A Sea Trial of Air-Lift Concept Artificial Upwelling in the East China Sea

Abstract

AbstractArtificial 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.