Contrasting micro- and macro-nutrient nourishment of the ocean

Abstract

There have been suggestions that an increase in the productivity of the ocean would store more carbon in the ocean organic carbon cycle, as well as enhancing the higher trophic levels of the marine food web. Proposals have included fertilisation of regions low in one or more of nitro- gen, phosphorus or iron, the latter being termed a micronutrient. Iron is available from mining, phos- phorus from mining or artificially induced upwelling, and the provision of nitrogen involves using either cyanobacteria, the Haber-Bosch process or artificially induced upwelling. All these fertilisation methods can be effective in locally increasing new primary production, but the global impact varies because of iron scavenging, nutrient stealing or the role of regenerative primary production. Exami- nation of these concepts leads to the conclusion that macronutrient nourishment supplied by the Haber-Bosch process is an attractive approach for slowing climate change and increasing marine productivity. The carbon storage capacity of nitrogen fertilisation appears to be limited by the supply of phosphorus to support additional new primary production.