CHS Creed

Report 3 - 21 May 1996
Final cruise report
Alas the weather has finally changed in our favor. It's hotter than Texas here - temps to get close to 100! I'm not sure what happened to spring.

We've now completed 7 of 8 legs. Laurie Schuur joined up for leg 7 - greatly appreciating the calm seas we enjoyed the entire time. She'll continue on for Leg 8 while I take a much needed break - a 6 on 6 off schedule takes its toll after a while.

We've completed our coverage out to the shelf break and just beyond. The best was clearly saved for last. Parts of the outer shelf are riven by scars which we presume were left by glaciers and/or bergs from the last ice age. This morphology appears to be bounded shoreward by the "Franklin Shore" - a fossil shoreline, one of several, left during the last sea level rise which followed the last ice age. In some parts this scarred morphology is overlain by smooth "dunes" - and, rarely, some of the dunes are scarred. All this suggests timing issues which we'll have to work through carefully.

At the shelf break we see two distinct types of morphology. Where the slope contains canyons, the shelf break is very sharp, and we find clear evidence for slides occurring right at the canyon heads - giving probable indication of the mechanism for canyon growth. Where canyons don't exist - i.e., along the Hudson Apron - the shelf break is very gradual.

The last leg will concentrate on expanding our shallow water coverage - particularly covering future ODP drill sites and expanding our sampling of several "scarps" which are likely additional fossil shore lines.

Another problem we are having is that we are not now covering as much territory as we had originally hoped. Much of the survey (depths below ~200 m) was planned at a track spacing of 5 times the water depth. Under most operating conditions, that is a good conservative estimate. However, the Creed has an unfortunate peculiarity. Mounted on the starboard pontoon, the transducer array's outermost port beams are masked by the noise of the engine operating in the port pontoon. The net result is that we must run the survey with a track spacing of ~4 times water depth to achieve full coverage - a loss of 20%. Fortunately, we still anticipate covering most if not all of the planned survey region, thanks to a fortuitous mishap. Because of a problem with the transducers (which I do not fully understand), we cannot survey in waters greater than about 200-300 m - though we had planned to survey to the reputed capacity of the system of 1000 m. The Canadian Hydrographic Survey had originally hoped to have this hardware problem fixed by the time our survey began, but were unable. Intending to honor our contract with them, they have offered to return at a later date to complete the survey coverage - in essence providing us with extra survey time. So sometimes two wrongs do make a right.

Other than that, things go well. The data look great and we are imaging scores of fascinating features that beg interpretation.

Data collection on our first leg went like a charm, and we covered more area than we had anticipated. We started work in about 60 m of water. Subtle sand waves and channels were readily evident. We'll work our way toward the shelf break to map the heads of numerous slope canyons. Right now I'm on shore for the second leg while Jamie takes my place. Weather looks stable for at least a week so we anticipate being able to get back on schedule by shortening a couple of our layovers from 24 hours to 12.

- John