Award: OCE-1536674

Breaking wind waves inject air into the suface ocean, which fragments into bubble plumes that rise to the surface, burst, and inject particles into the overlying atmosphere. This process is the dominant source of particle mass and a major source of particle number and particulate organic carbon (OC) in earth's atmosphere with important implications for geochemical cycles and climate. Major outstanding uncertainties involving primary marine aerosol (PMA) production include (1) the marine source for the emitted OC and (2) the associated impacts on the ocean and the atmosphere. It is widely assumed that particulate OC emitted from the ocean orginates from surface-active organic compounds (surfactants) produced by biota in the upper ocean. However, ~95% of dissolved OC (DOC) in seawater is thousands of years old and, thus, decoupled from recent biological activity. Although this massive pool of ancient recalcitrant DOC (RDOC) exceeds all terrestrial carbon combined, its sources and sinks are uncertain. The primary goals of this project were to quantify contributions of RDOC to particulate OC emitted from the ocean and to evaluate the importance of coupled ocean-atmosphere processing as a recycling pathway for RDOC. A high-capacity marine aerosol generator was reconfigured to produce bubble plumes using a novel forced-air Venturi nozzle and deployed to investigate PMA production during a 30-day research cruise on the R/V Endeavoe in the western North Atlantic Ocean during September-October 2016. Testing demonstrated that the Venturi generated bubble plumes that were representative to those produced in the surface ocean by wind waves. Surfactant concentrations and strengths, OC concentrations, and OC age (based on carbon isotopes) were measured in near-surface seawater and in PMA produced from that seawater at four hydrographic stations (two nutrient rich and two nutrient poor). North Atlantic Deep Water (NADW) sampled at a depth of 2500 m was also characterized for surfactants, OC, and carbon age. The concentrations and strengths of surfactants in NADW fell within the ranges of those in near-surface waters, which indicates that RDOC includes significant amounts of surface-active organic compounds that are susceptible to scavenging by bubbles and emission to the atmophere upon bubble bursting. The radiocarbon ages on RDOC in NADW was 4,900 +/-100 yr, the age of DOC in near-surface waters ranged from 2,010 to 2,700 yr, and the age of PMA OC generated from surface waters ranged from 1,150 to 1,600 yr. These results indicate that (1) PMA OM includes mixtures of ancient and recently produced OC and (2) aerosol production selectively scavenged an isotopically distinct reservoir of surfactant OC from seawater. Assuming that the age of RDOC was conservative with respect ot aerosol production, these results indicate that RDOC accounts for 19 +/-2% to 40 +/-4% of PMA OM. PMA production delivers an estimated 8 to 50 Tg C yr-1 from the ocean to the atmosphere and subsequent atmospheric processing (rapid acidification coupled with exposure to high concentrations of oxidants and full spectral radiation) leads to rapid oxidation of freshly emitted organic matter. Assuming that 19% to 40% of the emitted OC is RDOC and that all is either oxidized in the atmosphere to CO2, CO, or more labile OC or transported landward, PMA production removes between 2 and 20 Tg RDOC yr-1 from the ocean. When PMA processing is included in the RDOC budget, the total removal rate (27 to 137 Tg C yr-1) and turnover time (5,000 to 23,000 yr) encompass the estimated global production rate (43 to 140 Tg C yr-1) and turnover time (4,500 to 16,000) thereby balancing the RDOC budget within associated uncertainties. This project contributed to the professional development of nine early career scientists, five of whom are from underrepresented groups in the sciences and five of whom are graduate students or postdoctoral fellows. All gained valuable hands-on experience through participation in the project and all collaborated in preparing related conference papers and manuscripts for publications. Project results also contributed to two dissertations and one masters thesis. All project participants gained new knowledge regarding chemical processes in the surface ocean and lower atmosphere and related measurement techniques and data-analysis tools. Finally, the continuing educational development of the principal investigators has broad reaching potential for enhancing the infrastructure of science. Through classroom instruction, interaction with graduate and undergraduate students, collaboration with other scientists, and publications, knowledge gained through this effort will be disseminated to current and future scientists, thereby contributing to continued progress in this and related fields. Last Modified: 11/30/2018 Submitted by: William C Keene