Refining fire history in the Upper Rhine Graben region - Challenges and opportunities highlighted from a case study at Wildseemoor (northern Black Forest, Germany)

A 600 cm peat succession covering the last ca. 10,000 years from Wildseemoor, a perilacustrine ombrotrophic peat bog in the northern Black Forest, offers the opportunity to study Holocene environmental evolution and fire history in the Upper Rhine region. More particularly it is used here for a pilot study 1) dealing with the influence of potential peat growth disturbance on charcoal influx interpretation, and 2) proposing a new approach to disentangle regional from local influences on charcoal influx, based on the internal variability of charcoal particle size variations. The latter suggests a fluctuating local to regional main source of charcoal influx to Wildseemoor. Two plausible age-depth models were established based on seven identified radiocarbon-dated macrofossils, showing either reduced depositional rates or breaks in deposition during the early- to mid-Holocene and (less extensively) the Middle Ages, that are not visible to the naked eye in the sediment sequence. The Holocene Climatic Optimum, a time interval of particular interest with its climate conditions analogue to future projections, falls directly into an extensive period of reduced accretion or depositional hiatus. This severely impacts the interpretation of the charcoal record for that period but highlights potential impacts of climate variations on peat growth. Regardless which age-depth model is used, phases of high charcoal influx were identified after ca. 5,000 cal BP and can most likely be linked to anthropogenic pressure on the region. The findings of this study may be used in future Holocene fire dynamics reconstructions, as they stress the necessity for high-resolution age control, but also the opportunity to exploit periods of disturbed/halting peat growth as a proxy to detect past periods of climate change. Using the internal variability of charcoal particle size to estimate local versus regional charcoal transport tendency showed promising results and may help push forward charcoal record interpretations in the future.