Geophysical sensors are used routinely in industry surveys conducted prior to ground disturbing activities offshore in order to identify archaeologically significant resources such as shipwrecks. The primary sensors include sonar and magnetometers, but these systems cannot effectively identify all historic vessels located on, and particularly those buried underneath, seafloor sediments. Vessels that are lost on the OCS become incorporated into the natural environment offshore, and archaeological interpretation requires an understanding of these environments in order to accurately identify sites. This paper will discuss both primary and ancillary geophysical data sets used in the identification of historic resources on the Gulf of Mexico Outer Continental Shelf and introduce environmental data sets and observations from diver investigations that are used to further refine data interpretation.
Submerged cultural resource managers in the Gulf of Mexico are responsible for balancing the protection of the underwater cultural heritage while regulating economic development of the outer continental shelf (OCS). Archaeological sites do not exist in isolation on the world's seabeds; fishing, farming, aggragates extraction, and energy resource development (such as oil, gas, and renewables) are just some of the offshore activities that can be regulated at the local, national, and international level. For more on this subject see Conservation and Management of Archaeological Sites special issue Conserving Marine Cultural Heritage 11(1), March 2009.
Numerous stakeholders use coastal resources on the OCS. In the northern Gulf of Mexico, underwater archaeological resources such as historic shipwrecks and submerged prehistoric sites can and have been impacted by fishing, farming, and energy development (e.g., Atauz et al. 2006). In the United States, offshore oil and gas industry activities are regulated by the (at the time of writing) Bureau of Ocean Energy Management, Regulation, and Enforcement (BOEMRE). Submerged archaeological resources on the OCS were first managed by the Bureau of Land Management prior to the creation of the former Minerals Management Service (MMS now BOEMRE). The first archaeological lease stipulations were mandated in 1973. This lease stipulation was followed in April 1974 by the first Notice to Lessees (NTL) to feature geophysical survey and report requirements to meet the archaeological stipulation, NTL 74-10. Since the first requirements for archaeological surveys, approximately 500 vessels have been identified within the Gulf of Mexico region. It is unknown how many potential prehistoric archaeological sites may be located on the formerly exposed land mass of the outer continental shelf (Stright 1986).
In the Gulf of Mexico, submerged resources are defined and protected by federal legislation including the National Environmental Protection Act (NEPA 1969), National Historic Preservation Act (NHPA 1966), and Executive Order 11593, among others. When ground-disturbing activities are planned in areas designated as potentially archaeologically significant, offshore energy developers are required to submit a survey and assessment of potential cultural resources present in the project area that may be negatively impacted by lease development. If historically significant archaeological resources are identified, the federal government can and often does require that the operator move their proposed activity to avoid the resource. The assigned avoidance serves two purposes: it protects underwater cultural heritage for the benefit of future generations and also protects offshore workers during operations since archaeological sites can create hazardous working conditions.