Recent (1980 to 2015) Trends and Variability in Daily‐to‐Interannual Soluble Iron Deposition from Dust, Fire, and Anthropogenic Sources

• Published in: Geophysical research letters 2020-09, Vol.47 (17), p.n/a
• Main Authors: Hamilton, Douglas S., Scanza, Rachel A., Rathod, Sagar D., Bond, Tami C., Kok, Jasper F., Li, Longlei, Matsui, Hitoshi, Mahowald, Natalie M.
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; anthropogenic iron; Atmospheric particulates; Atmospheric pollution deposition; biogeochemical cycles; Biogeochemistry; Climate and human activity; Climate change; Combustion; Daily; Deposition; Dust; dust iron; Dust storms; Emission; Emissions; ENVIRONMENTAL SCIENCES; fire iron; Fires; Fluctuations; Flux; Human influences; Interannual variability; Iron; Ocean basins; Oceans; Perturbation; Phytoplankton; Seasonal variability; soluble iron deposition variability; Statistical analysis; Temporal variability; Temporal variations; Trends; Variability
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL089688

The iron cycle is a key component of the Earth system. Yet how variable the atmospheric flux of soluble (bioaccessible) iron into oceans is, and how this variability is modulated by human activity and a changing climate, is not well known. For the first time, we characterize Satellite Era (1980 to 2015) daily‐to‐interannual modeled soluble iron emission and deposition variability from both pyrogenic (fires and anthropogenic combustion) and dust sources. Statistically significant emission trends exist: dust iron decreases, fire iron slightly increases, and anthropogenic iron increases. A strong temporal variability in deposition to ocean basins is found, and, for most regions, dust iron dominates the absolute deposition magnitude, fire iron is an important contributor to temporal variability, and anthropogenic iron imposes a significant increasing trend. Quantifying soluble iron daily‐to‐interannual deposition variability from all major iron sources, not only dust, will advance quantification of changes in marine biogeochemistry in response to the continuing human perturbation to the Earth System. Plain Language Summary Iron is a limiting micronutrient for marine phytoplankton growth in many ocean basins. A major source of new iron to the open ocean is via atmospheric deposition and until recently was considered to be associated with mineral dust aerosol. However, growing evidence has shown that pyrogenic (fires and anthropogenic combustion) are equally important sources to many basins. Here, for the first time, we quantify the variability (1980 to 2015) in emission and deposition for all three sources across three model versions for robustness. We find that while dust iron dominates the absolute global deposition magnitude, fire iron is an important contributor to daily, seasonal, and interannual variability and that the anthropogenic iron deposition flux to important ocean basins has steadily increased with time. Characterizing more realistic deposition patterns on both short‐term (daily to monthly) and long‐term (annual to decadal) time scales will improve understanding of the biogeochemical response to the continuing human perturbation to iron emissions and their ocean deposition flux. Key Points Modeled soluble iron deposition variability (1980–2015) is characterized for dust, fires, and anthropogenic iron for the first time A new anthropogenic iron transient data set is developed, showing lifetime depends on particle emission size and thus air quality