Belize Cave Records El Niño Events

IOWA CITY, Iowa, October 22, 2002 (ENS) - Scientists have discovered a history of the past 30 years of El Niño events recorded in Central American stalagmites. The records stored in the cave formations can provide insights into ancient climate events and modern weather patterns, say the researchers from the University of Iowa and their University of New Hampshire colleagues.

Their findings, published in the October 18 issue of the journal "Science," indicate that variations in a stalagmite found in a cave in the Central American country of Belize reflect changes in the carbon cycle of the overlying rain forest that are related to El Niño weather events.

Amy Frappier of the University of New Hampshire records data on stalagmites found in the Actun Tunichil Muknal cave in central Belize. (Two photos by Brian Frappier, courtesy University of Iowa)

Luis Gonzalez, director of the Paul H. Nelson Stable Isotope Laboratory at the University of Iowa and researcher at the Center for Global and Regional Environmental Research (CGRER), said this is the first time that a correlation between El Niño and stalagmites has been documented.

Stalagmites are formations that grow up from the floor as mineral laden water drips from the cave ceiling. They are often found beneath stalactites: formations that grow down from the ceiling into icicle like spears. All cave formations are created very slowly - in most caves, at the rate of just an inch in 1,000 years.

The region of the Belize cave has no apparent weather effects correlated with El Niño, Gonzalez noted. But as changes in rainfall and temperature related to El Niño alter the growth and decay of rainforest vegetation above the cave, they also change the mineral components of the water percolating through the rock into the cave.

These changes were recorded as variations in the carbon isotope values in the stalagmite analyzed by the researchers.

The stalagmite, collected in January 2001 from the Actun Tunichil Muknal cave - also known as the cave of the stone tomb - in central Belize, contains visible growth bands associated with the onset of the dry season each year in March. The age of these bands has been confirmed by radiometric dating using lead.

Using a high resolution micro-sampling device designed and constructed by CGRER research scientist Scott Carpenter, his coworkers were able to mill tiny samples of the stalagmite's calcium carbonate. About 1,300 micro-samples were taken at increments of 20 microns over a 30 year period of stalagmite growth.

The blue flagged formation is a stalagmite studied by the climate researchers. Above the researcher are stalactites - spears of rock formed as mineral laden water drips from the cave ceiling.

Gonzalez, an internationally recognized expert on stalagmites and ancient climate changes, said he was surprised by the strong response of the stalagmite to El Niño.

"The Belize results are very encouraging because there are no other terrestrial records in tropical regions with the apparent sensitivity of this stalagmite," Gonzalez said. "I expect that my students working in Jamaica and Venezuela will find similar or stronger responses."

The data published by the Iowa researchers, along with Amy Frappier and Dork Sahagian of the University of New Hampshire, show carbon isotope levels peaking in 1974, 1983, 1988 and 1999 - roughly the dates of major El Niño events.

In their "Science" paper, the researchers write that their work suggests the impact of El Niño "extends over a much larger area than just where fluctuations in weather patterns are discernable" and that "stalagmites may record important information about weather and carbon fluxes in tropical rainforest ecosystems on interannual and shorter time scales."