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

Abstract

Here we report the ice nucleating temperatures of marine aerosols sampled in the subarctic Atlantic Ocean during a phytoplankton bloom. Ice nucleation measurements were conducted on primary aerosol samples and phytoplankton isolated from seawater samples. Primary marine aerosol samples produced by a specialized aerosol generator (the Sea Sweep) catalyzed droplet freezing at temperatures between −33.4 °C and − 24.5 °C, with a mean freezing temperature of −28.5 °C, which was significantly warmer than the homogeneous freezing temperature of pure water in the atmosphere (−36 °C). Following a storm‐induced deep mixing event, ice nucleation activity was enhanced by two metrics: (1) the fraction of aerosols acting as ice nucleating particles (INPs) and (2) the nucleating temperatures, which were the warmest observed throughout the project. Seawater samples were collected from the ocean's surface and phytoplankton groups, including Synechococcus, picoeukaryotes, and nanoeukaryotes, were isolated into sodium chloride sheath fluid solution using a cell‐sorting flow cytometer. Marine aerosol containing Synechococcus, picoeukaryotes, and nanoeukaryotes serves as INP at temperatures significantly warmer than the homogeneous freezing temperature of pure water in the atmosphere. Samples containing whole organisms in 30 g L−1 NaCl had freezing temperatures between −33.8 and − 31.1 °C. Dilution of samples to representative atmospheric aerosol salt concentrations (as low as 3.75 g L−1 NaCl) raised freezing temperatures to as high as −22.1 °C. It follows that marine aerosols containing phytoplankton may have widespread influence on marine ice nucleation events by facilitating ice nucleation.

Linking Marine Biological Activity to Aerosol Chemical Composition and Cloud‐Relevant Properties Over the North Atlantic Ocean

“…Indeed, the ice nucleation activity of marine aerosol has been related to the organic content of SSA (DeMott et al, 2016; McCluskey, Hill, Humphries, et al, 2018; McCluskey, Hill, Sultana, et al, 2018; McCluskey, Ovadnevaite, Rinaldi, et al, 2018; Wilson et al, 2015), while no ice nucleation ability is attributed in literature to secondary (organic or inorganic) particles. Supporting our findings, a relation between algal blooming and ice nucleating properties of SSA has already been reported in the literature (McCluskey et al, 2017; Wilbourn et al, 2020).…”

A link between the ice nucleation activity and the biogeochemistry of seawater

“…Our results augment previous findings that particle composition determines the ice nucleation activity of SSA (DeMott et al, 2016;McCluskey et al, 2017;Wilbourn et al, 2020;Wilson et al, 2012;Wolf et al, 2019). We also found that INP activity is uncorrelated with variables like nutrient concentration, wind speed, and chlorophyll concentration (Table S2 in the Supplement).…”

The ice-nucleating activity of Arctic sea surface microlayer samples and marine algal cultures

“…Note that this upper limit of the ice nucleation activity of the field samples, however, is still 1 order of magnitude lower than the n s parameterization for mineral dust (Fig. 5, Niemand et al, 2012), underlining the relatively poor heterogeneous ice nucleation activity of sea spray aerosol particles compared to other atmospherically relevant types of INPs in the temperature range above 248 K. In the (high) Arctic, both transported dust and sea spray aerosol (transported or local) can be present (see Willis et al, 2018, for a thorough review of literature). However, which source is dominant for ice nucleation might be locally very different.…”