DOI: 10.5285/1221bbbd-843e-46d6-b96c-9c559aecfb20
title: Gridded bathymetric compilation of selected areas within the Orkney Passage, Scotia Sea from multibeam echosounder data collected by multiple vessels (1989 - 2017)

description: We present two new gridded bathymetric compilations of the Orkney Passage, Scotia Sea here defined by the following bounding boxes: 39.1 to 39.6 W, 60.55 to 60.7 S and 41.7 to 42.6 W, 60.45 to 60.8 S. These bathymetry grids were compiled from a variety of multibeam swath bathymetry data acquired during 12 different cruises (see lineage). The data is available as grids of 50 m resolution in a GMT-compatible (2-D) NetCDF format using geographic coordinates on the WGS84 datum. This grid was compiled in support of the ongoing monitoring efforts in and around Orkney Passage as part of the Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA) programme and preceding BAS NC projects, and the Dynamics of the Orkney Passage Outflow (DynOPO) project. Funding was provided by the NERC grants NE/K012843/1 and NE/N018095/1 as well as national capability
description: The bathymetry map was compiled from a variety of different data sources. The primary data are multibeam swath bathymetry collected from scientific cruises undertaken by British Antarctic Survey (BAS), Alfred Wegener Institute (AWI), or acquired during ESPS RV Hesperides expeditions. The complete list of the cruises used for the compilation is the following: -RV Polarstern: ANT-VIII/5, ANT-XXII/4, ANT-XXIII/7 -RRS James Clark Ross: JR149, JR239, JR252, JR257/272A, JR259, JR281, JR310, JR16005 -ESPS RV Hesperides: hes97 The first grid (m41_swath_50m_nc.grd) was created using the mbgrid program from MB-system version 5.5.2336 , using the parameters "-E50/50/meters -R-39.6/-39.1/-60.7/-60.55 -G3 -A2 -T25 -W4 -M -N -C5/1 -P1 -F1 -V". This uses a Gaussian weighted mean filter. Values are interpolated using a spline (tension 25) up to five grid cells from the nearest data point only if additional data are found in two opposite directions. The second grid (m42-44_swath_50m_nc.grd) was created using the mbgrid program from MB-system version 5.5.2336, using the parameters "-E50/50/meters -R-42.6/-41.7/-60.8/-60.45 -G3 -A2 -T25 -W4 -M -N -C5/1 -P1 -F1 -V". Like the first grid, this uses a Gaussian weighted mean filter. Values are interpolated using a spline (tension 25) up to five grid cells from the nearest data point only if additional data are found in two opposite directions.
description: Quality control was undertaken manually to remove any outliers in the source datasets. This involved cleaning much of the raw data using the "mbedit" program from MB-system. For data processed in this way, edit files have been submitted to the Polar Data Centre. In source files that were ingested as text files, outliers were manually removed. To verify the accuracy of the resulting dataset, bottom depths were compared against CTD casts on cruise JR16005, excluding casts that were performed when the ship was moving and those where the CTD did not get within altimeter range of the bottom. Bottom depths were calculated from the CTD altimeter when near the bottom, and these were compared against the gridded dataset. On 81 casts, the median difference between the CTD-derived depths and gridded depths was 4.1 m with a standard deviation of 18.9 m. This compares favourably with GEBCO_2014, which had a median offset of 4.6 m with a standard deviation of 73.4 m, and GEBCO_2019, which has a median offset of 0.5 m but a standard deviation of 89.4 m.