Synchronizing Pu fallout and inorganic fly ash particles record in Northern Hemisphere peatlands

This study examines two critical markers of anthropogenic activity - plutonium (Pu) and inorganic fly ash particles, specifically spheroidal aluminosilicates (SAPs) and mullite - to evaluate their patterns of distribution across the Northern Hemisphere in 10 peat profiles. The global Pu fallout record is synchronous within the time uncertainties but shows differences in maximum activity concentration and calculated inventories. Higher inventories were recorded in Iceland, at Śnieżka and the Izery Mountains in Poland, as well as in Tomsk, Siberia, Russia (88.63-104.58 Bq m^-2). SAPs and crystalline mullite, byproducts of high-temperature coal combustion released into the atmosphere, first appeared during the mid-20th century industrial expansion, corresponding to the onset of the so-called Great Acceleration Event Array in remote regions like Spitsbergen and China, whereas in areas proximal to emission sources it is characterized by a pronounced and rapid increase. SAPs exhibit notable size variability, ranging from <2-5 μm in remote locations like Iceland, Spitsbergen, and mountainous regions of Northern China to <2-80 μm in peatlands close to industrial centres. This size distribution reflects the relationship between the distance (vertical and horizontal) from SAP emission sources and their deposition in peatlands. Despite differences in transport mechanisms and deposition pathways, both Pu and SAPs provide distinct, globally recognizable markers of human-induced change.