Get unlimited digital access to $0.99 for 4 weeks.

Mercury levels rise in oceans

Want less mercury in the ocean? Try driving less, study suggests
Scientists fine-tune ocean mercury estimates
Burning coal, making cement add tons of mercury to oceans and fish, study suggests

Man has pumped tens of thousands of tons of mercury into the world’s oceans in the last 500 years, nearly tripling the amount of the toxic heavy metal in sea water, according to a study published online Wednesday in the journal Nature.

The study, the first to be based on widespread and long-term sampling of ocean waters, found that the increase in mercury content in Earth’s waters follows the same pattern as the post-industrial increase in carbon dioxide in the planet’s atmosphere – an exponential rise often described as a “hockey stick” graph.

The strongest increase was evident in waters less than 328 feet deep, where dissolved mercury was 2.6 times higher than it was before humans began burning fossil fuels on a large scale, the study found.

The data also jibed with previous estimates based on computer modeling; its measurements landed roughly in the middle of those prognostications.

Researchers analyzed samples taken at varying depths over an eight-year period from different areas of the Atlantic, Pacific, Southern and Arctic oceans. Because of the differences in the rate that deep and shallow waters circulate, those samples offer a record of water chemistry over time, somewhat like rock strata.

“There’s sort of an age to water, in terms of the last time it was in contact with the atmosphere,” said the study's lead author, Carl H. Lamborg, a geochemist at Woods Hole Oceanographic Institution.

The densest water, formed during winter in the North Atlantic, sinks and moves like an excruciatingly slow conveyor belt, eventually pushing into the farthest reaches of the northern Pacific Ocean, Lamborg said.

“What we found is the young, deep water – the water in the North Atlantic – has a lot more mercury in it than the older deep water,” Lamborg said. That pattern suggests the difference can be explained by the steady increase in airborne mercury pollution, which precipitates from the atmosphere to Earth’s surface.

Of course, the mercury in the samples did not come with a stamp that said “Belched out in Birmingham, England, 1880” or “Made in China, 2010.” But, by measuring at the ratio of mercury to phosphate (which behaves in a similar manner to mercury), and indexing mercury levels to a broad database of carbon dioxide, researchers could determine what percentage of the mercury could not be attributed to natural sources and processes.

The study's findings contradict some high estimates of mercury levels, based on computer modeling. Those models assumed that past gold mining had contributed a large amount of mercury to oceans. Mercury from the Gold Rush and colonial times, the study suggests, might instead be locked up in sediments. 

Although the study used a wide array of samples, there are a lot of untested waters on Earth, so more sampling and analysis will be needed. The mercury measured by the study was elemental mercury, not methylated mercury, the kind that winds up in the ocean food chain and can cause neurological disorders in humans. While it is known that some elemental mercury is converted to its more dangerous form in sea water, mystery remains about how the process works.

For now, though, the evidence increasingly leans toward cutting energy consumption if you don't want to wind up like the Mad Hatter.

Copyright © 2015, The Baltimore Sun


Aug. 8 12:55 p.m.: This post was updated with further detail on the connection between elemental mercury and its more biologically active methylated form that can accumulate in fish.

This post was originally published Aug. 6, 6:45 p.m.

Related Content
  • Baltimore-born Ta-Nehisi Coates makes his case
    Baltimore-born Ta-Nehisi Coates makes his case

    The award-winning writer of the controversial 'Case for Reparations' traces his history to strong family roots in West Baltimore as he promotes an open discussion of race relations in modern-day America.

  • Maryland weddings
    Maryland weddings

    Browse photos of recent Maryland weddings -- from traditional church ceremonies to quirky, Baltimore-themed celebrations. To read more about each couple's story, go to Just wedded? Email your wedding details to

  • Celebrating Carnival around the world
    Celebrating Carnival around the world

    Carnival season technically begins on Jan. 6, also known as Twelfth Night and runs through Mardi Gras, which falls on Feb. 17, 2015, the Tuesday before Ash Wednesday. Big celebrations around the world usually occur in those final two weeks, but some happen earlier.

  • Adoptable pets at Baltimore-area shelters
    Adoptable pets at Baltimore-area shelters

    Here's a collection of a few of the dogs, cats and other critters in the Baltimore area who need homes. Be sure to check with the shelter before you go to verify that the animal you want is still there.

  • This Day in History: Jan. 29
    This Day in History: Jan. 29

    In 1845, Edgar Allan Poe's poem 'The Raven' was first published in the New York Evening Mirror.

  • The best and worst Super Bowl halftime performances
    The best and worst Super Bowl halftime performances

    Watch some football, eat some chicken wings and take a break in the middle of it all to be entertained by the likes of Bruno Mars, Beyonce or Prince.