Abstracts Earth and Environmental Sciences

Earth, humans, and metals: investigating the role of iron and other metals in the atmospheric, oceanic, and energy systems

by Ryan P., committee member Scott

Metals such as iron and copper have been an integral component of the Earth system since its beginnings and have formed the basis for modern human civilization growth since the Bronze and Iron Ages. Human activities include metals at various levels, from burning coal in power plants and mining ores lead to emissions of particulate and gaseous metallic products into the atmosphere. While suspended in the air, metal oxides such as hematite and magnetite absorb solar radiation, thus warming the atmosphere. After falling into the oceans, metals such as iron and magnesium act as important nutrients for oceanic biota, and thus affect the marine nutrient and carbon cycles. Human activities have increased many-fold since the beginning of the Industrial Era, and as the world moves from fossil fuel to renewable energy to reduce carbon emissions, the demand for metals is also projected to increase many folds. Yet, the past, present, and future impacts of anthropogenic activities on the atmospheric and marine metal cycles, particularly iron, remain poorly understood.In Chapter 2, I estimate the atmospheric radiative and oceanic biological impacts of anthropogenic iron emissions over the Industrial Era. I perform simulations using a mineralogy-based inventory and an Earth System Model and estimate the 1850-to-2010 global mean direct radiative forcing by anthropogenic iron to be +0.02 to +0.10 W/m2. I estimate that the enhanced phytoplankton primary production due to anthropogenic soluble iron deposition over the last 150 years caused carbon dioxide (CO2) sequestration of 0.2-13 ppmv. This sequestered CO2 also led to an 'avoided' CO2 forcing of -0.002 to -0.16 W/m2. While globally small, these impacts can be higher in specific regions; the anthropogenic iron oxide direct radiative forcing is +0.5 W/m2 over areas such as East Asia and India with more coal combustion and metal smelting. Anthropogenic soluble iron sustains >10% of marine net primary productivity in the high-latitude North Pacific Ocean, a region vulnerable to thermal stratification due to climate change. In Chapter 3, I focus on evaluating anthropogenic total iron emissions using observations and models. Performing the model-observation comparison only at sites where the modeled anthropogenic contribution is the highest, I find that the current emission inventory underestimates anthropogenic total iron emissions from North America and Europe by a factor of 3-5. Further isolating anthropogenic sectoral emissions over North America using Positive Matrix Factorization, I find that smelting and coal combustion emissions are overestimated by a factor of 3-10 in the current emission inventory, whereas heavy fuel oil emissions from ships and industrial boilers are underestimated by a factor of 2-5. By comparing modeled concentrations of iron oxides with observations from Japan, I find that the current smelting and coal combustion emissions from East Asia are only slightly overestimated in the inventory, by a factor of 1.2-1.5. Finally, in Chapter 4, I explore the…