May 5, 2009 -- As sea ice vanishes from the Arctic, levels of mercury will rise in the region's seals -- and in the people who eat them, suggests a new study. It's a complicated relationship, and far too soon to recommend that native seal-hunters stop eating their traditional diet. But the study, which found a shift in what the seals eat -- and an increase in mercury-contaminated foods -- when climate is at extremes, provides yet another example of global warming's reverberating effects. "Knowing what we know, if we continue to lose sea ice, the mercury concentration in seals may go up," said Gary Stern, senior research scientist at the Department of Fisheries and Oceans in Winnipeg. Arctic seals already face a number of threats, including a changing habitat. "Mercury contamination is just one additional stressor on top of the others." Researchers have been monitoring mercury levels in ringed seals in the western Canadian Arctic since the 1970s. Over that time, they've seen absolutely no trend whatsoever, Stern said. What they have seen is lots of variability. Some years, levels are high. Some years, levels are low. Related Content:
But further investigation showed that mercury levels in the seals is linked to the amount of cod the animals eat. And researchers found the amount of mercury-containing fish the seals eat is highest when ice-free days are at the extremes. Stern and colleagues looked at mercury levels in seal muscle tissues collected a handful of times between 1973 and 2007. Samples came from adult seals that were caught by hunters, and 13 to 20 seals were analyzed each time. For each year in the study period, the researchers also looked at available ice charts to see how many days were ice-free. Every winter, floating sea ice grows around the Arctic, and every summer, it melts again. But the number of ice-free days varies from year to year. Finally, the scientists compared the two sets of data. In the current issue of Environmental Science & Technology, they report that mercury levels in seals were highest in years with the most ice-free days and in years with the least ice-free days, but lowest in the less extreme years. "Lo and behold, we had a strong correlation suggesting a link between mercury in seals and sea-ice extent," Stern said. "It works extremely well." To explain the relationship, the team turned to cod. These fish make up a significant portion of a ringed seal's diet, and they are a key part of the food chain that passes mercury upwards, and magnifies the toxic metal as it goes. Get More NewsSpiders, Scorpions Among World's Oldest CreaturesMany creepy crawlies have been on Earth much longer than previously believed.Blood-Sucking Vampire Bats Sing DuetsWhite-winged vampire bats "harmonize" with separated roost mates.Oldest Hebrew Writing Possibly FoundAncient inscriptions on a 3,000-year-old pottery shard could make history.Rare, Prehistoric-Age Reptile Found in N.Z.A tuatara has been spotted on the New Zealand mainland for the first time in 200 years.Iceman Has No Living RelativesOetzi, the 5,300 year-old frozen mummy, left no living genetic legacy.SLIDE SHOW: Landscapes of TerrorWhat makes a place feel scary? There are scientific explanations.It's Official: People Are Warming the PolesHumans are conclusively to blame for polar warming, say scientists.Eight-Armed Animal Preceded DinosaursWhat may be one of Earth's first animals was no bigger than a coaster and had eight arms.Phoenicians Live on in People's GenesOne in 17 Mediterranean men may be descended from ancient Phoenicians.Pesticides, Fertilizers Linked to Frog DeclineA pesticide is found to promote parasites among amphibians.Hubble Telescope Taking Photos AgainThe Hubble Space Telescope is once again snapping stunning photos of the universe.Andean Mummy Hairs Show Hallucinogen UseScientists find direct evidence of hallucinogenic drug use among ancient Andeans.Opals on Mars Reveal Planet's Long Wet PastOpals found on Mars suggest the planet has been wet for much longer. |
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