ANNUAL GROWTH BANDING IN A CAVE STALAGMITE

THE presence of microscopic luminescence banding in cave calcite depos its (speleothems) has recently been reported1-3. The luminescence seem s to be caused by excitation of humic and fulvic acids derived from th e overlying soil and subsequently incorporated into the calcite3,4. We have tested whether such luminescence corresponds to annual growth la yers, using high-precision thermal-ionization mass-spectrometric U-238 -U-234-U-Th-230 ages from banded sections of a Holocene stalagmite. We report here that the timespans yielded by counting bands, on the assu mption that they are annual, agree within error limits with those obta ined by our uranium-thorium dating. This demonstration that the bandin g is annual should make banded speleothems valuable resources for prov iding high-resolution records of past climate (in which precipitation can be estimated from growth rates5,6 and temperatures from stable-iso tope measurements7) and solar-terrestrial correlations (as the lumines cence intensity can be related to the solar sunspot cycle1-3).