New study: Saharan dust, iron and fertilization of the ocean.

The journal Atmospheric Environment publishes a new study – performed by scientists of the Izaña Atmospheric Research Centre, the University of La Laguna and the Research Council of Spain CSIC – on the fertilization of the ocean by the iron present in the Saharan dust.

North Africa is the largest source of desert dust particles in the Earth. This desert emits 1 – 2 Teragrams of dust / year. Dust is mainly transported over the North Atlantic in the so-called Saharan Air Layer, an airstream that spreads the desert dust particles over the North Atlantic to the Caribbean and the Americas.

The new study found that part of the iron present in the Saharan dust (mainly linked to clays and iron oxides) is seawater soluble. It was found that fractional iron solubility is higher for particles smaller than 1 micron, and that the solubility of these particles is higher when they are mixed with sulphuric acid and ammonium sulphate. Mean fractional iron solubility is 0.7% for total iron and 6% for the iron present in submicron dust. The dust mixing with sulphuric acid and ammonium sulphate may increase to 8% the fractional iron solubility of submicron dust. The presence of these acid pollutants mixed with dust is linked to industrial emissions (refineries, manufacturing fertilizing factories and power plants) of North Africa and Europe and to ships in the Mediterranean.

Fig. 1. Saharan Air Layer detected by satellite remote sensing

(MODIS – Aerosol Optical Depth)

The ocean fertilization by iron plays a key role on the marine biogeochemistry and on climate due to it influences on (1) growth rates of phytoplankton and (2) on atmospheric CO₂ absorption by the marine biota.

This research is based on samples of dust samples directly collected into the Saharan Air Layer when it impacts in Izaña Observatory. This research is performed as part of the project AEROATLAN (2015-66229), funded by the Ministry of Economy and Competitiveness of Spain – Excellence research projects program.

The scientific team express their gratitude to the brotherhood of fishermen of La Punta del Hidalgo (Cofradía de Pescadores de La Punta del Hidalgo) for collecting offshore seawater.

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