Timbers archaeological

The marine environment presents a hostile and seemingly unlikely situation for the survival of archaeological wood, yet it does survive. Normally, wood does not survive long enough in marine environments to enter the archaeological record because of the activities of wood-boring animals and aerobic microbes. However, studies have shown that rapid burial in the anoxic sediments of the seabed will protect ships timbers and wooden artefacts from the physical, chemical and biological processes that influence the deterioration of exposed wood. 

Research at the Mary Rose Trust has shown that gamma irradiation is a superior alternative to low temperature and biocide treatments of polyethylene-wrapped timbers and has been adopted by the Trust since 1998. Screening a range of bacteria and fungi isolated from waterlogged archaeological wood revealed that a dose of 15 KGy is required for the inactivation of most organisms (see Table 2). 

Figure 15 Covering of exposed archaeological timbers with Terram 4000 (geotextile). Note the growth of marine plants on Terram surface (After Poumou, 1999)...

Several archaeological excavations provided samples of waterlogged European oak (Quercus sp.), European ash Fraxinus excelsior L.), Dutch elm Ulmus campestris L.), white-poplar Populus alba L.), and European spruce Picea abies (L.) Karst). The timbers were 400-2000 years old and had been covered by marine sediments. Cross sections were cut from timbers 10-20 cm in diameter and samples were taken from macroscopically discernible zones of different states of degradation, as well as from the border between these zones (Figure 1). 

Advanced bacterial attack has been observed in wooden foundation piles below the water table 101, 102, 113, 114). Waterlogged timber extracted at archaeological excavations in Uppsala, Sweden, was extensively degraded by erosion bacteria. 

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