June 21, 2008

Shedding Light on a Dark Day

By T.J. Greaney, Columbia Daily Tribune, Mo.

Jun. 21--On the morning of May 19, 1780, the sky over New England turned a dark red. By noon, people were conducting business by candlelight, nocturnal birds had taken flight and flowers had closed their petals.

In the deeply religious Colonies, many people thought Judgment Day was upon them.

"Men prayed, and women wept," wrote poet John Greenleaf Whittier in a poem composed years later. "All ears grew sharp/to hear the doom-blast of the trumpet shatter/ the black sky that the dreadful face of Christ might look down from the rent clouds. ..."

The cause of the event, known as New England's Dark Day, has been a mystery for more than two centuries, but new tree-ring research by University of Missouri scientists appears to have solved it. A paper co-authored by four local forestry scientists shows that smoke produced by massive wildfires in Canada was the likely cause of the darkness.

The eureka moment for the discovery occurred in 2004, when one of the co-authors, U.S. Forest Service research forester Dan Dey, was listening to a National Public Radio program about unsolved mysteries. He heard the account of the Dark Day and thought he could crack it.

In the vast archives of tree-trunk sections kept in the basement laboratories of MU's Anheuser-Busch Natural Resources Building, Dey had seen evidence of a 1780 fire. There, kept ordered and labeled in a splintery library, researchers store slices of trees from all over the world dating back thousands of years.

One prized specimen is a blackened 6,000-year-old hunk of oak pulled from a creek in north Missouri and has been used to track climate change.

The lab contains several tree sections from the eastern United States bearing "fire scars" from 1780. Some were collected in the early 1990s by Richard Guyette, an MU forestry professor, during a trip to the Algonquin Provincial Park in Ontario, Canada.

When Guyette heard the year of the Dark Day, he immediately knew it was a fire year. Tree-ring researchers memorize drought and fire dates the way schoolchildren memorize the dates of world events.

"Around here, it would be 1934, 1936, 1901, 1980, 1604. Those are your drought dates," Guyette said. "It's like if you knew a symphony by heart, and I just hummed you a stanza, you'd know right where it went in that symphony. That's kind of the way it is with tree-ring dating."

In a tree cross-section, each ring represents a year. A tree begins to grow in the month of May, putting on light colored, "spring wood" and then slows its growth around July, when it puts on darker wood. In the case of many of Guyette's Ontario sections, the May growth for 1780 was barely a hair's breadth wide. After that, the ring was superseded by a fire scar that resulted in growth curling around the deformity.

"The tree grows over itself to cover the wound," said Mike Stambaugh, a research associate with the MU Department of Forestry and co-author of the study. For years after the fire, rings were all very thick, indicating the tree grew rapidly thanks to few other living trees left standing around it and less competition for rain and sunlight.

"It doesn't tell you the day of the year, based on the cells in the wood," Stambaugh said. "But we know this wasn't September. This wasn't June. It was May."

The researchers used barometric pressure readings recorded in Massachusetts at the time to show that a low-pressure system would have pushed the smoke south. The smoke likely stayed high enough in the atmosphere that people on the ground didn't smell it, though some astute observers noted dark, sooty rain in the following days.

Most people, though, put their faith in God and believed they had been spared when the darkness lifted after several hours.

"There have been other dark days, but this was one of the most profound because of the settlers being there, and they didn't have any means of explaining what was causing it," MU Associate Researcher Erin McMurry said. "Today, we would have satellites showing the clouds moving and showing the smoke coming. It would still be really strange if it did happen, but back then, they just didn't have any idea."

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