Thermophilisation is the response of plants communities in mountainous areas to increasing temperatures, causing an upward migration of warm-adapted (thermophilic) species and consequently, the timberline. This greening, associated with warming, causes enhanced evapotranspiration that leads to intensification of the hydrological cycle, which is recorded by hydroclimate-sensitive archives, such as stalagmites and flowstones formed in caves. Understanding how hydroclimate manifests at high altitudes is important for predicting future water resources of many regions of Europe that rely on glaciers and snow accumulation. Using proxy data from three coeval speleothems (stalagmites and flowstone) from the Italian Alps, we reconstructed both the ecosystem and hydrological setting during the Last Interglacial (LIG); a warm period that may provide an analogue to a near-future climate scenario. Our speleothem proxy data, including calcite fabrics and the stable isotopes of calcite and fluid inclusions, indicate a +4.3 ± 1.6 °C temperature anomaly at ~2000 m a.s.l. for the peak LIG, with respect to present-day values (1961–1990). This anomaly is significantly higher than any low-altitude reconstructions for the LIG in Europe, implying elevation-dependent warming during the LIG. The enhanced warming at high altitudes must be accounted for when considering future climate adaption strategies in sensitive mountainous regions.

We report a new fluid inclusion dataset from northeastern Libyan speleothem SC-06-01, which is the largest speleothem fluid inclusion dataset for North Africa to date. The stalagmite was sampled in Susah Cave, a low-altitude coastal site, in Cyrenaica, on the northern slope of the Jebel Al-Akhdar. Speleothem fluid inclusions from the latest Marine Isotope Stage (MIS) 4 and throughout MIS 3 (∼67 to ∼30 kyr BP) confirm the hypothesis that past humid periods in this region reflect westerly rainfall advected through the Atlantic storm track. However, most of this moisture was sourced from the western Mediterranean, with little direct admixture of water evaporated from the Atlantic. Moreover, we identify a second moisture source likely associated with enhanced convective rainfall within the eastern Mediterranean. The relative importance of the western and eastern moisture sources seems to differ between the humid phases recorded in SC-06-01. During humid phases forced by precession, fluid inclusions record compositions consistent with both sources, but the 52.5–50.5 kyr interval forced by obliquity reveals only a western source. This is a key result, showing that although the amount of atmospheric moisture advections changes, the structure of the atmospheric circulation over the Mediterranean does not fundamentally change during orbital cycles. Consequently, an arid belt must have been retained between the Intertropical Convergence Zone and the midlatitude winter storm corridor during MIS 3 pluvials.

Cryogenic cave carbonates (CCCs) are a type of speleothem, typically dated with ${}^{\mathrm{230}}\mathrm{Th}/\mathrm{U}$ disequilibrium methods, that provide evidence of palaeo-permafrost conditions. In the field, CCCs occur as distinct patches of millimetre- to centimetre-sized loose crystals and crystal aggregates on the floors of cave chambers, so they lack a framework that would allow ages to be validated by stratigraphic order. Correction factors for the initial ²³⁰Th (²³⁰Th₀) are often based on the bulk-earth-derived initial ${}^{\mathrm{230}}\mathrm{Th}{/}^{\mathrm{232}}\mathrm{Th}$ activity ratio (${(}^{\mathrm{230}}\mathrm{Th}{/}^{\mathrm{232}}\mathrm{Th}{)}_{\mathrm{0}}$ ), which is a well-established approach when ²³⁰Th₀ is moderately low. For samples with elevated levels of ²³⁰Th₀, however, accuracy can be improved by constraining ${(}^{\mathrm{230}}\mathrm{Th}{/}^{\mathrm{232}}\mathrm{Th}{)}_{\mathrm{0}}$ independently. Here, we combine detailed morphological observations from three CCC patches found in Water Icicle Close Cavern in the Peak District (UK) with ${}^{\mathrm{230}}\mathrm{Th}/\mathrm{U}$ analyses. We find that individual CCC crystals show a range of morphologies that arise from non-crystallographic branching in response to the chemical evolution of the freezing solution. Results of ${}^{\mathrm{230}}\mathrm{Th}/\mathrm{U}$ dating indicate that samples with a large surface area relative to the sample volume are systematically more affected by contamination with ²³⁰Th₀. By fitting isochrons to these results, we test whether the CCCs in a patch formed during the same freezing event, and demonstrate that ${(}^{\mathrm{230}}\mathrm{Th}{/}^{\mathrm{232}}\mathrm{Th}{)}_{\mathrm{0}}$ can deviate substantially from the bulk-earth-derived value and can also vary between the different CCC patches. Where CCCs display elevated ²³⁰Th₀, isochrons are a useful tool to constrain ${(}^{\mathrm{230}}\mathrm{Th}{/}^{\mathrm{232}}\mathrm{Th}{)}_{\mathrm{0}}$ and obtain ages with improved accuracy. Detritus absorbed to the crystal surface is shown to be the most likely source of ²³⁰Th₀. Our results suggest that some previously published CCC ages may merit re-assessment, and we provide suggestions on how to approach future dating efforts.

Hydraulic redistribution (HR) of water from wet- to dry-soil zones is suggested as an important process in the resilience of forest ecosystems to drought stress in semiarid and tropical climates. Scenarios of future climate change predict an increase of severe drought conditions in temperate climate regions. This implies the need for adaptations of locally managed forest systems, such as European beech (Fagus sylvatica L.) monocultures, for instance, through the admixing of deep-rooting silver fir (Abies alba Mill.). We designed a stable-isotope-based split-root experiment under controlled conditions to test whether silver fir seedlings could perform HR and therefore reduce drought stress in neighboring beech seedlings. Our results showed that HR by silver fir does occur, but with a delayed onset of three weeks after isotopic labelling with ²H₂O (δ²H ≈ +6000‰), and at low rates. On average, 0.2% of added ²H excess could be recovered via HR. Fir roots released water under dry-soil conditions that caused some European beech seedlings to permanently wilt. On the basis of these results, we concluded that HR by silver fir does occur, but the potential for mitigating drought stress in beech is limited. Admixing silver fir into beech stands as a climate change adaptation strategy needs to be assessed in field studies with sufficient monitoring time.

The Younger Dryas stadial was characterised by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between −2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By combining ground temperatures with surface temperatures from high-resolution ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ± 2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m, which persisted for 233 ± 54 d per year. By identifying modern analogues from climate reanalysis data, we demonstrate that the inferred temperature and snow cover characteristics for the British Isles during the Younger Dryas are best explained by extreme temperature seasonality, comparable to continental parts of today's Arctic Archipelago. Such a climate for the British Isles necessitates a winter sea ice margin at approximately 45° N in the North Atlantic Ocean.