Artificial upwelling: boost for marine ecosystems: Artificial upwelling refers to the forced transport of nutrient-rich deep water into the sunlit surface layer to promote biological productivity. It aims to replicate processes typical for natural upwelling systems in oceanic regions impoverished in nutrients. Natural upwelling systems are characterised by high productivity, efficient food webs and high rates of export to depth via the biological carbon pump. In nutrient-poor regions artificial upwelling is known to drive biomass production. Whether this leads to the development of food webs as efficient as those typical of natural upwelling areas depends on various factors, including the type and duration of artificial upwelling, the composition of the upwelled deep water and the structure of the local pelagic community. Additional CO2 removal via the biological carbon pump only occurs if more CO2 is transported to depth by the sinking organic material than reaches the surface layer with the upwelled deep water. A positive CO2 balance can also be achieved through physicochemical processes that cause the deep water to bind additional CO2 when it comes into contact with the atmosphere. The technical maturity of possible processes for artificial upwelling is currently considered to be low. Approaches to ocean fertilisation of any kind, including artificial upwelling, are highly controversial for ecological, biogeochemical, ethical and legal reasons.