Good and bad – the news on climate change and shipwrecks

Around the 39,000km coastline of Australia, about 7500 ships lie beneath the water.

These sunken pieces of history can take visitors back hundreds of years to tragedies that saw lives and cargo lost.

Some are moments frozen in time. Others are now thriving reefs, their gently deteriorating decks and hulls home to generations of fish and coral.

Some of the wrecks attract thousands of visitors to locations around the country.

But as our oceans warm and the climate changes, what will happen to them?

“The impact of climate change on shipwrecks is complex and poorly understood,” a statement from the Department of Climate Change, Energy, the Environment and Water, the department behind the Australian Historic Shipwrecks Program, told Cosmos.

“Climate change can lead to increased mechanical, physical, chemical and biological deterioration of shipwrecks, dependent upon their location, depth, environment, construction and other factors.

“Conversely, climate change could result in positive impacts to some shipwrecks.”

For Dr James Hunter, the Australian National Maritime Museum’s Curator of Naval Heritage and Archaeology, climate change helped uncover the South Australian, off South Australia’s southern coast, a wreck that had lain forgotten until a systematic survey in April 2018.

“When we were talking to one of the guys from South Australia’s Department for Environment and Water, he made the comment that he and his sons actually swam over that same spot in December 2017 – so only a few months prior,” Hunter says.

“They were snorkelling and they didn’t see it.”

In April 2018, however, a survey showed timber from the wreck sticking out of the sand where seagrass beds had depleted.

Further visits to the wreck in 2017 and 2018 showed the wreck slowly emerging from the sand.

Shipwrecks like South Australian give up their secrets

“We know that there was a temperature spike in 2107-2018, and so the best theory that we have is that this temperature spike led to the die-off of the seagrass, which in turn disarticulated, which in turn released the sediment, and uncovered the site,” Hunter says.

The same process that led to the discovery had Hunter fearing for the shipwreck’s future if too much of the ship was exposed to natural processes, but further changes at the site have meant parts of the South Australian have once again been covered over.

An international paper published in 2022 – Of time and tide: the complex impacts of climate change on coastal and underwater cultural heritage – notes archaeological heritage is at risk from the effects of climate change.

“A wide range of physical, chemical and biological deterioration processes, or threats, already acting on these sites are being exacerbated by anthropogenic climate change, as well as by various direct human activities,” the paper says.

But it notes that despite 30 years of work, there was still no “coherent agenda or approach” that brought together all the scientific disciplines and stakeholders needed to study and sustainably manage coastal and underwater heritage.

The study does state there has been a “fundamental change” in the role of the public in heritage preservation, and an increasing awareness of the socio-cultural value of archaeology as part of the “blue economy”.

In Australia, shipwrecks are a strong tourism drawcard.

“Shipwrecks are recognised as a part of Australia’s blue economy, which generates more than $118 billion each year and supports 462,000 jobs,” the Department of Climate Change, Energy, the Environment and Water says.

In some cases, the wrecks help form the identity of a region, such as in the case of Western Australia’s Batavia Coast, or Victoria’s Shipwreck Coast.

“The destruction of these sites may have a direct impact to regional hubs and businesses as well as tourism operators including dive charter businesses and dive shops,” the department said.

So what does happen when a shipwreck is exposed to fresh elements?

According to Hunter, shipwrecks eventually achieve a state of equilibrium in their environment. They initially break up and deteriorate, and then are buried whole or in part by sand.

This creates a deoxygenated environment Hunter says is ideal for preserving wreck material.
“As long as there’s no oxygen in that environment, you don’t have bacteria, and you don’t have macro-organisms to feed on it – because they will,” he says.

“So as long as that environment exists, they’re fine.

“As soon as that protective layer of sediment comes off the reef, then you get oxygen introduced into the environment and that sparks a lot of reactions. You get microbial development, you get macro-organisms, you get sunlight, you get differences in temperature, pH, acidity of the water – all of these different things act on shipwrecks.

“In instances where you get increases in things like acidity, pH, water temperature and salinity, that sort of thing because of changes in climate, that accelerates those processes.

“So yes, we are seeing issues where certain shipwrecks are being affected because of these changes.”

The 2022 paper notes shipwrecks are also susceptible to erosion caused by tidal currents and wave action, which are in turn affected by changing storm and weather patterns.

Then there is the equation of warmer temperatures leading to greater corrosion on metal wrecks.

A 2006 study by researchers at the Western Australian Museum found the average long-term corrosion rate for iron in aerobic seawater was 0.1mm a year. This, the later international 2022 paper states, would lead to only a small increase in corrosion rates over the next 100 years based on worst-case models for temperature increase (2 degrees celsius).

“Temperature change, however, is only one part of a complex process,” the study explains.

In 2017 a review of meter long iron-rich rusticles on the RMS Titanic, the world’s most famous wreck, looked at “…physical, chemical and biological properties of seawater affect the corrosion rates of different metals, including the ratios of the concentrations of the major constituents; the presence of chloride; high electrical conductivity; pH; solubility of gases, especially oxygen and carbon dioxide; and the types of bacteria present and their resulting effect on the corrosion rate.”

The consensus seems to be that climate change can uncover our wrecks and help us in the discovery of ships that have lain forgotten for centuries.

But there is also concern that the same weather patterns that uncover this sunken treasure could also destroy it.

To find out more about where Australia’s shipwrecks are located, visit  SHIPWRECKS – Map Search (environment.gov.au)

To visit Australia’s Underwater Cultural Heritage Database, go to https://www.dcceew.gov.au/parks-heritage/heritage/underwater-heritage/auchd