Safety and conservation at the deepest place on Earth: a call for prohibiting the deliberate discarding of nondegradable umbilicals from deep-sea exploration vehicles

Exploration vehicles can introduce vast quantities of single-use, plastic-coated tether that have been deliberately discarded as observed at the deepest site of all Earth's oceans. Manned submersible dives to Challenger Deep (10,925 m deep) in the Mariana Trench in 2019 and 2020 revealed hundreds of metres of yellow and white tether strewn across the seafloor. Due to its composition, these fibre-optic tethers will not only persist environmentally, but form a significant risk to equipment and life should unmanned and manned craft become entangled. As a result, the site of the iconic first descent to the deepest place on Earth by Piccard and Walsh in 1960 is unlikely to be safely explored again if this practise continues.