Particle-Size Variability of Aerosol Iron and Impact on Iron Solubility and Dry Deposition Fluxes to the Arctic Ocean

Yuan Gao,Shun Yu,Pami Mukherjee,William M Landing,Christopher M Marsay,Songyun Fan,Clifton S Buck

doi:10.1038/s41598-019-52468-z

Abstract

This study provides unique insights into the properties of iron (Fe) in the marine atmosphere over the late summertime Arctic Ocean. Atmospheric deposition of aerosols can deliver Fe, a limiting micronutrient, to the remote ocean. Aerosol particle size influences aerosol Fe fractional solubility and air-to-sea deposition rate. Size-segregated aerosols were collected during the 2015 US GEOTRACES cruise in the Arctic Ocean. Results show that aerosol Fe had a single-mode size distribution, peaking at 4.4 µm in diameter, suggesting regional dust sources of Fe around the Arctic Ocean. Estimated dry deposition rates of aerosol Fe decreased from 6.1 µmol m−2 yr−1 in the areas of ~56°N–80°N to 0.73 µmol m−2 yr−1 in the areas north of 80°N. Aerosol Fe solubility was higher in fine particles (<1 µm) which were observed mainly in the region north of 80°N and coincided with relatively high concentrations of certain organic aerosols, suggesting interactions between aerosol Fe and organic ligands in the high-latitude Arctic atmosphere. The average molar ratio of Fe to titanium (Ti) was 2.4, substantially lower than the typical crustal ratio of 10. We speculate that dust sources around the Arctic Ocean may have been altered because of climate warming.

Highlights

Iron (Fe) is a limiting micronutrient for phytoplankton growth in surface waters of the remote ocean as demonstrated by meso scale Fe addition experiments[1,2,3]
While many studies on aerosols over the Arctic have focused on the winter and springtime Arctic haze, a phenomenon resulting from efficient meridional transport and low rates of wet deposition[32,33,34,35,36], fewer studies of aerosols have been conducted over the central Arctic Ocean in summer and fall[37,38]
We investigated the spatial variability of aerosol Fe particle size and aerosol Fe solubility based on the concentrations of aerosol Fe and its speciation in the particulate phase

Summary

Introduction

Iron (Fe) is a limiting micronutrient for phytoplankton growth in surface waters of the remote ocean as demonstrated by meso scale Fe addition experiments[1,2,3]. While many studies on aerosols over the Arctic have focused on the winter and springtime Arctic haze, a phenomenon resulting from efficient meridional transport and low rates of wet deposition[32,33,34,35,36], fewer studies of aerosols have been conducted over the central Arctic Ocean in summer and fall[37,38] At these times, the polar front retreats northwards, reducing the transport of polluted air from mid-latitude sources[32], and this time period provides a unique window to explore the background composition of the marine atmosphere over the Arctic. The measurements provide insight into the potential climate induced changes in the Arctic environment

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Conclusion