Epikarst hydrology and implications for stalagmite capture of climate changes at Grotta di Ernesto (NE Italy): results from long‐term monitoring

Abstract

Abstract:Grotta di Ernesto is a cave site well suited for palaeoclimate studies because it contains annually laminated stalagmites and was monitored from 1995 to the end of 2008 for microclimate, hydrology and hydrochemistry. Long-term monitoring highlighted that cave drips show three different hydrological responses to rainfall and infiltration: (1) fast seasonal drips in the upper part of the cave, which are mostly fed by fractures, (2) slow seasonal drips, located at mid-depth in the cave characterized by mixed feeding and (3) slow drips, mostly located in the deeper gallery, which are fed by seepage flow from bulk porosity with a minor fracture-fed component. The slow drips display daily cycles during spring thaw. Monitoring also indicated that drip waters are only slightly modified by degassing within the soil zone and aquifer and by prior calcite precipitation. Hydrochemical studies show a clear seasonality in calcite saturation index, which results in most cave calcite precipitation occurring during late autumn and winter with similar amounts of precipitated calcite on most stalagmites, regardless of drip rate (discharge) differences. Drip rate, and drip rate variability, therefore, has a minor role in modulating the amount of annual calcite formation. In contrast, drip rate, when associated with moderate reduction in calcite saturation index, clearly influences stalagmite morphology. Increasing drip rate yields a passage from candle-, to cone-to dome-shaped stalagmites. Very high drip rates feed speleothems with flowstone morphology. In summary, monitoring provides information about the karst aquifer and how hydrology influences those physical and chemical characteristics of speleothems which are commonly used as climate proxies.

Holocene climate variability in north-eastern Italy: potential influence of the NAO and solar activity recorded by speleothem data

“…Decade-long, extensive monitoring of cave physics and chemical parameters has revealed that stalagmite growth inside this cave is modulated by cave ventilation in response to the seasonal difference between cave and surface temperature (Frisia et al, 2011). Thus, the systematics of calcite growth are exceptionally well understood (Miorandi et al, 2010), which enabled the calculation of surface temperature variability for the past ∼ 500 a on the basis of annual lamina thickness changes in three stalagmites (Smith et al, 2006;Frisia et al, 2003).…”

“…The gallery is developed between ∼ 2 and ∼ 30 m below the surface, and this shallow setting is a pre-requisite for the preservation of seasonal climatic signals in speleothems (Fairchild et al, 2007). A decade-long monitoring programme provides the benchmark for the interpretation of the hydrological and physical processes regulating stalagmite growth (Miorandi et al, 2010;Frisia et al, 2011), the development of visible annual growth laminae (Frisia et al, 2000(Frisia et al, , 2003 and the seasonal variability of trace-element composition (Borsato et al, 2007a).…”

“…Cave air pCO 2 varies seasonally (Frisia et al, 2003) and is modulated by air advection due to the seasonal difference between surface air and cave temperature (Frisia et al, 2011). Cave air pCO 2 is lower in winter than during summer, which results in increased degassing of CO 2 from dripwater (Fairchild et al, 2007;Frisia, 2011) and, thus, higher calcite precipitation rates during winter (Miorandi et al, 2010).…”

Sulphate concentration in cave dripwater and speleothems: long-term trends and overview of its significance as proxy for environmental processes and climate changes

“…The present-day vegetation 238 11 above the cave is a mixed conifer -deciduous forest association, composed primarily of Fagus 239 sylvatica, Picea abies and Abies alba (Fairchild et al 2009; Miorandi et al 2010). Most trees started to 240 grow ca.80 years ago (Borsato et al, 2007a) following forest clearance carried out to facilitate military 241 operations before World War 1 (cf.…”

The magnesium isotope record of cave carbonate archives

“…control speleothem geochemistry include ambient environmental parameters (Baker and Genty, 1998;Spötl et al, 2005;Baldini et al, 2008), carbonate mineralogy (Frisia et al, 2000(Frisia et al, , 2002Frisia and Borsato, 2010;Wassenburg et al, 2012), as well as processes and conditions in the aquifer (Tooth and Fairchild, 2003;Miorandi et al, 2010;Sherwin and Baldini, 2011) and equilibrium and disequilibrium stable isotope fractionation during carbonate precipitation in the cave (White, 2004;Tremaine et al, 2011;Riechelmann et al, 2012a). Despite significant advances in field studies Asrat et al, 2008;Verheyden et al, 2008;Riechelmann et al, 2011), including experimental (Huang and Fairchild, 2001;Day and Henderson, 2011;Polag et al, 2010) and numerical (Mühlinghaus et al, 2007;Scholz et al, 2009;DePaolo, 2011;Dreybrodt and Scholz, 2011) work, several parameters that affect proxy data remain difficult to constrain.…”