Ice-flow patterns and precise timing of ice sheet retreat across a dissected fjord landscape in western Norway. (15th June 2019)

• Record Type: Journal Article
• Authors: Mangerud, Jan; Hughes, Anna L.C.; Sæle, Tone Herfindal; Svendsen, John Inge
• Is Part Of: Quaternary science reviews. Volume 214(2019)
• Page Start: 139
• Page End: 163
• Publication Date: 2019-06-15
• Subjects: Scandinavian ice sheet -- Fennoscandian ice sheet -- Ice-margin retreat rates -- Glacial striae -- Glacimarine terraces -- Ice-berg calving -- Glaciology -- Scandinavia -- Glacial geomorphology; Geology, Stratigraphic -- Quaternary -- Periodicals; Stratigraphie -- Quaternaire -- Périodiques; 551.79
• DOI: 10.1016/j.quascirev.2019.04.032
• Languages: English
• ISSNs: 0277-3791

Abstract

Abstract: We reconstruct patterns of ice flow and retreat of the southwestern Scandinavian Ice Sheet, from 2900 field observations of glacial striae and elevation measurements of 60 ice-marginal-deltas from a high-resolution LiDAR DEM. During the Last Glacial Maximum, ice flow was towards the west across the entire area, including across several-hundred meter deep north-south oriented fjords. During deglaciation, ice flow adjusted to topography and the dominant flow direction switched towards the south-west. We use a shoreline diagram constructed from relative sea-level curves to establish the age of each delta, which allows us to constrain the timing of retreat with almost decadal precision. Rapid ice sheet retreat commenced at the onset of the Holocene at 11, 600 cal years BP. Retreat rates were 160 m a −1 in the deepest fjords, 60–80 m a −1 in shallower fjords, and even slower for land-terminating margins. The fastest retreat rates, 240 m a −1 and 340 m a −1, were experienced in the largest fjords, Hardangerfjorden and Sognefjorden, which border the study area to the south and north. Crosscutting glacial striae indicate that calving bays developed during retreat along the widest fjords. The combination of complex fjord topography with fast ice-margin retreat by iceberg calving, led to isolation of ice remnants on islands and peninsulas, a process that accelerated the overall rate of deglaciation. Ice-margin retreat paused between 11, 300–11, 100 cal years BP, probably due to cooling during the Preboreal Oscillation. Highlights: Ice flowed across (not along) 700 m-deep fjords when the ice sheet was thick. Rapid ice-margin retreat commenced at the Younger Dryas/Holocene boundary. Retreat paused for 200 years during the Preboreal Oscillation. Retreat rates were 160 ma −1 in deep fjords and 60–80 ma −1 shallower fjords. Ice masses were isolated from the main ice sheet by rapid retreat in the fjords.