Project: Variability in particle size distributions, sinking velocities, and fluxes in the northern Gulf of Alaska

NSF abstract:
The sinking of particles from the sunlit zone of the ocean into the ocean interior constitutes a dominant component of the sequestering of carbon into the deep ocean, otherwise known as the ocean's biological carbon pump. The quantities of particulate matter being exported out of the sunlit zone, as well as the tapering-off of these fluxes with respect to depth, have a substantial impact on the distribution of carbon and other important elements throughout the oceans and control the concentration of carbon dioxide in the atmosphere. For these reasons, it is critical that we gain a comprehensive understanding of the magnitude of these elemental fluxes, their variability in space and time, and the processes that control them. The focus of the of this project is to make new, broadly informative discoveries with regard to the function of the ocean's biological carbon pump and the ability to quantify and monitor its strength and efficiency at high spatial and temporal resolutions. In addition, this project will provide the first quantitative and mechanistic study of sinking particle fluxes in the northern Gulf of Alaska by working in conjunction with the ongoing Seward Line Long-term Observational Program. The project will be carried out under the direction of an early career faculty member and provide a training opportunity for a postdoctoral researcher. Results from the study will be shared with the broader public through a variety of print and digital platforms.

The fluxes of carbon out of the euphotic zone and through subsurface waters are poorly quantified and understood, especially relative to other dominant oceanic carbon flows such as the air-sea gas exchange of carbon dioxide or rates of primary production in surface waters. The inability to differentiate between variability in particle concentration and sinking velocities as the drivers of flux variability is a critical gap in our understanding of the biological carbon pump. The Gulf of Alaska is an optimal site for investigating these processes as the cycling of carbon and other elements in waters above continental shelves, such as the Gulf of Alaska, is highly complex due to the dynamic interplay of chemical, physical, biological, and anthropogenic processes. Using a creative application of short-term sediment trap deployments combined with the use of a unique pair of in situ optical instruments, the researchers will aim to accomplish two specific goals: 1) Quantify the average sinking velocities of small particles and their contribution to the total carbon flux from particles of all sizes; and 2) Determine the relative variability in particle abundances and sinking velocities and assess how it translates into variable patterns of particle flux in the northern Gulf of Alaska.

Affiliated Programs:
Seward Line LTOP, NGA-LTER, US GO-SHIP