Crescentic submarine hills and holes produced by iceberg calving and rotation

Abstract

Late Weichselian maximum ice covered the entire Barents Sea continental shelf and a major ice stream delivered large amounts of glacial debris to the western slope (Fig. 1a). During deglaciation, one of several dynamic components of the ice sheet occupied Djuprenna, a glacially eroded trough offshore of the northernmost coast of mainland Norway (Fig. 1a). Mega-scale glacial lineations (MSGLs) indicate major ice flow when the main ice source had shifted eastwards and most of the SW Barents Sea was ice free (e.g. Ottesen et al. 2008). Spectacular seabed pits with adjacent crescentic hills are imaged on multibeam bathymetry of Djuprenna. Although morphologically similar to hill–hole pairs formed by glacitectonic processes (e.g. Saettem 1990) some critical differences suggest another genesis. Seafloor features of this type are probably uncommon and, to our knowledge, have not been described previously. Fig. 1. Images, metrics and interpretation of a field of over 60 hill–hole pairs located in the glacial trough, Djuprenna. ( a ) Location of study area (red box; map from GEBCO_08). Sun-illuminated multibeam-bathymetric images depict their morphological variation: ( b ) a non-crescentic hill; ( c ) a doublet with MSGLs; ( d ) adjoining but mirrored hills; ( e ) very concentric hill, up-ice side; ( f ) typical form; ( g ) hole both sides, hill convex down-ice; ( h ) no hole (infilled); ( i ) hole both sides, current scour-related, convex up-ice; ( j ) largest form, convex down-ice. Acquisition system Kongsberg EM1002. …