Improved Polycyclic Aromatic Hydrocarbon and n-Alkane Determination in Speleothems through Cleanroom Sample...

Area of Science:

• Geochemistry
• Paleoclimatology
• Organic geochemistry

Background:

• Speleothems offer continuous, unaltered records for paleoenvironmental reconstructions.
• Linking speleothem biomarker data with climate and vegetation history is valuable but methodologically challenging.
• Existing methods for quantifying organic molecules in stalagmites are scarce and face issues with contamination and low concentrations.

Purpose of the Study:

• To develop and validate a novel method for simultaneously determining polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in speleothems.
• To address challenges of low concentrations, contamination, and sample availability in speleothem biomarker analysis.
• To test the new method on stalagmite samples from the Australian tropics.

Main Methods:

• Developed a novel method for simultaneous determination of 18 PAHs and 26 n-alkanes (C10-C35).
• Utilized hand-held drill subsampling, complete matrix dissolution in HCl, liquid-liquid extraction, and GC-MS analysis.
• Implemented stringent contamination control measures, including sample preparation in a Class 10,000 cleanroom.

Main Results:

• Achieved detection limits of 0.3-9 ng for PAHs and 6-44 ng for n-alkanes.
• Detected fire-derived PAHs (phenanthrene, pyrene, benzo(e)pyrene, indeno(1,2,3-cd)pyrene) in one sample dated to ~2004 CE, correlating with a known fire event.
• Found n-alkanes (C23-C35) in all samples, exhibiting no odd-even preference, suggesting potential microbial or mixed sources.

Conclusions:

• The developed method is effective for quantifying PAHs and n-alkanes in speleothems, overcoming previous limitations.
• Speleothems can preserve fire-derived PAH signals, enabling high-resolution paleo-fire reconstructions.
• The method provides a valuable tool for detailed paleoenvironmental and paleoclimatic studies using speleothem biomarkers.