Revisiting properties and concentrations of ice nucleating particles in the sea surface microlayer and bulk seawater in the Canadian Arctic during summer

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 remain limited. We have investigated the properties and concentrations of INPs in sea surface microlayer and bulk seawater samples collected in the Canadian Arctic during the summer of 2016. We observed that 1) INPs were ubiquitous in the microlayer and bulk waters; 2) heat and filtration treatments reduced INP activity, indicating that the INPs were likely heat-labile biological materials between 0.2 and 0.02 μm in diameter; 3) there was a strong negative correlation between salinity and freezing temperatures, possibly due to INPs associated with melting sea ice; and 4) concentrations of INPs could not be explained by satellite-derived chlorophyll a concentrations. Although the spatial patterns of INPs and salinities were similar in 2014 and 2016, we did observe some differences between the years, notably: 1) the concentrations of INPs were higher on average in 2016 compared to 2014; and 2) INP concentrations were enhanced in the microlayer compared to bulk seawater in several samples collected in 2016, which was not the case in 2014.