Buried gold and treasure maps may bring to mind tall tales of swashbuckling pirates, but even today, “treasure hunters” endeavor to recover valuable items from shipwrecks. These haunting sites, mere skeletons of past expeditions, are both important historical markers and resting places for precious cargo (Figure 1). The exploration of such debris fields is a complex and precise science, regulated by many international guidelines.
Underwater archaeology, like traditional archaeology, is highly regulated in order to respect sites or artifacts of historical significance. UNESCO requires the preservation of any submarine evidence of human existence over one hundred years old (UNESCO, 2001). However, the historical significance of some shipwrecks necessitates their investigation in order to piece together age-old puzzles around the discovery of new territory, as in the case of the Franklin expedition shown in Figure 2 (Howard, 2014). Unethical activities, including the sale of heritage relics as commercial goods or the unnecessary disturbance of human remains or sites of religious or cultural significance, are also prohibited (O’Keefe, 2002).
Discovery and excavation in an aquatic environment are based on principles similar to those of terrestrial archaeology, but require different technologies, as the surrounding medium is water. Shipwrecks can be located by remote sensing methods, including sonar. This technique transmits sound, and detects the unique echoes as it bounces off submarine objects. Side-scan sonar, which is most commonly used in marine archaeology, allows for the imaging of large sections of the seafloor with two fanned sound beams (Singh, Mindell, & Foley, 2000). The distance of objects can then be determined using the speed of sound and the time between transmission and detection of sound waves (Benjamin & Hale, 2012).
Once the seafloor has been swept by sonar, the data collected can be used to create a 3-dimensional virtual model of submarine terrain. Depths and other spatial features can be included and assigned to geographical coordinates. This precise mapping of shipwreck sites with Geographic Information Systems allows for their future investigation and long-term preservation (Breman, 2003).
Excavation and conservation of shipwreck material, as with its discovery, demands great precision due to the pervading aquatic medium. First, a dredging device, as in Figure 3, uses suction to bring matter up from the seafloor to a mesh screen atop the water. This allows for easy transportation between sites, without the disruption of fragile material or the use of heavy machinery (Adovasio & Hemmings, 2012). Here, artifacts are carefully removed and quickly passed on to conservation experts. Structural and chemical methods must be employed in order to preserve these objects, which are very susceptible to changes in their surroundings. Organic material, while well preserved underwater, becomes structurally unstable upon introduction to fresh water, which leaches out supportive salt ions (Hamilton, 1997). These substances are either preserved by impregnation or bulking, which involve the filling of waterlogged cavities with stable material (Rodgers, 2004).
The exploration of sunken ships is certainly an interdisciplinary field, which requires painstaking spatial analysis, physical handling, and chemical preservation. The investigation of such mysterious ruination provides fascinating insight into the history of human curiosity, and our oceans are thought to contain over three million shipwrecks (UNESCO, n.d.)! In the future, we will no doubt look to marine archaeology and the wealth of information at the bottom of the sea for a greater understanding of past civilizations.
Sources:
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Boyer, T., 2014. New pictures of Franklin expedition’s HMS Erebus. CBC News. Available at: http://www.cbc.ca/news/canada/photos/new-pictures-of-franklin-expedition-s-hms-erebus-1.2785494 [Accessed October 4, 2014].
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Howard, B.C., 2014. Arctic Shipwreck Found After 170 Years, Solving “Great Mystery.” National Geographic. Available at: http://news.nationalgeographic.com/news/2014/09/140909-franklin-expedition-shipwreck-canada-arctic-archaeology/.
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