Seafloor ploughmarks on the mid-Norwegian continental shelf reveal iceberg trajectories during the last glacial period

Over 5000 linear to curvilinear depressions interpreted as iceberg ploughmarks were mapped across the mid-Norwegian continental shelf using high-resolution swath bathymetry data. The orientation and morphology of each iceberg ploughmark was calculated and analysed, with features being up to 30 km long and 500 m wide and located at depths of between ~130 m and ~650 m. The orientation of all ploughmarks across the mid-Norwegian continental shelf was strongly unimodal to the northeast, providing evidence for a sustained Norwegian Atlantic Current (NwAC) operating at the LGM and throughout deglaciation. In Trænadjupet glacial trough, a strong unimodal ploughmark orientation to the northwest suggests an alternative forcing to the NwAC, here interpreted as the combined action of the Norwegian Coastal Current and bathymetric constraints imposed by the ice sheet retreat pattern. Several ploughmarks with unique features, such as tidal ridges or highly sinuous geometries, suggest a localised importance of tidal forcing on ploughmark drift, particularly in western Trænabanken. Maximum iceberg ploughmark depths can be used to estimate maximum ice sheet thickness, returning a value of ~580-700 m for the Fennoscandian Ice Sheet (FIS) on the mid-Norwegian continental shelf. Ploughmark depth and orientation analysis suggests that icebergs were generally sourced from southern margins, as icebergs drifted to the northeast via the NwAC, with the exception of icebergs thick enough to scour the floor of deeper cross-shelf troughs, which were likely more locally sourced from ice stream calving margins. Furthermore, ploughmark morphometry analysis has revealed the existence of thick, multi-keeled ‘megabergs’ calved from the FIS during the last glacial period. The estimated maximum thickness of the FIS and record of large tabular icebergs indicate that, on the mid-Norwegian continental margin, marine ice cliff instability (MICI) – the process by which very large ice shelves calve rapidly due to overcoming an internal stability threshold – is unlikely to have taken place.

Level dc:type.qualificationlevel

Masters

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Mavra, Ana

Advisor dc:contributor.advisor

• Montelli, Aleksander

Licence

• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.115386

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/379223