Abstract
Chain-forming diatoms are key CO2-fixing organisms in the ocean. Under turbulent conditions they form fast-sinking aggregates that are exported from the upper sunlit ocean to the ocean interior. A decade-old paradigm states that primary production in chain-forming diatoms is stimulated by turbulence. Yet, direct measurements of cell-specific primary production in individual field populations of chain-forming diatoms are poorly documented. Here we measured cell-specific carbon, nitrate and ammonium assimilation in two field populations of chain-forming diatoms (Skeletonema and Chaetoceros) at low-nutrient concentrations under still conditions and turbulent shear using secondary ion mass spectrometry combined with stable isotopic tracers and compared our data with those predicted by mass transfer theory. Turbulent shear significantly increases cell-specific C assimilation compared to still conditions in the cells/chains that also form fast-sinking, aggregates rich in carbon and ammonium. Thus, turbulence simultaneously stimulates small-scale biological CO2 assimilation and large-scale biogeochemical C and N cycles in the ocean.
Highlights
Chain-forming diatoms are key CO2-fixing organisms in the ocean
In the Skeletonema population, we found that C-assimilation was significantly higher under turbulent shear relative to still conditions, but nitrate assimilation was not significantly increased under turbulent shear compared to still conditions
The recent introduction of Secondary ion mass spectrometry (SIMS) in biological oceanography has revealed a high variability of physiological rates at the single-cell level across field populations of various-organisms[23,24,25,26,27]
Summary
Chain-forming diatoms are key CO2-fixing organisms in the ocean. Under turbulent conditions they form fast-sinking aggregates that are exported from the upper sunlit ocean to the ocean interior. Chain-forming genera of diatoms, e.g. Chaetoceros, Skeletonema and Thalassiosira, are dominant primary producers in environments with high turbulent shear, silicate, and nitrate concentrations, e.g., spring blooms in the polar oceans and temperate regions, and in subtropical and tropical upwelling regions During these blooms, the formation of millimeter-sized, fast-sinking diatom aggregates in the upper sunlit ocean are instrumental for connecting the surface and the deeper ocean with respect to aggregate-attached biota, carbon (C) and nutrient sources, the aerobic and anaerobic nitrogen (N) cycles, and for biological CO2 sequestration to the mesopelagic ocean[2,3,4,5,6,7]. Turbulent shear is theoretically more significant for mass transfer to large cells compared to small cells (Fig. 1b; Eq (2)) and may alleviate diffusion-limited fluxes of gases and nutrients in large cells or colonies[9,10,11,12,13,18,19,20,21,22]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
