Abstract
Mineral dust aerosol (dust) is widely recognized as a fundamental component of the climate system and is closely coupled with glacial-interglacial climate oscillations of the Quaternary period. However, the direct impact of dust on the energy balance of the Earth system remains poorly quantified, mainly because of uncertainties in dust radiative properties, which vary greatly over space and time. Here we provide the first direct measurements of the aerosol optical thickness of dust particles windblown to central East Antarctica (Dome C) during the last glacial maximum (LGM) and the Holocene. By applying the Single Particle Extinction and Scattering (SPES) technique and imposing preferential orientation to particles, we derive information on shape from samples of a few thousands of particles. These results highlight that clear shape variations occurring within a few years are hidden to routine measurement techniques. With this novel measurement method the optical properties of airborne dust can be directly measured from ice core samples, and can be used as input into climate model simulations. Based on simulations with an Earth System Model we suggest an effect of particle non-sphericity on dust aerosol optical depth (AOD) of about 30% compared to spheres, and differences in the order of ~10% when considering different combinations of particles shapes.
Highlights
Dust influences global climate both directly, by changing the radiative properties of the atmosphere through scattering and absorption of solar and terrestrial radiation[1], and indirectly, by impacting on cloud formation and properties[2]
The EPICA-Dome C and Vostok Antarctic ice cores provide evidence of the significant increase in ice-age dust deposition flux that is inversely correlated with temperature, global sea level and atmospheric CO2 concentration over the last ~800 kyrs[6,7]
Dust could potentially play an important role in glacial-interglacial cycles[6,8], but model simulations show that dust can potentially dampen or reinforce glacial–interglacial climate changes depending on its optical parameters[9]
Summary
The last climatic cycle provides a logical first target for the analysis of the paleodust optical properties from central East Antarctica, since glacial and Holocene dust size, concentration in ice, depositional flux, and sources are relatively well known[29,30,31]. We consider the first-order impacts of different sets of optical properties derived from the SPES analyses on atmospheric dust AOD, based on dust mixing ratios simulated by the Community Earth System Model (CESM) tuned to match size and deposition at Dome C41 (supplementary information). While previous studies highlighted the role of particle shape[3,4,5] in association to mineralogy and size in determining dust impacts on climate, we applied here for the first time the SPES method to measure dust optical properties and shape in ice cores We anticipate that this technique will provide important constraints to climate and paleoclimate models determining the dust radiative forcing and its role on climate change
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