Cave's climate clues show ancient empires declined during dry spell

December 05, 2008

MADISON -- The decline of the Roman and Byzantine Empires in the Eastern Mediterranean more than 1,400 years ago may have been driven by unfavorable climate changes.

Based on chemical signatures in a piece of calcite from a cave near Jerusalem, a team of American and Israeli geologists pieced together a detailed record of the area's climate from roughly 200 B.C. to 1100 A.D. Their analysis, to be reported in an upcoming issue of the journal Quaternary Research, reveals increasingly dry weather from 100 A.D. to 700 A.D. that coincided with the fall of both Roman and Byzantine rule in the region.

The researchers, led by University of Wisconsin-Madison geology graduate student Ian Orland and professor John Valley, reconstructed the high-resolution climate record based on geochemical analysis of a stalagmite from Soreq Cave, located in the Stalactite Cave Nature Reserve near Jerusalem.

"It looks sort of like tree rings in cross-section. You have many concentric rings and you can analyze across these rings, but instead of looking at the ring widths, we're looking at the geochemical composition of each ring," says Orland.

Using oxygen isotope signatures and impurities -- such as organic matter flushed into the cave by surface rain -- trapped in the layered mineral deposits, Orland determined annual rainfall levels for the years the stalagmite was growing, from approximately 200 B.C. to 1100 A.D.

While cave formations have previously been used as climate indicators, past analyses have relied on relatively crude sampling tools, typically small dental drills, which required averaging across 10 or even 100 years at a time. The current analysis used an advanced ion microprobe in the Wisconsin Secondary-Ion Mass-Spectrometer (Wisc-SIMS) laboratory to sample spots just one-hundredth of a millimeter across. That represents about 100 times sharper detail than previous methods. With such fine resolution, the scientists were able to discriminate weather patterns from individual years and seasons.

Their detailed climate record shows that the Eastern Mediterranean became drier between 100 A.D. and 700 A.D., a time when Roman and Byzantine power in the region waned, including steep drops in precipitation around 100 A.D. and 400 A.D. "Whether this is what weakened the Byzantines or not isn't known, but it is an interesting correlation," Valley says. "These things were certainly going on at the time that those historic changes occurred."

The team is now applying the same techniques to older samples from the same cave. "One period of interest is the last glacial termination, around 19,000 years ago -- the most recent period in Earth's history when the whole globe experienced a warming of 4 to 5 degrees Celsius," Orland says.

Formations from this period of rapid change may help them better understand how weather patterns respond to quickly warming temperatures.

Soreq Cave -- at least 185,000 years old and still active -- also offers the hope of creating a high-resolution long-term climate change record to parallel those generated from Greenland and Antarctic ice cores.

"No one knows what happened on the continents... At the poles, the climate might have been quite different," says Valley. "This is a record of what was going on in a very different part of the world."
-end-
In addition to Valley and Orland, the paper was authored by Miryam Bar-Matthews and Avner Ayalon from the Geological Survey of Israel, Alan Matthews of the Hebrew University in Jerusalem and Noriko Kita of UW-Madison.

Funding for the project is from the Comer Science and Education Foundation, National Science Foundation, U.S. Department of Energy, Israel Science Foundation, Sigma Xi, and the UW-Madison Department of Geology and Geophysics.

Jill Sakai, 608-262-9772, jasakai@wisc.edu

PHOTO EDITORS: High-resolution images are available for download at http://www.news.wisc.edu/newsphotos/growthBands.html

CONTACT: Ian Orland, 608-262-8960, orland@geology.wisc.edu; John Valley, 608-263-5659, valley@geology.wisc.edu

University of Wisconsin-Madison

Related Precipitation Articles from Brightsurf:

Convection-permitting modelling improves simulated precipitation over the Tibetan Plateau
A China-UK research team explains the possible reasons for excessive precipitation over the TP in the mesoscale convection-parameterized models.

Spread of monsoon circulation changes explains uncertainty in global land monsoon precipitation projection
A new study emphasizes the importance of reliable prediction of circulation changes, to ensure that future projections of global land monsoon are suitable for use by policy makers.

GMMIP simulations on global monsoon interannual variability show higher skill than historical simulations
GMMIP simulations on global monsoon interannual variability show higher skill than historical simulations.

The spatial consistency of summer rainfall variability between the Mongolian Plateau and North China
The regional differences and similarities of precipitation variability are hotspots in climate change research.

Scientists find key factors impacting sideswiping tropical cyclone precipitation
Scientists find that the distribution of sideswiping tropical cyclones precipitation(STP) includes extreme STP events that appear not only over the island and coastal areas, but also over inland areas

Rainy season tends to begin earlier in Northern Central Asia
The researchers found robust increase of annual mean precipitation at the end of the 21st century under all modelling scenarios over northern central Asia.

Using cloud-precipitation relationship to estimate cloud water path of mature tropical cyclones
Scientists find the cloud water path of mature tropical cyclones can be estimated by a notable sigmoid function of near-surface rain rate.

Precipitation will be essential for plants to counteract global warming
A new Columbia Engineering study shows that increased water stress--higher frequency of drought due to higher temperatures, is going to constrain the phenological cycle: in effect, by shutting down photosynthesis, it will generate a lower carbon uptake at the end of the season, thus contributing to increased global warming.

Fall precipitation predicts abundance of curly top disease and guides weed management
Transmitted by an insect known as the beet leafhopper, curly top disease is a viral disease affecting many crops, including melons, peppers, sugar beets, and tomatoes.

Study confirms climate change impacted Hurricane Florence's precipitation and size
A new modeling framework showed that Hurricane Florence produced more extreme rainfall and was spatially larger due to human-induced climate change.

Read More: Precipitation News and Precipitation Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.