Underwater archaeology is the study of past
humanlife, behaviours and cultures using the physical remains found in salt or fresh wateror buried beneath water-logged sedimentMuckelroy, K., Maritime archaeology. Cambridge University Press 1978. ISBN 0-521-29348-0] . It is most often considered as a branch of maritime archaeology. Due to the difficulties of accessing underwater sites, the application of archaeology to underwater sites emerged from the skills and tools developed by salvagers [ [http://www.abc.se/~pa/uwa/history.htm A history of underwater archaeology] from Per Akesson, Nordic Underwater Archaeology] , and underwater archaeology initially struggled to establish itself as proper archaeological research [Gibbins, D., and Adams, J., Shipwrecks and maritime archaeology, in "World Archaeology", Vol 32(3) pp 279-291] . Underwater archaeologicalsites consist of wrecks ( shipwrecksor aircraft); the remains of structures created in water (such as crannogs, bridges or harbours); refuseor debrissites where people disposed of their waste, garbageand other items by dumping into the water; or places that where once people lived, that have been subsequently covered by water due to rising sea levels or other phenomena.
There are many reasons why underwater archaeology can make a significant contribution to our knowledge of the past. Some individual
shipwrecks are of significant historical importance either because of the magnitude of loss of life (such as the Titanic) [http://www.titanicinquiry.org/ Titanic inquiry] ,] , or circumstances of loss ("Housatonic" was the first vessel in history sunk by an enemy submarine [http://www.history.navy.mil/danfs/h8/housatonic-i.htm Dictionary of American Fighting Ships - Housatonic] ] ). Shipwrecks (such as The Mary Rose) can also be important for archaeology because they can form a kind of accidental time capsule, preserving an assemblage of human artifacts at the moment in time when the ship was lost.] [ [http://www.bbc.co.uk/worldservice/documentaries/2008/08/080821_what_lies_beneath.shtml BBC Radio World Service Broadcast, "What Lies Beneath" First broadcast Friday 22 August 2008] ] [http://www.maryrose.org/ Mary Rose official website] ] .
Sometimes it is not the wrecking of the ship that is important, but the fact that we have access to the remains of it, especially where the vessel was of major importance and significance in the history of science and engineering (or warfare), due to being the first of its type of vessel. The development of submarines, for example, can be traced via underwater archaeological research, via the "
Hunley" which was the first submarine to sink an enemy ship ] ("Hunley" also had unique construction details not found in previous vessels and was one of the only historic warships ever raised intact), the Resurgam II, the first powered submarine cite web | title=Advisory Committee on Historic Wreck Annual Report 2005 | url=http://www.english-heritage.org.uk/upload/pdf/ACHWS_annual_report_2005.pdf | accessdate = 2006-10-06] , and Holland 5, which provides insight into the development of submarines in the British Navy [http://www.culture.gov.uk/Reference_library/Press_notices/archive_2005/dcms001_05.htm DCMA press release on protection of Holland V] ] ;
Underwater archaeology is often complementary to archaeological research on dry sites because materials are preserved differently under water than on dry sites on land. In anaerobic, cold and dark conditions underneath waterlogged sediments, organics, such as
plants, leather, fabric and woodmay be preserved as on "Hunley" and "Mary Rose". These materials may still have evidence of how they were worked, such as tool markson the surface of wood. This evidence can provide new insights into ancient crafts, culturesand lifestyles.
Underwater archaeology is not just about shipwrecks. Changes in
sea-level, because of local seismicevents, such as the earthquakes that devastated Port Royal[http://nautarch.tamu.edu/portroyal/ Port Royal Project] ] and Alexandria, or more widespread climaticor changes on a continental scale mean that some sites of human occupation that were once on dry land are now submerged [http://www.soton.ac.uk/mediacentre/news/2007/jul/07_90.shtml University of Southampton Press Release about submerged Mesolithic Site] ] . At the end of the last ice age the North Seawas a great plain, and anthropological material, as well as the remains of animals such as mammoths are sometimes recovered by trawlers. Also, because human societies have always made use of water, sometimes the remains of structures that these societies built underwater still exist (such as the foundations of crannogs[http://www.crannog.co.uk/ The Scottish Crannog Centre] ] , bridges and harbours) when traces on dry land have been lost.
