Prof. Dr. Jan Berend Stuut

Marine geologist Dr Jan-Berend Stuut investigates desert dust’s role in the Earth’s climate. ‘We have placed a large series of measuring instruments in the Atlantic Ocean between Africa and the Caribbean, which all capture dust from the Sahara. When we first found sand grains of nearly half a millimetre in size in these traps, hardly anyone believed us because they seemed to be much too large. Now we have clearly shown that these large dust particles from the Sahara can be blown to the other side of the ocean. Satellite images beautifully reveal which dry riverbeds and dried-up lake floors this dust is emitted from. Furthermore, chemical analysis of the particles provides a sort of “fingerprint” as to where the dust comes from.’

Fertiliser for the ocean

‘This finding has consequences for both the atmosphere and the ocean. Dust scatters light and heat, influences the formation of raindrops and clouds, but also subdues the development of hurricanes. Furthermore, desert dust from the Sahara is full of nutrients as well as metals like iron. It therefore acts as a fertiliser that feeds the oceans. The growth of algae, for example, benefits from this fertiliser. This makes Sahara dust an important factor in the overall balance of algal growth in the oceans and therefore in global climate. Because when those algae die, they can take the carbon they have captured to the ocean floor, and that could somewhat counterbalance the emission of CO₂ from fossil-fuel burning’

Both reflector and warm blanket

‘Besides being a fertiliser, which encourages the ocean’s uptake of carbon dioxide from the atmosphere, Sahara dust can also act as a reflector high in the atmosphere, keeping the sun’s heat away from the earth’s surface. Lower in the atmosphere, however, this same dust acts as a strongly insulating blanket, just like the greenhouse gas CO₂, which retains heat. Amongst other things, our research provides meteorologists and other researchers with data about the quantity and quality of dust in the air. They can subsequently study the exact relationships between dust and temperature in the atmosphere.’

Past-dust deposits

‘Besides investigating the various processes in which desert dust plays a role in the current climate, we are also trying to reconstruct the climate of the past using desert dust that can be found in depositions on the seafloor.  The particle size of the dust tells us something about the strength of the ambient winds in the past and the amount of dust relative to river mud tells us something about the aridity in the source areas of these materials. In addition, by studying present-day relationships between wind and wind-blown sediments, we can try and infer quantitative wind-strength reconstructions from past dust deposits.’