Glacier response to Holocene warmth inferred from in situ ¹⁰Be and ¹⁴C bedrock analyses in Steingletscher's forefield (central Swiss Alps)

Mid-latitude mountain glaciers are sensitive to local summer temperature changes. Chronologies of past glacier fluctuations based on the investigation of glacial landforms therefore allow for a better understanding of natural climate variability at local scale, which is relevant for the assessment of the ongoing anthropogenic climate warming. In this study, we focus on the Holocene, the current interglacial of the last 11 700 years, which remains a matter of dispute regarding its temperature evolution and underlying driving mechanisms. In particular, the nature and significance of the transition from the early to mid-Holocene and of the Holocene Thermal Maximum (HTM) are still debated. Here, we apply an emerging approach by combining in situ cosmogenic 10Be moraine and 10Be–14C bedrock dating from the same site, the forefield of Steingletscher (European Alps), and reconstruct the glacier's millennial recession and advance periods. The results suggest that, subsequent to the final deglaciation at ∼10 ka, the glacier was similar to or smaller than its 2000 CE extent for ∼7 kyr. At ∼3 ka, Steingletscher advanced to an extent slightly outside the maximum Little Ice Age (LIA) position and until the 19th century experienced sizes that were mainly confined between the LIA and 2000 CE extents. These findings agree with existing Holocene glacier chronologies and proxy records of summer temperatures in the Alps, suggesting that glaciers throughout the region were similar to or even smaller than their 2000 CE extent for most of the early and mid-Holocene. Although glaciers in the Alps are currently far from equilibrium with the accelerating anthropogenic warming, thus hindering a simple comparison of summer temperatures associated with modern and paleo-glacier sizes, our findings imply that the summer temperatures during most of the Holocene, including the HTM, were similar to those at the end of the 20th century. Further investigations are necessary to refine the magnitude of warming and the potential HTM seasonality.

Climate warming may increase the frequency of cold-adapted haplotypes in alpine plants

Modelling of climate-driven range shifts commonly treats species as ecologically homogeneous units. However, many species show intraspecific variation of climatic niches and theory predicts that such variation may lead to counterintuitive eco-evolutionary dynamics. Here, we incorporate assumed intraspecific niche variation into a dynamic range model and explore possible consequences for six high-mountain plant species of the European Alps under scenarios of twenty-first century climate warming. At the species level, the results indicate massive range loss independent of intraspecific variation. At the intraspecific level, the model predicts a decrease in the frequency of warm-adapted haplotypes in five species. The latter effect is probably driven by a combination of leading-edge colonization and priority effects within the species’ elevational range and was weakest when leading-edge expansion was constrained by mountain topography The resulting maladaptation may additionally increase the risk that alpine plants face from shrinkage of their ranges in a warming climate.

Long-term mass-balance monitoring and evolution of ice in caves through structure from motion–multi-view stereo and ground-penetrating radar techniques

This study investigates the application of a terrestrial structure from motionmulti-view stereo (SfM-MVS) approach combined with ground-penetrating radar (GPR) surveys for monitoring the surface topographic change of two permanent ice deposits in caves located in the Julian Alps (south-eastern European Alps). This method allows accurate calculation of both seasonal and annual mass balance, estimating the amount of ice inside caves. The ground-based SfM approach represents a low-cost workflow with very limited logistical problems of transportation and human resources and a fast acquisition time, all key factors in such extreme environments. Under optimal conditions, SfM-MVS allows sub-centimetric resolution results, comparable to more expensive and logistically demanding surveys such as terrestrial laser scanning (TLS). Fourteen SfM acquisitions were made between the 2017–2020 ablation seasons (i.e. July–October) while 2 GPR surveys were acquired in 2012. The obtained dense point clouds and digital terrain models (DTMs) made possible a reliable calculation of topographic changes and mass balance rates during the analysed period. The integration of SfM-MVS products with GPR surveys provided comprehensive imaging of the ice thickness and the total ice volume present in each of the caves, proving to be a reliable, low cost and multipurpose methodology ideal for long-term monitoring.

Using the Ecosystem Services Concept to Assess Transformation of Agricultural Landscapes in the European Alps

Mountain farming sustains human well-being by providing various ecosystem services (ES). In the last decades, socio-economic developments have led to worldwide changes in land-use/cover (LULC), but the related effects on ES have not been fully explored. This study aimed at assessing the impacts of the transformation of agricultural land on ES in the European Alps. We mapped 19 ES within the agriculturally used areas in the year 2000 and analyzed LULC changes by 2018. We compared eight regions with a similar development, regarding social–ecological characteristics, to outline contrasting trends. Our results indicate that the ES decreased most strongly in regions with a massive abandonment of mountain grassland, while ES in the ‘traditional agricultural region’ remained the most stable. In regions with an intensification of agriculture, together with urban sprawl, ES had the lowest values. Across all regions, a shift from ES that are typically associated with mountain farming towards forest-related ES occurred, due to forest regrowth. By relating differing trends in ES to social–ecological developments, we can discuss our findings regarding new landscapes and farming systems across the European Alps. Our quantitative and spatially explicit findings provide a valuable basis for policy development, from the regional to the international/EU level, and for adopting sustainable management strategies.

