Sand from the Sahara

Record-breaking temperatures in recent weeks were due to warm air being pushed up from low latitude, bringing with it a plume of dust arising from wind storms in the Sahara. The plume even reached Iceland! Managing Director Steve had to wash his (black) car due to seagull ‘emissions’, and was surprised later to find a covering of reddish-orange dust on the patch that he had recently cleaned.

We were impressed that we had good intensities and were able to quantify the material using Rietveld analysis. The results of this are shown in the table below:

Illite Chlorite Quartz Feldspars Calcite Dolomite
Mass % 14.9 6.2 41.3 24.7 9.2 3.7

There are some fantastic images of previous events that have been collected by the Earth observation satellites operated by NOAA for the USA Department of Commerce. Here is one showing dust streaming out across the equatorial Atlantic from June 2018.

Digging around uncovered some interesting papers on dust emissions. It has been estimated that around 240 million tons of such dusts are deposited annually on and around the Atlantic Ocean, and the iron which is contained is a critical nutrient for marine algae in surface waters, the basis of the food chain, of course.

Iron is often difficult to pin down using XRD, since the iron oxides and hydroxides which give colour to geological materials is of poor crystallisation, or even amorphous. It is no surprise that iron-bearing phases are not detected in this diffuse and low-density XRD preparation.

All great XRD interest, but the rain from Storm Hannah washed it all away in a trice.

The science team was scrambled and we swabbed the area with a moistened filter paper to collect a sample on a flat surface for XRD as can be seen in the photograph.

Just 45 minutes later we had an analysis: peaks for quartz, feldspar, calcite, dolomite, illite and chlorite were clear as can be seen on the diffractogram above.

Image courtesy of NOAA.