Tree rings usually give scientists a window into the past, but the iconic redwoods have always had too erratic of growth patterns to get much information from their trunks. A new way of looking at the giant trees could change that.
"This is really the first time that climate reconstruction has ever been done with redwoods," Jim Johnstone, late postdoctoral position holder at the UW-based Joint Institute for the Study of the Atmosphere and the Ocean, said in a University of Washinton news release.
Redwoods, while not the oldest trees on the west coast, but are considered to be the tallest living things on Earth. They live in a uniquely foggy California climate, and researchers hoped to use the trees to determine information about the region's past.
"Redwoods are restricted to a very narrow strip along the coastline," Johnstone said. "They're tied to the coastline, and they're sensitive to marine conditions, so they actually may tell you more about what's happening over the ocean than they do about what's happening over land."
The researchers were able to use the trees' cores to determine 50 years of California climate history. Since the scientists' findings matched written climate records, the researchers showed their method could accurately look at local weather thousands of years back.
"Tree-ring research, or dendrochronology, typically involves a detailed look at a cross-section of a tree trunk. But the rings of a redwood are uneven and don't always fully encircle the tree, making it a poor candidate for anything except detecting historic fires," the news release reported.
Instead of the traditional way of looking at tree rings, the researchers sampled molecules contained within the wood in a similar fashion to the way they would treat ice cores.
The majority of Earth's atmospheric oxygen has an atomic mass of 16 (O-16), but some is slightly heavier at O-18. When seawater evaporates and becomes clouds it often releases O-18 rains, while the rain that falls on land is more likely to have an O-16 isotope.
Fog forms near the shore and "drips down through tree branches" when it is blown ashore. The team found they could measure the proportions of rain and fog by looking at these isotopes.
"We actually have two indicators that we can use in combination to determine if a particular summer was foggy with a little rain, foggy with a lot of rain, and various combinations of the two," Johnstone said.
Past research by Johnstone suggests the California fog is generally affected by ocean surface temperatures. If researchers can use the redwoods to gauge the behavior of fog throughout the centuries, they could potentially learn about ocean patterns as well.
"It's possible that the redwoods could give us direct indication of how that's worked over longer periods," Johnstone said. "This is just a piece that contributes to that understanding in a pretty unique place."
