Annual growth banding in a cave stalagmite

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