Archaeological Oceanography

Robert D. Ballard, Robert D. Ballard

• Editore: Princeton University Press
• Anno: 2021
• ISBN:
  9780691236995
• Argomento: Scienze fisiche
• Categoria: Oceanografia

Archaeological Oceanography is the definitive book on the newly emerging field of deep-sea archaeology. Marine archaeologists have been finding and excavating underwater shipwrecks since at least the early 1950s, but until recently their explorations have been restricted to depths considered shallow by oceanographic standards. This book describes the latest advances that enable researchers to probe the secrets of the deep ocean, and the vital contributions these advances offer to archaeology and fields like maritime history and anthropology.
Renowned oceanographer Robert Ballard--who stunned the world with his discovery of the Titanic deep in the North Atlantic--has gathered together the pioneers of archaeological oceanography, a cross-disciplinary group of archaeologists, oceanographers, ocean engineers, and anthropologists who have undertaken ambitious expeditions into the deep sea. In this book, they discuss the history of archaeological oceanography and the evolution and use of advanced deep-submergence technology to locate and excavate ancient and modern shipwrecks and cultural and other sites deep under water. They offer examples from their own expeditions and explain the challenges future programs face in obtaining access to the resources needed to carry out this important and exciting research.
The contributors are Robert D. Ballard, Ali Can, Dwight F. Coleman, Mike J. Durbin, Ryan Eustace, Brendan Foley, Cathy Giangrande, Todd S. Gregory, Rachel L. Horlings, Jonathan Howland, Kevin McBride, James B. Newman, Dennis Piechota, Oscar Pizarro, Christopher Roman, Hanumant Singh, Cheryl Ward, and Sarah Webster.

PART ONE

The Technology and Techniques of Archaeological Oceanography

1

Oceanographic Methods for Underwater Archaeological Surveys

Dwight F. Coleman and Robert D. Ballard

Geophysical prospecting techniques for land-based archaeological studies are fairly well established. For the most part this is true for marine archaeological studies as well (Oxley and O’Regan 2001). Oceanographic survey techniques that focus on mapping and exploring the marine environment are also well established, but traditional oceanographic methodologies are not typically applied to marine archaeology. A major limiting factor that influences this is the high cost. For example, the current operational cost for using an ocean-class research vessel can be more than $20,000 per day. Deep submergence vehicle systems and advanced geophysical survey equipment that are used with these research vessels can cost more than $10,000 per day. The total cost for one day of shipboard operations could be enough to fund an entire season of a terrestrial archaeological site excavation. But this example really does not represent a fair comparison. Such daily costs associated with doing research at sea are typically devoted to the study of natural history phenomena in the oceans and on the ocean floors. The following questions can be asked: Is the study of human history beneath the sea just as important as the study of natural history beneath the sea? Are cultural resources as significant as natural resources? Should federal dollars be equally spent to protect these resources? Should archaeology be federally funded to the same level as other oceanographic sciences? If the answer is yes to any of these questions, then we can justify the cost of conducting “archaeological oceanography.” Many of the well-established geophysical tools and techniques that have been employed by archaeologists in shallow water can also be used on larger ships and in deeper water, thereby employing an oceanographic approach. Deep-water oceanographic techniques do not differ greatly from shallow-water techniques, but a focus here is to present methodologies for surveying that optimize time on board expensive scientific research vessels.

Archaeologists have used side-scan sonar, subbottom profilers, magnetometers, and visual imaging techniques, although not nearly as extensively as scuba techniques, to search for and map submerged sites, especially shipwrecks (Oxley and O’Regan 2001). For exploration and mapping of terrestrial sites, use of ground-penetrating radar (GPR) has become more widespread to acoustically image the subsurface details of sites. Collection of sediment cores to ground-truth the GPR data and to characterize the depositional context of terrestrial sites is also common in terrestrial site surveys. In a similar manner to the way these geological techniques have been employed to investigate terrestrial archaeological sites, oceanographic techniques are now being employed to investigate underwater archaeological sites. These techniques (discussed below) are all commonly used during oceanographic research and exploration cruises and represent important methodologies employed to characterize underwater archaeological sites and landscapes.

Established Archaeological Survey

Archaeological survey strategies and techniques, particularly for terrestrial sites, are well established (Banning 2002) and include different approaches for exploration, reconnaissance surveying, and intensive site surveying. Regional scale surveying techniques (Dunnell and Dancey 1983) and sampling strategies (Nance 1983) are also well established, but these are also mainly for terrestrial archaeology. Archaeological survey can involve different techniques and methodologies, depending on the site. From a theoretical standpoint, there should be almost no difference between surveying on land or under water, except for the obvious logistical differences. For example, on land aerial photographs can be used as a base map similar to the underwater use of side-scan sonar mosaics. From a practical standpoint, however, there are significant differences. Firstly, many underwater sites are in regions of very poor visibility, so surveyors must rely more on acoustic strategies than visual strategies. Secondly, survey techniques for shipwreck archaeology differ from the techniques for surveying terrestrial (including inundated) sites. Ancient shipping trade routes or more modern naval battle locations—regions where shipwrecks would be expected, for example—would have well-defined boundaries that would bias the survey strategy. Thirdly, and perhaps most importantly, underwater surveys are much more difficult logistically, and the rigid limits set by cost, time, and weather for work at sea could significantly influence survey strategies.

