Preservation of shipwrecks and associated metal artifacts is an important aspect to preserve historical marine archaeological sites. Many shipwrecks are in oxygenated environments that result in some degree of corrosion of the metal components of the ships and metal artifacts. This process, though causing some damage, can act as a protective layer preventing further degradation. However, once portions of ships and other metal artifacts are retrieved, corrosion products removed and the underlying metal exposed to surface conditions, the metals experience additional and accelerated corrosion.
Marine iron corrosion products, called rusticles, are described as containing oxidized metals that are present as a result of bioaccumulation, have a high degree of porosity, and distinct microbial communities. Chemically, rusticles are purported to provide insights into goods ships were transporting at the time it sank. The idea being goods being transported would disassociate and their elements would become incorporated into the rusticle by bioaccumulation.
The purpose of this study is to determine the internal morphology of rusticles and the relationship between the internal speciation and spatial distribution of mineral phases and the elemental distribution in rusticles. This will be accomplished by examining rusticle samples from three historic shipwrecks from the Gulf of Mexico using synchrotron-based micro-XRD, micro-XAS and micro-XRF mapping along with traditional bulk powder XRD and ICP analyses.
The findings from this study will provide the first in-situ micro-scale assessment of the distribution of iron oxide/oxyhydroxides, their percent, the relative elemental distribution and general associations with the bacterial community within rusticles. This information is necessary to develop more effective preservation techniques of iron artifacts from marine archaeological sites. In addition this data set could also be used to develop more effective corrosion protection of iron-based metals used today in marine environments world-wide.
Tammie Gerke, Andrew Sylvester and Steven Marshall from Miami University investigate rusticles at 13 IDE. Rusticles were examined using in-situ micro-XRF to obtain the metal distribution throughout the rusticles and to obtain insights to Fe speciation and possible mechanism(s) of adsorption or inclusion into discrete phases.
Morphologically the rusticle from the Robert E. Lee was whorl-shaped and appeared to be composed of layers building from the center outward that were reddish-brown to orange in color. Mineralogically the rusticle consisted primarily of α-FeOOH (goethite) and minor amounts of γ-FeOOH (lepidocrocite).
Samples from the Gulf Penn had plate-like morphologies and were orange-brown mounds of α-FeOOH.
At 22.30 hours on 30 Jul 1942 the Robert E. Lee was hit by one torpedo from U-166. steaming at 16 knots about 25 miles southeast of the entrance to the Mississippi River. Lookouts had spotted the torpedo wake about 200 yards away before it struck just aft of the engine room.The badly damaged Robert E. Lee first listed to port then to starboard and finally sank by the stern about 15 minutes after the torpedo hit. One officer, nine crewmen and 15 passengers were lost.The German U-boat, U-166, which launched the attack, was sunk with no survivors. Its wreck cannot be disturbed, now protected as a war grave for the 52 crew lost.
The Exploration Vessel Nautilus’s cameras via a remotely controlled submersible, provide spectacular footage as it explores the site of SS Robert E. Lee. The stricken vessels lie almost 5,000 feet deep and serve as silent grave sites for the souls who lost their lives as they went down.