Relict charcoal hearth magnetic fingerprints in the forest topsoil

• Pyrogenic magnetic enhancement was observed in relict coal hearths (RCHs) • We provide evidence for the presence of superparamagnetics (SP) in the RCHs. • The presence of SP grains in the charcoal-enriched horizon (CEH) was found. • Iron oxides are responsible for magnetic enhancement in the RCHs. • χ, χ fd and χ/Fe show similar behaviours for the CEH. The relationship between the magnetic properties and fire-affected soil is crucial for environmental inference, especially in the case of soil magnetic enhancement by thermal transformation of iron minerals. Generally, there are no studies reporting relict charcoal hearths using magnetic analyses. This gap is addressed in our work. Moreover, we also fill the gap regarding how long fire-related magnetic enhancement may persist in soils. Hence, the data may also influence the development of research on pyrogenic magnetic enhancement of soils. The preliminary research was aimed at verifying the possibility of using some environmental magnetism parameters to detect differences in the soil magnetic signal with and without relict charcoal hearth (RCH). Consequently, to understand and describe the mechanism of pyrogenic magnetic enhancement in charcoal-enriched horizon (CEH), research into its magnetic features was initiated. This work was carried out on three soil profiles (Albic Brunic Arenosols ), both RCHs and reference. The magnetic data obtained during the study showed variable contribution of magnetic particles in soil horizons, which indicates pyrogenic magnetic enhancement related to the presence of superparamagnetic (SP) grains in the charcoal particles from CEH in the RCHs soil profile. Despite the oxidation of SP grains of ferrimagnetic minerals over time (200–250 years) superparamagnetic magnetite and/or maghemite are still responsible for the pyrogenic magnetic enhancement in soil.