Ancient Stalactites Have A Tale To Tell

June 02, 1997

The stalactites and stalagmites of Israel's Soreq Cave - a well-known local tourist attraction - now have another claim to fame: they provide the only continuous record known of eastern Mediterranean rainfall and vegetation over the past 58,000 years.

A study conducted by Dr. Aaron Kaufman of the Weizmann Institute's Environmental Sciences and Energy Research Department together with Drs. Miryam Bar-Matthews and Avner Ayalon of the Geological Survey of Israel demonstrates that these ancient cave formations are a unique repository of information about climatic fluctuations.

"Past changes in climate are reflected in the way stalactites and stalagmites grow and develop," says Kaufman. "By carrying out isotopic analyses on more than a hundred samples from each individual structure, we were able to piece together an ongoing picture of diverse climatic changes."

The study showed that throughout most of the period between 20,000 and 58,000 years ago, the climate in the region was dry and cool. Afterwards, the annual rainfall fluctuated significantly, and about 6,000 years ago the general climatic conditions became similar to those of today. These changes were reflected in the types of local vegetation.

Stalactites are icicle-shaped formations hanging down from cave roofs, while stalagmites look similar but point upward from the cave floor. Both are created when water picks up calcium carbonate from the soil and rocks surrounding the cave, and then trickles through cracks in the cave roof, leaving some of the mineral behind as it drips down onto the floor. Every hundred years or so a distinctive layer, or ring, is formed, so that the cross section of a stalactite or stalagmite resembles that of a tree trunk.

The scientists performed three types of isotopic analyses on the samples. For purposes of dating, they took advantage of the fact that when stalactites and stalagmites are first formed, they contain a known quantity of one particular radioactive isotope - uranium 234 - but none of a different isotope, thorium 230. Uranium 234 decays at a uniform rate, during which some of it is converted into thorium 230; the older a sample is, therefore, the higher its thorium-to-uranium ratio.

To obtain data about the climate from these same samples, the researchers analyzed the ratios of stable isotopes that are known to be a function of specific temperature and precipitation conditions: the ratios of carbon 13 to carbon 12, and of oxygen 18 to oxygen 16.

The knowledge of past climatic changes provided by this study may lead to a better understanding of today's climate and may also help make climatic projections for the future. These findings were partly reported in Quaternary Research (1997, Vol. 47, no. 2), and will be further described in the Proceedings of the International Symposium on Isotope Technique in the Study of Past and Current Environmental Changes in the Hydrosphere and the Atmosphere. (Color slides of the Soreq Cave are available).

The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel This publication, as well as other information on the Weizmann Institute, is posted on the World Wide Web at, and news releases are also available at http:/

American Committee for the Weizmann Institute of Science

Related Carbon Articles from Brightsurf:

The biggest trees capture the most carbon: Large trees dominate carbon storage in forests
A recent study examining carbon storage in Pacific Northwest forests demonstrated that although large-diameter trees (21 inches) only comprised 3% of total stems, they accounted for 42% of the total aboveground carbon storage.

Carbon storage from the lab
Researchers at the University of Freiburg established the world's largest collection of moss species for the peat industry and science

Carbon-carbon covalent bonds far more flexible than presumed
A Hokkaido University research group has successfully demonstrated that carbon-carbon (C-C) covalent bonds expand and contract flexibly in response to light and heat.

Metal wires of carbon complete toolbox for carbon-based computers
Carbon-based computers have the potential to be a lot faster and much more energy efficient than silicon-based computers, but 2D graphene and carbon nanotubes have proved challenging to turn into the elements needed to construct transistor circuits.

Cascades with carbon dioxide
Carbon dioxide (CO(2)) is not just an undesirable greenhouse gas, it is also an interesting source of raw materials that are valuable and can be recycled sustainably.

Two-dimensional carbon networks
Lithium-ion batteries usually contain graphitic carbons as anode materials. Scientists have investigated the carbonic nanoweb graphdiyne as a novel two-dimensional carbon network for its suitability in battery applications.

Can wood construction transform cities from carbon source to carbon vault?
A new study by researchers and architects at Yale and the Potsdam Institute for Climate Impact Research predicts that a transition to timber-based wood products in the construction of new housing, buildings, and infrastructure would not only offset enormous amounts of carbon emissions related to concrete and steel production -- it could turn the world's cities into a vast carbon sink.

Investigation of oceanic 'black carbon' uncovers mystery in global carbon cycle
An unexpected finding published today in Nature Communications challenges a long-held assumption about the origin of oceanic black coal, and introduces a tantalizing new mystery: If oceanic black carbon is significantly different from the black carbon found in rivers, where did it come from?

First fully rechargeable carbon dioxide battery with carbon neutrality
Researchers at the University of Illinois at Chicago are the first to show that lithium-carbon dioxide batteries can be designed to operate in a fully rechargeable manner, and they have successfully tested a lithium-carbon dioxide battery prototype running up to 500 consecutive cycles of charge/recharge processes.

How and when was carbon distributed in the Earth?
A magma ocean existing during the core formation is thought to have been highly depleted in carbon due to its high-siderophile (iron loving) behavior.

Read More: Carbon News and Carbon Current Events 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