5. Ridge Study
5.3 Dive Profiling Alice Orlich
Dive Report for April 7th & 10th, 2007 Pat McKeown – Lead diver, coordinator Keith van Thiel – Lead diver, coordinator Mitch Osborne - Diver, photographer Doug Allen - Diver, photographer Kevin Parkhurst - Dive-tender Robert Chadwell – Dive-tender Alice Orlich – Research Assistant
One of the field methods employed by the SEDNA project at the APLIS 2007 camp to observe and record dynamic ice features was to utilize a dive team. The divers were deployed to traverse a portion of a pressure ridge located north of camp. The goal of the multiple dives was to better understand the sub-surface features of a ridge by documenting characteristics like the depth and shape of the blocks composing the keel which forms beneath the ice surface. In addition to a Sea-Bird Electronics 37-SM MicroCAT used to collect pressure, salinity and temperature data, personal underwater cameras and professional video equipment were helpful in capturing visual records of the expeditions.
To prepare for the dives, two dive holes were surveyed then melted out to create an ice-free access to the ocean. For the purposes of the report, the hole located closer to the ridge is known as the “North Hole,” whereas the one more distant is referred to as the “South Hole.” Plywood and foam board covered the holes when no diving activity was scheduled, therefore slowing the formation of new ice. A series of marker lines set into the ice along one of the camp’s calibration
transects guided the divers to the ridge and beyond and was meant to provide a reference for the dive plan as well as later offer corresponding data points.
The teams of divers were supported by dive tenders on the ice surface who were assisting with gear maintenance, diver preparations, and feeding or pulling in
safety lines. A dive coordinator led the logistics for each dive. He was outfitted with a communication system that allowed conversation between him and the divers throughout the operation. The dives were recorded by a research assistant noting communications, times of entry, exit, and other important events to be later synchronized with the MicroCAT data and visual imagery.
A few practice dives were performed in advance of the scientific dives. These were meant to test gear in the challenging environment of ice diving that includes maintaining dry suits, sensitive valves and hose connections in varying weather conditions that not only include cold water temperatures, but sometimes harsh wind speeds and air temperatures. Although the first science dive, conducted on the 7th of April, was at a location where the divers and support crew were
exposed to the weather, the second dive on the 10th of April was sheltered by the heated comfort of the GAVIA hut. This allowed for more extensive filming and interviewing by the Discovery Channel film crew.
The first dive was initially delayed by a few complications with each of the diver’s gear. Doug’s leaky drysuit, Mitch’s free flowing regulator, and the foggy mask of Pat’s were all deftly overcome by astute and efficient solutions put forth by diver-tender Robert Chadwell. The divers began their swim away from the ridge, soon to correct their direction. The keel was reached and navigated along a west-east course. Poor communications with Doug’s headset caused dive coordinator Keith to call him in early. Also, fast near surface currents resulted in lead diver Pat aborting the lateral transects. The currents were estimated to be about a knot by Pat. On entering the water, the MicroCAT conductivity cell probably formed or trapped an ice crystal in its intake tube. This resulted in unusable salinity data throughout the first dive. As the divers entered the water from a heated hut in the second dive, the salinity data from dive 2 is reliable. Total time for dive 1 was approximately 18 minutes.
07 April 2007 Dive at Ridge Site Entry at North Dive Hole
Lead Diver - Pat McKeown
Route AK GMT*
EXIT 17:27:41 2:27:41 0.374 10.096 "Crystals and current"
* 08 April 2007, Daylight Savings
ACTUAL DIVE ROUTE
Ridge
The second dive took Keith and Doug back along the similar dive plan. Again, a few gear issues kept the divers at the surface to adjust Keith’s o-ring and Doug’s inflation hose. The Discovery Channel’s interviews also added to the casual start.
This time, the dive crew swam beyond the ridge keel to a few green line markers, then back to the ridge. After the eastward travel along the keel, they performed two transects at decreasing depths along the keel. The team reported
discovering a “shrimp-like thing” in the ice at depth of approximately 15’. Total time was approximately 28 minutes.
South Hole and route (above). Right top and bottom panels show pressure/salinity profiles for the dive.
Figure 5.6: Dive 2 route.
10 April 2007 Dive at Ridge Site In GAVIA Hut
Lead Diver - Keith van Thiel
Route AK GMT MicroCAT
Pressure
MicroCAT
Salinity Depth Line Comments ENTRY 12:09:19 20:09:19 0.064 14.7828 Gear issue Ridge swim along keel to farthest W est point
Figure 5.7: Pressure and salinity profiles for dive 2
5.4 Under-ice surveys using GAVIA autonomous underwater vehicle (AUV)