Recessional moraines in nearshore waters, northern Scotland

Abstract

Suites of relatively small, similar-sized and regularly spaced sediment ridges are commonly found fronting the termini of modern tidewater glaciers in fjords and marine embayments. These ice-flow transverse subaqueous moraine ridges, sometimes referred to as De Geer moraines, record the incremental retreat of the ice front grounding-line over time (De Geer 1889; Linden & Moller 2005). The distribution and pattern of well-preserved recessional moraines in nearshore waters around Scotland provides insight into the pattern, timing and style of retreat of the last British–Irish Ice Sheet (Bradwell et al. 2008 a , b ; Stoker et al. 2009). A suite of 40–50 seabed ridges occurs in water depths of typically 30–80 m on shallow banks surrounding the Summer Isles, NW Scotland (Fig. 1). The ridges comprise two morphological groups: a more delicate set with smaller dimensions and a more substantial set. Each ridge displays different planform morphology ranging from curvilinear to intricate (Fig. 1a, b). Occasionally ridges continue into water depths of c. 100 m, but the ridges are notably absent from basins and bathymetric depths of >100 m (Fig. 1a). The trend of the ridge crests is generally SSW–NNE and individual ridges vary in length. The ridges can typically be traced …