Corrosion and conservation management of iron shipwrecks in Chuuk Lagoon, Federated States of Micronesia

Abstract

A series of in situ corrosion measurements on World War II Japanese merchant and military vessels sunk in Chuuk (Truk) Lagoon in 1944 was conducted in 2002 as part of a study of the cultural heritage values of the wreck sites. The data provide evidence of episodic loss of the protective layer of marine concretion, which directly increases corrosion of the underlying metal and removal of the archival microenvironment record. It is likely that dynamite ‘fishing’ is the most likely cause of such losses. All the vessels, apart from the Fujikawa Maru, showed a corrosion mechanism that is common to historic iron shipwrecks. The apparent sensitivity of the corrosion potentials and the pH of the corroding interfaces to water depth have been interpreted in terms of the overall amount of water movement and the aspect or orientation of the wrecks with regard to being horizontal, upside down or inclined. Corrosion rate equations predict that many of the wrecks in Chuuk Lagoon will retain their existing integrity for the next ten to fifteen years before undergoing significant collapse. The corrosion rates in Chuuk Lagoon were between 26%and 30% lower than the iron shipwrecks at the same depth in open-ocean waters.