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Abstract. Characterizing the temporal uncertainty in palaeoclimate records is crucial for analysing past climate change, correlating climate events between records, assessing climate periodicities, identifying potential triggers and evaluating climate model simulations. The first global compilation of speleothem isotope records by the SISAL (Speleothem Isotope Synthesis and Analysis) working group showed that age model uncertainties are not systematically reported in the published literature, and these are only available for a limited number of records (ca. 15 %, n=107/691). To improve the usefulness of the SISAL database, we have (i) improved the database's spatio-temporal coverage and (ii) created new chronologies using seven different approaches for age–depth modelling. We have applied these alternative chronologies to the records from the first version of the SISAL database (SISALv1) and to new records compiled since the release of SISALv1. This paper documents the necessary changes in the structure of the SISAL database to accommodate the inclusion of the new age models and their uncertainties as well as the expansion of the database to include new records and the quality-control measures applied. This paper also documents the age–depth model approaches used to calculate the new chronologies. The updated version of the SISAL database (SISALv2) contains isotopic data from 691 speleothem records from 294 cave sites and new age–depth models, including age–depth temporal uncertainties for 512 speleothems. SISALv2 is available at https://doi.org/10.17864/1947.256 (Comas-Bru et al., 2020a).

Chemical mobility of crystalline and amorphous SiO2 plays a fundamental role in several geochemical and biological processes, with silicate minerals being the most abundant components of the Earth’s crust. Although the oldest evidences of life on Earth are fossilized in microcrystalline silica deposits, little is known about the functional role that bacteria can exert on silica mobility at non-thermal and neutral pH conditions. Here, a microbial influence on silica mobilization event occurring in the Earth’s largest orthoquartzite cave is described. Transition from the pristine orthoquartzite to amorphous silica opaline precipitates in the form of stromatolite-like structures is documented through mineralogical, microscopic and geochemical analyses showing an increase of metals and other bioessential elements accompanied by permineralized bacterial cells and ultrastructures. Illumina sequencing of the 16S rRNA gene describes the bacterial diversity characterizing the consecutive amorphization steps to provide clues on the biogeochemical factors playing a role in the silica solubilization and precipitation processes. These results show that both quartz weathering and silica mobility are affected by chemotrophic bacterial communities, providing insights for the understanding of the silica cycle in the subsurface.

Detailed geomorphological analysis has revealed that subhorizontal gypsum caves in the Northern Apennines (Italy) cut across bedding planes. These cave levels formed during cold periods with stable river beds, and are coeval with fluvial terraces of rivers that flow perpendicular to the strike of bedding in gypsum monoclines. When rivers entrench, renewed cave formation occurs very rapidly, resulting in the formation of a lower level. River aggradation causes cave alluviation and upward dissolution (paragenesis) in passages nearest to the river beds. The U-Th dating of calcite speleothems provides a minimum age for the formation of the cave passage in which they grew, which in turn provides age control on cave levels. The ages of all speleothems coincide with warmer and wetter periods when CO 2 availability in the soils covering these gypsum areas was greater. This climate-driven speleogenetic model of epigenic gypsum caves in moderately to rapidly uplifting areas in temperate regions might be generally applicable to karst systems in different geological and climatic conditions.

Abstract:Although outcropping rarely in Italy, evaporite (gypsum and anhydrite) karst has been described in detail since the early 20 th century. Gypsum caves are now known from almost all Italian regions, but are mainly localised along the northern border of the Apennine chain (Emilia Romagna and Marche), Calabria, and Sicily, where the major outcrops occur. Recently, important caves have also been discovered in the underground gypsum mines in Piedmont. During the late 80s and 90s several multidisciplinary studies were carried out in many gypsum areas, resulting in a comprehensive overview, promoting further research in these special karst regions. More recent and detailed studies focused on the gypsum areas of Emilia-Romagna and Sicily. Sinkholes related to Permian-Triassic gypsum have been studied in Friuli Venezia Giulia. This article reviews the state of the art regarding different aspects of evaporite karst in Italy focusing on the main new results.