Underwater sites are inevitably difficult to access, and more hazardous, compared with working on dry land. In order to access the site directly,
diving equipmentand diving skills are necessary. The depths that can be accessed by divers, and the length of time available at depths, are limited. For deep sites beyond the reach of divers, submarinesor remote sensingequipment are needed.
For a marine site, some form of working platform (typically a
boator ship) is needed. This creates logisticsproblems. A working platform for underwater archeology needs to be equipped to provide for specialist remote sensing equipment, analysis of archaeological results, support for activities being undertaken in the water, storage of supplies, facilities for conservation for any items recovered from the water, as well as accommodation for workers. Equipment used for archaeological investigation, including water dredgeand air liftscreate additional hazards and logistics issues. Moreover, marine sites may be subject to strong tidalflows or poor weather which mean that the site is only accessible for a limited amount of time.
Underwater sites are often dynamic, that is they are subject to movement by currents, surf,
stormdamage or tidal flows. Structures may be unexpectedly uncovered, or buried beneath sediments. Over time, exposed structures will be eroded, broken up and scattered. The dynamic nature of the environment may make in-situ conservationinfeasible, especially as exposed organics, such as the wood of a shipwreck, are likely to be consumed by marine organisms such as piddocks. In addition, underwater sites can be chemically active, with the result that iron can be leached from metal structures to form concretions. The original metal will then be left in a fragile state. Artifacts recovered from underwater sites need special care. Visibilitymay be poor, because of sediments or algaein the water and lack of light penetration. [cite journal |author=FJ Cantelas and BA Rodgers |title=Tools, Techniques, and Zero Visibility Archaeology. |journal=In: EJ Maney, Jr and CH Ellis, Jr (Eds.) Diving for Science...1997. |volume=Proceedings of the American Academy of Underwater Sciences |issue=17th Annual Scientific Diving Symposium |date=1997 |url=http://archive.rubicon-foundation.org/4636 |accessdate=2008-07-04 ] This means that survey techniques that work well on land (such as triangulation), generally can not be used effectively under water.
In addition it can be difficult to allow access to the results of the archaeological research as underwater sites do not provide good
outreachpossibilities or access for the general public. Work has been done to bridge this difficulty with the excavation of the " Queen Anne's Revenge". [cite journal |author=C Southerly and J Gillman-Bryan. |title=Diving on the Queen Anne's Revenge. |journal=In: SF Norton (ed). Diving for Science...2003. |volume=Proceedings of the American Academy of Underwater Sciences |issue=22nd Annual Scientific Diving Symposium |date=2003 |url=http://archive.rubicon-foundation.org/4760 |accessdate=2008-07-04 ]
Although specialised techniques and tools have been developed to address the challenges of working under water, the archaeological goals and process are essentially the same as in any other context. Investigating an underwater site however, is likely to take longer and be more costly than an equivalent terrestrial one.
An important aspect of project design is likely to be managing the
logisticsof operating from a boat and of managing diving operations. The depth of water over the site, and whether access is constrained by tides, currents and adverse weather conditions will create substantial constraints on the techniques that can feasibly be used and the amount of investigation that can be carried out for a given cost or in a set timescale. Many of the most carefully investigated sites, including the "Mary Rose" ] have relied substantially on avocational archaeologists working over a considerable period of time.
As with archaeology on land, some techniques are essentially manual, using simple equipment (generally relying on the efforts of one or more scuba divers), while others use advanced technology and more complex logistics (for example requiring a large support vessel, with equipment handling cranes, underwater communication and computer visualisation).
Knowing the location of an archaeological site is fundamental to being able to study it. In the open sea there are no landmarks, so
position fixingis generally achieved using GPS. Historically, sites within sight of the shore would have been located using transects. A site may also be located by visually surveying some form of marker (such as a buoy) from two known (mapped) points on land. The depth of water at a site can be determined from charts or by using the depth sounding sonar equipment that is standard equipment on ships. Such sonar can often be used to locate an upstanding structure, such as a shipwreck, once GPS has placed the research vessel in approximately the right location.
The type of survey required depends on the information that is needed to resolve archaeological questions, but most sites will need at least some form of topographical survey and a site plan showing the locations of artifacts and other archaeological material, where samples were taken and where different types of archaeological investigation were carried out. Environmental assessment of archaeological sites will also require that environmental conditions (water chemistry, dynamic properties) as well as the natural organisms present on the site are recorded. For shipwrecks, particularly post-industrial age shipwrecks, pollution threats from wreck material may need to be investigated and recorded.
