Saharan dust events in the European Alps: role in snowmelt and geochemical characterization

Abstract

Abstract. The input of mineral dust from arid regions impacts snow optical properties. The induced albedo reduction generally alters the melting dynamics of the snowpack, resulting in earlier snowmelt. In this paper, we evaluate the impact of dust depositions on the melting dynamics of snowpack at a high-elevation site (2160 m) in the European Alps (Torgnon, Aosta Valley, Italy) during three hydrological years (2013–2016). These years were characterized by several Saharan dust events that deposited significant amounts of mineral dust in the European Alps. We quantify the shortening of the snow season due to dust deposition by comparing observed snow depths and those simulated with the Crocus model accounting, or not, for the impact of impurities. The model was run and tested using meteorological data from an automated weather station. We propose the use of repeated digital images for tracking dust deposition and resurfacing in the snowpack. The good agreement between model prediction and digital images allowed us to propose the use of an RGB index (i.e. snow darkening index – SDI) for monitoring dust on snow using images from a digital camera. We also present a geochemical characterization of dust reaching the Alpine chain during spring in 2014. Elements found in dust were classified as a function of their origin and compared with Saharan sources. A strong enrichment in Fe was observed in snow containing Saharan dust. In our case study, the comparison between modelling results and observations showed that impurities deposited in snow anticipated the disappearance of snow up to 38 d a out of a total 7 months of typical snow duration. This happened for the season 2015–2016 that was characterized by a strong dust deposition event. During the other seasons considered here (2013–2014 and 2014–2015), the snow melt-out date was 18 and 11 d earlier, respectively. We conclude that the effect of the Saharan dust is expected to reduce snow cover duration through the snow-albedo feedback. This process is known to have a series of further hydrological and phenological feedback effects that should be characterized in future research.

Preferential Deposition of Snow and Dust Over Hills: Governing Processes and Relevant Scales

“…However, the same physical process is relevant to deposition of other heavy particles. Wind-blown volcanic ashes and desert dust deposit on snow-covered mountain regions at global scale, causing a decrease in surface albedo and a faster snow melt (Di Mauro et al, 2018;Painter et al, 2010). Moreover, dust deposition on complex landforms provides a fundamental supply of nutrients to a variety of ecosystems, whose long-term productivity is limited by the availability of dustborne phosphorus (Kok et al, 2012;Okin et al, 2004).…”

Introducing Thermal Inertia for Monitoring Snowmelt Processes With Remote Sensing

“…= 60). During the melting period, part of the variability in the AP s series may be due to the resurfacing of LAPs that induce a further decrease in snow albedo, increase in grain size, and a warming of the snowpack (Di Mauro et al, ). This may partially explain the higher scattering of data in Figure and affect the correlation between AP s and snow density.…”

“…dev.) equal to 147 J · m −2 ·K −1 ·s − Mauro et al, 2019). This may partially explain the higher scattering of data in Figure 3 and affect the correlation between AP s and snow density.…”

Dust Deposited on Snow Cover in the San Juan Mountains, Colorado, 2011–2016: Compositional Variability Bearing on Snow‐Melt Effects

“…The possibility that black carbon contributed to diminished snow‐cover albedo at the SASP site is implied by the correspondence between relatively low reflectance values and relatively high amounts of organic carbon. The close correspondences between organic carbon and certain trace metals and among these metals further suggest genetic connections to anthropogenic emissions, including those from coal combustion (Nriagu & Pacyna, 1988; Pacyna et al, 1995; Vassilev & Vassilev, 1997; Goldhaber et al, 2004; Ruhl et al, 2009; Reynolds et al, 2010; Reynolds, Goldstein et al, 2014: Carling et al, 2012; Di Mauro et al, 2019; Figure 8). This interpretation implies that black carbon was a constant proportion of the carbonaceous matter.…”

“…Numerous studies have addressed the role of black carbon to promote melting of snow and ice (e.g., Bond et al, 2013; Bond & Bergstrom, 2006; Dang & Hegg, 2014; Doherty et al, 2014; Flanner et al, 2007, 2009, 2012; Gieré & Querol, 2010; Hadley & Kirschstetter, 2012; Qian et al, 2015; Ramanathan et al, 2007; Ramanathan & Carmichael, 2008; Wu et al, 2018). Moreover, several investigations have examined the combined effects of dust and black carbon on snow and ice melt in middle‐latitude settings of North America (Hadley et al, 2010; Nagorski et al, 2019; Oaida et al, 2015), as well as Asia (Himalayas, Tibet, North China) and Europe (Alps) (Dang et al, 2017; Di Mauro et al, 2019; Ginot et al, 2014; Kaspari et al, 2014; Thind et al, 2019; Zhang et al, 2017, 2018; Zhao et al, 2014). In contrast, few studies have considered specific minerals in dust for their potential heat‐absorbing effects on melting of snow cover (Axson et al, 2016; Kaspari et al, 2014; Lawrence et al, 2010; Reynolds, Goldstein et al, 2014).…”