Atmospheric aerosols play a crucial role in the global climate, and in the polar regions, where anthropogenic and terrestrial aerosol sources are relatively small, marine aerosols become particularly important. In addition, the climatic effect of those aerosols is more convoluted in the polar regions, because although aerosols cool the climate during daylight (by blocking incoming solar radiation), in the dark, during the long polar night, those same aerosols can warm the climate, by retaining outgoing heat emitted by the surface. In an effort to better understand those polar marine aerosol sources, we're working with a brilliant group of atmospheric chemists (CIce2Clouds) to tease apart the surface ocean and sea-ice processes that control the emissions of aerosols to the polar atmosphere. A major part of the CIce2Clouds effort is turning out to be simply teaching each other about our respective disciplines and rectifying our vocabulary, while we are also designing the ideal interdisciplinary field study.

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Sea-surface microlayer sampling

As part of our past efforts to understand the chemistry of air-sea exchange, we devoted a lot of effort towards measuring the sea-surface microlayer, the upper 50-200 micrometers of the ocean that's in direct contact with the atmosphere. Back in the naughties, the Institute of Ocean Sciences (namely former post-doc Magnus Wendeberg, Lucius Perrault, and Svein Vagle) developed an automated sampler based on 10 rotating glass plates that are able to collect 3 L of microlayer sample a minute, enough material not only for chemical analyses to characterize the composition of the microlayer, but also to run experiments. This sampler design has since become standard for the discipline, and those who want to do this kind of work themselves should first consult the definitive manual of sea-surface microlayer measurements prepared by another of our former post-docs, Oliver Wurl.

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Our ability to collect large quantities of sea-surface microlayer material led to some exciting collaborations with atmospheric chemists. Under the fearless leadership of Jon Abbatt, of the University of Toronto, the NETCARE project brought together ocean and atmosphere scientists to try to tease apart the role of the ocean in Arctic atmospheric chemistry. Interestingly, despite confirmation that the sea-surface microlayer is rich in material that makes good aerosols, it seems that bulk surface waters, not the microlayer, may be a larger source of aerosol particles. This makes some sense, since there's very little microlayer and a LOT of bulk surface waters to get blown into the atmosphere from breaking waves. However, the microlayer material seems to create much more climatically-active aerosols, so it might actually be more important, after all....

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UofT student Emma Mungall, discovered that reactions (maybe photochemical?) occurring in the sea-surface microlayer release organic gases that can further react in the atmosphere to form aerosols. Most interestingly, Emma's measurements indicated that river waters might have been the source of the reactive material in the microlayer, but at the location of her measurements, the most direct source of river waters is the coast of Siberia. Thus, that reactive organic matter had survived a journey all the way across the central Arctic basin, before emerging from beneath the sea ice in northern Baffin Bay.

 

 

 

 

 

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