The simplest approach to survey is to carry out three dimensional
surveying[http://www.threeh.demon.co.uk/ 3D survey resource site from 3H] ] by divers using depth gauges and tape measurements. Research [http://www.threeh.demon.co.uk/Downloads/Tape%20Accuracy%20Paper.pdf Research on the accuracy of tape survey methods from 3H] ] shows that such measurements are typically less accurate than similar surveys on land. Where it is not practical or safe for divers to physically visit a site, Remotely Operated Vehicles (ROVs) enable observation and intervention with control by personnel located at the surface [http://oceanexplorer.noaa.gov/technology/subs/rov/rov.html NOAA Ocean Explorer: Remotely Operated Vehicle] ] . The low technology approach of measuring using tape measures and depth gauges can be replaced with a more accurate and quicker high technology approach using acoustic positioning [http://www.wessexarch.co.uk/projects/marine/alsf/wrecks_seabed/round2/acoustic-positioning.html Acoustic Tracking system used by Wessex Archaeology] ] . Remote sensingor Marine Geophysics [http://www.wessexarch.co.uk/projects/marine/alsf/wrecks_seabed/geophysical_survey_methodology.html Marine Geophysics from Wessex Archaeology] ] is generally carried out using equipment towed from a vessel on the surface and therefore does not require any one, or any equipment to actually penetrate to the full depth of the site. Sensitive sonar, especially side-scan sonaror multi-beam sonar[http://www.wessexarch.co.uk/projects/marine/alsf/wrecks_seabed/multibeam_sonar.html Multibeam sonar evaluated by Wessex Archaeology] as part of ALSF funded "Wrecks on the Seabed" project] may be used to image an underwater site. Magnetometry [http://www.wessexarch.co.uk/projects/marine/alsf/wrecks_seabed/magnetometer.html Magnetometry evaluated by Wessex Archaeology] as part of ALSF funded "Wrecks on the Seabed" project] can be used to locate metal remains such as metal shipwrecks, anchorsand cannons. Sub-bottom profiling[http://www.wessexarch.co.uk/projects/marine/alsf/wrecks_seabed/sub_bottom_profiler.html Sub-bottom profiling sonar evaluated by Wessex Archaeology] as part of ALSF funded "Wrecks on the Seabed" project] [http://eprints.soton.ac.uk/39914/01/pdf_paper.pdf Sub-bottom profile investigation of the "Grace Dieu" from The University of Southampton] ] utilizes sonar to detect structures buried beneath sediment.
A variety of techniques are available to divers to record findings underwater.
Scale drawingis the basic tool of archaeology and can be undertaken underwater. Pencils will write underwater on permatrace, plastic dive slates, or matt laminatedpaper. Photographyis the mainstay of recording, and with the advent of digital cameras is cheap and convenient. For underwater use, cameras, including video camerascan be provided with special housingsthat enables them to be used underwater. Low visibility underwater and distortion of image due to refraction mean that perspective photographs can be difficult to obtain. However, it is possible to take a series of photographs at adjacent points and then combined into a single photomontage or photomosaic image of the whole site .
Where intrusive underwater excavation is appropriate, silts and sediments can be removed from an area of investigation using a
water dredgeor airlift. When used correctly, these devices have an additional benefit in tending to improve the visibility in the immediate vicinity of the investigation.
A variety of
archaeological sciences are used in underwater archaeology. Dendrochronologyis an important technique especially for dating the timbers of wooden ships. It may also provide additional information, including the area where the timber was harvested (i.e. likely to be where the ship was built) and whether or not there are later repairs or reuse of salvaged materials. Because plant and animal material can be preserved underwater, archaeobotanyand archaeozoologyhave roles in underwater archaeology. For example, for submerged terrestrial sites or inland water, identification of pollensamples from sedimentary or silt layers can provide information on the plants growing on surrounding land and hence on the nature of the landscape. Information about metal artifacts can be obtained through X-rayof concretions. Geologycan provide insight into how the site evolved, including changes in sea-level, erosionby rivers and depositionby rivers or in the sea.
