Abstract
Abstract. To investigate the characteristics of particulate methanesulfonic acid (MSA(p)), non-sea-salt sulfate (nss SO42-) and organic carbon (OC) aerosols, aerosol and seawater samples were collected over the Southern Ocean (43–70∘ S) and the Amundsen Sea (70–75∘ S) during the ANA06B cruise conducted in the austral summer of 2016 aboard the Korean icebreaker IBR/V Araon. Over the Southern Ocean, the atmospheric MSA(p) concentration was low (0.10±0.002 µg m−3), whereas its concentration increased sharply up to 0.57 µg m−3 in the Amundsen Sea where Phaeocystis antarctica (P. antarctica), a producer of dimethylsulfide (DMS), was the dominant phytoplankton species. Unlike MSA(p), the mean nss SO42- concentration in the Amundsen Sea was comparable to that in the Southern Ocean. Water-soluble organic carbon (WSOC) concentrations over the Southern Ocean and the Amundsen Sea varied from 0.048 to 0.16 and 0.070 to 0.18 µgC m−3, with averages of 0.087±0.038 and 0.097±0.038 µgC m−3, respectively. For water-insoluble organic carbon (WIOC), its mean concentrations over the Southern Ocean and the Amundsen Sea were 0.25±0.13 and 0.26±0.10 µgC m−3, varying from 0.083 to 0.49 and 0.12 to 0.38 µgC m−3, respectively. WIOC was the dominant organic carbon species in both the Southern Ocean and the Amundsen Sea, accounting for 73 %–75 % of the total aerosol organic carbon. WSOC/Na+ and WIOC/Na+ ratios in the fine-mode aerosol particles were higher, especially in the Amundsen Sea where biological productivity was much higher than the Southern Ocean. The fluorescence properties of water-soluble organic aerosols investigated using a fluorescence excitation–emission matrix coupled with parallel factor analysis (EEM–PARAFAC) revealed that protein-like components were dominant in our marine aerosol samples, representing 69 %–91 % of the total intensity. Protein-like components also showed a significant positive relationship with the relative biomass of diatoms; however, they were negatively correlated with the relative biomass of P. antarctica. These results suggest that the protein-like component is most likely produced as a result of biological processes of diatoms in the Amundsen Sea.
Highlights
Marine aerosols have been recognized to play an essential role in global climate due to their impact on the radiation budget and cloud microphysics by scattering solar radiation and acting as cloud condensation nuclei (CCN) (Andreae and Crutzen, 1997; O’Dowd et al, 2004)
water-soluble organic carbon (WSOC)/Na+ and water-insoluble organic carbon (WIOC)/Na+ ratios in the fine-mode aerosol particles were higher, especially in the Amundsen Sea where biological productivity was much higher than the Southern Ocean
No significant differences in mean WSOC and WIOC concentrations were found between the Southern Ocean and the Amundsen Sea, suggesting that the chlorophyll a (Chl a) concentration is not a direct factor controlling the atmospheric organic carbon (OC) concentration in our study area (Quinn et al, 2014), a significant correlation between atmospheric OC and Chl a concentrations was observed in the Austral Ocean (Amsterdam Island; 37◦48 S, 77◦34 E; Sciare et al, 2009)
Summary
Marine aerosols have been recognized to play an essential role in global climate due to their impact on the radiation budget and cloud microphysics by scattering solar radiation and acting as cloud condensation nuclei (CCN) (Andreae and Crutzen, 1997; O’Dowd et al, 2004). The biogeochemical cycle of sulfur between the marine atmosphere and the ocean has received much attention, especially after the proposal by Charlson et al (1987), who postulated that the most significant source of CCN in the marine environment is non-sea-salt sulfate (nss SO24−) derived from the atmospheric oxidation of dimethylsulfide (DMS). The conversion of DMS into nss SO24− aerosols is an essential process because of the potential interaction of sulfur aerosols with incoming solar radiation and their role in cloud microphysics, which could result in a negative climate feedback mechanism (Legrand and Pasteur, 1998). Quinn and Bates (2011) questioned the role of sulfur-containing aerosols derived from DMS in the climate feedback, but it is still clear that DMS emissions contribute significantly to sulfur-containing aerosols acting as CCN over the oceans (Sanchez et al, 2018)
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