Airborne pollen, wildfires, and Saharan dust control atmospheric carbohydrates and shape their biogeochemical impacts in northern Mediterranean

Abstract. Carbohydrates are ubiquitous, water-soluble organic compounds that serve as tracers of atmospheric organic matter sources, participate in cloud chemical processes, and, once deposited to surface waters, provide readily bioavailable carbon that can stimulate microbial activity and affect marine biogeochemistry. The Mediterranean Sea, influenced by variable natural and anthropogenic inputs, is a key region for assessing how emission sources affect atmospheric organic matter composition and fluxes. Here, we studied the impact of three key sources, pollen episodes, Saharan dust intrusions, and biomass burning, on atmospheric carbohydrate concentrations, deposition pathways (dry, wet, and total), and their effects on northern Mediterranean coastal waters. Carbohydrate composition varied seasonally, reflecting shifts in local emissions, long-range transport, and meteorological conditions, with wet deposition as the dominant removal pathway. Spring pollen episodes were the dominant source of primary sugars, while summer sugar alcohols indicated minor fungal contributions. Biomass burning, including residential heating and wildfires, produced the highest anhydrosugars levels and significantly increased total dissolved carbohydrates. In contrast, Saharan dust contributed insignificant organic carbon fractions and had limited impact on carbohydrate deposition. Event-based analysis showed that pollen and dust episodes increased surface dissolved organic carbon by 0.2–0.7 %, whereas biomass burning induced short-term increases of up to 5 %. Although overall atmospheric contributions to marine dissolved organic carbon pool were modest, the high fraction of labile carbohydrates indicated that episodic deposition events delivered important pulses of bioavailable carbon. These findings emphasize the need to resolve short-term atmosphere-ocean interactions to better understand coastal carbon cycling and its broader environmental implications.