Abstract
AbstractOcean deoxygenation is a threat to marine ecosystems. We evaluated the potential of two ocean intervention technologies, that is, “artificial downwelling (AD)” and “artificial upwelling (AU),” for remedying the expansion of Oxygen Deficient Zones (ODZs). The model‐based assessment simulated AD and AU implementations for 80 years along the eastern Pacific ODZ. When AD was simulated by pumping surface seawater to the 178–457 m‐depth range of the ODZ, vertically integrated oxygen increased by up to 4.5% in the deployment region. Pumping water from 457 m depth to the surface (i.e., AU), where it can equilibrate with the atmosphere, increased the vertically integrated oxygen by 1.03%. However, both simulated AD and AU increased biological production via enhanced nutrient supply to the sea surface, resulting in enhanced export production and subsequent aerobic remineralization also outside of the actual implementation region, and an ultimate net decline of global oceanic oxygen.
Highlights
In the ocean, oxygen is biologically produced through photosynthesis and consumed through the respiration and remineralization of organic matter
We evaluated the potential of two ocean intervention technologies, that is, “artificial downwelling (AD)” and “artificial upwelling (AU),” for remedying the expansion of Oxygen Deficient Zones (ODZs)
The control run simulated an increase in global mean surface air temperature by 2.72°C from year 2020 to 2099, while global oceanic oxygen decreased by 3% (Table 1)
Summary
Oxygen is biologically produced through photosynthesis and consumed through the respiration and remineralization of organic matter. In addition to biological oxygen sources and sinks in the sea, oxygen is supplied via air‐sea gas exchange from the atmosphere. This supply is, predicted to become inhibited under global warming because of reduced oxygen solubility and strengthened ocean stratification (Keeling et al, 2010). One notable case of its kind is a 2.5 yearlong experiment employing artificial downwelling (AD) to oxygenate the anoxic deep water at the By Fjord in southwestern Sweden (Stigebrandt et al, 2014) In their test, oxygen‐rich surface water was pumped into the deep anoxic bottom waters (40 m depth) via vertical pipes, and dissolved oxygen concentrations of the previously anoxic bottom waters were stabilized at 60 to 180 μmol L−1 with no anoxia being observed during operation of the AD devices. AD might be considered as a possibly effective tool to oxygenate ODZs so that the expansion of marine dead zones could be mitigated or even stopped
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