Project: Hawaii Aerosol Time-Series (HATS):Quantifying Marine Dust Deposition and Composition in an Oligotrophic Gyre

NSF Award Abstract:
The chemistry of the ocean can be changed by the introduction and removal of elements, including trace elements which are present at low concentrations. In some cases, these elements are known to be vital to biological processes and ocean food webs. Near the shore, rivers are a large source for material from land to the ocean. Beyond the reach of rivers, and for most of the oceans, material blown from land through the air is the largest source of trace elements to surface waters. This material enters the oceans dissolved in rain or by settling of dust particles. Understanding atmospheric sources of trace elements to the oceans is thus important to understanding both global chemical cycles and patterns of biological production. This project will sample the atmosphere and the surface ocean near Hawaii over two years to gain a deeper understanding of the sources and fates of trace metals in the ocean. The study will examine how particles from the atmosphere interact with the surrounding water as they sink through the ocean. The project will contribute to global synthesis and modeling efforts. It will directly support graduate and undergraduate students. Results of the project and their relevance will be communicated to the public through campus open house events and a public lecture series.

The processes that supply and remove trace elements in the ocean are ongoing areas of research. An important focus is on understanding the sources and fate of aerosol trace elements deposited to the ocean as this represents a major source of micronutrients and contaminants into the open ocean. Field observations of wet and dry atmospheric inputs are limited in number, and few methods are available to transform readily measured aerosol trace element concentrations into deposition fluxes. Thus, atmospheric fluxes of trace elements to most ocean regions remain poorly constrained and their impact on ocean biochemical cycles, including the marine carbon cycle, are uncertain. Directly quantifying atmospheric fluxes of key trace elements to the ocean and identifying their fates and chemical transformations after deposition are critical areas of continued investigation and are included, for example, as a core component of the GEOTRACES program. Similarly, aerosol fractional solubility and the flux of bioavailable trace elements is not well understood. There is a corresponding need to test and improve estimates of total dust deposition fluxes alongside simultaneous observations of particle composition in the open ocean. This project will address these needs through a two-year land-based sampling effort and six seasonal cruises aimed at three tasks. (1) Use the deposition flux of beryllium-7 measured from aerosols, precipitation, and the upper ocean inventory to directly estimate dust and aerosol trace element fluxes to the Hawaii Ocean Time-series Station Aloha, a representative and remote oligotrophic site. This region is characterized by a predictable seasonal variability in dust concentrations and precipitation and is an exceptionally applicable region for testing the limits of dust deposition techniques by observing seasonal variability in ocean-atmosphere coupling over a multi-year cycle. (2) Explore the extent to which seasonal variations in aerosol trace element flux to the surface of the North Pacific, and mineralogy of that input drive variability in the composition and inventories of marine particles. (3) Investigate the extent to which the fractional solubility of aerosol trace elements collected over the North Pacific shows temporal variability and calculate flux rates of soluble aerosol trace elements. The study will advance understanding of dust and soluble aerosol trace element flux from the atmosphere to the ocean and link that flux to upper ocean particle inventory, mineralogy, and chemical composition.

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.