How climate change rewrites metal decay: forecasting ancient shipwreck corrosion under acidified seawater

Underwater cultural heritage sites are under increasing pressure from emerging environmental risks: warmer waters and changing seawater chemistry are accelerating corrosion processes in ways that remain difficult to quantify in terms of their impacts on protected archaeological metals. This work proposes an experimental approach that makes these changes measurable and comparable across sites using metallic coupons carefully selected to match materials revealed from a series of wrecks. Coupons were deployed at different depths at four different locations, and retrieved at fixed time intervals. The development of corrosion layers, concretions, and biofouling in the natural environment was investigated. Observations were integrated with results from a second experimental approach. The same set of coupons was exposed to controlled environmental conditions using a custom Micro-Environment Simulator (MES). MES was set to reproduce marine conditions at 4 bar gauge pressure (40 m depth), 20 °C water temperature, and pH 7.7, simulating ocean acidification by the end of this century according to the CMIP6 projections for the Mediterranean under the SSP5-8.5 Warming 4 °C scenario. Results have shown a significant shift in electrochemical equilibria under declining pH, significantly influencing the stability of the corrosion products, and determining a shift in the behaviour of the corrosion layers from protective barrier to pathway for continued metal loss. By linking corrosion behaviour to specific environmental settings, the approach provides indicators of when and where deterioration is likely to accelerate under future scenarios. These outputs support preventive strategies for underwater metallic heritage by identifying high-risk wreck contexts, and guiding actions before irreversible loss occurs.

Acknowledgement:

This research has been funded by European Union’s Horizon Europe research and innovation programme under THETIDA project (Grant Agreement No. 101095253) (Technologies and methods for improved resilience and sustainable preservation of underwater and coastal cultural heritage to cope with climate change, natural hazards and environmental pollution).