14-04-2014, 03:20 PM
New Bathymetry from the 2011 Canada—U.S. Joint Expedition for Continental Shelf Mapping in the Arctic Ocean
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SUMMARY
In August and September of 2011, Canada and the United States combined resources for a fourth
season of joint extended continental shelf data acquisition and mapping in the Arctic Ocean. The
2011 cruise was a combined expedition of the icebreakers CCGS Louis S. St-Laurent and USCGC
Healy. As in previous expeditions, Louis S. St-Laurent was equipped with a seismic profiling
system and Healy with a multibeam system. Both ships were fitted with high-resolution
subbottom profilers. The 2011 joint expedition began with a long northward seismic line from the
Chukchi Plateau, over the Alpha-Mendeleev Ridge, through the Makarov Basin, and onto the
Lomonosov Ridge. Although primarily a seismic line, high-quality multibeam and single-beam
bathymetric data were obtained. At the northern end of this line, at 88° 28' north latitude, the
priority shifted to bathymetry along the flanks of the Lomonosov Ridge and across Marvin Spur.
From there, the ships again crossed the Alpha-Mendeleev Ridge, collecting bathymetry and
subbottom profiles over highly irregular seafloor characterized by hyperbolic echoes. The ships
continued eastward, pushing into areas of the Arctic never before penetrated by icebreakers, and
collecting the first lines of multibeam bathymetry in these areas. At Sever Spur an AUV was
successfully deployed under the ice from Louis S. St-Laurent resulting in the acquisition of high-
quality multibeam bathymetry crossing the Spur. During the AUV deployment, Healy detached
for additional bathymetric mapping. The combined data sets greatly improved the quality of
seafloor bathymetry in this area with important extended continental shelf implications.
INTRODUCTION
In August and September of 2011, Canada and the United States combined resources for a fourth
consecutive season of joint extended continental shelf data acquisition and mapping in the Arctic
Ocean. The 2011 cruise was a combined expedition of the icebreakers CCGS Louis S. St-Laurent
and USCGC Healy. As in previous expeditions, Louis S. St-Laurent’s primary mission was
seismic reflection profiling. In addition to its seismic system, Louis S. St-Laurent was equipped
with a Knudsen 320 B/R Plus 12 kHz single beam echo sounder and a Knudsen 3260 chirp high
resolution (~3.5 kHz) subbottom profiler (Mosher, et al, 2011 and Canadian Hydrographic
Service [Biggar], 2011) and a 12 kHz Knudsen 320M helicopter-borne spot sounder. Healy’s
primary mission was multibeam echo sounding. Healy was equipped with a Kongsberg EM122
(12 kHz, 288 beam) multibeam echo sounder. Healy also operated a Knudsen 320B shallow-
penetration chirp subbottom profiling system (~3.5 kHz) (Mayer and Armstrong, 2011).
Healy departed Barrow, Alaska on August 16th; Louis S. St-Laurent departed Kugluktuk,
Northwest Territories on August 18th. An August 23rd rendezvous of the two ships took place near
the northern end of Chukchi Plateau. Before the rendezvous, Healy spent five days mapping the
continental slope of the Barrow Margin. Seafloor mapping operations began with a Conductivity
Temperature Depth (CTD) cast to establish a sound speed profile and a multibeam patch test to
calibrate any timing or attitude offsets. On the second day of mapping, an interesting conical-
shaped feature measuring 500 meters across and 80 meters high was located in 2000 meters of
water. Although similar in size and shape to the ice-cored ”pingos” often found on shallower
water of the nearby Mackenzie River delta, this feature, shown in Figure 1, is much deeper than
we would expect for a pingo. Pingos have not been charted off the Alaska coast; however, the
presence of this feature suggests that their existence should not be ruled out.