INVESTIGATION OF 18TH-20TH CENTURY DUST FLUX IN THE AMERICAN WEST: INSIGHTS FROM THE UPPER FREMONT GLACIER ICE CORE, WY, USA

Airborne mineral particles (dust) in the atmosphere are capable of influencing local and global climate via radiative forcing and can supply critical nutrients to marine and terrestrial biospheres. Additionally, dust deposited on snowpacks and glaciers may cause earlier seasonal melting affecting the hydrological cycle. The sources and transport pathways of dust during the Agricultural and Industrial Revolution in North America have not yet been investigated, and the impacts of human-related activity upon the dust cycle is not well-documented or well understood. Recent increased dust generation and deposition in the western United States (US) has been attributed to livestock grazing, agriculture, and rising population. Here we isotopically, chemically, and physically characterize dust particles entrained within the 160-m long Upper Fremont Glacier (UFG) ice core (Wyoming, USA) over a semi-continuous time record from ~1715 to 1974 A.D. to examine the dust flux in the western US during the onset of the US Industrial Revolution and ensuing westward expansion. This study utilizes radiogenic strontium (⁸⁷Sr/⁸⁶Sr) and neodymium (¹⁴³Nd/¹⁴⁴Nd) isotopes of dust particles creating an “isotopic fingerprint” to identify provenance by comparison of the samples to potential source areas. The samples show distinct variation between 0.711 to 0.716 and -22 to -4.9 in ⁸⁷Sr/⁸⁶Sr and ε_Nd isotopic ratios respectively. Additionally, trace element concentrations of both dust and meltwater from the UFG ice were analyzed to detect the influence of increasing industrial activity (i.e. mining and smelting) reflected in the concentrations of heavy trace metals throughout the time record. The crustal enrichment of trace metals associated with industrial activity (Cr, As, Cd, Pb, Cu and Zn) are consistently well over 10, with several samples reaching Pb enrichment factors on the order of several hundred. Our dust concentration and particle diameter analysis identify individual dust events with concentrations reaching up to 1600 ppb, and our results demonstrate that the sources and pathways of dust deflated to the UFG have changed throughout the timescale analyzed here, with evidence of a transition from global to local transport as the average dust particle diameter has increased from 2 μm (1816 A.D.) to 5 μm (1974 A.D).