The Belgica Fan, Bellingshausen Sea, documents dynamics of the West Antarctic Ice Sheet

The Bellingshausen Sea sector frames the eastern part of the West Antarctic Ice Sheet (WAIS). Between 83 and 89°W the Bellingshausen Sea margin is characterised by the 150 km wide Belgica Fan, a large trough mouth fan extending from the shelf break into the deep sea to about 3000 m water depth. Sedimentary material from the hinterland has been transported to the Belgica Fan via the Belgica Trough, a major glacial morphological feature on the Bellingshausen Sea shelf. Thus, the fan constitutes an important archive of the WAIS dynamics of this sector.  Still, little is known about the development of the fan and the potential to unlock this sedimentary archive.

A recently collected set of seismic reflection data has been analysed and interpreted with the aim to reveal the formation of the fan and decipher the glacially controlled transport, deposition and erosion processes. A seismic link to ODP Leg 178 Sites 1095 and 1096 enables the age dating of prominent reflections and seismic units. The fan is underlain by several basement highs. The lowermost two seismic units (M6, > 25 Ma, and M5, 25-15 Ma) fill and level the basement relief. Unit M4 (15-9.5 Ma) shows erosive structures such as channels and mass transport deposits in its upper part. These occur mainly in the far west and east of the fan. This erosion appears intensified in the lower part of unit M3 (9.5-5.3 Ma). In units M2 and M1 the erosional features are localised in the western and distal part of the fan.

These observations indicate an increased input of material following the mid-Miocene Climatic Transition pointing towards the beginning of an expanding, shelf-crossing WAIS in the Bellingshausen Sea sector.