Bullets, bombs, cans and plastic litter the bottom of the Pacific Ocean
The largest ever study of waste found at the bottom of the central Pacific is showing how even the most remote and protected areas are being impacted by our rubbish.
The Pacific Ocean is vast, covering some 33% of the Earth's surface. Its central and western regions contain not only the world's deepest point, but also some of the largest protected areas on the planet.
These include Marine National Monuments set up by the USA, such as Papahānaumokuākea which surrounds the Northwestern Hawaiian Islands, Rose Atoll near to American Samoa and the Marianas Trench.
Marine biologist Dr Diva Amon, a researcher at the Museum, was exploring the Marianas area with remotely-operated vehicles (ROVs) onboard the NOAA Ship Okeanos Explorer when she started to notice a significant amount of debris littering the seafloor thousands of metres beneath the surface.
'Most of the sites we surveyed had never been visited or explored by people in any capacity before,' says Diva. 'But we found these big pieces of trash down there even in these really remote places. That was rather shocking.'
By using the footage recorded by the ROVs taken during 188 dives across the central and western Pacific, Diva and her colleagues have been able to assess just how prevalent the human-made debris is throughout the central and western Pacific Ocean.
A legacy of war
Almost a fifth of all sites they explored between 233 and 6,000 metres deep contained human trash.
'Some of these items were literally in the middle of the central Pacific where the closest inhabited island was thousands of kilometres away,' says Diva. 'On top of that, as some of it was household items, it was very surreal to see them down there - it was bordering on hilarity.'
These items included a perfectly preserved can of Spam at the bottom of the Mariana Trench, a can of Budweiser, and an inflated, sealed plastic bag that looked like it was thrown overboard just the day before.
The most common type of debris was not plastic, but metal. This accounted for almost half of all bits of trash identified and is most likely a result of the region's history.
'There was quite a lot of debris related to armed conflict,' explains Diva. 'About 5% of the debris that we saw was from what we guessed would be the Second World War, mostly either bombs or bullets.'
An entire scuttled military dock off the coast of Hawaii showed how the legacy of the Second World War is still very much evident throughout the Pacific.
The closer the surveying team were to landfall, the more trash there was to be found.
How long these pieces of trash have been down there - and so for how long they may persist in the environment - is very difficult to determine.
Second World War debris will have been sitting in the depths for almost a hundred years now, with much of it still looking remarkably intact and pieces of plastic are known to be able to survive in water for many decades. The environments in the deep oceans, coupled with the types of material used by industry, suggest that some of this debris will likely persist for hundreds to thousands of years.
Diva and the team did observe many deep-sea corals entangled in fishing gear, but they note that many of their encounters did not show negative interactions with wildlife. Instead they saw anemones using the trash as a substrate to anchor to or crabs hiding among it, although Diva clarifies that this was 'obviously only a limited snapshot.'
This study only looked at large pieces of debris over around two centimetres in size, but we know that as waste breaks down it doesn't actually disappear.
'Because the deep sea is cold and the oxygen levels are low, it means that things hang around for longer,' explains Diva. 'But even when they do break down, there may be a lot of sub-lethal impacts on animals as chemicals leach out of them or they turn into microplastics.'
There is now strong evidence to show that plants and animals in the oceans are being harmed by these sub-lethal affects, meaning that while the creatures may not be killed initially, they may be impacted by exposure over the long term.
How to stem the flow
Cleaning up this waste is not going to be easy.
One of the most confusing aspects of marine debris is that the type of trash that dominates appears to be different depending on which of the world's oceans are being focused on.
'The Indian Ocean sites that have been investigated tend to be dominated by fishing gear, in the Mediterranean and Arctic there is a lot of plastic, while in the North Atlantic deep-sea trash comes from a variety of types,' explains Diva. However, only a very small area of the deep-ocean's seafloor has been surveyed. More investigation will help to clarify these trends.
'Ultimately, we need to be taking more steps to try and stem that flow of debris into the ocean,' says Diva. 'This can be done at point sources such as rivers, but it is not just about preventing debris from entering the ocean.
'It is also about preventing the manufacturing of this kind of debris in the first place and moving towards a more circular economy.'