Strong links between Saharan dust fluxes, monsoon strength, and North Atlantic climate during the last 5000 years

Despite the multiple impacts of mineral aerosols on global and regional climate and the primary climatic control on atmospheric dust fluxes, dust-climate feedbacks remain poorly constrained, particularly at submillennial time scales, hampering regional and global climate models. We reconstruct Saharan dust fluxes over Western Europe for the last 5000 years, by means of speleothem strontium isotope ratios (87Sr/86Sr) and karst modeling. The record reveals a long-term increase in Saharan dust flux, consistent with progressive North Africa aridification and strengthening of Northern Hemisphere latitudinal climatic gradients. On shorter, centennial to millennial scales, it shows broad variations in dust fluxes, in tune with North Atlantic ocean-atmosphere patterns and with monsoonal variability. Dust fluxes rapidly increase before (and peaks at) Late Holocene multidecadal- to century-scale cold climate events, including those around 4200, 2800, and 1500 years before present, suggesting the operation of previously unknown strong dust-climate negative feedbacks preceding these episodes.

Desert dust aerosols affect Earth’s global energy balance in multiple ways, including by scattering and absorbing radiation, modifying cloud albedo and lifetime, and affecting the carbon cycle by ecosystem fertilization (1). Also, they regionally affect the water cycle by influencing cloud formation and precipitation (2) and affect human health through air pollution (3). On a global scale, the largest source of mineral dust for the atmosphere is located in the northern African desert, from where huge amounts of dust are exported continuously (but not steadily) via the atmosphere over the Atlantic Ocean and the Mediterranean (4). Understanding dust-climate relationships is a major scientific challenge for climate modeling (5, 6) and, despite notable advances, considerable uncertainties remain because of the number and complexity of processes that affect radiative fluxes. Difficulties are further aggravated because atmospheric dust fluxes vary at all temporal scales and can be difficult to quantify at climate-relevant time scales. Saharan dust fluxes show strong interannual and interdecadal variability (7), both of which influence and are affected by a multitude of regional-scale processes. Some recent work on Mediterranean and north African lake records (8–10), European ice cores (11), and Atlantic sediments (12–16) indicate considerable variability also at longer time scales. Despite these advances, our knowledge on dust changes occurring at centennial to millennial time scales is still very limited and strongly hampers robust quantitative evaluation of desert dust–climate feedbacks.

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