Submarine Glacial Landforms

Abstract

The development of a range of geophysical imaging techniques, including multi-beam swath bathymetry and shallow-acoustic profiling, has enabled the identification and interpretation of submarine glacial landforms on and beneath the seafloor of formerly-glaciated continental margins. The analysis of these landforms provides information about past ice-sheet dynamic behaviour and the mechanisms by which sediment is eroded, transported and deposited by ice sheets. Submarine glacial landforms can be categorised into subglacial, ice-marginal and glacimarine features. The majority of subglacially produced landforms, including mega-scale glacial lineations and drumlins, are elongate features that are orientated parallel to the direction of former ice flow. In contrast, ice-marginal landforms, including moraines and grounding-zone wedges, are orientated transverse to the former ice-flow direction. Ice-marginal landforms reveal the positions of still-stands or minor re-advances in the grounding-zone during general ice-sheet retreat. Glacimarine landform associations include ploughmarks that are formed by the grounding of iceberg keels on the seafloor, and smooth basin-fill sediments produced by suspension settling of material derived from meltwater plumes. The typical distribution of glacial landforms on formerly glaciated continental margins is illustrated using the case study of the Norwegian continental shelf and slope. The locations of former fast-flowing ice streams are associated with deep cross-shelf troughs that contain elongate subglacial landforms. Major glacial-sedimentary depocentres or trough-mouth fans are typically present on the continental slope beyond trough mouths. In contrast, relatively shallow inter-ice stream banks on the continental shelf are characterised by transverse moraine ridges and widespread iceberg ploughmarks.