A multinational team of scientists has discovered unprecedented amounts of mercury in the deepest trenches of the Pacific Ocean that exceed any value ever recorded in remote marine sediments.
The study, published in the journal Scientific Reports on Wednesday, was a multi-national effort with scientists from Canada, Denmark, Germany, and Japan participating. The researchers report the first-ever direct measurements of mercury deposits in one of the most challenging environments on Earth.
The researchers took mercury measurements in sediments up to 10 kilometers (6.2 miles) below the surface of the Pacific, according to CTV News Canada. The ocean trenches in the study included the Atacama Trench, off the coast of Peru and Chile, and the Kermadec Trench off the coast of New Zealand.
Lead author Professor Hamed Sanei, Director of the Lithospheric Organic Carbon Laboratory (LOC) at the Department of Geoscience, Aarhus University, stated the amount of mercury discovered in this area was even higher than many areas directly contaminated by industrial releases.
“The bad news is that these high mercury levels may be representative of the collective increase in anthropogenic emissions of Hg into our oceans,” he said. “But the good news is that ocean trenches act as a permanent dump, and so we can expect the mercury that does end up there will be buried for many millions of years. Plate tectonics will carry these sediments deep into the earth’s upper mantle.”
“But even as mercury is being removed from the biosphere, it remains quite alarming how much mercury has ended up in the ocean trenches. This may be an indicator of the overall health of our oceans.”
The scientists recorded mercury measurements of up to 400 nanograms (ng), while mercury levels in other parts of the world’s oceans have been recorded at less than 80 ng, on average. Sediments in the Atacama Trench had higher levels of mercury than the Kermadec Trench.
Research scientist with Natural Resources Canada and study co-author Peter Outridge said the study will “help fulfill a key knowledge gap in the mercury cycle – the true rate of mercury removal from the global environment into deep-ocean sediments.”
The research team is calling for extensive additional sampling of the deep-ocean to collect more data and to improve global mercury contamination modelling.
The Atacama Trench is located about 160 kilometers (99 miles) off the coast of Peru and Chile. It reaches a maximum depth of 8,065 meters (26,460 ft) below sea level and is approximately 5,900 kilometers (3,666 miles) long.
The Atacan=ma Trench forms the boundary between the subducting Nazca Plate and the overriding South American Plate. With the Nazca plate subducting below the South American Plate, numerous earthquakes are produced, some of them quite notable, like the 1960 Valvidia Earthquake that measured 9.5 on the Richter scale, making it the most powerful earthquake ever recorded.
The Kermadec Trench is a linear trench in the South Pacific Ocean, stretching about 1,000 kilometers (620 miles) from the Louisville Seamount Chain in the north to the Hirurangi Plateau in the south, north-east of New Zealand’s North Island. Together with the Tonga Trench to the north, it forms the 2,000 kilometers (1,200 mile)-long, near-linear Kermadec-Tonga Sunduction system.
Convergence rates along this subduction system are among the fastest on Earth, moving 80 millimeters (3.1 inches) a year. The Kermadec Trench is also one of Earth’s deepest oceanic trenches, reaching a depth of 10,047 meters (32,963 feet).
