Millions of tons of aerosol particles are transported to remote oceans and forests each year. These particles, once deposited, provide the ecosystems with an external source of nutrients, such as iron, phosphorus, and nitrogen. This, in turn, stimulates primary production (a plant’s ability to produce complex organic compounds from water, carbon dioxide, and simple nutrients) and enhances carbon uptake and thus indirectly affects the climate.
To discuss current scientific knowledge of atmospheric nutrients and their impact on the Earth system, 30 scientists from seven countries met in July 2015 in Leeds, United Kingdom. The aim of the workshop was to identify the most prominent uncertainties in quantifying the effects of atmospheric nutrients on ecosystems and the climate. The workshop focused on two key questions:
- What is the flux of atmospheric nutrients to the ecosystems?
- What is the impact of atmospheric nutrients on global biogeochemical cycles and the climate?
Results presented at the workshop show that mineral dust from the deserts is the dominant source of total atmospheric iron and phosphorus on a global scale, but only a small fraction of these nutrients is bioavailable. However, organic and inorganic acids formed mainly from anthropogenic gaseous emissions can transform insoluble iron and phosphorus from the dust, making these nutrients bioavailable. New results also show that biomass and fossil fuel combustion contribute significantly to the atmospheric deposition of iron because the solubility of iron from these sources is much higher than that from dust.
Most recent modeling studies estimated that the deposition of soluble iron and reactive nitrogen into the ecosystems may have increased by more than 100% and more than 400%, respectively, on a global scale since the Industrial Revolution. However, much uncertainty remains regarding soluble iron flux to the oceans in global models, particularly in the nutrient-limited Southern Ocean. On the other hand, flux of reactive nitrogen appears to be well quantified.
There is strong evidence that atmospheric deposition affects iron and nitrogen budgets and enhances primary production and nitrogen fixation rates in the open ocean. Atmospheric nutrients may also enhance algae growth in melting glaciers, which decreases the albedo of the glaciers and accelerates their melting.
Higher dust and iron deposition in the Southern Ocean during the Last Glacial Maximum may have enhanced the biological pump (the biological processes that remove carbon dioxide from the atmosphere and store it in the deep sea), contributing to the decrease in atmospheric carbon dioxide concentration during this period. More recent studies also suggest that atmospheric phosphorus deposition may help to enhance primary production and carbon uptake in the Amazon rainforests.
Meeting participants agreed that there are major uncertainties in the flux of atmospheric nutrients to the ecosystems, particularly those from anthropogenic and biogenic sources. The impact of atmospheric nutrients on ecosystems and the climate is also poorly understood.
Close collaborations between experimentalists and modelers are essential to reducing uncertainties in our knowledge of the emission, transport, transformation, and deposition of atmospheric nutrients and in determining the ecosystem’s response to these nutrients—an essential factor in producing better representations of the atmospheric nutrients in Earth system models.
This workshop was partly funded by the Natural Environment Research Council (NE/I021616/1), the Aerosol Society, and the Institute for Climate and Atmospheric Science at the University of Leeds and by grant RPG 406 from the Leverhulme Trust. We thank all participants for their active contribution to this meeting.
—Zongbo Shi, School of Geography, Earth and Environmental Sciences, the University of Birmingham, Birmingham, U.K.; email: [email protected]; and Ross Herbert, School of Earth and Environment, University of Leeds, Leeds, U.K.
Citation: Shi, Z., and R. Herbert (2016), The importance of atmospheric nutrients in the Earth system, Eos, 97, doi:10.1029/2016EO044133. Published on 27 January 2016.