Impact of Changes to the Atmospheric Soluble Iron Deposition Flux on Ocean Biogeochemical Cycles in the Anthropocene

• Published in: Global biogeochemical cycles Vol. 34; no. 3
• Main Authors: Hamilton, Douglas S., Moore, J. Keith, Arneth, Almut, Bond, Tami C., Carslaw, Ken S., Hantson, Stijn, Ito, Akinori, Kaplan, Jed O., Lindsay, Keith, Nieradzik, Lars, Rathod, Sagar D., Scanza, Rachel A., Mahowald, Natalie M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-03-2020; American Geophysical Union (AGU)
• Subjects: Anthropocene; Anthropogenic factors; Atmospheric particulates; Bioavailability; Biogeochemical cycle; Biogeochemical cycles; Biogeochemistry; Carbon; Carbon cycle; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide concentration; Climate; Denitrification; Deposition; Dust storms; Earth and Related Environmental Sciences; Emissions; Exports; Geovetenskap och miljövetenskap; Human influences; Industrial emissions; Iron; iron cycle; Land use; Limiting factors; marine net primary productivity; Meteorologi och atmosfärforskning; Meteorology and Atmospheric Sciences; Natural Sciences; Naturgeografi; Naturvetenskap; Net Primary Productivity; Nitrogen; Nitrogen cycle; Nitrogen fixation; Nitrogenation; Northern Hemisphere; Oceanografi, hydrologi och vattenresurser; Oceanography, Hydrology, Water Resources; Oceans; Physical Geography; Phytoplankton; Plankton; Primary production; Shipping; Southern Hemisphere; Uptake; Wildfires; Southern Ocean
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1029/2019GB006448

Iron can be a growth‐limiting nutrient for phytoplankton, modifying rates of net primary production, nitrogen fixation, and carbon export ‐ highlighting the importance of new iron inputs from the atmosphere. The bioavailable iron fraction depends on the emission source and the dissolution during transport. The impacts of anthropogenic combustion and land use change on emissions from industrial, domestic, shipping, desert, and wildfire sources suggest that Northern Hemisphere soluble iron deposition has likely been enhanced between 2% and 68% over the Industrial Era. If policy and climate follow the intermediate Representative Concentration Pathway 4.5 trajectory, then results suggest that Southern Ocean (>30°S) soluble iron deposition would be enhanced between 63% and 95% by 2100. Marine net primary productivity and carbon export within the open ocean are most sensitive to changes in soluble iron deposition in the Southern Hemisphere; this is predominantly driven by fire rather than dust iron sources. Changes in iron deposition cause large perturbations to the marine nitrogen cycle, up to 70% increase in denitrification and 15% increase in nitrogen fixation, but only modestly impacts the carbon cycle and atmospheric CO2 concentrations (1–3 ppm). Regionally, primary productivity increases due to increased iron deposition are often compensated by offsetting decreases downstream corresponding to equivalent changes in the rate of phytoplankton macronutrient uptake, particularly in the equatorial Pacific. These effects are weaker in the Southern Ocean, suggesting that changes in iron deposition in this region dominates the global carbon cycle and climate response.
Key Points
Human activity significantly modifies the magnitude and location of atmospheric soluble iron deposition to the oceans
Marine carbon cycle responses to Anthropocene iron flux changes are modest but more sensitive to varying fire than dust iron emissions
Increasing the iron flux produces offsetting patterns in phytoplankton macronutrient uptake and productivity rates at the basin scale