First direct observation of sea salt aerosol production from blowing snow above sea ice

• Main Authors: Frey, Markus M, Norris, Sarah J, Brooks, Ian M, Anderson, Philip S, Nishimura, Kouichi, Yang, Xin, Jones, Anna E, Nerentorp Mastromonaco, Michelle G, Jones, David H, Wolff, Eric W
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union 2020
• Subjects: 37 Earth Sciences; 3708 Oceanography; 3709 Physical Geography and Environmental Geoscience; 3701 Atmospheric Sciences; 13 Climate Action; Antarc*; Antarctic; Antarctica; Sea ice; Weddell Sea
• Online Access: https://www.repository.cam.ac.uk/handle/1810/303042; https://doi.org/10.17863/CAM.50118

Two consecutive cruises in the Weddell Sea, Antarctica, in winter 2013 provided the first direct observations of sea salt aerosol (SSA) production from blowing snow above sea ice, thereby validating a model hypothesis to account for winter time SSA maxima in the Antarctic. Blowing or drifting snow often leads to increases in SSA during and after storms. For the first time it is shown that snow on sea ice is depleted in sulfate relative to sodium with respect to seawater. Similar depletion in bulk aerosol sized ∼0.3–6 µm above sea ice provided the evidence that most sea salt originated from snow on sea ice and not the open ocean or leads, e.g. >90 % during the 8 June to 12 August 2013 period. A temporally very close association of snow and aerosol particle dynamics together with the long distance to the nearest open ocean further supports SSA originating from a local source. A mass budget estimate shows that snow on sea ice contains even at low salinity (<0.1 psu) more than enough sea salt to account for observed increases in atmospheric SSA during storms if released by sublimation. Furthermore, snow on sea ice and blowing snow showed no or small depletion of bromide relative to sodium with respect to seawater, whereas aerosol was enriched at 2 m and depleted at 29 m, suggesting that significant bromine loss takes place in the aerosol phase further aloft and that SSA from blowing snow is a source of atmospheric reactive bromine, an important ozone sink, even during winter darkness. The relative increase in aerosol concentrations with wind speed was much larger above sea ice than above the open ocean, highlighting the importance of a sea ice source in winter and early spring for the aerosol burden above sea ice. Comparison of absolute increases in aerosol concentrations during storms suggests that to a first order corresponding aerosol fluxes above sea ice can rival those above the open ocean depending on particle size. Evaluation of the current model for SSA production from blowing snow showed that the ...