Artificial Ocean Upwelling

In a similar way to artificial ocean fertilisation, this CDR approach aims to provide nutrient-poor marine regions with additional nutrients in order to stimulate phytoplankton growth. The sunlit ocean zone where phytoplankton grow is low in nutrients. Just a few hundred metres further down, the situation is quite different. There, bacterial decomposition of biomass gradually sinking from the surface to the depths releases numerous nutrients back into the water – but also CO2 that is likewise a product of bacterial decomposition. This means the deeper ocean zones are generally rich in nutrients. Off some coasts, such as the coasts of Namibia and Peru, this nutrient-rich water is brought by currents from greater depths to the surface. These upwelling zones are consequently especially rich in plankton and fish. The idea of artificial upwelling is to use large pumps and tubes to bring water from deeper zones to the ocean surface in order to stimulate phytoplankton growth – and with it the uptake of CO2 from the atmosphere.

Potential
Several years ago, a company applied for a patent for the construction of floating pumps that could be powered by wave energy. In total, however, this method has relatively minor potential of less than a billion tonnes of CO2 per year. This is mainly because the nutrient-rich deeper ocean water is also rich in CO2, which is brought up to the surface and consequently counteracts the fertilisation effect.

Scale 
The results of computer modelling show that very large numbers of pumps would be needed to capture a climatically significant quantity of CO2 by increased phytoplankton growth. With the pump technology mentioned above, several million pumps would be needed worldwide to attain significant upwelling volumes. In total, artificial upwelling would have to occur over about 50 percent of the ocean’s surface – an enormous technical challenge.

Application readiness and research needs
Artificial upwelling is currently being tested in research projects in China, Japan and Europe. However, the main aim of those projects is to see if providing nutrients from the depths can increase fish production. There are currently no large-scale experiments in the context of climate engineering. Modelling shows that artificial upwelling also has its problems. Redistributing cold water to the sea surface would cool the atmosphere above the sea as a positive side effect. This effect would reverse, however, as soon as the pumps are switched off. The heat transported downwards by the redistribution would quickly well up to the surface again and escape into the atmosphere, which would very quickly intensify global heating. According to the models, this effect would even be stronger than if artificial upwelling had never been used. Temperatures would be higher than in a business-as-usual scenario – a scenario in which climate mitigation action continues at its current slow pace – for decades or even for centuries. In the end, most researchers have now distanced themselves from the idea of artificial upwelling as a CDR method, partly also because of the unpredictable consequences for marine habitats.