‘Fire Islands’: Holocene wildfire intensity as a critical determinant of carbon accumulation in South Atlantic peatlands

Until recently, quantifying wildfire intensity in palaeoecological records has not been possible. Therefore, little is known about the link between past wildfire intensity, carbon accumulation and climate. This study presents a history of burning and carbon accumulation spanning ∼15,500 years across a peat profile recovered from the Falkland Islands, including commonplace charcoal as evidence for frequent natural burning since the onset of peat formation. Utilising Raman spectra of preserved macrocharcoal fragments, we applied a recent cone calorimeter-based calibration to reconstruct changes in multi-fire intensity. In the early Holocene, wetter local conditions are reflected in higher carbon accumulation rates, variable charcoal fluxes, low burning intensities, and more diverse vegetation. Wildfire intensity started to increase between 8000 and 6000 cal BP with maximum intensities between approx. 4000 and 1000 cal BP, while carbon accumulation rates constantly declined. These developments concur with major changes in climate and in the position and strength of the southern westerly winds, potentially desiccating biomass and fuelling combustion. Fuel availability and type due to peatland succession processes also plays a role in wildfire intensity changes. Our data show a strong negative correlation between burning intensities and carbon accumulation rates and, strikingly, between burning intensity and charcoal flux. This demonstrates that high charcoal fluxes are not necessarily equivalent to high fire intensities, and that the opposite might often be true. Given the latter, we suggest caution to researchers extrapolating wildfire behaviour solely upon the presence of macrocharcoal. • Comprehensive fire intensity reconstruction using Raman spectroscopy on charcoal from near-continuous wildfires on Falkland Islands' peatlands since the late Pleistocene. • Fire intensity, carbon accumulation and charcoal flux shifted ∼8000 cal BP. • Changes are linked to climate, natural peatland succession, and vegetation. • Peat carbon accumulation has a strong negative correlation with fire intensity. • Charcoal count, concentration or flux: Not necessarily equivalent to fire intensity.