Maritime archaeology
Maritime archaeology is a discipline within archaeology as a whole that specifically studies human interaction with the sea, lakes and rivers through the study of associated physical remains, be they vessels, shore-side facilities, port-related structures, cargoes, human remains and submerged landscapes. A specialty within maritime archaeology is nautical archaeology, which studies ship construction and use.
As with archaeology as a whole, maritime archaeology can be practised within the historical, industrial, or prehistoric periods. An associated discipline, and again one that lies within archaeology itself, is underwater archaeology, which studies the past through any submerged remains be they of maritime interest or not. An example from the prehistoric era would be the remains of submerged settlements or deposits now lying under water despite having been dry land when sea levels were lower. The study of submerged aircraft lost in lakes, rivers or in the sea is an example from the historical, industrial or modern era. Another example are the remains of discovered and potential medieval bridges connecting the islands on the lake with the mainland. Many specialist sub-disciplines within the broader maritime and underwater archaeological categories have emerged in recent years.
Maritime archaeological sites often result from shipwrecks or sometimes seismic activity, and thus represent a moment in time rather than a slow deposition of material accumulated over a period of years, as is the case with port-related structures where objects are lost or thrown off structures over extended periods of time. This fact has led to shipwrecks often being described in the media and in popular accounts as 'time capsules'.
Archaeological material in the sea or in other underwater environments is typically subject to different factors than artifacts on land. However, as with terrestrial archaeology, what survives to be investigated by modern archaeologists can often be a tiny fraction of the material originally deposited. A feature of maritime archaeology is that despite all the material that is lost, there are occasional rare examples of substantial survival, from which a great deal can be learned, due to the difficulties often experienced in accessing the sites.
There are those in the archaeology community who see maritime archaeology as a separate discipline with its own concerns and requiring the specialized skills of the underwater archaeologist. Others value an integrated approach, stressing that nautical activity has economic and social links to communities on land and that archaeology is archaeology no matter where the study is conducted. All that is required is the mastering of skills specific to the environment in which the work occurs.
Integrating land and sea
Before the industrial era, travel by water was often easier than over land. As a result, marine channels, navigable rivers and sea crossings formed the trade routes of historic and ancient civilisations. For example, the [|Mediterranean Sea] was known to the Romans as the inner sea because the Roman Empire spread around its coasts.The historic record as well as the remains of harbours, ships and cargoes, testify to the volume of trade that crossed it. Later, nations with a strong maritime culture such as the United Kingdom, the Netherlands, Denmark, Portugal and Spain were able to establish colonies on other continents. Wars were fought at sea over the control of important resources.
The material cultural remains that are discovered by maritime archaeologists along former trade routes can be combined with historical documents and material cultural remains found on land to understand the economic, social and political environment of the past. Of late maritime archaeologists have been examining the submerged cultural remains of China, India, Korea and other Asian nations.
Preservation of material underwater
There are significant differences in the survival of archaeological material depending on whether a site is wet or dry, on the nature of the chemical environment, on the presence of biological organisms and on the dynamic forces present. Thus rocky coastlines, especially in shallow water, are typically inimical to the survival of artifacts, which can be dispersed, smashed or ground by the effect of currents and surf, possibly leaving an artifact pattern but little if any wreck structure.Saltwater is particularly inimical to iron artefacts including metal shipwrecks, and sea organisms will readily consume organic material such as wooden shipwrecks. On the other hand, out of all the thousands of potential archaeological sites destroyed or grossly eroded by such natural processes, occasionally sites survive with exceptional preservation of a related collection of artifacts. An example of such a collection is. Survival in this instance is largely due to the remains being buried in sediment.
Of the many examples where the sea bed provides an extremely hostile environment for submerged evidence of history, one of the most notable,, though a relatively young wreck and in deep water so calcium-starved that concretion does not occur, appears strong and relatively intact, though indications are that it has already incurred irreversible degradation of her steel and iron hull. As such degradation inevitably continues, data will be forever lost, objects' context will be destroyed and the bulk of the wreck will over centuries completely deteriorate on the floor of the Atlantic Ocean. Comparative evidence shows that all iron and steel ships, especially those in a highly oxygenated environment, continue to degrade and will continue to do so until only their engines and other machinery project much above the sea-floor. Where it remains even after the passage of time, the iron or steel hull is often fragile with no remaining metal within the layer of concretion and corrosion products., having been found in the 1970s, was subjected to a program of attempted in situ preservation, for example, but deterioration of the vessel progressed at such a rate that the rescue of her turret was undertaken lest nothing be saved from the wreck.
Some wrecks, lost to natural obstacles to navigation, are at risk of being smashed by subsequent wrecks sunk by the same hazard, or are deliberately destroyed because they present a hazard to navigation. Even in deep water, commercial activities such as pipe-laying operations and deep sea trawling can place a wreck at risk. Such a wreck is the Mardi Gras shipwreck sunk in the Gulf of Mexico in of water. The shipwreck lay forgotten at the bottom of the sea until it was discovered in 2002 by an oilfield inspection crew working for the Okeanos Gas Gathering Company. Large pipelines can crush sites and render some of their remnants inaccessible as pipe is dropped from the ocean surface to the substrate thousands of feet below. Trawl nets snag and tear superstructures and separate artifacts from their context.
The wrecks, and other archaeological sites that have been preserved have generally survived because the dynamic nature of the sea bed can result in artifacts becoming rapidly buried in sediments. These sediments then provide an anaerobic environment which protects from further degradation. Wet environments, whether on land in the form of peat bogs and wells, or underwater are particularly important for the survival of organic material, such as wood, leather, fabric and horn. Cold and absence of light also aid survival of artifacts, because there is little energy available for either organic activity or chemical reactions. Salt water provides for greater organic activity than freshwater, and in particular, the shipworm, Teredo navalis, lives only in salt water, so some of the best preservation in the absence of sediments has been found in the cold, dark waters of the Great Lakes in North America and in the Baltic Sea.
While the land surface is continuously reused by societies, the sea bed was largely inaccessible until the advent of submarines, scuba equipment and remotely operated underwater vehicles in the twentieth century. Salvagers have operated in much earlier times, but much of the material was beyond the reach of anyone. Thus Mary Rose was subject to salvage from the sixteenth century and later, but a very large amount of material, buried in the sediments, remained to be found by maritime archaeologists of the twentieth century.
While preservation in situ is not assured, material that has survived underwater and is then recovered to land is typically in an unstable state and can only be preserved using highly specialised conservation processes. While the wooden structure of Mary Rose and the individual artifacts have been undergoing conservation since their recovery, provides an example of a relatively recent wreck for which extensive conservation has been necessary to preserve the hull. While the hull remains intact, its machinery remains inoperable. The engine of that was recovered in 1985 from a saline environment after over a century underwater is presently considered somewhat anomalous, in that after two decades of treatment it can now be turned over by hand.
A challenge for the modern archaeologist is to consider whether in-situ preservation, or recovery and conservation on land is the preferable option; or to face the fact that preservation in any form, other than as an archaeological record is not feasible. A site that has been discovered has typically been subjected to disturbance of the very factors that caused its survival in the first place, for example, when a covering of sediment has been removed by storms or the action of man. Active monitoring and deliberate protection may mitigate further rapid destruction making in situ preservation an option, but long-term survival can never be guaranteed. For very many sites, the costs are too great for either active measures to ensure in situ preservation or to provide for satisfactory conservation on recovery. Even the cost of proper and complete archaeological investigation may be too great to enable this to occur within a timescale that ensures that an archaeological record is made before data is inevitably lost.