Combined fluorescence imaging and LA-ICP-MS trace element mapping of stalagmites: Microfabric identification and interpretation

Here, we map a series of stalagmites from Asturias, Spain, by laser ablation inductively-coupled-plasma mass spectrometry and confocal laser scanning (fluorescence) microscopy and discuss the origins of trace element and fluorescence variations. Seasonal banding is evident with both methods and may be attributed to lignins/humic acids based on fluorescence absorption and emission characteristics. Some lateral variations in fluorescence present as saw-tooth fluorescent spires and demonstrate disruptions of seasonal banding, corroborated by trace element variations (most prominently Mg and Na). Such features likely reflect the differential partitioning of trace elements by sectoral zoning as a result of low supersaturation and/or high organic matter load, combined with the effects of dissolved organic matter on the calcite growth surface and the association of each element with colloidal organic matter. The lateral variability of trace elements demonstrates the pitfalls of obtaining trace element information from one-dimensional transects without prior reconnaissance mapping. It is, however, possible that traditional drilling with similar to 1 mm holes homogenizes these features and provides reliable trace element estimates.

Automated summary

By analyzing stalagmites from Asturias, Spain using laser ablation inductively-coupled-plasma mass spectrometry and confocal laser scanning microscopy, seasonal banding and variations in trace elements and fluorescence were observed. Lateral fluorescence variations in saw-tooth patterns indicate disruptions in seasonal banding, which are corroborated by trace element differences such as Mg and Na. The findings suggest that caution should be taken when obtaining trace element information without prior reconnaissance mapping. Traditional drilling may homogenize lateral variations and provide more reliable trace element estimates.