Current CTD Cross Section
October 4th 2004 - CCGS Amundsen
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.
|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
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:
created by John E. Hughes Clarke email@example.com