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Measurements of ocean surface and atmospheric dimethyl sulfide (DMS) and particle size distributions were made in the Canadian Arctic Archipelago during the fall of 2007 and the late summer of 2008 aboard the Canadian Coast Guard Ship Amundsen. Nucleation‐mode particles were observed during the 2008 cruise, which took place in the eastern Arctic from August to September when the atmosphere and ocean were more photo‐active as compared to the October 2007 transit in the Beaufort Sea during which no nucleation/growth events were observed. The observed nucleation periods in 2008 coincided with high atmospheric and ocean surface DMS concentrations, suggesting that the particles originated from marine biogenic sources. An aerosol microphysics box model was used to simulate nucleation given the measured conditions in the marine boundary layer. Although other sources may have contributed, we find that the newly formed particles can be accounted for by a marine biogenic DMS source for combinations of the following parameters: [OH] ≥ 3 × 105 molecules cm−3, DMS mixing ratio is ≥ 100 pptv, the activation coefficient is ≤ 10−7 and the background particle concentration is ≤ 100 cm−3.

The role of viral activity with respect to bloom dynamics and production of dissolved dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) was investigated in Norwegian coastal waters and in sea water mesocosms during blooms of the coccolithophorid Emiliania huxleyi (Lohm.) Hay & Mohler. In coastal waters the collapse of the E. huxleyi bloom was accompanied by a simultaneous increase in large virus-like particles (LVLP) and there was a significant inverse relationship between cell-specific calcification rate and LVLP abundance. Results from the mesocosm study indicate that the viral actlv~ty may either prevent or termlnate the development of E. huxleyi blooms. No significant relationships were found between the abundance of LVLPs and the concentrations of dissolved DMSP and DMS in the field or in the mesocosms. This may be explained by the relatively small size of the E. huxlep blooms (maximum cell concentration of 11 X 106 I-') and bacterial degradation of DMSP and DMS, which may have been sufficient to prevent the accumulation of sulfur compounds released after lysis of the cells.

Dimethyl sulfide (DMS) and its oxidation products, which have been proposed to provide a climate feedback mechanism by affecting aerosol and cloud radiative properties, were measured on board the Canadian Coast Guard ship Amundsen in sampling campaigns in the Arctic in the fall of 2007 and 2008. DMS flux was calculated based on the surface water measurements and yielded 0.1–2.6 μmol m−2 d−1 along the Northwest Passage in 2007 and 0.2–1.3 μmol m−2 d−1 along Baffin Bay in 2008. DMS oxidation products, sulfur dioxide (SO2), methane sulfonic acid (MSA), and sulfate in aerosols were also measured. The amounts of biogenic SO2 and sulfate were approximated using stable isotope apportionment techniques. Calculating the threshold amount of SO2 needed for significant new particle formation from the formulation by Pirjola et al. (1999), the study suggests that instances of elevated biogenic SO2 concentrations (between 8 and 9 September 2008) derived using conservative assumptions may have been sufficient to form new aerosols in clean air conditions in the Arctic region.

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