Project: Collaborative Research: Seasonal Variability in refractory dissolved organic carbon fluxes associated with primary marine aerosol emitted from the oceans

NSF Award Abstract:

Collaborative Research: Seasonal variability in refractory dissolved organic carbon fluxes associated with primary marine aerosol emitted from the oceans

The oceans hold a massive quantity of organic carbon that is greater than all terrestrial organic carbon biomass combined. Nearly all marine organic carbon is dissolved. On average, it is thousands of years old, chemically stable, and carried throughout the entire ocean several times before complete removal. However, little is known about the processes that produce and remove this old carbon, referred to as refractory dissolved organic carbon (RDOC). One potential removal pathway involves RDOC adhering onto the surfaces of rising bubbles produced by breaking waves. The bubbles ultimately burst at the sea surface, ejecting tiny particles (primary marine aerosol, “PMA”) that carry the RDOC into the atmosphere. Most of this PMA organic carbon is associated with the smallest particles (less than 1 μm diameter) that drift in the atmosphere for several days to weeks. During this time, RDOC in these particles can be degraded photochemically (by sunlight), partially transported landward, and/or returned to the sea. When this RDOC is converted to inorganic carbon (e.g., carbon dioxide) or degraded to more reactive constituents in the atmosphere, it is effectively removed from the marine RDOC reservoir. Based on preliminary results, the annual rate at which RDOC is removed from the ocean by this process is similar to all other known RDOC losses (interactions with particles, biological degradation, and hydrothermal circulation), except for photochemical degradation in seawater. Building on this prior research, this project will identify seasonal changes in the removal of RDOC from the oceans through this process during three research cruises to the northwestern Atlantic Ocean. Results from this project will provide important findings about the coupled ocean-atmosphere loss of RDOC and improve understanding of the role of RDOC in the global carbon cycle and Earth's climate. The research will involve two early career faculty, and will provide training for undergraduate, graduate, and postdoctoral researchers.

Radiocarbon (C-14) measurements indicate that RDOC comprises 19 to 40 % of the organic carbon associated with PMA produced by bursting bubbles at the sea surface. Injection of RDOC into the atmosphere in association with PMA is a potentially important process that removes as much as 2 to 20 Tg RDOC yr-1 from the oceans. This project will measure seasonal variations in the PMA-mediated emission of marine RDOC to the atmosphere by quantifying: (1) the fraction of RDOC in PMA OC and (2) its relationship to the abundance of biologically produced labile and semi-labile dissolved organic matter in near surface seawater. These relationships will be evaluated at the Bermuda Atlantic Time-series Station during three research cruises (one in July, two in January). During the cruises, the investigators will measure: (1) the natural abundance C-14 values for PMA and its organic source materials in seawater; (2) the dynamic and equilibrium surface tension and physical properties of seawater, including bubble size distributions; (3) concentrations of major ions, organic carbon, carbohydrates, peptides and proteins, and surfactants in PMA; and (4) chromophoric dissolved organic matter (CDOM) and the concentrations of dissolved organic carbon, chlorophyll a, major ions, carbohydrates, peptides and proteins, and surfactants in near-surface seawater and in the sea-surface microlayer. Based on these chemical measurements and physical properties, this study will reveal the magnitude and potential controls on RDOC inputs into the atmosphere as a component of PMA.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.