Quantifying Sequestration of Carbon in the Ocean following Addition of Macronutrient

The effects of addition of limiting nutrients to the surface waters of the deep ocean has been investigated for the last twenty years, partly to explore ocean biogeochemical processes and partly because of the potential for sequestration of carbon in the deep ocean. Investigations have been performed for micronutrients (iron) and macronutrients (nitrogen and phosphorous). A methodology of estimating carbon stored is introduced here based on fertilization with nitrogen in those regions in which nitrogen is the limiting nutrient. The basis of the methodology is a combination of measurements in the photic zone and numerical modelling of the biogeochemical cycle. The calculation of the quantity of sequestered carbon is, after allowance for losses, equal to the carbon that is taken up by photosynthesis (new primary production equals export production) resulting from the added nitrogen. An essential feature of the biogeochemical process is that the added nitrogen is not lost from the upper waters by export to the deep ocean unless accompanied by carbon, in approximately the Redfield ratio. Determination of the quantity of carbon sequestered consists of three steps: (1.) Determination of the quantity of carbon converted by photosynthesis to biological form (new primary production). (2.) Allowance for factors potentially affecting carbon sequestration, such as: Loss of reactive nitrogen from the ocean; Greenhouse Gas (GHG) production by photosynthesis; GHG production by denitrification; GHG production following upwelling; Air-sea carbon transfer efficiency; Calcium carbonate production; Alkalinity change; and Respiration. (3.) Allowance for carbon dioxide released to the atmosphere during the manufacture and transport processes involved in providing added nutrients to the ocean. With these three steps, the net quantity of carbon sequestered by fertilisation may be determined.