Ice core insights into the morphology and composition of mineral dust deposited in the tropical Peruvian Andes

Abstract

Mineral dust plays an important role in governing Earth's energy balance by scattering electromagnetic radiation back to space and by reducing the surface albedo of glaciers. However, in the tropical Andes of South America, long-term mineral dust observational records are extremely scarce and spatially limited; likewise, little has been done to characterize the morphological and mineralogical properties of dust in this region. Here we present a multidecadal mineral dust record obtained from a tropical ice core with emphasis on the size distributions, shape characteristics, and mineral compositions of single particles. We used a scanning electron microscope with energy dispersive x-ray spectrometry (SEM-EDS) to characterize 1887 individual mineral grains (< 5 µm) preserved in an ice core from Nevado Huascarán (Peru) and we interpret the results in context of dust provenance. The SEM-derived particle sizes are found to follow a lognormal distribution with circularities (median 0.75) and aspect ratios (median 1.42) typical of mineral dust. Approximately 60 % of the mineral particles are consistent with clay mineralogy (e.g., illite, kaolinite, montmorillonite), indicating that the particles originate primarily from soils in distal source areas. The relative abundance of quartz, feldspar, and mica in the ice core is comparatively low and likely reflects local dust derived from granodiorites and phyllites near the glacial margins.