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Viscosity, or the "thickness," of aerosols plays a key role in atmospheric processes like ice formation, water absorption, and heterogeneous kinetics. However, the viscosity of sea spray aerosols (SSA) has not been widely studied. This research explored the relationship between particle size and viscosity of authentic SSA particles through particle bounce, atomic force microscopy analysis, and predictive viscosity modeling from molecular composition. The study found that 40 nm SSA particles had estimated viscosities around 10 4 Pa·s and bounce fractions three times higher than 100 and 200 nm particles with less than 10 2 Pa·s at a relative humidity (RH) of 60%. Additional studies revealed the Kelvin effect and particle density, influenced by particle size, have a greater impact on size-dependent bounce fractions than changes in RH across impactor stages. While changes in the level of surfactants can impact particle bounce, the increased viscosity in smaller SSA is attributed to the formation of gel-like phase states caused by cation-organic cross-links between divalent calcium ions and organic anions enriched in the smaller particles. This work shows the smallest gel-like SSA particles observed in the field are highly viscous, which has implications for cloud formation, secondary aerosol growth, and pollutant transport in coastal environments.

Blooms of Ostreopsis cf. ovata pose an emerging health threat, causing respiratory disorders in various coastal regions. This dinoflagellate produce potent phycotoxins named ovatoxins that can be transferred from the seawater to the atmosphere. However, the biotic and abiotic conditions affecting their transfer are still unknown. In this study, we investigate the sea-to-air transfer of O. cf ovata phycotoxins using a process study in an aerosol reference tank (MART) and field observations. The process study exhibited a positive correlation between the phycotoxin content in sea spray aerosol (up to 832.59 ng m -3 ) and the particulate phycotoxin fraction in the water column and surface microlayer. In contrast, in the natural system, aerosolized phycotoxins were only observed in one out of six air collection (total toxins 0.59 ng m -3 ) despite optimal wind conditions. In both the process study and the natural system, ovatoxins represented only a minor fraction of the total toxin content, which was comprised of up to 90% liguriatoxins. In seawater, while no solubilized ovatoxins were detected, the concentration in dissolved liguriatoxin-a reached up to 19.07 μg L -1 . These results underscore the need for future research on the liguriatoxins, and on their toxicity to establish safe exposure thresholds for beachgoers.

Variable wind speeds over the ocean can have a significant impact on the formation mechanism and physical-chemical properties of sea spray aerosols (SSA), which in turn influence their climate-relevant impacts. Herein, for the first time, we investigate the effects of wind speed on size-dependent morphology and composition of individual nascent SSA generated from wind-wave interactions of natural seawater within a wind-wave channel as a function of size and their particle-to-particle variability. Filter-based thermal optical analysis, atomic force microscopy (AFM), AFM infrared spectroscopy (AFM-IR), and scanning electron microscopy (SEM) were employed in this regard. This study focuses on SSA with sizes within 0.04-1.8 μm generated at two wind speeds: 10 m/s, representing a wind lull scenario over the ocean, and 19 m/s, indicative of the wind speeds encountered in stormy conditions. Filter-based measurements revealed a reduction of the organic mass fraction as the wind speed increases. AFM imaging at 20% relative humidity of individual SSA identified six main morphologies: prism-like, rounded, core-shell, rod, rod inclusion core-shell, and aggregates. At 10 m/s, most SSA were rounded, while at 19 m/s, core-shells became predominant. Based on AFM-IR, rounded SSA at both wind speeds had similar composition, mainly composed of aliphatic and oxygenated species, whereas the shells of core-shells displayed more oxygenated organics at 19 m/s and more aliphatic organics at 10 m/s. Collectively, our observations can be attributed to the disruption of the sea surface microlayer film structure at higher wind speeds. The findings reveal a significant impact of wind speed on morphology and composition of SSA, which should be accounted for accurate assessment of their climate effects., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The ecology of the SAR11 clade, the most abundant bacterial group in the ocean, has been intensively studied in temperate and tropical regions, but its distribution remains largely unexplored in the Southern Ocean. Through amplicon sequencing of the 16S rRNA gene, we assessed the contribution of the SAR11 clade to bacterial community composition in the naturally iron fertilized region off Kerguelen Island. We investigated the upper 300 m at seven sites located in early spring phytoplankton blooms and at one high-nutrient low-chlorophyll site. Despite pronounced vertical patterns of the bacterioplankton assemblages, the SAR11 clade had high relative abundances at all depths and sites, averaging 40% (±15%) of the total community relative abundance. Micro-autoradiography combined with CARD-FISH further revealed that the clade had an overall stable contribution (45%-60% in surface waters) to bacterial biomass production (determined by 3 H-leucine incorporation) during different early bloom stages. The spatio-temporal partitioning of some of the SAR11 subclades suggests a niche specificity and periodic selection of different subclades in response to the fluctuating extreme conditions of the Southern Ocean. These observations improve our understanding of the ecology of the SAR11 clade and its implications in biogeochemical cycles in the rapidly changing Southern Ocean., (© 2022 Society for Applied Microbiology and John Wiley & Sons Ltd.)

