In this study, we show that the high stresses within these zones occur as a result of a loss of contact with features at ice shelf edges. We propose that the regions where sidewall or island contact is lost may be an important indicator of future iceberg calving and changes in larger scale ice shelf stability. Key Points Many calving events originate as near‐margin rifts where ice shelves flow beyond lateral obstructions or boundaries Physical detachment from lateral obstructions is a major source of near‐margin tension and fracture Within shelf‐marginal detachment zones, thinning/changes to fracture patterns may presage ice shelf destabilization