Airborne SnowSAR data at X- and Ku- bands over boreal forest, alpine and tundra snow cover

The European Space Agency SnowSAR instrument is a side looking, dual polarized (VV/VH), X/Ku band synthetic aperture radar (SAR), operable from a small aircraft. Between 2010 and 2013, the instrument was deployed at several sites in Northern Finland, Austrian Alps, and northern Canada. The purpose of the airborne campaigns was to measure the backscattering properties of snow-covered terrain to support the development of snow water equivalent retrieval techniques using SAR. SnowSAR was deployed in Sodankylä, Northern Finland for a single flight mission in March 2011 and twelve missions at two sites (tundra and boreal forest) in the winter of 2011–2012. Over the Austrian Alps, three flight missions were performed between November 2012 and February 2013 over three sites located in different elevation zones, representing a montane valley, Alpine tundra, and a glacier environment. In Canada, a total of two missions were flown in March and April 2013, over sites in the Trail Valley Creek watershed, Northwest Territories, representative of the tundra snow regime. This paper introduces the airborne SAR data, as well as coincident in situ information on land cover, vegetation and snow properties. To facilitate easy access to the data record the datasets described here are deposited in a permanent data repository (https://doi.pangaea.de/10.1594/PANGAEA.933255; Lemmetyinen et al., 2021). A temporary link to access the data without login information is provided for reviewers of this manuscript: https://www.pangaea.de/tok/e8c562c3c8a15ac34daa83d00c76fcb347330884.

Precise timing of MIS 7 substages from the Austrian Alps

Investigating the precise timing of regional-scale climate changes during glacial terminations and the interglacial periods that follow is key to unraveling the mechanisms behind these global climate shifts. Here, we present a high-precision time series of climate changes in the Austrian Alps that coincide with the later portion of Termination III (TIII), the entire penultimate interglacial (Marine Isotope Stage (MIS) 7), Termination IIIa (TIIIa), and the penultimate glacial inception (MIS 7–6 transition). Using state-of-the-art mass spectrometry techniques, we have constructed a uranium-series chronology with relative age uncertainties averaging 1.7 ‰ (2σ) for our study period (247 to 191 thousand years before present, ka). Results reveal the onset of warming in the Austrian Alps associated with TIII at 242.5 ± 0.2 ka and the duration of MIS 7e warming between 241.8 and 236.7 (±0.6) ka. An abrupt shift towards higher δ18O values at 216.8 ka marks the onset of regional warming associated with TIIIa. Two periods of high δ18O values (greater than −10 ‰ Vienna Pee Dee Belemnite (VPDB)) between 215.9–213.3 and 204.3–197.5 (±0.4) ka coincide with interglacial substages MIS 7c and 7a, respectively. Multiple fluorescent inclusions suggest a partial retreat of the local Alpine glacier during peak obliquity forcings at 214.3 ± 0.4 ka. Two newly collected stalagmites from Spannagel Cave (SPA146 and 183) provide high-resolution replications of the latter portion of the MIS 7a-to-6e transition. The resulting multi-stalagmite record reveals important chronological constraints on climate shifts in the Austrian Alps associated with MIS 7 while offering new insight into the timing of millennial-scale changes in the North Atlantic realm leading up to TIII and TIIIa.

Controls on the formation and size of potential landslide dams and dammed lakes in the Austrian Alps

Controls on landsliding have long been studied, but the potential for landslide-induced dam and lake formation has received less attention. Here, we model possible landslides and the formation of landslide dams and lakes in the Austrian Alps. We combine a slope criterion with a probabilistic approach to determine landslide release areas and volumes. We then simulate the progression and deposition of the landslides with a fluid dynamic model. We characterize the resulting landslide deposits with commonly used metrics, investigate their relation to glacial land-forming and tectonic units, and discuss the roles of the drainage system and valley shape. We discover that modeled landslide dams and lakes cover a wide volume range. In line with real-world inventories, we further found that lake volume increases linearly with landslide volume in the case of efficient damming – when an exceptionally large lake is dammed by a relatively small landslide deposit. The distribution and size of potential landslide dams and lakes depends strongly on local topographic relief. For a given landslide volume, lake size depends on drainage area and valley geometry. The largest lakes form in glacial troughs, while the most efficient damming occurs where landslides block a gorge downstream of a wide valley, a situation preferentially encountered at the transition between two different tectonic units. Our results also contain inefficient damming events, a damming type that exhibits different scaling of landslide and lake metrics than efficient damming and is hardly reported in inventories. We assume that such events also occur in the real world and emphasize that their documentation is needed to better understand the effects of landsliding on the drainage system.

