Two glaciers and one sedimentary sink: the competing role of the Aare and the Valais glaciers in filling an overdeepened trough inferred from provenance analysis

The extent and distribution of glaciers on the Swiss Plateau during the Last Glacial Maximum (LGM) can be determined from the geological record. However, similar reconstructions for the glaciations that preceded the LGM are far more difficult to be made due to the destruction of suitable sedimentary records through recurring glaciations or due to the inaccessibility of preserved records. Here, we explored Quaternary sediments that were deposited during the Marine Isotope Stage (MIS) 8 glaciation at least around 250 ka, and which were recovered in a drilling that was sunk into an overdeepened bedrock trough west of Bern (Switzerland). We analyzed the sediment bulk chemical composition of the deposits to investigate the supply of the material to the area by either the Aare Glacier, the Saane Glacier, or the Valais Glacier, and we complement this investigation with the results of heavy mineral analyses and geochemical information from detrital garnet. The potential confluence of the Valais and the Aare glaciers in the Bern area makes this location ideal for such an analysis. We determined the sediment bulk chemical signal of the various lithological units in the central Swiss Alps where the glaciers originated, which we used as endmembers for our provenance analysis. We then combined the results of this fingerprinting with the existing information on the sedimentary succession and its deposition history. This sedimentary suite is composed of two sequences, Sequence A (lower) and Sequence B (upper), both of which comprise a basal till that is overlain by lacustrine sediments. The till at the base of Sequence A was formed by the Aare Glacier. The overlying lacustrine deposits of an ice-contact lake were mainly supplied by the Aare Glacier. The basal till in Sequence B was also formed by the Aare Glacier. For the lacustrine deposits in Sequence B, the heavy mineral and garnet geochemical data indicate that the sediment was supplied by the Aare and the Saane glaciers. We use these findings for a paleogeographic reconstruction. During the time when Sequence A and the basal till in Sequence B were deposited, the Aare Glacier dominated the area. This strongly contrasts with the situation during the LGM, when the Aare Glacier was deflected by the Valais Glacier towards the northeast. The Valais Glacier was probably less extensive during MIS 8, but it was potentially presentin the area, and it could have been essential for damming a lake in which the material supplied by the Aare and the Saane glaciers accumulated. In conclusion, combining provenance with sedimentological data, we could document how sediment was supplied to the investigated overdeepened basin during the MIS 8 glacial period and how glaciers were arranged in a way that was markedly different from the LGM

New vegetation history reconstructions suggest a biostratigraphic assignment of the lowermost Rodderberg interglacial (Germany) to MIS 11

Along with the ongoing climate crisis, research efforts increasingly focus on Pleistocene environmental archives. Interglacial periods are of special interest, as they offer crucial information about natural interactions (i.e. not influenced by human activities) between climate and ecosystems within a climatic setting comparable to the Holocene and/or climate change projections. The sedimentary infill of the Rodderberg crater, 10 km south of the city of Bonn (Germany), records several glacial-interglacial cycles in superposition, which makes it a rare and promising environmental archive. One of the most challenging targets is to establish a robust chronological framework for the Rodderberg sediment sequence. In the present study we reconstruct the vegetation history of the basal and most prominent interglacial sequence, the lowermost Rodderberg interglacial (LRI), and apply the principles of pollen biostratigraphy to estimate the depositional age. At the base of the sequence steppe tundra conditions prevailed during the cryocratic phase before the onset of the interglacial. Rising temperatures caused afforestation of the landscape with boreal forests during the protocratic phase, which subsequently were replaced by temperate forests in the mesocratic phase. The sequence continues under unstable vegetation conditions characterized by temperate forests dominated by Carpinus and Abies during the oligocratic phase. During the terminal part of the LRI, the telocratic phase, boreal to nemoboreal forests covered the landscape. Due to climatic deterioration these forests collapsed and a steppe tundra evolved again (cryocratic phase). This climate-driven glacial-interglacial cycle is followed by an interstadial with rather closed nemoboreal forest vegetation. Based on the occurrences of characteristic taxa as well as the vegetation assemblages and succession, we refrain from correlating the LRI with any of the warm stages between c. 240 and 180 ka BP, i.e. roughly corresponding to MIS 7. A correlation with the Holsteinian, which was previously physically dated to c. 340e325 ka BP, cannot unambiguously be excluded, however, the absence of Pterocarya during the LRI argues against it. Instead, the LRI has striking similarities with the Kärlich interglacial, which has been previously physically dated to c. 400 ka BP, making it chronologically equivalent to MIS 11

