Ice-nucleating particles in Canadian Arctic sea-surface microlayer and bulk seawater

Abstract

Abstract. The sea-surface microlayer and bulk seawater can contain ice-nucleating particles (INPs) and these INPs can be emitted into the atmosphere. Our current understanding of the properties, concentrations, and spatial and temporal distributions of INPs in the microlayer and bulk seawater is limited. In this study we investigate the concentrations and properties of INPs in microlayer and bulk seawater samples collected in the Canadian Arctic during the summer of 2014. INPs were ubiquitous in the microlayer and bulk seawater with freezing temperatures in the immersion mode as high as −14 • C. A strong negative correlation (R = −0.7, p = 0.02) was observed between salinity and freezing temperatures (after correction for freezing depression by the salts). One possible explanation is that INPs were associated with melting sea ice. Heat and filtration treatments of the samples show that the INPs were likely heat-labile biological materials with sizes between 0.02 and 0.2 µm in diameter, consistent with previous measurements off the coast of North America and near Greenland in the Arctic. The concentrations of INPs in the microlayer and bulk seawater were consistent with previous measurements at several other locations off the coast of North America. However, our average microlayer concentration was lower than previous observations made near Greenland in the Arctic. This difference could not be explained by chlorophyll a concentrations derived from satellite measurements. In addition, previous studies found significant INP enrichment in the microlayer, relative to bulk seawater, which we did not observe in this study. While further studies are needed to understand these differences, we confirm that there is a source of INP in the microlayer and bulk seawater in the Canadian Arctic that may be important for atmospheric INP concentrations.

Ice Nucleation by Marine Aerosols Over the North Atlantic Ocean in Late Spring

“…At present, global coverage of INP measurements lack data from many locations. Our measurements indicate that North Atlantic aerosols have ice‐nucleating temperatures between −22.4 and −35.4 °C, broadly consistent with the ice‐nucleating properties of marine aerosol sampled in other clean marine locations (DeMott et al, ; Irish et al, , ; McCluskey et al, ; Wilson et al, ). In addition, this study provides marine INP measurements coordinated with detailed biological sorting by flow cytometry.…”

“…In fact, observations of sea spray diameters include particles ranging from 0.1 to 100 μm diameter (Blanchard & Woodcock, ), but the mean diameter is small (0.1 μm) (Clarke et al, ). In the Irish et al () study, the freezing capacity of many (though not all) samples was significantly reduced after filtration, suggesting that the majority of INPs were between the sizes of 0.2 and 0.02 μm. While the possibility cannot be ruled out entirely, it is unlikely that larger particles and/or organisms represent a major unsampled marine INP source in our study.…”

“…Flow cytometer sorting provides a limit on the size of organism considered, with an upper limit of ~50 μm (nanoeukaryotes). In a previous ice nucleation study conducted in the Canadian Arctic, samples of bulk sea water and the sea surface microlayer were filtered through PTFE filters with 10, 0.2, and 0.02 μm pore sizes (Irish et al, ). In the unfiltered bulk water and microlayer samples, a wide range of freezing temperatures were observed, with peak temperatures significantly higher than those observed in our study.…”

Heterogeneous Ice Nucleation Ability of NaCl and Sea Salt Aerosol Particles at Cirrus Temperatures

“…During periods of phytoplankton blooms, SSA particles enriched in insoluble and high‐molecular‐mass organic matter can be formed (O'Dowd et al, ). This organic material is supposed to be capable of nucleating ice via immersion freezing in low‐altitude mixed‐phase clouds (Irish et al, ; McCluskey et al, ; Schnell & Vali, ; Wilson et al, ). The present study does not address the potential role of biogenic constituents of SSA particles in ice formation but specifically asks for the heterogeneous ice nucleation ability of the purely inorganic components of sea salt.…”

HOVERCAT: a novel aerial system for evaluation of aerosol–cloud interactions

“…Further, previous work has evaluated INP concentrations and at times composition in detritus, soil, water from lakes and oceans, surface microlayers, and precipitation samples to assess INP sources (e.g., Conen et al, 2016;Creamean et al, 2014;DeMott et al, 2016;Hill et al, 2016;Irish et al, 2017;Moffett, 2016;O'Sullivan et al, 2014;Petters and Wright, 2015;Pietsch et al, 2017;Pouzet et al, 2017;Schnell, 1977;Schnell and Vali, 1972, 1973, 1975Stopelli et al, 2015;Tobo et al, 2014). Analysis of INPs in precipitation samples takes a step in the direction of vertical profiling of INPs, making the assumption that the INPs in precipitation are what initiated ice formation in the clouds above; however, there are caveats associated with artifacts from scavenging during raindrop or snowflake descent, aerosolization methods, and redistribution of residue particles in collected liquid precipitation samples Hanlon et al, 2017;Petters and Wright, 2015).…”