Geomorphic Investigations of the NorthWest Passage
using CHS archived single beam:
Preparations for the CCGS Amundsen 2004 transit.

John E. Hughes Clarke
Ocean Mapping Group
University of New Brunswick

Most regional images of the bathymetry of the NorthWest Passage are based on coarse resolution gridded products derived from variable density source data. The IBCAO data set is probably one of the most generally stable. Underlying the interpolated surface within the passage are sounding data sets primarily acquired by the Canadian Hydrographic Service.

These CHS data vary in age from the 60's to the 90's (no significant regional surveys have been done since the turn of the millenium). The data quality vary strongly , primarily in density, positioning accuracy and confidence in datums. For the Eastern Arctic and the Beaufort, the regional data is generally old and analog.  Nevertheless a critical subset of the data has been acquired at higher resolution in the 80's and 90's. These data were primarily focussed on that section of the Passage that provides a potential bathymetric hazard to shipping. This area extends from Dolphin and Union Strait to Victoria Strait (including of course the route round the back of King William Island).

If one superimposes the available digital  source CHS data at scales of 1-2 km's (fig to left) it would appear that the digital archives in the critical shipping corridor region exhibit  near complete coverage. One has to bear in mind, however, the scale of these surveys. They include:

  • ~ 6000m spacing sparse through ice samples.
  • ~ 1000m spacing denser through ice samples.
  •  TIBS (electromagnetic) and/or Larsen 500 (laser) solutions (max depth ~ 40m)
  • ~ 300m spacing regional systematic acoustic single beam surveys.
  • ~ 100m spacing denser acoustic single  surveys in critical choke-points or over sills.

Depending on the density of the data, significant  insights into the regional geomorphology can be obtained from this data down to wavelengths as short as ~ 200m.  In order to present this data in a more useful way (CHS sounding sheets are conventional sounding plots that don't well express the morphology), I have generated a series of ~100 x 100 km images at 100m pixel size that (with slight interpolation) reveal the geomorphology of the Passage (presented below).

I'm not sure how widely available these data have been before? I'm assuming Ron MacNab had access to all of this as part of the collaborative GSC-CHS compilations, but whether anyone presented this data at these scales and in this way before I don't know.  It certainly provides a stunning view of regional ice-stream fabrics.

To better comprehend the difference in scale of surveys I have taken one of the map sheets (Victoria Strait?) and presented at the same scale, the IBCAO bathymetry (below left), the Canada 3D land topography and the source CHS data (below right).  There are a number of horizontal datum concerns that I have ignored at this scale.

Ideally I should plot the Amundsen 2003 shiptrack and the rotated mapsheets used in the web-based data archives so that you can envisage the proposed sampling sites in the regional morphology.  Will try to do this when I get into the office. Also we are extracting the coordinates of the proposed core sites indicated by Steve and Andre to overplot.

Note that all these images will be available fully georeferenced on the ship for the geo-scientific party to examine and interrogate for coordinates for sampling and survey design. I would strongly encourage dedicated survey regions in the passage as you rush through. Using these images as a guide you may be able to find more suitable depocentres or even investigate palaeo-shorelines and/or delta locations (the ends of the incised gorge within Icebreaker Channel?). Based on last year's experience, we feel there is little to be gained at this time in twinning the outbound track. Ideally a zig-zag like return track (ice conditions allowing) would open up the maximum knowledge of the likely variability in surficial morphology and shallow sediments and help us design future surveys.

I have actually extended these images into the Beaufort and into the Eastern Arctic, but the low available data density and the fact that much of the data is analog preclude gleaning much information outside the region presented here.

The one thing that is of concern, is that all these images have been generated from the CHS digital archives that they kindly allowed me access to in support of ArcticNet. Whilst we have free access to the data for survey design and planning, the relationship of the data copyright between CHS and that NF company still remain slightly unclear at this time and thus we cannot freely distribute and publish these images (yet).

~100km by 100km areas
showing short wavelength (> 200m) morphology revealed from CHS archived data
(terrain from Canada3D topography - NRCan)

last modified by John E. Hughes Clarke, June 2004