To elucidate the seawater biological and physicochemical factors driving differences in organic composition between supermicron and submicron sea spray aerosol (SSA super and SSA sub ), carbon isotopic composition (δ 13 C) measurements were performed on size-segregated, nascent SSA collected during a phytoplankton bloom mesocosm experiment. The δ 13 C measurements indicate that SSA super contains a mixture of particulate and dissolved organic material in the bulk seawater. After phytoplankton growth, a greater amount of freshly produced carbon was observed in SSA super with the proportional contribution being modulated by bacterial activity, emphasizing the importance of the microbial loop in controlling the organic composition of SSA super . Conversely, SSA sub exhibited no apparent relationship with biological activity but tracked closely with surface tension measurements probing the topmost ∼0.2-1.5 μm of the sea surface microlayer. This probing depth is similar to a bubble's film thickness at the ocean surface, suggesting that SSA sub organic composition may be influenced by the presence of surfactants at the air-sea interface that are transferred into SSA sub by bubble bursting. Our findings illustrate the substantial impact of seawater dynamics on the pronounced organic compositional differences between SSA super and SSA sub and demonstrate that these two SSA populations should be considered separately when assessing their contribution to marine aerosols and climate.

Marine aerosols strongly influence climate through their interactions with solar radiation and clouds. However, significant questions remain regarding the influences of biological activity and seawater chemistry on the flux, chemical composition, and climate-relevant properties of marine aerosols and gases. Wave channels, a traditional tool of physical oceanography, have been adapted for large-scale ocean-atmosphere mesocosm experiments in the laboratory. These experiments enable the study of aerosols under controlled conditions which isolate the marine system from atmospheric anthropogenic and terrestrial influences. Here, we present an overview of the 2019 Sea Spray Chemistry and Particle Evolution (SeaSCAPE) study, which was conducted in an 11 800 L wave channel which was modified to facilitate atmospheric measurements. The SeaSCAPE campaign sought to determine the influence of biological activity in seawater on the production of primary sea spray aerosols, volatile organic compounds (VOCs), and secondary marine aerosols. Notably, the SeaSCAPE experiment also focused on understanding how photooxidative aging processes transform the composition of marine aerosols. In addition to a broad range of aerosol, gas, and seawater measurements, we present key results which highlight the experimental capabilities during the campaign, including the phytoplankton bloom dynamics, VOC production, and the effects of photochemical aging on aerosol production, morphology, and chemical composition. Additionally, we discuss the modifications made to the wave channel to improve aerosol production and reduce background contamination, as well as subsequent characterization experiments. The SeaSCAPE experiment provides unique insight into the connections between marine biology, atmospheric chemistry, and climate-relevant aerosol properties, and demonstrates how an ocean-atmosphere-interaction facility can be used to isolate and study reactions in the marine atmosphere in the laboratory under more controlled conditions.