Spatial variability of bottom turbulence over a linear sand ridge mooring deployment and AUTOSUB AUV survey cruise report R/V RRS Challenger, cruise number 146 Broken Bank, North Sea, U.K., 17 – 28 August 1999 cruise report

Funding was provided by the Office of Naval Research under Contract No. N00014-01-10255 and the Natural Environment Research Council, UK Award GST/02/2155 to the University of Southampton.

Two successful AUTOSUB deployments were carried out during August 1999 as part of the AUTOSUBThematic Program project titled “Spatial Variability of Bottom Turbulence over a Linear Sand Ridge,” fundedby the Natural Environment Research Council (NERC), U.K. The AUTOSUB Autonomous Underwater Vehicle(AUV) was deployed and used to survey flow patterns at a location near the Broken Bank, southern North Sea,U.K. The AUV was equipped with acoustic flow and turbulence sensors and its surveys aimed at mapping thespatial variation of flow and turbulence near the bed and over topographic features.Three instrumented bottom mounted frames were also deployed, around the AUV survey area, for a period ofapproximately 5 days. The purpose of this array was to gather information on the temporal variability of the flowand turbulence near the seabed and to identify the important terms that drive circulation around the bank.Additional data were gathered including CTD casts, seabed samples and acoustic images of the seabed (side-scansonar).The purpose of this data collection was to help identify the flow patterns around ridges and to understand themechanisms controlling the maintenance and evolution of such features.This report describes the operations carried out by researchers from the University of South Carolina, WoodsHole Oceanographic Institution, Southampton Oceanography Centre and the AUTOSUB Team on the R.V. RRSChallenger during the period 17th –28th August 1999.