Rusticle

Abstract: During a post-installation inspection of a polyester and chain mooring system in water depths of approximately 6,000 ft, evidence of microbiologically influenced corrosion (MIC) was found in the form of rust tubercles known as rusticles. These porous concretions commonly form on submerged steel shipwrecks and provide evidence that subsea corrosion occurs in a hypoxic environment. Iron and sulfate-reducing bacteria cause corrosion in marine environments. This paper will discuss one form of MIC found on submerged steel structures, analyze the ambient conditions required for MIC to occur, and compare rusticles found during the mooring inspection to those found on other subsea shipwrecks such as the RMS Titanic. An analysis of the type of iron used in mooring chains and the rate of rusticle formation will be presented. Possible remedies to prevent rusticle growth on mooring chains will be summarized.

Abstract: Since the sinking of the RMS Titanic in 1912, there has occurred a growing mass of iron-rich bioconcretious structures called rusticles, on the steel surfaces of the ship. Recording the growth rates has only been possible since the ships discovery in 1986, but a cycle has been established in which iron and other elements are being biologically extracted from the steel into therse rusticle structures and exported into the oceanic environment as biocolloids.

Abstract: Meter length iron-rich rusticles on the RMS Titanic contain bacteria that reportedly mobilize iron from the ship structure at a rate that will reduce the wreck to rust in decades. Other sunken ships, such as the World War II shipwrecks in the Gulf of Mexico (GOM) are also similarly covered. However, at the GOM sites, rusticles are only centimeters in length. Minimal differences in water temperature (a few °C) between the two sites and comparable exposure times from wreckage to discovery cannot rationalize the extreme differences in rusticle length. One possible explanation for the observed difference in rusticle size is the differing amounts of dissolved or colloidal iron at the two locations.