Sea ice concentration impacts dissolved organic gases in the Canadian Arctic

[摘要] The marginal sea ice zone has been identified as a sourceof different climate-active gases to the atmosphere due to its uniquebiogeochemistry. However, it remains highly undersampled, and the impact ofsummertime changes in sea ice concentration on the distributions of thesegases is poorly understood. To address this, we present measurements ofdissolved methanol, acetone, acetaldehyde, dimethyl sulfide, and isoprene inthe sea ice zone of the Canadian Arctic from the surface down to 60 m. Themeasurements were made using a segmented flow coil equilibrator coupled to aproton-transfer-reaction mass spectrometer. These gases varied inconcentrations with depth, with the highest concentrations generallyobserved near the surface. Underway (3–4 m) measurements showed higherconcentrations in partial sea ice cover compared to ice-free waters formost compounds. The large number of depth profiles at different sea iceconcentrations enables the proposition of the likely dominant productionprocesses of these compounds in this area. Methanol concentrations appear tobe controlled by specific biological consumption processes. Acetone andacetaldehyde concentrations are influenced by the penetration depth of lightand stratification, implying dominant photochemical sources in this area.Dimethyl sulfide and isoprene both display higher surface concentrations inpartial sea ice cover compared to ice-free waters due to ice edge blooms.Differences in underway concentrations based on sampling region suggest thatwater masses moving away from the ice edge influences dissolved gasconcentrations. Dimethyl sulfide concentrations sometimes display asubsurface maximum in ice -free conditions, while isoprene morereliably displays a subsurface maximum. Surface gas concentrations were used toestimate their air–sea fluxes. Despite obvious in situ production, weestimate that the sea ice zone is absorbing methanol and acetone from theatmosphere. In contrast, dimethyl sulfide and isoprene are consistently emitted from theocean, with marked episodes of high emissions during ice-free conditions,suggesting that these gases are produced in ice-covered areas and emittedonce the ice has melted. Our measurements show that the seawaterconcentrations and air–sea fluxes of these gases are clearly impacted by seaice concentration. These novel measurements and insights will allow us tobetter constrain the cycling of these gases in the polar regions and theireffect on the oxidative capacity and aerosol budget in the Arcticatmosphere.

[学科分类] 大气科学