Although much of surface-derived matter fluxes to the ocean interior and the sea floor in the form of macroscopic aggregates known as marine snow, little is known about the processes governing the production of these large particles in the ocean. One source of marine snow of potential global significance is the mass flocculation and settlement of living diatoms following diatom blooms. While this phenomenon is known only inferentially from sediment trap studies and no published empirical accounts of marine snow formation by diatoms in nature yet exist, the PI has regularly observed, using scuba, living diatoms forming abundant aggregates of marine snow centimeters in diameter in the Southern California Bight. She has conducted preliminary investigations of the species composition and sinking rates of these flocs. This research continues along those lines. The objectives of this proposal are to: 1) document the duration, timing, floc abundance and characteristics, and impact on vertical flux of diatom flocculation events; 2) determine the state, and species composition and abundance, associated with marine snow formation by diatoms in nature; and 3) investigate the physical and biological mechanisms by which diatoms collide and stick to form aggregates. This research will provide the first empirical data on diatom aggregation as a significant source of marine snow. It will further our understanding of the mechanisms of large particle formation in the ocean necessary to fully understand and predict ocean flux .
