ABSTRACT

This is a project that is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (UKRI/NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own investigators and component of the work.

This project takes a small-scale approach to look at individual cells to investigate the sinking of marine diatoms, which on larger scales has implications for how food for larger organisms, carbon, and organic particles move throughout the ocean. Diatoms are a type of phytoplankton, cells that use photosynthesis in surface waters to produce roughly half of the world?s oxygen and the food to support ocean food webs. They have a heavy, glass-like outer wall which causes them to sink and move up to 40% of particulate organic carbon from the ocean?s surface to the deep sea. The investigators are using novel methods to determine how diatoms regulate their sinking quickly in response to different environmental conditions. These include state-of-the-art video measurements of individual cells, a micoelectrode approach to understand changes at cell surfaces, and microscopy to see changes inside and at the surface of cells. The resulting information will be used to build a model to understand how and why diatoms use unsteady sinking behavior based on their environment. The project supports early career investigators, provides training for a postdoctoral scientist and undergraduate students, and develops a collaboration between US and UK scientists. The team is also developing lesson plans in conjunction with local high schools with high populations of underrepresented students in STEM fields.

The problem of sinking and suspension of diatoms has received considerable attention because of its ecological, evolutionary and biogeochemical significance, yet understanding of the processes that regulate sinking rates remains rudimentary. The investigators have used new techniques to make preliminary observations showing that some species of diatom exhibit an unsteady sinking behavior that consists of rapid changes of buoyancy on time scales of seconds. However, it remains unclear how widely this behavior matters across species and ocean conditions. In this study, the team of investigators is using state-of-the-art video-based measurements of sinking rates of individual cells to assess the prevalence of unsteady sinking among centric and pennate diatoms of varying cell sizes and quantify how this behavior changes in response to sharp gradients in nutrients and light. The project leverages an interdisciplinary, international collaboration to combine innovative optical techniques, advanced tools to assess cell physiology, and numerical modeling approaches to characterize suspension properties for individual diatom cells. Results are likely to transform the way we think about the ecology of diatoms, their strategies for nutrient acquisition, and mechanisms to control their buoyancy, in particular the modulation of volume and membrane of the central vacuole. This project contributes to the development of novel tools for single cell physiological studies, most notably direct measurement of diffusive boundary layers around cells under varying flow conditions and numerical modeling of cell-level processes.

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.

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