Researchers from the University of Buffalo and the University of Alberta are conducting studies in gold mines west of Fairbanks, Alaska, to find clues on how the area has responded to prehistoric global warming events and how it might respond in coming years as the planet heats up again.
Placer mines dirt contains chemical compounds that can reveal information about whether Alaska became wetter or drier as the temperature shifted in ancient times
In detail, the scientists are collecting samples from placer mines located south of the Arctic Circle where ancient creeks once flowed and left behind deposits of gold-bearing gravel. Today, the gravel is buried under hundreds of feet of loess deposits that originate in nearby mountains when glaciers crush rock into dust
To get to the precious metal, miners must carve deep trenches into the landscape and the walls of the canyons they ‘build’ act as a record of prehistoric time. They hold layer upon layer of loess that can be analyzed to learn about the region’s climate history.
“[This] is an urgent topic of study, as the state is already feeling the effects of climate change,” the researchers said in a media statement. “According to the 2014 National Climate Assessment, Alaska has, on average, warmed much more quickly than the rest of the U.S. in recent decades. The report finds that glaciers are melting, wildfire risks are going up and local fisheries are vulnerable to changes in ocean temperature.”
According to the geologists and Earth sciences experts involved in the project, their collaboration with miners in the area has been crucial to advance the project because the gold-diggers are already excavating giant mounds of silt, so all the researchers have to do is observe, collect and measure sediment samples.
They say that the walls of the mines show the remains of ancient forests as layers of rooted trees, pieces of moss, and rich, dark soil. These forests formed atop the loess when the climate warmed and glaciers shrank. In cooler times, glaciers would grow and loess was rapidly deposited nearby in thick layers. These were cycles that took place over and over again.
They are also studying chemicals called glycerol dialkyl glycerol tetraethers or GDGTs, which are embedded in the loess and are produced by bacteria, as well as the remnants of ancient leaf waxes also found in the sediment. They believe that these compounds can shed light on how the region’s effective moisture — influenced by humidity and rainfall levels — fluctuated over time.