Abstract
Abstract. Despite growing evidence that the ocean is an important source of ice-nucleating particles (INPs) in the atmosphere, our understanding of the properties and concentrations of INPs in ocean surface waters remains limited. We have investigated INPs in sea surface microlayer and bulk seawater samples collected in the Canadian Arctic during the summer of 2016. Consistent with our 2014 studies, we observed that INPs were ubiquitous in the microlayer and bulk seawaters; heat and filtration treatments reduced INP activity, indicating that the INPs were likely heat-labile biological materials between 0.22 and 0.02 µm in diameter; there was a strong negative correlation between salinity and freezing temperatures; and concentrations of INPs could not be explained by chlorophyll a concentrations. Unique in the current study, the spatial distributions of INPs were similar in 2014 and 2016, and the concentrations of INPs were strongly correlated with meteoric water (terrestrial runoff plus precipitation). These combined results suggest that meteoric water may be a major source of INPs in the sea surface microlayer and bulk seawater in this region, or meteoric water may be enhancing INPs in this region by providing additional nutrients for the production of marine microorganisms. In addition, based on the measured concentrations of INPs in the microlayer and bulk seawater, we estimate that the concentrations of INPs from the ocean in the Canadian Arctic marine boundary layer range from approximately 10−4 to <10-6 L−1 at −10 ∘C.
Highlights
Ice-nucleating particles (INPs) are atmospheric particles that catalyse the formation of ice crystals in clouds at warmer temperatures and lower vapour saturations than needed for homogeneous ice nucleation, thereby influencing cloud properties and potentially impacting the Earth’s radiative properties and hydrological cycle (Boucher et al, 2013; Lohmann, 2002; Lohmann and Feichter, 2005; Tan et al, 2016)
Freezing temperatures as warm as −6 ◦C were observed. These results indicate the presence of ice-active material in all bulk seawater samples
The INP concentrations in microlayer and bulk seawater samples were determined at 11 stations in the Canadian Arctic during the summer of 2016 and compared to measurements made in 2014 (Irish et al, 2017)
Summary
Ice-nucleating particles (INPs) are atmospheric particles that catalyse the formation of ice crystals in clouds at warmer temperatures and lower vapour saturations than needed for homogeneous ice nucleation, thereby influencing cloud properties and potentially impacting the Earth’s radiative properties and hydrological cycle (Boucher et al, 2013; Lohmann, 2002; Lohmann and Feichter, 2005; Tan et al, 2016). A small subset of atmospheric particles (about 1 in 106) act as INPs (DeMott et al, 2010, 2016). INPs can catalyse the formation of ice by four different mechanisms: contact freezing, condensation freezing, deposition freezing, and immersion freezing. Irish et al.: Revisiting properties and concentrations of ice-nucleating particles in the Canadian Arctic
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