A 20th-century Cannabis pollen increase in a Pyrenean varved record and its potential causes

The continuous, varved and absolutely dated sedimentary record of Lake Montcortes (Iberian Pyrenees) has provided evidence for a distinct and characteristic 20th century (1980s) increase in Cannabis pollen (20C) that persists today. This event was coeval with the geographical shift of the hemp production center in the Iberian Peninsula from east to northeast (where Lake Montcortes lies), which was accompanied by a significant production increase. This increasing trend was fostered by the renewed interest of the paper industry in hemp and was promoted by the onset of European Union subsidies to hemp cultivation. Illegal cannabis crops could have also contributed to the Cannabis pollen increase, but sound evidence is still lacking. These preliminary conclusions should be reinforced by increasing the resolution of the current palynological record and modeling the dispersal of Cannabis pollen around the Montcortes region. More similar high-resolution records are needed to verify the geographical extent of the 20C event. Additionally, Lake Montcortes varved sediments are proposed as a suitable candidate to characterize the onset of the "Anthropocene" epoch (mid-20th century), as currently defined by the Anthropocene Working Group.