Degradation condition and microbial analysis of waterlogged archaeological wood from the second shipwreck site on the northwestern continental slope of the South China Sea

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Abstract

The No. 2 Shipwreck Site on the northwestern continental slope (1488–1505 AD) is situated on the seabed between Hainan Island and the Xisha Islands in the South China Sea, at a depth of ~1500 m. Numerous wooden logs were discovered inside the shipwreck. This study assessed the degradation status of the waterlogged archaeological wood comprehensively. It also employed modern biotechnological methods to analyze the microbial communities within the wood and its surrounding environment. The results revealed that the waterlogged archaeological wood had experienced varying degrees of degradation. Even seemingly intact wood has undergone significant microstructural and chemical changes. Specifically, the secondary cell walls have been damaged, but the compound middle lamella remains relatively intact. Chemically, the degradation of hemicellulose and cellulose has resulted in a disordered arrangement of cellulose microfibrils, thereby weakening the mechanical properties of the wood cell walls. Additionally, a significant amount of iron salts was detected in some of the waterlogged archaeological wood. The microbial community within the wood was found to be predominantly composed of bacteria, with the Proteobacteria and Bacteroidetes phyla being the dominant groups. It is notable that the microbial community within the waterlogged archaeological wood exhibits a high degree of similarity with the microbial communities present in the surrounding seabed sediments and seawater. In conclusion, while some of the waterlogged archaeological wood has retained a relatively intact macroscopic appearance, its microstructure and chemical composition have undergone significant deterioration. Therefore, future conservation efforts should prioritise reinforcement and de-ironing to preserve the research value of these artifacts.

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