In this context, the attention of scientists is now focused on studying in depth the cycle of this element to understand the importance of each of the planetary sinks of mercury, which are the soil and, especially, oceanic sediments, which they are surely the largest long-term deposit of this element. Now, an international team of scientists has discovered large amounts of mercury in the Pacific ocean trenchesThey exceed any value ever recorded in marine sediments and are even higher than those measured in areas directly contaminated by industrial discharges.
The work, which is published in Nature’s Scientific Reports journal, reveals the first direct measurements of mercury deposition at depths of between five and ten kilometers, a logistical challenge due to the extreme conditions of this environment.
“The bad news is that these very high levels of mercury could be representative of the global increase in anthropogenic emissions in our oceans”, reflects Hamed Sanei, director of the Lithospheric Organic Carbon Laboratory (LOC) of the Department of Geosciences of the University of Aarhus (Denmark). “But the good news is that the sea trenches act as a kind of permanent landfill., so it is likely that the mercury that ends up there will be buried for many millions of years and plate tectonics will eventually carry these sediments deep into the Earth’s upper mantle. “
Objective: quantify mercury on a global scale
The authors acknowledge that this work is only a first approach to a more exhaustive analysis at a global level, since it is about data limited in number and geographic scope, but it already shows that Mercury accumulation in the deep ocean is likely to be much greater than previously estimated. “We have shown that sediments in ocean trenches are ‘hot spots’ of mercury accumulation, with rates much higher than previously believed,” says Peter Outridge, research scientist at Natural Resources Canada and lead author of the Global Assessment of the United Nations Mercury. “The results of this research help fill a key knowledge gap in the mercury cycle, that is, the actual rate of removal of mercury from the global environment into deep ocean sediments.”
The authors indicate that their results require extensive additional sampling from the deep ocean to better narrow these preliminary estimates and improve global mercury modeling. “Despite finding that it is being removed from the biosphere, the enormous amount of mercury that is ending up in ocean trenches is still very alarming and can be an indicator of the overall health of our oceans,” concludes Sanei.
Reference: High mercury accumulation in deep-ocean hadal sediments. Hamed Sanei, Peter M. Outridge, Kazumasa Oguri, Gary A. Stern, Bo Thamdrup, Frank Wenzhöfer, Feiyue Wang & Ronnie N. Glud. Scientific Reports volume 11, Article number: 10970 (2021).