A Marine Biogenic Source of Atmospheric Ice Nucleating Particles
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. Researchers, including a Department of Energy scientist at Pacific Northwest National Laboratory, 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 likely biogenic and less than ~0.2 μm in size. They found that exudates (organic material secreted by an organism) separated from cells of the marine diatom T. Pseudonana nucleate ice. The researchers 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 the study’s 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 and North Atlantic.
T.W.W., B.J.M. and T.F.W. acknowledge the assistance provided by the crew and other scientists onboard the R/V Knorr and the RRS James Clark Ross, the British Antarctic Survey, K. Baustian, J. McQuaid, A. Windross, J. Knulst, J. F. Wilson, A. M. Booth, R. Chance, L. J. Carpenter, S. Peppe, D. O’Sullivan, N. Umo, I. Cotton, H. Pearce, H. Price and M. J. Callaghan. The STXM/NEXAFS analysis was performed at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231 (user award to D.A.K./J.Y.A. ALS-05955). STXM analyses were facilitated by A. L. D. Kilcoyne and M. K. Gilles. L.A.L. acknowledges assistance from R. Leaitch, E. Mungall, R. Christensen and J. Li, and the Pacific region Department of Fisheries and Oceans staff. The Marine Boundary Layer sampling site in Ucluelet is jointly supported and maintained by Environment Canada, the British Columbia Ministry of the Environment and Metro Vancouver. We acknowledge funding from the Natural Environment Research Council (NE/K004417/1, NE/I020059/1, NE/I013466/1, NE/I028696/1, NE/I019057/1, NE/H009485/1), the European Research Council (FP7, 240449 ICE, BACCHUS 603445), the UK Aerosol Society, National Science Foundation (AGS-1232203), German Research Foundation (WU585/6-1), the Climate Change and Atmospheric Research Program of the Natural Sciences and Engineering Research Council of Canada (for NETCARE), Fisheries and Oceans Canada, Environment Canada, NOAA’s Climate Program Office (for WACS II), and the DOE Office of Science (BER) Earth System Modeling Program.