Variation in Demography and Life-History Strategies Across the Range of a Declining Mountain Bird Species

Species- and population-specific responses to their environment may depend to a large extent on the spatial variation in life-history traits and in demographic processes of local population dynamics. Yet, those parameters and their variability remain largely unknown for many cold-adapted species, which are exposed to particularly rapid rates of environmental change. Here, we compared the demographic traits and dynamics for an emblematic bird species of European mountain ecosystems, the ring ouzel (Turdus torquatus). Using integrated population models fitted in a Bayesian framework, we estimated the survival probability, productivity and immigration of two populations from the Western European Alps, in France (over 11 years) and Switzerland (over 6 years). Juvenile apparent survival was lower and immigration rate higher in the Swiss compared to the French population, with the temporal variation in population growth rate driven by different demographic processes. Yet, when compared to populations in the northwestern part of the range, in Scotland, these two Alpine populations both showed a much lower productivity and higher adult survival, indicating a slower life-history strategy. Our results suggest that demographic characteristics can substantially vary across the discontinuous range of this passerine species, essentially due to contrasted, possibly locally evolved life-history strategies. This study therefore raises the question of whether flexibility in life-history traits is widespread among boreo-alpine species and if it might provide adaptive potential for coping with current environmental change.

Holocene History of Río Tranquilo Glacier, Monte San Lorenzo (47°S), Central Patagonia

The causes underlying Holocene glacier fluctuations remain elusive, despite decades of research efforts. Cosmogenic nuclide dating has allowed systematic study and thus improved knowledge of glacier-climate dynamics during this time frame, in part by filling in geographical gaps in both hemispheres. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9,860 ± 180 and 6,730 ± 130 years. This event(s) was followed by a sequence of slightly smaller advances at 5,750 ± 220, 4,290 ± 100 (?), 3,490 ± 140, 1,440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 years ago. The Tranquilo record documents centennial to millennial-scale glacier advances throughout the Holocene, and is consistent with recent glacier chronologies from central and southern Patagonia. This pattern correlates well with that of multiple moraine-building events with slightly decreasing net extent, as is observed at other sites in the Southern Hemisphere (i.e., Patagonia, New Zealand and Antarctic Peninsula) throughout the early, middle and late Holocene. This is in stark contrast to the typical Holocene mountain glacier pattern in the Northern Hemisphere, as documented in the European Alps, Scandinavia and Canada, where small glaciers in the early-to-mid Holocene gave way to more-extensive glacier advances during the late Holocene, culminating in the Little Ice Age expansion. We posit that this past asymmetry between the Southern and Northern hemisphere glacier patterns is due to natural forcing that has been recently overwhelmed by anthropogenic greenhouse gas driven warming, which is causing interhemispherically synchronized glacier retreat unprecedented during the Holocene.

The interaction of climate history and evolution impacts alpine biodiversity assembly differently in freshwater and on land

Quaternary climate fluctuations can affect biodiversity assembly through speciation in two non-mutually-exclusive ways: a glacial species pump, where isolation in glacial refugia accelerates allopatric speciation, and adaptive radiation during ice-free periods. Here we detected biogeographic and genetic signatures associated with both mechanisms in the generation of the European Alps biodiversity. Age distributions of endemic and widespread species within aquatic and terrestrial taxa (amphipods, fishes, amphibians, butterflies and flowering plants) revealed that endemic fish evolved only in lakes, are highly sympatric and mainly of Holocene age, consistent with adaptive radiation. Endemic amphipods are ancient, suggesting preglacial radiation with limited range expansion and local Pleistocene survival, perhaps facilitated by a groundwater-dwelling lifestyle. Terrestrial endemics are mostly of Pleistocene age, and are thus more consistent with the glacial species pump. The lack of evidence for Holocene adaptive radiation in the terrestrial biome may be attributable to a faster range expansion of these taxa after glacial retreats, though fewer stable environments may also have contributed to differences between terrestrial areas and lakes. The high proportion of young, endemic species make the Alps vulnerable to climate change, but the mechanisms and consequences of species loss will likely differ between biomes because of their distinct histories.