Previous research has shown that humic substances, mainly fulvic acid, incorporated into the secondary calcite crystals of cave speleothems produce a distinct luminescence banding. The bands are best observed in longitudinal sections of cylindrical stalagmites and in cores or slabs cut from planar flowstone deposits. The bands have widths on the order of 10 - 100 micrometers and appear to represent annual wet and dry cycles where each band represents one year's growth of the stalagmite. There is much additional detail within the banding. A 1-meter high stalagmite might contain bands representing 20,000 years of deposition. The luminescence bands, therefore, have the potential for being a very high resolution climatic record.
The intent of this proposal is to establish a sound basis for the paleoclimatic interpretation of the luminescence banding in speleothems. There are three main objectives.
(i) Construct an apparatus that will measure laser excited luminescence intensity along longitudinal sections of speleothems with high photometric accuracy, spatial resolution of a few micrometers, and tracking of spatial position within a few micrometers. This is to be accomplished by using an existing microfocus Raman spectrometer as a base instrument and constructing a computer controlled mechanical stage to translate the slab of stalagmite.
(ii) Conduct an extensive series of measurements intercomparing the records obtained from multiple transects of the same specimen, specimens collected from the same location within the same cave, and specimens collected from caves within a small geographic area. These measurements are needed to establish the reproducibility of luminescence banding records and to test methods for matching the records for speleothems of overlapping but not identical ages.
(iii) Construct luminescence-banding profiles for very recent speleothem growth to compare with contemporary climatic records. This is a calibration step to correlate specific variations in luminescence intensity with known precipitation and other climatic events in the historical record.
(iv) Construct profiles spanning late Holocene speleothems so that the details of luminescence banding may be compared with other recent paleoclimatic records.
(v) If items (i - iv) work out as planned, this project would lay the groundwork for a more extensive study of speleothem records extending farther back into the Pleistocene.
