Evaluation of anhydrosugars as a molecular proxy for paleofire activity: A case study on a Holocene sediment core from Agios Floros, Peloponnese, Greece

Elin Norströma,b,c, Johannes Westa,dKaterina Koulie, Christos Katrantsiotis b,c,f, Martina Hättestrandb,c, and Rienk H.Smittenberga,c

a Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden
b Department of Physical Geography, Stockholm University, 106 91 Stockholm, Sweden
c Bolin Centre for Climate Research, Stockholm University, Sweden
d Department of Environmental Science, Stockholm University, 106 91 Stockholm, Sweden
e Department of Geology and Geoenvironment, National and Kapodistrian University of Athens Panepistimiopolis Zografou Athens, 15784, Greece
f Environmental Archaeology Laboratory, Department of Historical, Philosophical and Religious Studies, Umeå University, 90187 Umeå, Sweden

https://doi.org/10.1016/j.orggeochem.2021.104193

Abstract
The anhydrosugars levoglucosan, mannosan and galactosan have been regarded a suitable molecular indicator of natural biomass combustion. Here we evaluate the summed anhydrosugars (SAS) as paleofire indicator in a 6000 year-long fossil core from Agios Floros fen, Peloponnese, Greece, by analyzing charcoal fragments in parallel throughout the sediment sequence. Modern surface soil samples from the same region were analysed for presence of SAS, confirming the biomarker as an indicator of recent fire activity. The highest SAS concentrations in the fossil core were found in sections representing periods of wet conditions both on local and regional scale, and regionally widespread arboreal vegetation. Low or absence of SAS in the fossil core is associated with periods of dryness, regional dominance of non-arboreal vegetation and a fen rather than lake ecosystem at the site. Micro-charcoal fragments were generally more abundant under these conditions. This suggests that SAS yield and deposition may vary with fuel availability and fire behavior which in turn is affected by climate, local moisture and vegetation type. Forest fires result in more SAS compared to grass fires. SAS yield is also favored by low-temperature fires sustained under wet climate conditions. Preservation of SAS is likely to be compromised in the only seasonally wet fen ecosystem under the dry and warm Mediterranean climate conditions. The moist and shallow conditions in the wetland during hot summer months are probably promoting oxidation and biodegradation of the labile SAS molecules compared to the more robust charcoal fragments. Thus, a multiproxy approach - using several proxies, both for fire, hydroclimate and vegetation change - is preferred when aiming to reconstruct past biomass burning from wetland ecosystems in a Mediterranean environment. The micro-charcoal record from Agios Floros reveals significant fire activity between 4400-2800 cal yr BP. This partly overlaps the Bronze Age period, associated with intense human environmental interaction and climate change in this area of Peloponnese, Greece.