In recent years, the use of stalagmites and other speleothems as high resolution paleoclimatic indicators is advancing with the recognition of annual growth layers in stalagmites. Research has tended to focus on characteristics of microlayers which were formed along the growing axes of stalagmites and can be identified under microscopes. It has been supported that the microlayers almost are annual layers by TIMS-U series, AMS14C and other dating methods. Speleothem microlayers can be manifested in several manners defined by①alternating luminescent/non-uminescent laminae;②alternating fibrous porosity/density laminae;③alternations of aragonite and calcite laminae. Observed under transmitted light and fluorescent respectively, bi-optical microlayers (transmitted-light microlayers and luminescent microlayers) can be found in many Holocene stalagmites of China.
Microlayers are endured a forming process with high frequency. The growth rate of stalagmites has been demonstrated to be dependent on the calcium concentration of the drip water, the water drip rate, the temperature, the thickness of the water film on the stalagmite cap and the carbon dioxide concentration in the cave air. The presence of annual growth microlayers also has implications for the interpretation of growth rate variations. Annual microlayer is not observed in all stalagmite samples. Previous studies have quoted mixing of groundwater in the aquifer, soil water residence characteristics and depth in the aquifer as a primary cause of the lack of lamina preservation.Great potential exists for the utilization of stalagmites as high resolution proxies in the karsted regions and could potentially allow for acquisition of long annual proxy record of the continent paleoenvironment. Information of precipitation, temperature, paleosoil and vegetation can be got from this kind ideal material. In this paper, several proxies were discussed, such as oxygen and carbon isotopes, growth rate and pattern, chemical components, thickness, gray level, and optical characteristics of microlayers.
Paleoenvironmental reconstruction using speleothem samples should ideally use multiple samples. In the near future, critical projects include the calibration of the stalagmite growth lamina record with instruments and historical records and cross-calibration with other annually dated proxies such as tree-rings. Besides, three aspects of research on speleothem microlayers are needed, ie. improved analytical techniques and instrumentation that allow dating of smaller samples of speleothem calcite with higher precision, an improved understanding of speleothem forming processes, and more accurate information translation.