New techniques for the extraction and analysis of biomarkers from speleothem calcite have revealed many organic molecules decline in concentration from outer sample surfaces towards the speleothem interior, suggestive of a contamination effect. However, concentrations of organic-iodine compounds in excess of 500ppm in stalagmites from Australia appear to be indigenous to speleothem calcite and may serve as a proxy indicator for biomass burning in the landscape.
The impacts of biomass burning associated with land-use practices in the past are still widely debated although in many cases are seen as the key agent of change for vegetation regime and long-term negative consequences associated with biodiversity. The intensity of burning activity has varied throughout time reflecting the variable drivers of climate, vegetation and anthropogenic interference. To evaluate the relative impact of these drivers behind biomass burning activity in the landscape today and understand associated contemporary issues of carbon dioxide release, vegetation change and species diversity, it is important to understand fire-vegetation-climate relationships in the past. Organic iodine compounds extracted from speleothem calcite provide the opportunity to establish an integrated palaeo fire-vegetation-climate record based around oxygen and carbon stable isotope reconstructions of palaeoclimate and vegetation respectively.
Uptake of iodine compounds from soil by vegetation, followed by periodic biomass burning, enriches residual ash deposits in soluble iodine and allows leaching into groundwater systems. If karst terrain is underlain by cave environments, incorporation of iodine pulses into speleothem calcite may provide a high resolution record of burning events. Where cave sites are influenced by maritime air masses, iodine incorporated into speleothem calcite could be of either marine or terrestrial origin. Co-analysis of sulphur isotopes will help provenance the iodine between sources.
The interpretation of iodine compounds in speleothems which already support well established palaeoclimate and vegetation records thus enable assessment of the frequency and impact of burning in the context of an integrated palaeo fire-vegetation-climate record.
