Labrador Current CTD Cross Section
October 4th 2004 - CCGS Amundsen

John E. Hughes Clarke
Ocean Mapping Group
Dept. Geodesy and Geomatics Engineering
University of New Brunswick

On the 4th of October 2004, the CCGS Amundsen was transiting through the Labrador Sea on route to Quebec City after  completion of the 2003-2004 CASES-ArcticNet Arctic Expeditions. In this area she was performing deep water EM300 trials in depth of 2500m  and ice-scour surveys on the top of Makkovik Bank. As part of a test of the performance of the Brooke Ocean MVP-300 underway oceanographic profiler, 18 CTD profiles were recorded along a 180 km NE-SW section across the Labrador Current.

The data were collected in preparation for a hydrographic survey of iceberg scouring on the top of Makkovik Bank.  Prelimnary results are available elsewhere. The big concern for the area was the proximity of the Labrador Current over whose front, sound speed variability was pronounced.

area
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Prior to arriving at the Makkovik survey site, the MVP was experimentally deployed at 30  minute intervals whilst steaming in transit up the continental margin at 12 knots. The system cycled to 300m depth for areas with greater depths. In shallower depths, the towfish was set to recover at a depth of 20m above the seabed. These data were used to examine the transition from the Labrador Sea water masses (surface temperatures up to 9 degrees C) across the edge of the Labrador Current.
The Labrador current was particularily evident with surface salinities of as low as 30.5 ppt and deeper temperatures as low as 2 degrees C (as opposed to a toasty 9 degrees out in the centre of the Labrador Sea). The front between the two water masses is very abrupt, occuring within a zone around 10 km wide. The location of the front is extremely close to the site of the desired bank survey indicating that the spatial variation in oceanographic properties were likely to be a cause of concern in the refraction correction of the EM300 multibeam data. Converting the CTD data to density and sound speed, one clearly sees that the temperature signature dominates the sound speed structure, whereas the salinity variations dominate the density field (that in turn controls the baroclinic component of the circulation).

In order to allow other users access to the data, a gzipped tar file of the raw BOT format MVP data files are available:

          MVP_Labrador_Current_Transect_October_2004.tar.gz

created by John E. Hughes Clarke jhc@omg.unb.ca                         January 10th 2004