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Arctic lead deposits trace European history from the Roman Empire to modern day

By environment reporter Nick Kilvert, Wednesday July 17, 2019 - 14:30 EST
ABC licensed image
Lead deposits in Arctic ice plummeted during the time of the Black Death. - ABC licensed

Since humans developed industry in Europe, prevailing winds have carried fine deposits of lead to the frozen Arctic, where they've been laid down like annual signatures in the permafrost.

In simplest terms, the more industry in Europe, the more lead has been deposited each year in the ice.

Now scientists have found frozen ice cores taken from the Arctic read like a European history book stretching back 2,200 years.

While they were expecting some correlation between lead levels and historic events, even the researchers were surprised by what they found, according to Joseph McConnell of the Desert Research Institute in Reno, Nevada.

"This array of 13 accurately dated and precisely synchronised ice-core records shows in amazing detail exactly when changes happened," Dr McConnell said.

"[There are] common increases across the [ice-core] array, coincident with the discovery and opening of new mining regions and political changes, [and] decreases coincident with plagues, wars, and climate disruptions."

Their research, published today in the journal shows a long period of high lead levels during the prosperous Pax Romana (Roman peace) era.

The Romans minted coins made of silver, which is extracted from the lead ore galena.

But as the Roman Empire declined and less silver was being mined, annual Arctic lead deposits waned, punctuated by two sharp falls during regional plague outbreaks.

By the late 700s, industry was back to levels not seen since the peak of the Roman Empire and a discovery of new lead-silver deposits in the Harz Mountains in Germany coincided with another lead peak toward 1000 CE.

"This particular production cycle in the Harz-region mines ended between 1002 and 1016 CE," the researchers note in the paper.

"Famine and pestilence resulted in the abandonment and flooding of the mines, coincident with an immediate and persistent decline in the [Greenland ice core] record."

While the record fluctuates with the outbreak of disease, local and regional fighting, and even the Little Ice Age which began in the late Middle Ages, the most dramatic downward signature came from the Black Death.

When the second great plague pandemic hit Europe in 1348, up to half the continent's population was wiped out, and industry ground to a near standstill.

"That was the clearest signal, but only up until the start of the Industrial Revolution in the 19th century," Dr McConnell said.

"That was when widespread fossil-fuel burning in Europe and North America resulted in major increases in Arctic lead pollution."

Only Great Depression enough to slow industrial revolution

The Industrial Revolution from the late 1700s saw lead deposits surge by up to 250-fold, dwarfing any period that had come before.

Sources of lead include leaded petrol, ore and metals processing, coal burning, waste incineration and lead battery manufacture.

Only the Great Depression was enough to slow rising pollution from industry during this era, and only for a short period.

That was, until the 1970s.

At this time, early incarnations of Europe-wide air pollution reduction measures were put in place, while in the US, initiatives like the Clean Air Act began cracking down on pollutants including lead, from industry.

Since then, the ice core record shows that lead deposits in the Arctic have been declining.

While lead levels in the Arctic ice are still orders of magnitude higher than during the height of the Roman Empire, it demonstrates that government policies to reduce emissions can have significant global impacts, according to glaciologist Mark Curran from the Australian Antarctic Division.

"I think the interesting thing in this paper is we can record the impacts of humans through pollution — as economies grow we can see increases in that impact," Dr Curran said.

"[And] you can see the impact of direct government legislation that targeted lead."

He said that governments today can take a lesson from that success as they grapple with the challenge of reducing carbon emissions in the fight against climate change.

"It shows us that things can be done and there's an incentive there, that decisions can be made and we can see the positive results from government policies."


© ABC 2019

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