Pioneering insights into the global and local origins of Betula spp. pollen in Iceland: Tracing long-distance transport pathways

• Potential distributions for downy and dwarf birch were modelled for Iceland. • Long-distance birch pollen transport to Iceland from across the Atlantic was studied. • Local weather and wind direction shape birch pollen transport pathways in Iceland. • Pre-season and peak-season pollen transport pathways differ significantly. • Pollen dispersal dynamics vary annually between Reykjavik (SW) and Akureyri (N). Iceland’s natural woodlands are dominated by the downy birch ( Betula pubescens ), while the dwarf birch ( B. nana ) is common in shrublands. These two species are the local sources of allergenic pollen that, however, may also be transported from outside Iceland (distant sources). This study aims to detect long-distance pollen transport, elucidate its mechanisms, and assess the relative contributions of local and distant sources to Iceland’s birch pollen pool. Pollen records (1998–2023) for Akureyri and Reykjavik were investigated using surface meteorological data, back-trajectories calculated by the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) and transformed into Potential Source Contribution Function (PSCF), complemented with Sea Level Pressure (SLP) and 500 hPa geopotential height (z500) patterns. Moreover, distributions of Betula spp. were modelled using random forest models to show the location of potential birch pollen sources. We evidenced that birch pollen was transported across the Atlantic Ocean to Iceland, especially before the local pollen season, from Eastern Europe and Scotland, sometimes in large quantities (max:456 pollen m -3 ). The SPIn in Akureyri was higher when pollen transported from the eastern part of Iceland or Scandinavia overlapped with the local pollen pool. In Reykjavik, pollen was transported from northern, western Iceland, but probably also from Greenland and Labrador. Betula spp. distribution maps in Iceland can aid future species distribution modelling under climate change. This research enhances the understanding of Arctic pollen transport dynamics and highlights the need for further research on high-latitude pollen dispersion mechanisms.