Atmospheric Radiative and Oceanic Biological Productivity Responses to Increasing Anthropogenic Combustion-Iron Emission in the 1850-2010 Period

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.