Caves containing perennial ice deposits make up a little-known, but emerging part of the cryosphere under increasing scrutiny from the scientific community. M-17, a sag-type ice cave opening at 1879 m asl in the Tolminski Migovec massif of the Julian Alps (NW Slovenia) contains a perennial underground ice deposit whose paleoclimate sensitivity is poorly understood and whose longevity under current climate change is at risk. The past mass balance of this cave is constrained using wood macro-remains embedded in ice. Accelerator mass spectrometry radiocarbon dating of 18 wood samples embedded in ice provides the largest currently available dataset for a subterranean ice deposit in the southern European Alps. The reconstructed chronostratigraphy reveals three main phases of likely positive ice balance around 900–1100 AD, 1200–1300 AD, and 1700–1800 AD, as well as a period of negative mass balance around 1300–1400 AD. The onset of cave glaciation is deemed to have occurred no later than about 900 AD, with evidence of overall positive ice mass balance during multi-decadal periods characterized by cooler-than-average summers and wetter-than-average springs. Conversely, negative mass balance is recorded during a period warmer-than-average summers and dry springs. The cave has experienced ice mass loss since its discovery in the 1980s.

This survey presents the first high-throughput characterisation of fungal distribution based on ITS2 Illumina sequencing of uncultured microbiome from a 1500 years old perennial ice deposit in Scărișoara Ice Cave, Romania. Of the total of 1 751 957 ITS2 sequences, 64% corresponded to 182 fungal operational taxonomic units, showing a low diversity, particularly in older ice strata, and a distinct temporal distribution pattern. Ascomycota was the major phylum in all ice samples, dominating the 400 and 1500 years old ice strata deposited during the cold Little Ice Age (LIA) and Dark Ages Cold Period, while Basidiomycota was mostly present in 900-years old ice formed during the Medieval Warm Period (MWP). Chytridiomycota and Mucoromycota phyla were present in recently formed and 400-years old ice, respectively. Among the 80 identified genera, Cryptococcus victoriae, commonly found in glacial habitats, was identified in all strata. A positive correlation between fungal distribution and ice conductivity, Ca, Na and Sr concentrations was observed across the ice block, with pH values trailing climate variations during LIA and MWP, respectively. Our record highlighted the presence of a complex climate and environmental-driven fungal community in perennial ice strata accumulated during the last 1500 years in Scărișoara Ice Cave.

Organic material and a few tree trunks have been recovered from the shrinking ice deposits of Velebit Mountain, Croatia. Ten radiocarbon (14C) dates, seven new measurements and three recalibrated ones, from three cave ice deposits were evaluated. The new data argue for the preservation of a ~1000-yr-old deposit in the Kugina Ice Cave and a <500-yr-old accumulation in the Ledena Pit. A 14C age suggests that the ice in the lower section of Vukušić cave ice deposit is very likely older than 3500 yr. The work is in progress to verify this suggestion. Evaluation of the temporal distribution of the calibrated ages of the 14C-dated vegetal remains allowed constraining the accumulation and ablation history of cave ice in the northern and central Velebit. Periods lacking vegetal remains in these cave ice deposits (before the 11th century and in the 15th century) tend to match with similar patterns from other cave ice deposits from the Eastern Alps and the Swiss Jura Mountains, suggesting large-scale coherence regulating European cave ice mass balance changes over the past ~1200 yr.

Measurements of the radiocarbon (14C) and tritium (3H) activity in a 5.8-m-long ice core from the Saarhalle, Dachstein-Mammoth Cave allowed a substantial revision of previous opinions concerning the age of the ice block, and provide useful experience that may be applied to future 14C dating of cave ice deposits. The stepped combustion technique results in a remarkably older radiocarbon age for the 800°C than for the 400°C fractions of the carbonaceous matter from ice layer samples. The highest tritium activity (37.2±1.2 TU) can be linked to the period of anthropogenically increased tritium activity of atmospheric precipitation at the mid-1960s, providing a well-dated radiochemical reference horizon. Compared the 3H-based extrapolated ages of two shallow samples to the expected atmospheric signal an average 14C reservoir bias of ~1500 BP was obtained for the insoluble organic fraction combusted at 400°C. The conventional 14C age measured for the 400°C fraction of the deeper samples has been corrected with the average reservoir bias. The median calibrated age of the deepest analyzed sample of the ice profile is ~1830 cal BC and a linear extrapolation to the bottom ice layer gave 2590 cal BC, making the Saarhalle ice block among the oldest dated cave ice deposits known in the Alpine domain.

Mid-latitude ice caves are assumed to be highly sensitive to climatic changes and thus represent a potentially interesting environmental archive. Establishing a precise chronology is, however, a prerequisite for the understanding of processes driving the cave-ice mass balance and thus allows a paleoenvironmental interpretation. At St. Livres ice cave (Jura Mountains, Switzerland), subfossil trees and organic material are abundant in the cave-ice deposit, therefore allowing the dating of individual ice layers. The dendrochronological analysis of 45 subfossil samples of Norway spruce (Picea abies (L.) Karst.) from the overhanging front of the ice outcrop as well as the dating of seven wood samples with 14C dating allowed for a reconstruction of the St. Livres cave-ice sequence and for the determination of periods of ice accumulation and ablation. Results suggest a maximal age of 1200 ± 50 14C yr BP for the observed ice sequence and indicate the presence of four major deposition gaps dated to the 14th, 15th, mid-19th and late 19th century, which can be related with periods of positive North Atlantic Oscillation anomalies (NAO+) over the winter half-year and/or anthropogenic cave-ice abstraction. Similarly, there is evidence that periods of cave-ice accumulation as observed between AD 1877–1900 and AD 1393–1415 would correspond with phases of negative NAO indices. Cave ice represents therefore an original climate archive for the winter half-year and is complementary to other continental proxies recording preferentially summer conditions (e.g., tree rings, varves).