Using Fourier Transform Infrared spectroscopy to produce high-resolution centennial records of past high-intensity fires from organic-rich sediment deposits

Background. Current observational or instrumental records of past fires are historically limited, and information on fire characteristics tends to be confined to the recent past. Aims and methods. Here, we reconstruct a record of high-intensity fire events that extends beyond the historical record using carbon (C) and nitrogen (N) content and Fourier Transform Infrared (FTIR) spectroscopy applied to swamp sediment deposits in the Blue Mountains of south-eastern Australia. Each site has a different fire history over the past 50 years, and the known fire record was used to corroborate fire signatures before extending the record. Key results. FTIR spectra show an increase in the aromatic/ aliphatic ratio for sediments corresponding to known fire events. Higher aromatic/aliphatic ratios suggest exposure to higher-intensity fire conditions. Conversely, the C and N content and C/N ratio show no association with known historic fire events. Conclusions. Sediment deposition at one site recorded three major fire events during the past ~500 years. Sediments recording the most recent fire event show a more significant increase in the aromatic/aliphatic ratio, suggesting that this event burnt at a higher intensity than the previous two. Implications. All sites show a promising extension of the existing fire record by decades to centuries.