To complete a well-planned archaeological survey, whether on land or under water (shipwrecks or inundated terrestrial sites), the entire region of interest should be mapped and investigated, even if there are no suspected sites in parts of the survey region. The absence of sites in particular locations provides scientific data and evidence to support the regional archaeological interpretation. For example, to search for shipwrecks along suspected trade routes, surveyors must also search away from the suspected trade routes to verify working hypotheses about delineation of the suspected routes.

Established guidelines for underwater survey exist, primarily, for the purposes of cultural resource management. Several federal agencies in the United States, such as the Army Corps of Engineers, the Minerals Management Service, the National Park Service, and the National Oceanic and Atmospheric Administration, either suggest or require that survey operations follow their guidelines. These guidelines vary depending on the particular archaeological sites and the scope of work. For the most part, the survey guidelines were established to protect submerged cultural resources from being damaged by activities that involve disturbance of the seabed, such as dredging, construction projects, and oil well drilling. For these activities in U.S. waters, compliance with the National Historic Preservation Act of 1966 is a requirement, and a complete site survey and characterization is necessary and must be approved prior to further site activity. Many individual coastal states have rules and regulations in addition to the requirements by federal law. Organizations such as UNESCO (United Nations Educational, Scientific and Cultural Organization) have worked to develop international guidelines and codes of ethics for conducting archaeology under water.

A variety of geophysical methods have been used in land-based archaeological exploration and surveying, including, but not limited to, satellite remote sensing, airborne imaging, ground-penetrating radar, and magnetic techniques (Renfrew and Bahn 2000). These are primarily tools for prospecting. Other terrestrial archaeological methods that involve geophysical techniques include archaeo-magnetism, radioisotope studies, dendrochronology, palynology, paleontology, and provenance studies. These are primarily analytical methods and are useful in absolute dating and understanding past environmental conditions and archaeological associations. For buried terrestrial archaeological sites, a regional sampling strategy can be employed to test for potential sites (Nance 1983). This could include coring or excavating test pits situated in high-probability locations.

For the marine environment, similar sets of prospecting and analytical techniques exist. The primary focus here will be on marine geophysical exploration and surveying techniques, but techniques analogous to those used on land can be used once an archaeological site is identified for higher-resolution investigations. Intrusive techniques have been employed as part of the survey phase of underwater archaeology (Oxley and O’Regan 2001). This primarily involves limited sampling of material from the site to better characterize and understand its nature, such as the collection of organic material for radiocarbon dating. Excavation, such as trial trenching on land to test whether a site exists, is intrusive and can be very destructive, and this is not very practical for investigating underwater sites (Oxley and O’Regan 2001). Techniques for underwater site excavation are well established (e.g., Green 1990), and typically involve intensive surveying to carefully map the site prior to excavation and subsequent site disturbance. New oceanographic methodologies that employ remotely operated vehicle systems for high-precision site surveys can now be utilized in both shallow- and deep-water settings (Foley and Mindell 2002).

Archaeological Oceanographic Surveys

The nature of the survey strategy is dependent on whether archaeological sites are known to exist within the region to be surveyed. Exploratory and reconnaissance surveys can take many forms, but for targeting inundated archaeological sites, certain methodologies work better than others. A full range of geophysical methods can be applied to archaeological oceanography, and these methods help to define this new field. Interpretation of the survey data will help to delineate sites for further exploration and detailed investigation. These oceanographic methods include bathymetric mapping, side-scan sonar surveying, high-resolution reflection surveying (including subbottom profiling and lower-frequency seismic methods), magnetometer surveys, and visual imaging surveys using remotely operated vehicle (ROV) systems (Oxley and O’Regan 2001). Other geophysical methods, including electrical resistivity and marine gravimetry methods, can be used to explore for and characterize underwater archaeological sites.

For the survey of submerged terrestrial sites, the strategy must be different from shipwreck mapping surveys because prehistoric sites are typically buried in the shelf sediment. The process of coastal inundation due to rising sea level is generally destructive to archaeological sites. If sites are rapidly buried, there is a greater chance for preservation of delicate materials. But for the most part, what survives are the nondelicate cultural and human remains—lithic artifacts (stone tools, points), kitchen middens (mammal and fish bones, shells), gravesites (human bones and associated artifacts), stone foundations of dwellings, pottery, hearths, postholes, and other cultural features. Remot...