Spatial patterns and long-term trends of primary marine organic aerosol in the Arctic

Primary marine organic aerosol (PMOA) constitutes an important fraction of the aerosol population over remote oceanic regions and plays a relevant role in aerosol–cloud–climate interactions. In the Arctic, ongoing sea-ice retreat and intensified summer ice loss are expected to enhance marine aerosol emissions. Here, we employ an extended version of the aerosol–climate model ECHAM6.3-HAM2.3 to examine the spatial distribution and long-term temporal evolution of PMOA emissions and transport in the Arctic for the period 1990–2019, accounting for changing climatic and sea-ice conditions. Marine biogeochemical fields are provided by the offline model FESOM2.1-REcoM3, from which three aerosol-relevant biomolecular species groups - polysaccharides (PCHO), amino acids (DCAA), and polar lipids (PL) - are represented. Their transfer from the ocean to the atmosphere is parameterized using OCEANFILMS, recently implemented in ECHAM6.3-HAM2.3 to enhance the marine emission scheme.

The model results indicate that PMOA emission fluxes are primarily controlled by marine biological activity and sea-salt production, the latter mainly depending on near-surface winds. Biomolecular concentrations show limited variability in equatorial regions but pronounced seasonal cycles toward high latitudes. In seawater, PCHO dominates the simulated organic pool, followed by DCAA and PL. In contrast, PL contributes the largest fraction to aerosol-phase organic matter due to the comparatively strong air-seawater affinity of lipids. Arctic PMOA emissions and atmospheric transport peak between May and September, coinciding with the phytoplankton bloom and the seasonal sea-ice minimum. Substantial regional differences are evident in the timing of biomolecule production and aerosol emissions across the Arctic. Simulated PMOA seasonality agrees reasonably well with available ground-based observations, given the uncertainties in both measurements and model assumptions.

Over the 30-year period, accumulated Arctic aerosol emissions and burdens increased by at least 7% and 4%, respectively, when comparing the first and second halves of the study period. Summer (June–August) trend analyses reveal a pronounced decline in sea ice that is associated with increasing concentrations of organic biomolecules in inner Arctic waters. Positive PMOA emission anomalies have become more frequent over the past 15 years, indicating a sustained upward trend. On average, PMOA production has increased by 0.8% per year since 1990, with changes varying among biomolecular groups and Arctic subregions.