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This study addresses, through two types of experiments, the potential for the oceans to act as a source of atmospheric ice-nucleating particles (INPs). The INP concentration via deposition mode nucleation was measured in situ at a coastal site in British Columbia in August 2013. The INP concentration at conditions relevant to cirrus clouds (i.e., −40 °C and relative humidity with respect to ice, RH ice = 139%) ranged from 0.2 L −1 to 3.3 L −1 . Correlations of the INP concentrations with levels of anthropogenic tracers (i.e., CO, SO 2 , NO x , and black carbon) and numbers of fluorescent particles do not indicate a significant influence from anthropogenic sources or submicron bioaerosols, respectively. Additionally, the INPs measured in the deposition mode showed a poor correlation with the concentration of particles with sizes larger than 500 nm, which is in contrast with observations made in the immersion freezing mode. To investigate the nature of particles that could have acted as deposition INP, laboratory experiments with potential marine aerosol particles were conducted under the ice-nucleating conditions used in the field. At −40 °C, no deposition activity was observed with salt aerosol particles (sodium chloride and two forms of commercial sea salt: Sigma-Aldrich and Instant Ocean), particles composed of a commercial source of natural organic matter (Suwannee River humic material), or particle mixtures of sea salt and humic material. In contrast, exudates from three phytoplankton ( Thalassiosira pseudonana, Nanochloris atomus, and Emiliania huxleyi ) and one marine bacterium ( Vibrio harveyi ) exhibited INP activity at low RH ice values, down to below 110%. This suggests that the INPs measured at the field site were of marine biological origins, although we cannot rule out other sources, including mineral dust.

The oceans cover most of the Earth's surface, contain nearly half the total global primary biomass productivity, and are a major source of atmospheric aerosol particles. Here we experimentally investigate links between biological activity in seawater and sea spray aerosol (SSA) flux, a relationship of potential significance for organic aerosol loading and cloud formation over the oceans and thus for climate globally. Bubbles were generated in laboratory mesocosm experiments either by recirculating impinging water jets or glass frits. Experiments were conducted with Atlantic Ocean seawater collected off the eastern end of Long Island, NY, and with artificial seawater containing cultures of bacteria and phytoplankton Thalassiosira pseudonana, Emiliania huxleyi, and Nannochloris atomus. Changes in SSA size distributions occurred during all phases of bacterial and phytoplankton growth, as characterized by cell concentrations, dissolved organic carbon, total particulate carbon, and transparent exopolymer particles (gel-forming polysaccharides representing a major component of biogenic exudate material). Over a 2 week growth period, SSA particle concentrations increased by a factor of less than 2 when only bacteria were present and by a factor of about 3 when bacteria and phytoplankton were present. Production of jet-generated SSA particles of diameter less than 200 nm increased with time, while production of all particle diameters increased with time when frits were used. The implications of a marine biological activity dependent SSA flux are discussed.

The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea-air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.

Dissolved organic polymers released by phytoplankton and bacteria abiologically self-assemble in surface ocean waters into nano-to micro-sized gels containing polysaccharides, proteins, lipids and other components. These gels concentrate in the sea surface microlayer (SML), where they can potentially contribute to sea spray aerosol (SSA). Sea spray is a major source of atmospheric aerosol mass over much of the earth's surface, and knowledge of its properties (including the amount and nature of the organic content), size distributions and fluxes are fundamental for determining its role in atmospheric chemistry and climate. Using a cascade impactor, we collected size-fractionated aerosol particles from ambient air and from freshly generated Sea Sweep SSA in the western North Atlantic Ocean together with biological and chemical characterization of subsurface and SML waters. Spectrophotometric methods were applied to quantify the polysaccharide-containing transparent exopolymer (TEP) and protein-containing Coomassie stainable material (CSM) in these particles and waters. This study demonstrates that both TEP and CSM in surface ocean waters are aerosolized with sea spray with the greatest total TEP associated with particles 5 000 nm. The higher concentrations of TEP and CSM in particles >5 000 nm most likely reflects collection of microorganism cells and/or fragments. The greater concentration of CSM in larger size particles may also reflect greater stability of proteinaceous gels compared to polysaccharide-rich gels in surface waters and the SML. Both TEP and CSM were measured in the ambient marine air sample with concentrations of 2.1 ± 0.16 μg xanthan gum equivalents (XG eq.) m − 3 and 14 ± 1.0 μg bovine serum albumin equivalents (BSA eq.) m −3 . TEP in Sea Sweep SSA averaged 4.7 ± 3.1 μg XG eq. m −3 and CSM 8.6 ± 7.3 μg BSA eq. m −3 . This work shows the transport of marine biogenic material across the air-sea interface through primary particle emission and the first demonstration of particle size discriminated TEP and CSM characterization of SSA and ambient aerosol under field conditions.