Abstract
Abstract. The concentrations of submicron aerosol particles in maritime regions around Antarctica are influenced by the extent of sea ice. This effect is two ways: on one side, sea ice regulates the production of particles by sea spray (primary aerosols); on the other side, it hosts complex communities of organisms emitting precursors for secondary particles. Past studies documenting the chemical composition of fine aerosols in Antarctica indicate various potential primary and secondary sources active in coastal areas, in offshore marine regions, and in the sea ice itself. In particular, beside the well-known sources of organic and sulfur material originating from the oxidation of dimethylsulfide (DMS) produced by microalgae, recent findings obtained during the 2015 PEGASO cruise suggest that nitrogen-containing organic compounds are also produced by the microbiota colonizing the marginal ice zone. To complement the aerosol source apportionment performed using online mass spectrometric techniques, here we discuss the outcomes of offline spectroscopic analysis performed by nuclear magnetic resonance (NMR) spectroscopy. In this study we (i) present the composition of ambient aerosols over open-ocean waters across bioregions, and compare it to the composition of (ii) seawater samples and (iii) bubble-bursting aerosols produced in a sea-spray chamber onboard the ship. Our results show that the process of aerosolization in the tank enriches primary marine particles with lipids and sugars while depleting them of free amino acids, providing an explanation for why amino acids occurred only at trace concentrations in the marine aerosol samples analyzed. The analysis of water-soluble organic carbon (WSOC) in ambient submicron aerosol samples shows distinct NMR fingerprints for three bioregions: (1) the open Southern Ocean pelagic environments, in which aerosols are enriched with primary marine particles containing lipids and sugars; (2) sympagic areas in the Weddell Sea, where secondary organic compounds, including methanesulfonic acid and semivolatile amines abound in the aerosol composition; and (3) terrestrial coastal areas, traced by sugars such as sucrose, emitted by land vegetation. Finally, a new biogenic chemical marker, creatinine, was identified in the samples from the Weddell Sea, providing another confirmation of the importance of nitrogen-containing metabolites in Antarctic polar aerosols.
Highlights
The Antarctic continent is one of the last pristine areas of our planet, but its natural ecosystems are threatened by an acceleration of the effects of global warming
Dissolved organic carbon (DOC) is mostly contributed by the excreta and metabolites of the marine biota but it accounts for a pool of refractory compounds, resistant to microbial degradation, and is well mixed in the water column (Hertkorn et al, 2013)
During the process of bubble-bursting performed in the tank experiments, aerosol particles became depleted in sea salt with respect to seawater and enriched in surfaceactive dissolved organic carbon (DOC) components and in buoyant particulate organic carbon (POC) substances
Summary
The Antarctic continent is one of the last pristine areas of our planet, but its natural ecosystems are threatened by an acceleration of the effects of global warming. (Rintoul et al, 2018) As all these specific ecosystem impacts involve factors deemed important for aerosol production in Antarctica (Davison et al, 1996; Schmale et al, 2013; Kyrö et al, 2013; Barbaro et al, 2017), a significant effect of climate change on atmospheric concentrations of aerosols and cloud condensation nuclei (CCN) must be expected to occur by the end of this century. The sea ice recedes, allowing wind stress over the oceanic surface and sea spray to occur closer to the continent, increasing the production of primary marine aerosols. Marine aerosols impact global climate by reducing the amount of solar radiation reaching dark surface of the ocean, both directly (through scattering) and indirectly (by modulating cloud formation and lifetime; O’Dowd and de Leeuw, 2007). In polar regions, cloud seeding by marine aerosols transported over glaciated regions affects the longwave radiation budget (Willis et al, 2018)
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