Abstract
Abstract. The Amazon Basin is one of the major contributors to global biomass burning emissions. However, regional paleofire trends remain particularly unknown. Due to their proximity to the Amazon Basin, Andean ice cores are suitable to reconstruct paleofire trends in South America and improve our understanding of the complex linkages between fires, climate and humans. Here we present the first refractory black carbon (rBC) ice-core record from the Andes as a proxy for biomass burning emissions in the Amazon Basin, derived from an ice core drilled at 6300 m a.s.l. from the Illimani glacier in the Bolivian Andes and spanning the entire Holocene back to the last deglaciation 13 000 years ago. The Illimani rBC record displays a strong seasonality with low values during the wet season and high values during the dry season due to the combination of enhanced biomass burning emissions in the Amazon Basin and less precipitation at the Illimani site. Significant positive (negative) correlations were found with reanalyzed temperature (precipitation) data for regions in eastern Bolivia and western Brazil characterized by substantial fire activity. rBC long-term trends indirectly reflect regional climatic variations through changing biomass burning emissions as they show higher (lower) concentrations during warm–dry (cold–wet) periods, in line with climate variations such as the Younger Dryas, the 8.2 ka event, the Holocene Climatic Optimum, the Medieval Warm Period and the Little Ice Age. The highest rBC concentrations of the entire record occurred during the Holocene Climatic Optimum between 7000 and 3000 BCE, suggesting that this exceptionally warm and dry period caused high levels of biomass burning activity, unprecedented in the context of the past 13 000 years. Recent rBC levels, rising since 1730 CE in the context of increasing temperatures and deforestation, are similar to those of the Medieval Warm Period. No decrease in fire activity was observed in the 20th century, in contradiction to global biomass burning reconstructions based on charcoal data.
Highlights
Fires play a major role in the global carbon cycle by emitting aerosols and greenhouse gases
Significant correlations were found between the 20th century refractory black carbon (rBC) record and reanalyzed temperature– precipitation datasets from the Amazon Basin, with regions located in eastern Bolivia and western Brazil experiencing high levels of biomass burning
The long-term rBC record was shown to behave like an indirect regional temperature–moisture proxy through biomass burning variations, with low values during cold–wet periods such as the Younger Dryas and the Little Ice Age and higher concentrations during warm–dry periods such as the Holocene Climatic Optimum and the Medieval Warm Period
Summary
Fires play a major role in the global carbon cycle by emitting aerosols and greenhouse gases. Osmont et al.: A Holocene rBC ice-core record from Illimani ica remained fairly stable over the 20th century (Mouillot and Field, 2005; Schultz et al, 2008) This trend masks regional discrepancies: while burning decreased along the Brazilian coast, it has strongly increased in the western part due to deforestation (Mouillot and Field, 2005). Ice-core records from Antarctica have already been connected to paleofire trends in the Southern Hemisphere They revealed elevated biomass burning activity around 8000 to 6000 BP in southern America (Arienzo et al, 2017) and confirmed an overall agreement with the aforementioned global trend (Wang et al, 2010). After discussing the seasonality of the rBC signal and the connections with regional climate parameters and biomass burning, we will present rBC longterm trends of the last millennium and through the Holocene, link them with climate variability, and compare them to existing ice-core and lake sediment records
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