30 BASICPRINCIPLES – MAKING THEMOST OF THECLUES
opposed to the short-lived but intense process of a ship-
wreck. This may mean that less material is eventually
deposited, as the occupants will have the opportunity to
remove what they want. However, the process of inunda-
tion is likely to be far gentler than the process of ship-
wreck, so more material may survive very near to where
it was actually used and in association with related
objects rather than being scattered.
As soon as objects or structures have fallen out of
use or are lost to become part of the archaeological
record, the environment remains important in helping
to determine what evidence survives, in what form and
in what position. Certain specific conditions will promote
the survival of particular material types. In general, the
more robust materials (such as stone and pottery) survive
better than others (such as wood, textile or leather). The
more aggressive the environment, the less well will deli-
cate materials survive. Studying the nature and impact
of the environment of a site is vital to understanding the
evidence that may eventually be recovered.
The deterioration of organic and inorganic materials
on an underwater site is dependent on physical, chem-
ical and biological factors. The initial formation of a
wreck-site will of course be dependent on physical pro-
cesses such as the nature of the wrecking, the area the
ship is wrecked in (e.g. geographical and topographical)
and type of sea-bed the wreck is finally deposited on
or in. Thereafter, physical processes still play an import-
ant part in the formation of the wreck. The marine
environment is dynamic; wave or tidal action and cur-
rents will affect the sedimentary regimes around a wreck-
site and may cause scouring or silting around a site. Once
the wreck has to some extent stabilized on or in the
sea-bed, chemical and biological processes come into
play and affect the long-term preservation of the wreck-
site. These processes will of course differ depending
on the material in question and there is certainly a need
for further research to investigate the deterioration
of all the different types of materials encountered on
underwater sites. However, one material that is com-
monly encountered on underwater sites is wood and the
processes of its deterioration serves as a good example
to highlight the complex interactions of chemical and
biological processes in the underwater and marine
environment.
THE DETERIORATION OF WOOD
Wood exposed to seawater is rapidly colonized by a vari-
ety of biological agents (rather than chemical agents),
including seaweed, barnacles, wood-boring molluscs
(shipworm) and crustacea (gribble), fungi and bacteria.
Organisms such as seaweeds and barnacles will not cause
extensive deterioration because they are merely using the
wood as a substrate to attach to and not as a source
of nutrients. However, even these can decrease the archa-
eological value of an artefact, as they will degrade the
object’s surface. The major problem under water is the
activity of the wood-borers, fungi and bacteria. Under
the right conditions, they will all rapidly colonize and
utilize various components of the wood as part of their
respiration. This colonization, if left unchecked, will lead
to the complete deterioration of wood in a matter of years
or decades rather than centuries.
This gives rise to the interesting question: why is
archaeological wood preserved at all? The answer lies in
the fact that the organisms that cause deterioration have
particular environmental requirements for their survival.
Shipworm (Teredo spp.) and gribble (Limnoria spp.) are
among the wood-borers that cause the most deterioration
(and concern). All wood-borers require specific salinity,
temperature, depth and dissolved oxygen in order to
respire and grow. As shown by the many well-preserved
wrecks of the Baltic, salinity and temperature are impor-
tant factors. In the Baltic, both of these parameters are
too low to sustain wood-borer activity and as a result
there are some fine examples of organic preservation
(plate 4.3). However, of paramount importance to wood-
borers is the dissolved oxygen within seawater. Even with
optimal temperature and salinity, without dissolved
oxygen the various wood-boring organisms cannot
respire. Thus, if a wooden artefact is rapidly buried in sed-
iments, or lies in anoxic waters, attack by these organisms
will be limited.
This leaves us with the fungi and bacteria. These
micro-organisms will utilize the various celluloses and
lignin within the cell wall as part of their respiration.
Fungi are the most destructive of these micro-organisms
and it is the so-called Brown and White rot fungi
(Basidiomycetes) which are more than likely the cause
for deterioration of wooden finds in non-waterlogged
terrestrial contexts such as the Viking-age ship-grave at
Ladby in Denmark, the remains of which were merely
an imprint of the former ship in the ground. This is
because certain species are capable of completely destroy-
ing wood by utilizing not only the cellulose within
the cell wall but also the lignin, which is the backbone
of wood. These fungi are similarly influenced by environ-
mental factors. In their case, adequate moisture and
oxygen are essential for decomposition to occur. Most
Brown and White rot fungi will tolerate low oxygen
concentrations but they will not grow under anaerobic
conditions and, importantly, they will not tolerate water-
logged conditions. In addition to the Basidiomycetes,
what is termed ‘soft rot’ can be caused by Ascomycetes