Historical contribution of African dust outbreaks to northern tropical Atlantic temperatures

Dust storms from Africa are a persistent feature in the skies over the northern tropical Atlantic, and strong variability in Atlantic dust cover has been observed on seasonal to decadal time scales. It is well known that over water surfaces the net radiative effect from mineral aerosols at the surface is negative, and recent work has shown that this reduction in downwelling radiation translates into localized cooling of the mixed layer. Recent studies have also demonstrated that over the last quarter century roughly 25% of the observed upward trend in sea surface temperatures can be attributed to declines in Atlantic dust cover over the same time period. However, to-date observation-based studies of the effect of African dust have been limited to the last 25 years, and therefore it is unknown to what extent dust plays a role in observed decadal scale variability of tropical Atlantic temperatures,

Here we use a new proxy dust record obtained from the Crustal 4He flux of coral at Cape Verde to examine the effect of dust on ocean temperature from 1955 through the present. We develop a statistical model for using this proxy record to extend back in time spatially explicit satellite dust optical depth retrievals, and then use this reconstructed 60-year “satellite” climatology to estimate dust surface forcing using a simple radiative transfer model. We examine the effect of African dust outbreaks on decadal scale surface and subsurface northern tropical Atlantic temperature anomalies using a stochastic mixed-layer model and an ocean GCM.