Abstract
ABSTRACTThe tree-ring stable carbon and oxygen isotope chronologies from two forest sites located in the Forni Glacier forefield (Italy)—one along the glacier stream (GL) and the other toward the valley slope (SL)—were analyzed with the aim of disentangling the precipitation and glacier meltwater inputs in source water δ18O, as reflected by the tree-ring cellulose δ18O. The cellulose δ18O from the GL trees has a negative correlation with winter and summer temperatures, whereas the cellulose δ18O from the SL trees has a positive correlation with precipitation δ18O. The isotopic signature of the source water at the GL site is also influenced by waters of glacial origin, as confirmed by the 18O-depleted glacier meltwater inputs (GMWI_δ18O) estimated by means of an isotope model. The GMWI_δ18O values are consistent with the mean difference measured between the δ18O in the glacier stream and in the precipitation and the winter and summer temperature explains up to 37 percent of the GMWI_δ18O variance. Our results show an increasing influence of glacier meltwater throughout the past decade for the GL site. Our analysis opens new opportunities to reconstruct changes in water regimes of the glacier streams by means of the tree-ring cellulose δ18O.
Highlights
Stable carbon and stable oxygen isotopes in relation to climate and climate-related dynamics have often been applied both in forest ecology, for assessing climatechange impacts (e.g., Battipaglia et al 2013; Wieser et al 2016), and in paleoclimate studies, for reconstructing past climatic conditions on a yearly basis (e.g., Kress et al 2010; Sidorova et al 2013; HartlMeier et al 2015)
The two standard chronologies of European larch constructed at the SL and glacier stream (GL) sites show a good agreement in growth patterns during the analyzed period 1980–2010 (Figure 2)
Both series show a maximum enrichment in δ13C in 1992, and the difference between the GL and the SL chronologies shows no trend throughout the considered period (Figure 3c)
Summary
Stable carbon and stable oxygen isotopes in relation to climate and climate-related dynamics have often been applied both in forest ecology, for assessing climatechange impacts (e.g., Battipaglia et al 2013; Wieser et al 2016), and in paleoclimate studies, for reconstructing past climatic conditions on a yearly basis (e.g., Kress et al 2010; Sidorova et al 2013; HartlMeier et al 2015). The annual number of days with snow cover is generally decreasing at high latitudes (e.g., Dye and Tucker 2003) and at high altitudes in the Alps (e.g., Hantel and Lucia-Maria 2007; Marty et al 2017) This decrease in snow cover contributes to changes in the hydrological cycle in mountain catchments in terms of thaw anticipation, high glacier ablation rates, and higher water discharges in the glacier streams. Trees in glacier forefields typically grow on initial and very young soils formed on glacial deposits and till These recently deglaciated areas at elevations below the plant species’ limit and below the treeline—which is the case for most of the large valley glaciers in the Alps, including our study site —typically undergo primary successions and forest invasion (Huggett 1998; Walker et al 2010; Garbarino et al 2010; D’Amico et al 2015; D’Agata et al 2019)
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