Abstract
In the summer of 2003 and 2004, characterized by a rapid glacier retreat, a stony surface covered by well-structured organic-rich mineral debris was observed very close to the Indren glacier terminus (Monte Rosa Massif, NW Italy, 3100 m ASL), on an area covered by the glacier tongue till the year before. The origin and type of this organic-rich material were investigated, in order to detect their characteristics, potential sources and fate within the foreland system. The deposits were dated using Carbon-14 and analyzed for the chemical characteristics of the organic component, the elemental composition of the mineral fraction and presence of microbial markers. The material, granular and dark in color, had a total organic carbon (TOC) content ranging between 17.4 ± 0.39 and 28.1 ± 0.63 g kg−1 dry weight (dw), significantly higher than the surrounding glacial till (~ 1.4 g kg−1 dw), although only 0.33% of it was in water soluble form. Microbial carbon (C) and nitrogen (N) accounted for 10.6% and 3.13% of TOC and total N, respectively. Dissolved nitrogen (N), mainly present as ammonium, represented 2.40% of the total N. The low aromatic component and large presence of nitrogen (N)-derived compounds suggested that most of the organic carbon (OC) in these organic-rich mineral deposits was derived from microbial cells, although the high average radiocarbon age of about 2900 years may also point to the contribution of aeolian depositions of anthropogenic or natural origin. Elemental composition and the crustal enrichment factor of trace elements in the mineral fraction of the aggregates corroborated the hypothesis that most part of the accumulated material derived from ice meltwater. Some indicators of the colonization of these deposits by microbial communities were also reported, from the abundance of DNA and phylogenetic markers, to the presence of bacterial taxa commonly able to thrive in similar habitats. All these elements suggested that such kind of deposits may have a potential role as energy and nutrient sources in recently deglaciated areas, highlighting the necessity to better understand the processes underlying their formation and their evolution.
Highlights
Many alpine areas are experiencing numerous changes that affect biogeochemical cycling, including increase in air temperature and deglaciation, along with changes in the quality of atmospheric deposition in wetfall and dryfall (Fountain et al 2012; Mladenov et al 2012)
The low aromatic component and large presence of nitrogen (N)derived compounds suggested that most of the organic carbon (OC) in these organic-rich mineral deposits was derived from microbial cells, the high average radiocarbon age of about 2900 years may point to the contribution of aeolian depositions of anthropogenic or natural origin
The general characteristics of the organic-rich mineral deposits and the meltwater samples are summarized in Table 1 and Table 2
Summary
Many alpine areas are experiencing numerous changes that affect biogeochemical cycling, including increase in air temperature and deglaciation, along with changes in the quality of atmospheric deposition in wetfall and dryfall (Fountain et al 2012; Mladenov et al 2012). As glaciers undergo negative mass balance that give rise to retreat, new areas become ice-free. The newly deglaciated areas - often called glacier forefields - are subjected to changes in mineral weathering, biogeochemical cycling, and soil formation processes (Dümig et al 2011; D’Amico et al 2014, 2015). There is some urgency to understand the sources, transport and fate of nutrients to highelevation areas undergoing rapid environmental change (Ren et al 2019; Wadham et al 2019)
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