Mercury is accumulating in deep ocean trenches

The highest measured concentrations were also nearly as high as some of the most contaminated bodies of water on the planet—a jarring finding given that these locations (the Atacama and Kermadec trenches) aren't in the vicinity of any known mercury sources.This finding shows that a lot is still left to understand about how much mercury is in the environment, where it's going, and how it's getting there.Tracking where mercury is and what it's doing in the environment is complicated by the many physical and chemical transformations that are possible—not all of which are well understood. "Think about trying to try to take a sediment core at the end of a seven- or eight-kilometer-long cable from a ship that's bobbing around on the ocean—it takes many hours to send the sampler down and bring it back up, and then you have to hope that there's actually a sample there and that you didn't hit a boulder or something."These sediment cores give the first direct evidence of how deep-ocean mercury concentrations have been changing over the last 60-190 years (i.e., the flux). While such evidence isn't available yet, it's also not a complete surprise that the oceans' mercury might end up in trenches."I think that we would expect concentrations to increase in the sediment as you go from coastal areas into the deep ocean," says Outridge. I think what's going on here is that we're seeing a particle filtering effect, where the finest sediment makes it to the deepest part of the ocean and the coarsest sediment settles out in the coastal areas."With relatively little life down there and low chances of the mercury moving out before it's buried by plate tectonics, we should be somewhat reassured that mercury might be concentrating in these trenches.