Biogeochemical regimes control marine aerosol emission of hydrogels in the Southwestern Pacific Ocean

Abstract. Ambient marine aerosols are frequently enriched in biogenic material. It was suggested that a critical fraction may be attributed to colloids and aggregates, which are composed of carbohydrates and proteins. Those hydrogels possess excellent cloud condensation and ice nucleation properties. Yet, most atmospheric measurements fail to detect marine hydrogels in aerosols directly, and the few studies which exist were conducted in the Northern hemisphere. Here, we present a comprehensive data set of carbohydrate and protein-enriched hydrogels in in sea spray aerosols (SSA) generated within representative regimes of the Southwestern Pacific Ocean. We relate the concentration of hydrogels in SSA to the occurrence of their precursors in surface seawater and other biogeochemical variables. The highest concentration (0.91 ± 0.72 × 10⁵ m^-3, corresponding to 4.1 ± 2.1 × 10³ particles ng^-1 Na⁺) and highest relative enrichment (5.3 ± 3.9 × 10⁵) of hydrogels in SSA (size range: 0.5–30 µm) was observed within the subtropical front, which is biologically most active. This was contrasted by subtropical waters, in which SSA concentration and enrichment decreased by one order of magnitude. Interestingly, the carbohydrate-to-protein ratio shifted with size in SSA hydrogels, while no such size-shift existed for marine samples. In comparison to their marine precursors, supermicron hydrogels in SSA were primarily composed of carbohydrates. Our results suggest that hydrogels may complement a considerable fraction of ambient marine aerosols, and significantly contribute to the atmospheric pool of cloud condensation and ice nuclei, in particular above the remote oceans of the Southern hemisphere.