“There is a growing concern that deep-sea ecosystems have already been and will be seriously impacted by direct exploitation of biological and non-biological resources, deep-sea trawling and mining, and infrastructure development, such as hydrocarbon plants and submarine cables,”
Michael Daly | Stuff NZ | May 11 2018
A plastic bag has been seen nearly 11km under the ocean in the Earth’s deepest feature, the Mariana Trench.
The discovery was revealed in a recently-established database that shows the deep oceans are awash with rubbish.
Set up by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in March 2017, the database lists 3425 items of human-made debris seen in the deep sea.
The items were spotted during a total of 5010 dives made since 1983 by deep sea submersibles and remotely operated vehicles.
More than a third of the items were plastic, and of those, 89 per cent were single-use products, a study in Marine Policy said.
The plastic bag found in the Mariana Trench was at a depth of 10,898 metres. That’s not far from the very bottom, which scientists revealed to be 10,994m in a 2011 survey, The Telegraph reported.
“The data shows that … the inﬂuence of land-based human activities has reached the deepest parts of the ocean in areas more than 1000km from the mainland,” the study said.
The items reported in the database mostly came from the western North Pacific Ocean.
Metal debris was the second most common of the items seen on the dives at 26 per cent, rubber accounted for 1.8 per cent, ﬁshing gear for 1.7 per cent, glass for 1.4 per cent, cloth/paper/lumber for1.3 per cent, and other anthropogenic items accounted for 35 per cent.
Most of the debris was seen at depths of 1000-2000 metres, but that was also the depth of most of the dives in the database. The ratio of plastic to other debris increased with depth, getting to 52 per cent below 6000m.
“There is a growing concern that deep-sea ecosystems have already been and will be seriously impacted by direct exploitation of biological and non-biological resources, deep-sea trawling and mining, and infrastructure development, such as hydrocarbon plants and submarine cables,” the study said.
“In addition to those direct impacts, the observed distribution of plastic debris clearly indicates that land-based human activities have also been affecting deep-sea ecosystems.”
Researchers speculated organisms could hitch-hike on plastic bags from shallow waters to the deeper ocean. “This stepping stone effect may alter the food web and biogeo-chemical function of the deep sea ecosystems,” they said.
Deep sea anemones had been seen on plastic bags on the muddy sea floor during several dives. “Because those animals need hard substrates to attach to and thus cannot inhabit soft bottoms, deep-sea plastic debris possibly plays the role of a stepping stone for sessile animals to expand their original distribution.”
The database only showed information of the sea floor, and most of the areas covered were within countries’ exclusive economic zones, the study said.
“However, as the deep sea is likely to be the ﬁnal destination of ﬂoating plastic debris, the frequent occurrence and widespread distribution of plastic debris in the deep sea, far away from populated coastal areas, indicate that large numbers of plastic debris pieces are distributed throughout the water column and in the high seas.”
The study indicated “a clear link between daily human activities and remote environments where no direct human activities occur”.
“Plastic is estimated to potentially remain for hundreds to thousands of years once they are deposited in the deep sea where there is no UV light and less turbulence,” the authors said.
“Minimising the production of plastic waste and its ﬂow into the coastal areas and the ocean is the only fundamental solution to the problem of deep-sea plastic pollution.”
The authors called for biologically and ecologically important areas with high plastic debris concentrations to be prioritised in future studies. They also wanted priority to be given to working out where the plastic getting to those areas came from.