Atmospheric Radiative and Oceanic Biological Productivity Responses to Increasing Anthropogenic Combustion‐Iron Emission in the 1850–2010 Period. Issue 16 (19th August 2022)

• Record Type: Journal Article
• Authors: Rathod, S. D.; Hamilton, D. S.; Li, L.; Mahowald, N. M.; Matsui, H.; Pierce, J. R.; Bond, T. C.
• Is Part Of: Geophysical research letters. Volume 49:Issue 16(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-19
• Subjects: anthropogenic -- iron emissions -- radiative forcing -- net primary productivity -- soluble iron -- phytoplankton; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL099323
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Anthropogenic emission is an important component of the present‐day iron cycle yet its long‐term impacts on climate are poorly understood. Iron mineralogy strongly affects its radiative and oceanic interactions and was unrepresented in previous studies. We perform simulations using a mineralogy‐based inventory and an atmospheric transport model and estimate the 1850–2010 global mean direct radiative forcing (DRF) to be +0.02 to +0.10 W/m 2 . We estimate that the CO2 sequestration of 0.2–13 ppmv over the last 150 years due to enhanced phytoplankton productivity by anthropogenic iron deposition causes an avoided CO2 forcing of −0.002 to −0.16 W/m 2 . While globally small, these impacts can be higher in specific regions; the anthropogenic DRF is +0.5 W/m 2 over areas with more coal combustion and metal smelting, and anthropogenic soluble iron sustains >10% of marine net primary productivity in the high‐latitude North Pacific Ocean, a region vulnerable to stratification due to climate change. Plain Language Summary: This study examines the question of whether iron released into the atmosphere from human activities could be important in the Earth system. Iron is released from burning fuels, such as coal and oil, and from processing metal ores. The emitted particles contain iron, among other chemical species. This iron absorbs incoming sunlight and warms the atmosphere while it is suspended in the air. Iron is also an essential nutrient for phytoplankton and can enhance their growth when it falls in ocean areas where it is lacking. These stimulated phytoplankton then draw more carbon dioxide from the atmosphere. We evaluate the influence of these two mechanisms on Earth's heat balance (radiative forcing) since pre‐industrial times and include sensitivity studies to examine the highest possible contribution. We find that even with the upper bounds, the global average forcing is much smaller than the total effects of human emissions of species such as carbon dioxide and black carbon. However, in regions with more coal‐burning and smelting, iron aerosol causes noticeable warming and after deposition may be responsible for more than 10% of phytoplankton growth in the higher‐latitude North Pacific Ocean. Key Points: Direct radiative forcing and net primary productivity impacts of anthropogenic iron emissions over the 1850–2010 period are estimated Both the effects are globally small but higher over specific regions Anthropogenic iron is estimated to sustain about 10% of marine productivity in the iron‐limited North Pacific Ocean