Iron fertilisation and century-scale effects of open ocean dissolution of olivine in a simulated CO2 removal experiment

Abstract

Carbon dioxide removal (CDR) approaches are efforts to reduce the atmospheric CO _2 concentration. Here we use a marine carbon cycle model to investigate the effects of one CDR technique: the open ocean dissolution of the iron-containing mineral olivine. We analyse the maximum CDR potential of an annual dissolution of 3 Pg olivine during the 21st century and focus on the role of the micro-nutrient iron for the biological carbon pump. Distributing the products of olivine dissolution (bicarbonate, silicic acid, iron) uniformly in the global surface ocean has a maximum CDR potential of 0.57 gC/g-olivine mainly due to the alkalinisation of the ocean, with a significant contribution from the fertilisation of phytoplankton with silicic acid and iron. The part of the CDR caused by ocean fertilisation is not permanent, while the CO _2 sequestered by alkalinisation would be stored in the ocean as long as alkalinity is not removed from the system. For high CO _2 emission scenarios the CDR potential due to the alkalinity input becomes more efficient over time with increasing ocean acidification. The alkalinity-induced CDR potential scales linearly with the amount of olivine, while the iron-induced CDR saturates at 113 PgC per century (on average $\sim 1.1\;$ PgC yr ^−1 ) for an iron input rate of 2.3 Tg Fe yr ^−1 (1% of the iron contained in 3 Pg olivine). The additional iron-related CO _2 uptake occurs in the Southern Ocean and in the iron-limited regions of the Pacific. Effects of this approach on surface ocean pH are small $(\lt 0.01)$ .

Keywords

• geoengineering
• carbon dioxide removal
• enhanced weathering
• biological carbon pump
• iron fertilisation
• ocean alkalinisation