Award: OCE-1536608

Breaking wind waves entrain air into the surface ocean as bubble plumes that rise, burst, and inject particles into the marine atmosphere. This process is a dominant source of particles and particulate organic carbon (OC) in earth?s atmosphere with implications for the chemistry of marine air, geochemistry, marine clouds and precipitation, radiative transfer, and climate. Among major outstanding uncertainties regarding primary marine aerosol (PMA) production are the marine sources for the emitted OC and the implications for the ocean and atmosphere. It has been assumed that particulate OC emitted from the ocean originates primarily from surface-active organic compounds (surfactants) produced by recent biological activity in the upper ocean. However, most (about 95%) dissolved OC (DOC) in the ocean is thousands of years old and, thus, decoupled from recent biological activity. Although this pool of ancient recalcitrant DOC (RDOC) exceeds all terrestrial OC combined, its sources and sinks are uncertain. The overall objectives of this project: 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. To address them, the University of Virginia?s high-capacity marine aerosol generator was modified with a forced-air Venturi and deployed to investigate aspects of PMA production as part of a 30-day research cruise on the R/V Endeavor in the western North Atlantic Ocean during September and October 2016. Testing demonstrated that the Venturi produced bubble size distributions in the aerosol generator that are representative of those produced by ambient wind waves on the ocean surface. Surfactant concentrations and strengths, DOC concentrations, and the age of DOC carbon (based on measurements of carbon isotopes) in near-surface seawater and the corresponding surfactants, OC, and carbon age associated with PMA produce artificially from that seawater were characterized at four hydrographic stations (two nutrient rich, biologically productive and two nutrient poor). Surfactants, DOC, and carbon age in North Atlantic Deep Water (NADW) sampled at a depth of 2500 m were also characterized. Virtually all DOC in NADW is comprised of RDOC whereas near-surface waters include mixtures of RDOC and DOC of more recent biological origin. 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 subsequent emission to the atmosphere upon bursting. The radiocarbon age of 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 near-surface waters ranged from 1,150 to 1,610 yr. Results indicate that (1) PMA OM included mixtures of recently produced and ancient OC and (2) aerosol production selectively scavenged an isotopically-distinct reservoir of surfactant OC from seawater. Assuming the age of RDOC was conservative with respect to aerosol production, these results indicate that the proportion of RDOC in PMA OM was between 19 ±2% and 40 ±4%. Available evidence suggests that PMA production delivers 8 and 50 Tg C yr-1 OC from the ocean to the atmosphere and that subsequent atmospheric processing leads to rapid oxidation of freshly emitted organic matter. Assuming that 19% and 40% of the emitted OC is RDOC and that all is either oxidized in the atmosphere to CO2, CO, or labile OC compounds or transported landward, PMA production removes between 2 and 20 Tg RDOC y‑1 from the ocean. When PMA processing is included in the RDOC budget, the total removal rate of RDOC (27 to 137 Tg C yr-1) and turnover time (5,000 – 23,000 yr) encompass the estimated global production rate (43 to 140 Tg C yr-1) and turnover time (4,500 to 16,000 yr) thereby balancing the RDOC budget within uncertainties. This project provided opportunities for 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 hands-on experience in this line of research through participation in the project and all collaborated in preparing related conference papers and manuscripts for publications. Results from the project also contributed to two dissertations and one MS thesis. All participants in the project gained knowledge regarding chemical processes in the surface ocean and lower atmosphere and related measurement techniques and data-analysis tools through interactions with collaborating investigators. The continuing educational development of the PIs and associated investigators has a broad reaching potential for enhancing the infrastructure of science. Through classroom instruction, interaction with graduate and undergraduate students, collaboration with other colleagues, and publications, knowledge gained in this effort will be disseminated to current and future scientists, thereby contributing to continued progress. Last Modified: 11/30/2018 Submitted by: Michael S Long