Fire history of the western Amazon basin recorded by multiple pyrogenic carbon proxies

Abstract

Charcoal abundance has been used as a fire proxy to reconstruct human settlement and climate records, but analyses of pyrogenic carbon (PyC) have become more widespread. To compare these proxies, fire records spanning the past 3000 y of Western Amazon Lakes Ayauchi, Gentry and Parker region soil and sediments were determined by visually identified charcoal, chemical-thermal oxidation (CTO) and benzene polycarboxylic acid (BPCA) markers. Charcoal represented the smallest portion of PyC and, with its irregular distribution, it likely indicated only local or large fires. PyC via CTO concentrations were highest and most uniform, suggesting lower sensitivity in detecting fire. BPCA-derived PyC distributions in soils were consistent with more human occupation and higher temperature fires in the Lake Ayauchi region and, in lake sediments, BPCA-derived PyC bore the closest resemblance to patterns of climate and human influence. Thus, BPCAs were more sensitive indicators of fire over regional scales. The combined information from multiple fire proxies revealed a history of frequent fires in western Amazon. Lake Ayauchi region had greater fire frequency and higher temperature fires than the Gentry/Parker region, suggesting greater human occupation. The greater fire frequency in wetter periods and regions of western Amazon, suggest a major influence of human activity on PyC production over the past 3000 years. Each fire proxy examined in this study had strengths and weaknesses and the use of a combination of fire proxies can provide a fuller picture of fire history than any single approach.