Effects of wood anisotropy on Teredo naval is attack and its implications for in -situ preservation of archaeological wood in the marine environment

Anne Marie Eriksen, Niels Lynnerup, Chiara Villa, David Gregory, Knud Bo Botfeldt, Arne Redsted Rasmussen

Publikation: KonferencebidragPosterForskningpeer review

Abstrakt

When exposed on the seabed, waterlogged archaeological wood in the marine
environment can be subjected to degradation by Teredo navalis (commonly
known as shipworm). The degradation is swift and devastating as the artefact
can disappear within months. In-situ preservation of archaeological materials has
become more widespread since the UNESCO Convention on the Protection of
the Underwater Cultural Heritage and the Valletta Treaty. Therefore, there is a
need to understand the attack rate of T. navalis taking the anisotropy of wood into
consideration, primarily because in the past ship building has often exploited the
different structural properties created by the material’s inherent anisotropy. When
experimenting with protective methods against marine borers, such as shipworm,
the British Standard BS EN 275:1992 is often used. The standard states that wood
blocks are cut in tangential section, but to the authors’ knowledge no published
experiments about the effects of wood anisotropy on shipworm attack have been
carried out. The aim of this study was to investigate whether shipworms preferentially
degraded one orientation over another, i.e. radial, tangential or cross-sectional
and if the resulting tunnels are oriented in a specific direction according to the
tree fibres within the wood. Computed tomography (CT) scanning is a digital
geometry process used to generate a three-dimensional image of the inside of an
object such as a wooden block. Blocks of pine were cut with tangential, radial
and cross sections, the remaining sides were closed with epoxy and the blocks
were placed in the sea at a location where shipworms were known to be prolific.
After one year’s submersion, an attack was detected and the blocks were weighed,
x-rayed, CT-scanned and entrance holes were counted. The preliminary results
show a significant difference in the weight loss between all three sections, where
the tangential section suffered a 15% weight loss, radial 24% and cross section
13%. The number of larval entrance holes on the surface also varied, where twice
as many were seen in the radial section compared to the cross section, indicating
a selective attack pattern. X-ray imaging shows a severe attack on all blocks, but
the single tunnels can be difficult to follow on the image. CT-scanning images
make it possible to isolate single tunnels and follow them throughout the block,
making it possible to examine the specific direction. The current results show
that the attack is likely to follow the radial section of the wood fibres. These
results have implications for archaeological interpretation and conservation.
For example, the results show that ships built in a radial cut may require more
protection than those built in tangential or cross section. As the results also show
that new attacks happen more often in radial than in tangential section, there is
a need for a refinement of the existing test standards.
OriginalsprogEngelsk
Publikationsdato2014
StatusUdgivet - 2014
BegivenhedICOM-CC 17th Triennial Conference: Building Strong Culture through Conservation - ICOM-CC, Melbourne, Australien
Varighed: 15 sep. 201419 sep. 2014

Konference

KonferenceICOM-CC 17th Triennial Conference
LokationICOM-CC
LandAustralien
ByMelbourne
Periode15/09/201419/09/2014

Kunstnerisk udviklingsvirksomhed (KUV)

  • Nej

Citationsformater

Eriksen, A. M., Lynnerup, N., Villa, C., Gregory, D., Botfeldt, K. B., & Redsted Rasmussen, A. (2014). Effects of wood anisotropy on Teredo naval is attack and its implications for in -situ preservation of archaeological wood in the marine environment. Poster session præsenteret på ICOM-CC 17th Triennial Conference, Melbourne, Australien.