The variety and distribution of submarine glacial landforms and implications for ice-sheet reconstruction

Glacimarine processes affect about 20% of the global ocean today, and this area expanded considerably under cyclical full-glacial conditions during the Quaternary (Fig. 1) (Dowdeswell et al. 2016 b ). Many of the submarine landforms produced at the base and margin of past ice sheets remain well preserved on the seafloor in fjords and on high-latitude continental shelves after the retreat of the ice that produced them. These glacial landforms, protected from subaerial erosion and beneath wave-base and tidal currents in water that is often hundreds of metres deep, are gradually buried by both hemipelagic and glacimarine sedimentation; they may be preserved over long periods in the geological record if palaeo-continental shelves are not reworked by subsequent glacier advances or bottom currents (Dowdeswell et al. 2007). This means that, first, submarine glacial landforms can be observed at or close to the modern seafloor after retreat of the last great ice sheets from their most recent Quaternary maximum about 18–20 000 years ago using swath-bathymetric mapping systems and, secondly, buried glacial landforms may also be identified and examined within glacial-sedimentary sequences from Quaternary and earlier ice ages using seismic-reflection methods. Fig. 1. The global distribution of glaciers and ice sheets and the glacier-influenced, or glacimarine, environment. The approximate modern (yellow dotted line) and Quaternary full-glacial (yellow dashed line) limits of ice-rafting and ice-keel ploughing of the seafloor are shown (modified from Anderson 1983). GEBCO World Map: Gall projection. Numbered yellow dots refer to the locations of subsequent figures. The development of multibeam echo sounding over the past two decades, coupled with high-accuracy GPS positioning, has allowed morphological mapping of the seafloor at an unprecedented level of detail. In this paper, the variety of submarine glacial landforms observed in modern, Quaternary and more ancient sediments is described. Landforms produced subglacially, those formed at and beyond …