Artifact recovery and conservation
Artifacts recovered from underwater sites need stabilization to manage the process of removal of water and conservation [ [https://www.denix.osd.mil/denix/Public/ES-Programs/Conservation/Underwater/archaeology.html Basic Methods of Conserving Underwater Archaeological Material Culture] ] [ [http://oregonstate.edu/~veilleuc/UnderwaterArch/UnderwaterArch.htm Conservation methods of underwater artifacts] ] . The artifact either needs to be dried carefully, or the water replaced with some inert medium (as in the case of
The Mary Rose). Artifacts recovered from salt water, particularly metalsand glassneed be stabilized following absorption of salt or leaching of metals. In-situ conservation of underwater structures is possible, but consideration needs to be given to the dynamic nature of the site. Changes to the site during intrusive investigation or removal of artifacts may result in scouringwhich exposes the site to further deterioration.
Interpretation and presentation of underwater archaeology
Diver trailscan be used to allow scuba-divers to visit and understand archaeological sites that are suitable for scuba-diving. Otherwise presentation will typically rely on publication (book or journalarticles, web-sites and electronic media such as CD-ROM). Television programmes can attempt to provide an understanding of underwater archaeology to a broad audience.
Publication is an essential part of the archaeological process and is particularly crucial for underwater archaeology, where sites are generally not accessible and it is often the case that sites are not preserved in-situ.
The specialist journals on
maritime archaeology, which include the long established International Journal of Nautical Archaeology and the recently launched Journal of Maritime Archaeology [http://www.springer.com/11457 Journal of Maritime Archaeology] ] publish articles about archaeological research under water. However, research on underwater sites can also be published in mainstream archaeological journals, or thematic archaeological journals.
The public interest market is covered by a number of diving, shipwreck and underwater archaeology books, beginning with the works of
The techniques of underwater archaeology are also documented in published works, including a number of handbooks [http://www.springer.com/978-0-306-46345-7 International Handbook of Underwater Archaeology] ] Archaeology Underwater, The NAS Guide to Principles and Practice; eds Martin dean, Ben Ferrari, Ian Oxley, Mark Redknap and Kit Watson. Published by Nautical Archaeology Society, Archetype Press, 1992 ISBN 1-873132-25-5] , and Muckelroy's classic work on Maritime Archaeology ] .
UNESCO Convention on the Protection of the Underwater Cultural Heritage
Archaeological Divers Association
Nautical Archaeology Society
Archaeology of shipwrecks
Underwater Archaeology Centre
Sea Research Society
Underwater search and recovery
* [http://www.uri.edu/mua The Museum of Underwater Archaeology (MUA)]
* [http://www.LAMPmaritime.org Lighthouse Archaeological Maritime Program (LAMP), St. Augustine, Florida]
* [http://www.cma.soton.ac.uk Centre for Maritime Archaeology University of Southampton]
* [http://www.science.ulster.ac.uk/cma/ Centre for Maritime Archaeology, University of Ulster, Coleraine]
* [http://ina.tamu.edu/ Institute of Nautical Archaeology]
* [http://www.abc.se/~pa/uwa/ Nordic Underwater Archaeology]
* [http://www.bris.ac.uk/archanth/postgrad/maritime.html/ Centre for Historical and Maritime Archaeology, University of Bristol]
* [http://ehlt.flinders.edu.au/archaeology/welcome/maritime.php Flinders University Maritime Archaeology Program]
* [http://www.aima.iinet.net.au/home/aimaethic.html A Code of Ethics for Maritime Archaeologists by Australian AIMA]
* [http://www.shipwrecks.com/ethics_in_underwater_archaeology.htm Ethics in Underwater Archaeology (Capitalism versus Socialism in Underwater Archaeology) by E. Lee Spence]
* [http://www.science.ulster.ac.uk/cma/slan/ Submerged Landscapes Archaeological Network]
* [http://vanth.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus%3Atext%3A1999.04.0006%3Aid%3Dshipwrecks "Shipwrecks" in Stillwell, Richard, William L. MacDonald, Marian Holland McAllister, eds. "Princeton Encyclopedia of Classical Sites", 1976, Includes alphabetized list of known wreck sites from Classical Antiquity.]
* [http://gmsbc.blogspot.com/ Resources for maritime archaeologists]
* [http://tauac.typepad.com/ac/2007/05/tau_researchers.html Maritime Archeology in Israel]
* [http://www.maritimehistory.org/ Institute of Maritime History]
* [http://www.ecu.edu/maritime/ East Carolina University Maritime Studies]
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