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Project Progress

During this past year, we have successfully formed visible (>0.1 mm up to 1.5 mm in diameter) aggregates of the Synechococcus in roller tanks with a new rolling set-up. We have also refined our methods to characterize and quantify those aggregates (number, size, sinking velocity, etc.) using a new particle sizer (Beckman-Coulter Multisizer III). We are currently investigating the effects of the clays kaolinite and bentonite in a series of concentrations on Synechococcus aggregation at two initial cell densities in roller tanks. We observed aggregate sinking velocities of around 400 m/d without, and up to 800 m/d with ballasting clays. We also compared the effect of two clay types (at the same initial cell density) using paired T-tests. Aggregates formed with kaolinite had greater number (significant at the 10⁷ initial cell density) and smaller sizes (significant at both initial cell densities) compared to those formed with bentonite (Refer to Figure 1). These experiments will enable us to observe Synechococcus aggregation and carbon export potential under different environmental conditions both in the Proterozoic and extant oceans. Additionally, following input from collaborator Watson Gregg, we made progress during this summer in collaboration with Dr. Stephen Romaniello and former SESE undergraduate Benjamin Brugman to refine a Matlab routine to be able to use parameters obtained in the laboratory experiments to model differences in carbon export, as a function of aggregate sinking rate.