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On the Alaskan Seafloor: Diving on the Kad'yak Wreck "Tracking Down Kad'yak"
August 26, 2004

[image] Measuring underwater artifacts (Courtesy Tane Casserley, NOAA) [LARGER IMAGE]

Archaeological excavations require specialized skills, painstaking carefulness, time, and money. Underwater archaeological work requires all of these things and more. Working in conditions with far less visibility and limited time on the bottom requires special training, which is available at only a handful of graduate schools--and no undergraduate schools--across the country. A program typically involves coursework and field schools. For instance, students at East Carolina University, which sent out archaeologists for the Kad'yak wreck, complete a two year M.A. degree that includes summer and fall field schools during which students work on actual sites. For instance, last summer they held a field school in Alpina, Michigan, and focused on some of Lake Huron's 100 shipwrecks.

Along with specialized training, underwater archaeologists need specialized gear to deal with different conditions. Water temperature, for instance, dictates the type of suit worn. For Kad'yak, which was located in water that measured 46 degrees Farenheit in July, most divers wore dry suits. A dry suit has rubber seals at the wrist, neck, and feet. These seals keep out water, and the entire body stays dry except for the head, hands, and feet. Another option in cold water is a conventional wet suit that is extremely thick, which can protect skin against colder waters. Co-principle investigator Tim Runyan, wore one such thick wet suit during dives. Since salt water freezes at a lower temperature than fresh water, divers can work in water below 32 degrees.

Divers must also choose what type of gas to breath, since that affects the amount of time a diver can spend in the water. Although several types of manufactured gases are available to divers (such as Nitrox, Heliox, and Trimix), many dive on air. Although it allows for less bottom time than a gas such as Trimix, which is a mix of oxygen, helium, and nitrogen, air is easier to obtain. On the Kad'yak wreck, archaeologists dived on air, which, combined with the wreck's 80-foot depth, limited their time at the bottom to two half-hour sessions per day.

Divers must be concerned not only with replacing oxygen, but also with eliminating nitrogen that enters their system. The deeper one dives, the less time there is to spend on the bottom and the more decompression time must be taken to allow the body to rid itself of nitrogen and become re-accustomed to normal atmospheric conditions. On the Kad'yak dive, for instance, time at the bottom was only 30 minutes long at a depth of 80 feet, so there was no need for divers to spend a large amount of time decompressing. Kad'yak divers would spend just five minutes decompressing, hovering ten to 15 feet below the water's surface. When divers push the limit of deep-sea diving, they might reach depths of up to 500 feet, well over the conventional 180-foot limit of scuba diving. At greater depths, the body quickly absorbs nitrogen, which necessitates long decompression periods. For instance, when divers worked on the U.S.S. Monitor off Cape Hattaras, they worked at 240 feet for short periods of time. They were supplied with air from the surface, which was pumped down to them through tubes, and they had to go into a recompression chamber for several hours after returning to the surface. If they had they used Trimix, they would have had just 20 minutes on the bottom and would have needed an hour to decompress at different depths. Any way you cut it, the deeper one dives, the greater the ratio of decompression time to actual bottom time becomes. One reason that underwater archaeologists must always dive in pairs (at least) is to keep careful track of their air supply and decompression time.

[image] Underwater archaeologists plan on the surface. (Courtesy Tane Casserley, NOAA) [LARGER IMAGE]

Finally, underwater archaeologists must account for variable visibility at the site on which they are working. The Kad'yak dive was a survey of the site as opposed to an excavation. The archaeologists essentially worked on producing maps on land for days from the few hours that they spent measuring, triangulating, and photographing on the bottom. The fact that the shipwreck was scattered over a few hundred yards complicated matters.

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© 2004 by the Archaeological Institute of America