Dust concentrations measured in Barbados were much higher during the 1980s than in the 1960s. My PhD investigated what caused this increase.

Large dust storms can lift enormous quantities of mineral dust from North Africa into the atmosphere, where winds can carry it across the Atlantic to the Caribbean.

I developed a model of the desert dust cycle linking vegetation, dust emissions and atmospheric transport. The simulations showed that expansion of the Sahara and Sahel during the 1980s increased dust emissions, but not enough to explain the full rise observed in Barbados.

This supported the idea that other changes in North African land surfaces, including human driven soil degradation, may also have contributed to the increase in dust reaching the Caribbean.

Modelling the dust cycle

I used a dynamic vegetation model to estimate how dust-source areas changed over time, then used those results as input to a dust emissions model and the TOMCAT atmospheric transport model.

Dust emissions were calculated from wind-driven saltation and sandblasting, before being transported through the atmosphere. I also added dry deposition and sub cloud scavenging to TOMCAT so that the model could represent how dust was removed from the atmosphere.

Left: Modelled dust source area derived from vegetation and soil moisture conditions. Right: Dust emissions calculated from wind driven saltation and sandblasting.

From North Africa to the Caribbean

The atmospheric model reproduced the large scale transport of Saharan dust across the Atlantic, including the strong summer dust plume extending towards the Caribbean.

Left: Modelled dust concentrations over the North Atlantic. Right: Satellite observations of aerosol optical depth from TOMS.

Why this matters

Desert dust links changes at the land surface to the atmosphere and to regions thousands of kilometres downwind. It can also deliver nutrients such as iron and phosphorus to the ocean, which can stimulate phytoplankton growth.

Understanding why dust emissions change requires following that chain from vegetation and soil conditions, through emission and atmospheric transport, to the concentrations and deposition observed far from the source.