Decennial multi-approach monitoring of thermo-hydro-mechanical processes, Kammstollen outdoor laboratory, Zugspitze (Germany)

<p>The warming of alpine bedrock permafrost in the last three decades and consequent reduction of frozen areas has been well documented. Its consequences like slope stability reduction put humans and infrastructures at high risk. 2020 in particular was the warmest year on record at 3000m a.s.l. embedded in the warmest decade.</p><p>Recently, the development of electrical resistivity tomography (ERT) as standard technique for quantitative permafrost investigation allows extended monitoring of this hazard even allowing including quantitative 4D monitoring strategies (Scandroglio et al., in review). Nevertheless thermo-hydro-mechanical dynamics of steep bedrock slopes cannot be totally explained by a single measurement technique and therefore multi-approach setups are necessary in the field to record external forcing and improve the deciphering of internal responses.</p><p>The Zugspitze Kammstollen is a 850m long tunnel located between 2660 and 2780m a.s.l., a few decameters under the mountain ridge. First ERT monitoring was conducted in 2007 (Krautblatter et al., 2010) and has been followed by more than one decade of intensive field work. This has led to the collection of a unique multi-approach data set of still unpublished data. Continuous logging of environmental parameters such as rock/air temperatures and water infiltration through joints as well as a dedicated thermal model (Schröder and Krautblatter, in review) provide important additional knowledge on bedrock internal dynamics. Summer ERT and seismic refraction tomography surveys with manual and automated joints’ displacement measurements on the ridge offer information on external controls, complemented by three weather stations and a 44m long borehole within 1km from the tunnel.</p><p>Year-round access to the area enables uninterrupted monitoring and maintenance of instruments for reliable data collection. “Precisely controlled natural conditions”, restricted access for researchers only and logistical support by Environmental Research Station Schneefernerhaus, make this tunnel particularly attractive for developing benchmark experiments. Some examples are the design of induced polarization monitoring, the analysis of tunnel spring water for isotopes investigation, and the multi-annual mass monitoring by means of relative gravimetry.</p><p>Here, we present the recently modernized layout of the outdoor laboratory with the latest monitoring results, opening a discussion on further possible approaches of this extensive multi-approach data set, aiming at understanding not only permafrost thermal evolution but also the connected thermo-hydro-mechanical processes.</p><p> </p><p> </p><p>Krautblatter, M. et al. (2010) ‘Temperature-calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps)’, Journal of Geophysical Research: Earth Surface, 115(2), pp. 1–15. doi: 10.1029/2008JF001209.</p><p>Scandroglio, R. et al. (in review) ‘4D-Quantification of alpine permafrost degradation in steep rock walls using a laboratory-calibrated ERT approach (in review)’, Near Surface Geophysics.</p><p>Schröder, T. and Krautblatter, M. (in review) ‘A high-resolution multi-phase thermo-geophysical model to verify long-term electrical resistivity tomography monitoring in alpine permafrost rock walls (Zugspitze, German/Austrian Alps) (submitted)’, Earth Surface Processes and Landforms.</p>

Glacial-driven sea-level changes in the Late Triassic

<p>Projecting future anthropogenic sea-level rise requires a comprehensive understanding of the mechanistic links between climate and short-term sea-level changes under a warming climate. Two different hypotheses, glacioeustasy and groundwater aquifer eustasy, have been proposed to explain short-term, high amplitude sea-level oscillations during past greenhouse intervals. However, the aquifer eustasy hypothesis – supported by subjective evidence of sequence stratigraphy in the Late Triassic greenhouse, has never been rigorously tested. Here we test these competing hypotheses using a recently proposed, objective approach of sedimentary noise modeling for both sea- and lake-level reconstructions for the first time. Sedimentation rate estimates and astronomical calibration of multiple paleoclimate proxies from the lacustrine Newark Basin and the marine Austrian Alps enable the construction of a highly resolved astronomical time scale for the Late Triassic. Using this timescale, sedimentary noise modeling for both lacustrine and marine successions is carried out through the Late Triassic. Lake level fluctuations reconstructed by sedimentary noise modeling and principal component analysis revealed that million-year scale lake-level variations were linked to astronomical forcing with periods of ~3.3 Myr, ~1.8 Myr, and ~1.2 Myr. Our objective water-depth reconstructions demonstrate that lake-level variations in the Newark Basin correlate with sea-level changes in the Austrian Alps, rejecting the aquifer eustasy hypothesis and supporting glacioeustasy as the sea-level driver for the Late Triassic. This study thus emphasizes the importance of high-resolution, objective reconstruction of sea- and lake-levels and supports the hypothesis that fluctuations in continental ice mass drove sea-level changes during the Late Triassic greenhouse.</p>