Climate History of North America Revealed by Growth Rings on Rocks

Most people know that there are growth rings on trees, but did you know that there are also growth rings on rocks? Scientists have found a new way to tease out signals about Earth's climatic past from soil deposits on gravel and pebbles.

In this latest study, the researchers obtained soil samples from Wyoming's Wind River Basin, using thousand-year resolutions in order to look at a time period spanning the past 120,000 years, which covered glacial and interglacial periods during the Pleistocene Epoch. More specifically, they conducted microanalysis of carbonate deposits that formed growth rings around rocks, some measuring just 3 millimeters thick.

"The cool thing that this study reveals is that within soil-an unlikely reservoir given how 'messy' most people think it is-there is a mineral that accumulates steadily and creates some of the most detailed information to date on the Earth's past climates," said Ronald Amundson, the senior author of the new study, in a news release.

While the researchers only focused on samples in Wyoming, soil deposits are commonly found in drylands all over the world. This means that they could potentially provide a rich source of data about past climate.

But what did they find with the new data? The researchers discovered that 70,000 to 55,000 year ago, during the middle of a minor ice age, the pattern of precipitation in North America shifted from one dominated by west-to-east flow of storms to a south-to-north flow from the Gulf of Mexico. The researchers attributed it to a stable, high-pressure system that parked itself over massive ice sheets that covered eastern Canada and northeastern United States, which helped bring up more air from the south.

"This is a new insight from geologic sources of paleoclimate data," said Erik Oerter, one of the researchers. "The techniques that we developed can now be applied to similar soil deposits to fill in key gaps in the paleoclimate record. The information will be useful to improve the accuracy of climate models by providing known conditions to calibrate them to."

The findings are published in the journal Proceedings of the National Academy of Sciences.

Related Stories

Rainforest Structure is Shaped by a Constant Battle for Sunlight

Arctic's Frigid, Dark Winter Causes Marine Creatures to Migrate by the Light of the Moon

For more great science stories and general news, please visit our sister site, Headlines and Global News (HNGN).