Building an interdisciplinary bridge of wood … samples

By Mohamed Traoré

Interest in visiting the sampling site

The shared scientific interests between the members of ForSEAdiscovery may strengthen relationships within the project, yet some joint contributions stem from outside the scientific viewpoint, strictly speaking. It was obvious that during the project’s first nautical archaeology timber sampling campaign in Galicia, members were glad to have the encouragement from fellows outside their own discipline even as they took the responsibility for supplying the wood scientists with materials from underwater.

The 2015 campaign in Galicia was a great opportunity for other project fellows outside the field of nautical archaeology to learn about this unique methodology. Being in the field with them was also an ideal way to satisfy a bit of curiosity related to doing archaeology underwater, and scientifically, this background knowledge may have laboratory relevance as we go through the processes of analytical data interpretation.

Observations of nautical archaeology at work

Getting wood samples from shipwrecks is not quite simple as it sounds. It requires not only looking for appropriate samples on shipwreck sites, but ensuring the safety of diving archaeologists in the meantime. Before jumping into the sea, all of the diving equipment has to be checked off from the supervisor’s checklist, and only then is the diver is ready for the next adventure. Not all of the diving team gets in the water at the same time; there is always one diver fully dressed who stays out of water, the standby diver. The presence of a standby diver is not surprising considering the risks, but at the same time, the importance of this person’s role cannot be underestimated.

Diving archaeologists waiting at the anchor for permission to descend.

Diving archaeologists waiting at the anchor line in Ribadeo for permission to descend.

Yet another great part of that archaeological sampling work has to be done outside the sea, when the team gets back to land. That work concerns sample inventory, organization, and basic conservation. The samples are technically described in as much detail as possible in order to fully document each piece of shipwreck wood for what it is: an archaeological artefact. This part is also very important and requires patience and attention until forwarding the samples on to the various wood science laboratories for further analyses.

These different stages of in situ shipwreck sampling demonstrate the importance of teamwork. In addition to the technical skills needed to work in this research field, the personality of each team member plays a significant role in how results are obtained.

The first step to geochemical analysis is taking the sample

The nautical archaeology and wood science components of ForSEAdiscovery are complementary within the project framework, of which one primary element is determining sources for shipbuilding timber in the Early Modern period. Nautical archaeologists are needed by wood scientists for their skills to detect and identify certain ship parts, and diagnose based on context, in addition to their abilities to hunt down the perfect wood sample underwater. Therefore, successes of the analytical investigation process are in part based on the quality of samples delivered by the archaeologists. That is another reason for keeping regular contact with the archaeologists during their sampling campaigns, in order to be able to advise them during sample management.

The diversity of underwater wood samples

Our project is investigating the feasibility of archaeological wood characterization with Fourier Transform Infrared (FTIR) and Pyrolysis coupled with Gas Chromatography / Mass Spectrometry (Py-GC/MS). Using FTIR or Py-GC/MS, the definition of the term ‘sample’ has a variant. Using these techniques, each wood piece could provide a large number of samples depending on the characteristics of the wood fragment and also the objective of the planned analysis. With FTIR and Py-GC/MS, managing a great number of samples is not problematic.

Well-preserved sample of pine hull planking from La Magdalena.

Sample of pine hull planking from La Magdalena. Despite the shipworm damage, this piece was so well-preserved that the whole nave smelled like pine resin!

Wood samples least (or not at all) damaged by natural processes or storage conditions are the best analytical materials. There is a great potential for more accurate data from  undamaged samples than from those with more shipworm holes than actual wood. Since we are trying to analyze samples consistently, those with few tree rings are also less important due to limitations for their use in dendrochronology. Those elusive perfect samples are ones with complete cross-sections (including sapwood and bark), with rings indicating a long-lived tree, and undamaged by wood-boring organisms or poor storage conditions. However, seeing the reality of archaeological wood samples and how they’re obtained, the perfect sample may be more elusive than we’d thought!

Mohamed Traoré is a PhD student studying wood biomarkers by Infrared Spectroscopy and Gas Chromatography-Mass Spectrometry at the Universidad de Santiago de Compostela, Spain.

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One thought on “Building an interdisciplinary bridge of wood … samples

  1. Pingback: Dendroprovenancing shipwreck timbers: on overlaps and pizzas… | ForSEAdiscovery

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