Esker systems in the Gulf of Bothnia

Abstract

Eskers, straight-to-sinuous ridges of waterlain sand and gravel, and their erosional meltwater channel counterparts are geomorphological imprints of the palaeo-glacial hydrological system. Esker networks hundreds of metres to hundreds of kilometres long are widespread features of Quaternary glaciations and are used to reconstruct regional and continental patterns of deglaciation. However, they have been less commonly reported from sedimentary marine environments. Esker systems from the southern Gulf of Bothnia are imaged with unprecedented clarity in new multibeam datasets which reveal a highly connected subglacial hydrological network and its relationship to an underlying drumlin field. Sinuous, elongate sediment ridges thread through a drumlin field which rises from about 80 to 50 m water depth in the southern Gulf of Bothnia (Fig. 1a–i). Individual ridge segments range from 4 km long and are c. 50–200 m wide and c. 2–20 m high. They connect into much longer esker chains over 15 km long, broken only by small gaps. The longer esker paths form a broadly dendritic network, with up to fourth-order ‘tributaries’, converging southward in the direction of ice-flow. Within tributary sections, localized braiding and anabranching occur; occasionally isolated distributaries do not reconnect to the main …