Formation processes in underwater archaeology: A study of chemical and biological deterioration.

Archaeological formation processes involve the interactions whereby intrusive human induced evidence reaches a state of balance with its environment. Archaeological material in seawater is subject to a particularly complex set of formation influences because of the range of physical, chemical and biological factors concerned. Controlled experiments were conducted in the laboratory and on three submerged sites in British waters over 52 weeks to determine which chemical and biological processes were responsible for the deterioration of a range of modern organic materials and metals. Understanding the effects these processes had on the materials would enable better interpretation of the submerged archaeological record. In addition, by understanding the environmental factors which affected the deterioration of the materials, it would be possible to suggest methods to mitigate there effects and facilitate better in situ stabilisation and preservation of submerged sites. The results showed that the two categories of material were deteriorated by quite different processes. Essentially the organic materials were subject to biodeterioration through successive colonisation by micro and macro organisms and algae. The most important environmental parameters governing biodeterioration being seasonality and the presence of oxygen in seawater. The metals mainly underwent electrochemical corrosion, although there was evidence of corrosion induced by micro and macro organisms. The environmental parameters affecting corrosion were mainly the salinity of the seawater. To mitigate the effects of these environmental parameters it is suggested that organic materials be re-buried and the redox potential and biochemical oxygen demand of the interstitial water of the re-buried sediment be monitored. It is suggested that in order to preserve metal artefacts in situ the corrosion potential of the surface of corroding metal artefacts should be measured and sacrificial anodes attached.