Artificial upwelling (AU), as one of the geoengineering tools, has received worldwide attention because of its potential ability to actualize ocean fertilization in a sustainable way. The severe challenges of AU are the design and fabrication of a technologically robust device with structural longevity that can maintain the function in the variable and complex hydrodynamics of the upper ocean. In this work, a sea trial of an air-lift concept AU system driven by self-powered energy was carried out in the East China Sea (ECS; 30°8′14″N, 122°44′59″E) to assess the logistics of at-sea deployment and the durability of the equipment under extremely complex hydrodynamic conditions from 3 to 7 September 2014. Seawater below the thermocline layer was measured to be uplifted from approximately 30 m to the euphotic layer with a volumetric upwelling rate of 155.43 m3 h−1 and total inputs of 2.8 mol h−1 NO3−, 0.15 mol h−1 PO43−, and 4.41 mol h−1 SiO43−. A plume formed by cold, saline deep ocean water (DOW) was tracked by a drifting buoy system with a mixing ratio of 37%–51% DOW at the depth of 18–22 m, which conforms to the simulation results. During the AU’s application, disturbance in the vertical hydrological structure could be observed. However, diatom (Skeletonema costatum) blooming from somewhere in the outer ECS floated to the sea trial region on the second day after the AU’s application, which makes it hard to strip off the biochemical effects of AU from the effects of S. costatum bloom.
Artificial upwelling (AU) is considered a potential means of reducing the accumulation of anthropogenic CO 2 . It has been suggested that AU has significant effects on regional carbon sink or source characteristics, and these effects are strongly influenced by certain technical parameters, the applied region, and the season. In this study, we simulated the power needed to raise the level of deep ocean water (DOW) to designated plume trapping depths in order to evaluate the effect of changing the source DOW depth and the plume trapping depth on carbon sequestration ability and efficiency. A carbon sequestration efficiency index (CSEI) was defined to indicate the carbon sequestration efficiency per unit of power consumption. The results suggested that the CSEI and the carbon sequestration ability exhibit opposite patterns when the DOW depth is increased, indicating that, although raising a lower DOW level can enhance the regional carbon sequestration ability, it is not energy-efficient. Large variations in the CSEI were shown to be associated with different regions, seasons, and AU technical parameters. According to the simulated CSEI values, the northeast past of the Sea of Japan is most suitable for AU, and some regions in the South China Sea are not suitable for increasing carbon sink.
Turbulence is one of the ubiquitous aspects of aquatic systems and affects many physical and biological processes. Based on direct velocity measurements and a computational fluid dynamics (CFD) simulation, we characterized the distribution of the turbulent kinetic dissipations rates (ε) in an orbital shaker system within a range of rotation frequencies. CFD was able to estimate the ε distribution in containers accurately, which was confirmed by other two methods and was independent of velocity measurement. The results showed that ε was linearly correlated with the rotational frequencies. Despite the existence of gradients of ε and the fact that a mean circular horizontal flow was formed within the tank, the energy levels of the whole tank varied spatially within an order of magnitude and the ε distributions at different rotational frequencies were similar, suggesting that the ε distribution in the whole tank could be seen as quasi-homogeneous. To investigate the influence of turbulence on algae growth, culture experiments of a typical diatom—Skeletonema costatum were carried out under different turbulence conditions. Our results suggested turbulence mixing promoted nutrient uptake and growth of Skeletonema costatum, which could be attributed to the break of the diffusion-limited resource concentration boundary layer surrounding phytoplankton.
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