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.

Shipwreck wood often contains soluble salts and iron sulfides, which pose a threat to its stability. Therefore, desalination treatment must be carried out during protection. In this study, deionized water and ethylene diamine tetraacetic acid disodium salt (EDTA-2Na) solution were used to extract soluble salts and iron sulfides from the 511 wood components of the “Huaguangjiao I” shipwreck. The extraction lasted for 1120 days, during which extraction progress was monitored by measuring the electrical conductivity and iron content of the soaking solution. The results indicated that the extraction experiment reached its endpoint when the conductivity of the soaking solution was maintained at 80~100 μs/cm and the iron content was maintained at 8~15 mg/L. More than 143.35 kg of iron were extracted from the wood of the “Huaguangjiao I” shipwreck. After extraction, the content of soluble salt ions in the wood were less than 5 μg/g, with an iron content below 5%. The wood has returned to its original color and with a certain degree of degradation. “Huaguangjiao I” was the first large-scale marine shipwreck to complete the desalination treatment of all wooden components. This study provides guidance for the desalination treatment of large-scale wooden shipwrecks.

Gray siliceous concretions represent the most ubiquitous surface deposits on marine-excavated ceramics from the Nanhai No. 1 shipwreck. These concretions obscure decorative motifs and glaze surfaces of the artifacts, posing challenges to archeological interpretation and heritage conservation. This study conducted a multi-technique characterization of one representative gray siliceous concretion using micro-CT, PLM, SEM-EDS, XRD, FTIR, and micro-Raman spectroscopy. The concretion exhibits distinct three-tier density stratification and consists of quartz, muscovite, calcite, pyrite, and Mg-rich authigenic silicates (serpentine and talc), with quartz and muscovite as the dominant crystalline phases. Its mineral components are inferred to originate from terrigenous clastic, biogenic, and authigenic sources. This work provides fundamental mineralogical data to support the development of targeted conservation strategies for analogous marine-excavated ceramic heritage.