US GEOTRACES GP17-OCE and GP17-ANT: Atmospheric Deposition and Aerosol Fractional Solubility in Remote Ocean Regions

Trace Elements are defined by their low concentrations in the open ocean and their addition and removal rates are key uncertainties in our understanding of ocean chemistry. In spite of their scarcity, trace elements can play an outsized role in determining where living things thrive in the open ocean. Near the coasts, these elements may be found in abundance because of features like rivers which bring source material from the continents to the ocean.

Far from land, however, trace elements are scarce. The most significant source of these elements to the open ocean may come from dust and other particles falling onto the surface water either directly, or within rain droplets. An improved understanding of this process will further knowledge of element cycling in the ocean, including the carbon cycle.

This project will sample the atmosphere of the South Pacific Ocean and the Pacific sector of the Southern Ocean around Antarctica. Input from the atmosphere to these waters is not well known and the research results will provide much needed information to the scientific community. This project will support an early career researcher as well as a graduate student.

The deposition and subsequent dissolution of aerosols in surface waters remains a critical research area in the oceanographic community. Much of the ocean remains poorly sampled and improvements in flux estimates, chemical characterization, and fractional solubility estimates are necessary to improve the understanding of this important trace element source.

This project will include a cruise in the South Pacific Ocean and one in the Amundsen Sea sector of the Southern Ocean, both as part of the GEOTRACES program. The cruise tracks will cover regions which lie downwind of dust producing regions of Australia and where atmospheric deposition could play a role in dictating distributions of trace elements in the water column.

The flux of aerosols across the air-sea interface is a key research area within GEOTRACES and the broader oceanographic community. Flux from the atmosphere to the ocean is highly episodic making the capture of this important term difficult in the open ocean. Flux rates will be determined by the use of the cosmogenic isotope 7Be, providing a rate estimate for time scales longer than the cruise period.

Aerosol trace element fractional solubility remains poorly constrained and is one of the reasons that biogeochemical models show poor agreement for marine trace element distributions. Aerosol dissolution will be tested in several solution of varying chemistry to provide a range of solubility estimates which are representative of conditions in precipitation, surface seawater, and in more aggressive environments which provide a high-end solubility estimate.

Calculated terms like residence time are also poorly constrained due to this uncertainty. This project will address these questions by capturing bulk and size-fractionated aerosol samples as well as samples of precipitation. The study will advance understanding of dust and soluble aerosol trace element flux from the atmosphere to the ocean and provide contextual data for complimentary studies associated with these GEOTRACES section cruises.

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.