First high-resolution chirp sonar profiles from the central Arctic Ocean reveal erosion of Lomonosov Ridge sediments

The Swedish 'Arctic Ocean-96' expedition to the central Arctic Ocean with the icebreaker Oden carried out a geological/geophysical program focused mainly on Lomonosov Ridge sediments. Approximately 195 km of high-resolution seismic data from the ridge crest and slope were collected with a chirp sonar system providing new insights into the sediment stratigraphy and the accompanying depositional history. These data reveal evidence of substantial erosion that acted in laterally limited areas on shallow parts of the investigated ridge segment. More than 50 m of sediment stratigraphy is missing in the most eroded parts. Moreover, the chirp sonar records indicate that, below the erosional surface, the ridge crest and slope is characterized by a low-energy sedimentary environment. The termination of the erosional phase is indicated by a prominent reflector. The subsequent depositional phase resulted in an approximately 3 m thick stratigraphic unit. The cause of the erosion is attributed to either ice grounding or current erosion. Furthermore, Oden echo sounding data has been used together with data from the US Navy SCICEX program in order to update existing bathymetric charts in the 'Arctic Ocean-96' working area. The update shows a narrower ridge crest with a different outline than in previously published charts with a minimum depth of 607 m which is the shallowest depth of the Lomonosov Ridge recorded (in the public domain) in the central Arctic Ocean. (C) 1999 Elsevier Science B.V. All rights reserved.