Abstract
Abstract. Ice-stream networks constitute the arteries of ice sheets through which large volumes of glacial ice are rapidly delivered from the continent to the ocean. Modifications in ice-stream networks have a major impact on ice sheet mass balance and global sea level. Reorganizations in the drainage network of ice streams have been reported in both modern and paleo-ice sheets and usually result in ice streams switching their trajectory and/or shutting down. While some hypotheses for the reorganization of ice streams have been proposed, the mechanisms that control the switching of ice streams remain poorly understood and documented. Here, we interpret a flow switch in an ice-stream system that occurred prior to the last glaciation on the northeastern Baffin Island shelf (Arctic Canada) through glacial erosion of a marginal trough, i.e., deep parallel-to-coast bedrock moats located up-ice of a cross-shelf trough. Shelf geomorphology imaged by high-resolution swath bathymetry and seismo-stratigraphic data in the area indicate the extension of ice streams from Scott and Hecla & Griper troughs towards the interior of the Laurentide Ice Sheet. Up-ice propagation of ice streams through a marginal trough is interpreted to have led to the piracy of the neighboring ice catchment that in turn induced an adjacent ice-stream flow switch and shutdown. These results suggest that competition for ice discharge between the two ice streams, which implies piracy of ice drainage basins via marginal troughs, was the driving mechanism behind ice flow switching. In turn, the enlargement of the ice catchment by piracy increased the volume and discharge of Scott Ice Stream, allowing it to erode deeper and flow farther on the continental shelf. Similar trough systems observed on many other glaciated continental shelves may be the product of such competition for ice discharge between catchments.
Highlights
Ice flow switching was first invoked to explain the recent stagnation of the Kamb Ice Stream – previously known as Ice Stream C – on the West Antarctic Ice Sheet (Conway et al, 2002)
5.1 Ice-stream tracks In Scott Trough, the occurrence of mega-scale glacial lineations (MSGLs) extending to the shelf break, together with a till unit extending on the trough– mouth fan and glacial debris flows on the shelf edge, indicates that the Laurentide Ice Sheet reached the shelf break during the Last Glacial Maximum (LGM; Brouard and Lajeunesse, 2017; Jenner et al, 2018)
While the glacial origin of Scott Trough is obvious from its overdeepening and the numerous ice flow landforms, the glacial origin of Sam Ford Trough is confirmed by the presence of (1) Ice-stream lateral moraines (ISLMs), (2) Grounding-zone wedges (GZWs) in the trough, and (3) a small overdeepened basin on Sam Ford Fiord sill (Figs. 1, 6–8)
Summary
Ice flow switching was first invoked to explain the recent stagnation of the Kamb Ice Stream – previously known as Ice Stream C – on the West Antarctic Ice Sheet (Conway et al, 2002). Networks of glacial troughs on continental shelves may offer such insights for identifying and understanding flow-switching mechanisms as they were overdeepened by past ice streams. These networks generally consist of cross-shelf troughs often interconnected up-ice to marginal troughs (Anderson, 1999; Nielsen et al, 2005; Batchelor and Dowdeswell, 2014).
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