Jan. 5, 2007 — The sun may be off the hook for directly causing global warming, but a new study of cave formations in New Mexico indicates solar cycles may still have big local effects on rainfall in the American Southwest and Asia.
The discovery comes from the first solid record of climate in the Southwest, found in Pink Panther Cave in southern New Mexico’s Guadalupe Mountains. The record extends back some 12,300 years.
Chemical isotopes inside a stalagmite that grew there suggest that whenever the sun has been more active and slightly brighter, the summer monsoon rains have been weaker in the Southwest desert. The reverse also seems to apply to the Asian monsoons, which are stronger when the sun is more active.
The finding is particularly surprising in light of the fact that the variation in the sun's power output is considered too weak to account for the current trends in climate change and global warming.
"Just how the small — less than one percent — change in luminosity affects this, we don’t know," said Yemane Asmerom of the University of New Mexico in Albuquerque. He and his colleagues published their discovery in the January issue of the journal Geology.
The climate data they gathered from the stalagmite was in the form of oxygen atoms of different weights. It turns out that the winter rains and snow in New Mexico come from the Pacific Ocean, which has a higher concentration of oxygen-16 than the Gulf of Mexico -- where the summer monsoon rains come from.
Those monsoon rains have more oxygen-18. This variation is preserved in the chronological bands of minerals found in the five-and-a-half-inch (14-cm) New Mexican stalagmite.
Asmerom and his colleagues analyzed the oxygen isotopes in 681 mineral samples from the stalagmite, which equates to about one sample every 17 years of the stalagmite’s existence.
They then compared the oxygen data to carbon isotope data found by other researchers, which shows how the sun's activity has fluctuated over millennia.
The wiggly lines created by both set of data match remarkably well. The big mystery is why.
