Massive reserves of mercury found hidden in permafrost

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Researchers have discovered permafrost in the northern hemisphere that stores massive amounts of natural mercury.

In the new study, scientists measured mercury concentrations in permafrost cores from Alaska and estimated how much mercury has been trapped in permafrost north of the equator since the last Ice Age. The study reveals that the northern permafrost soils are the largest reservoir of mercury on the planet, storing nearly, twice as much mercury, as all other soils, the ocean, and the atmosphere combined. The study was published in Geophysical Research Letters.

Warmer air temperatures due to climate change could thaw much of the existing permafrost layer in the northern hemisphere. This thawing permafrost could release a large amount of mercury that could potentially affect ecosystems around the world. Mercury accumulates in aquatic and terrestrial food chains and has harmful neurological and reproductive effects on animals.

Natural mercury found in the atmosphere binds with organic material in the soil, gets buried by sediment, and becomes frozen into permafrost, where it remains trapped for thousands of years unless liberated by changes such as permafrost thaw.

The study found approximately 793 gigagrams, or more than 15 million gallons, of mercury frozen in northern permafrost soil. That is roughly 10 times the amount of all human-caused mercury emissions over the last 30 years, based on emissions estimates from 2016.

The study also found all frozen and unfrozen soil in northern permafrost regions containing a combined 1,656 gigagrams of mercury, making it the largest known reservoir of mercury on the planet. This pool houses nearly twice as much mercury as soils outside of the northern permafrost region, the ocean and the atmosphere combined.

Scientists are still unsure how much of the stored mercury would affect ecosystems if the permafrost were to that. One major question revolves around how much of the mercury would leach out of the soil into surrounding waterways.

Maps of mercury concentrations (micrograms of mercury per square meter) in Northern hemisphere permafrost zones for four soil layers: 0-30 centimeters, 0-100 centimeters, 0-300 centimeters, and permafrost. The permafrost map represents the mercury bound to frozen organic matter below the Active Layer Depth (ALD) and above 300 cm depth.

If the mercury is transported across waterways, it could be taken up by microorganisms and transformed into methylmercury. This form of mercury is a dangerous toxin that causes neurological effects in animals ranging from motor impairment to birth defects.

This research gives policymakers and scientists, new numbers to work with and calibrate their models as they begin to study this new phenomenon in more detail. The researchers intend to release another study modeling the release of mercury from permafrost due to climate change.

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