From glacial erosion to basin overfill: a 240 m-thick overdeepening–fill sequence in Bern, Switzerland

We drilled a 210 m-thick succession of Quaternary sediments and extended it 30 m upsection with information that we collected from an adjacent outcrop. In the 240 m-thick succession we identified 12 different lithofacies, grouped them into five facies assemblages, and distinguished two major sedimentary sequences. A sharp contact at 103 m depth cuts off cross-beds in sequence A and separates them from the overlying horizontal beds in sequence B. Although the lowermost facies assemblage of each sequence includes a till deposited during a period of ice cover, the two tills differ from each other. In particular, the till at the base of sequence A is dominated by large clasts derived from the underlying Molasse bedrock, whereas the till at the base of sequence B has no such Molasse components. Furthermore, the till in sequence A bears evidence of glaciotectonic deformation. Both tills are overlain by thick assemblages of subaqueous, most likely glaciolacustrine and lacustrine facies elements. The cross-bedded and steeply inclined sand, gravel, and diamictic beds of sequence A are interpreted as deposits of density currents in a subaqueous ice-contact fan system within a proglacial lake. In contrast, the lacustrine sediments in sequence B are considered to record a less energetic environment where the material was most likely deposited in a prodelta setting that gradually developed into a delta plain. Towards the top, sequence B evolves into a fluvial system recorded in sequence C, when large sediment fluxes of a possibly advancing glacier resulted in a widespread cover of the region by a thick gravel unit. Feldspar luminescence dating on two samples from a sand layer at the top of sequence B provided uncorrected ages of 250.3 ± 80.2 and 251.3 ± 59.8 ka. The combination of these ages with lithostratigraphic correlations of sedimentary sequences encountered in neighboring scientific drillings suggests that sequence B was deposited between Marine Isotope Stage 8 (MIS 8; 300–243 ka) and MIS 7 (243–191 ka). This depositional age marks the end of one stage of overdeepening–fill in the perialpine Aare Valley near Bern

Palynological investigations reveal Eemian interglacial vegetation dynamics at Spiezberg, Bernese Alps, Switzerland

Interglacial pollen records are valuable archives of past vegetation dynamics and provide important information about vegetation responses to different-than-today climates. Interglacial pollen archives pre-dating the Last Glacial Maximum (LGM) are scarce on the Swiss Plateau in contrast to the many available Late Glacial and Holocene records. This is mainly due to the rapidly changing palaeo- environmental conditions throughout the Quaternary and the low preservation potential of material suitable for palynological investigations. The Spiezberg site offers a palynological record situated most proximal to the Alps in Switzerland. Previous investigations tentatively assigned this record to the Eemian interglacial (MIS 5e). We have conducted additional pollen analytical investigations to increase the quantity of pollen information. Besides biostratigraphic interpretations, we use numerical methods such as distance analysis (distantia) and ordination techniques (PCA) to evaluate the similarities and differences between the Spiezberg record and its geographically and chronostratigraphically closest physically dated (U/Th, luminescence) analogues from the Eemian (MIS 5e) and Meikirch 3 (MIS 7a) interglacials. Our palynological investigations reveal the predominance of closed temperate forests with abundant fir (Abies) and spruce (Picea) as well as evergreen broad-leaved taxa (e.g. Hedera). The attri- bution to the Eemian interglacial relies on the observation of very rare beech (Fagus) occurrences, a phase with prominent yew (Taxus) and the unimportance of hornbeam (Carpinus), all of which are typical Eemian features on the Swiss Plateau. An Eemian age is supported by the numerical comparison with the Beerenmo€sli (MIS 5e) and Meikirch 3 (MIS 7a) reference records. Furthermore, the Picea, Taxus and Fagus dynamics observed on the Swiss Plateau during the Eemian are in excellent agreement with vegetational patterns observed elsewhere in Central Europe. Surprisingly, Carpinus was almost absent on the Swiss Plateau during the Eemian, whereas it was a major component of the forest at other European sites with a similar elevation as Spiezberg. We explain this by environmental conditions and the strong competition with Abies alba. In particular, considering the European Eemian vegetation history and the results of our reconstructions from the Swiss Plateau, we find that Abies alba was a highly competitive tree under natural warmer-than-today conditions. This finding provides further evidence that Abies alba may benefit from future climate warming

Comparisons of interglacial vegetation responses to climate variability between the Massif Central, France, and the Balkan Peninsula since 423 ka

Palynological long sequences offer a unique possibility to study the effect of pronounced climate change on vegetation dynamics over several glacial-interglacial cycles. Such long sequences are rare, especially outside of the Mediterranean realm. Additionally, they often lack robust chronologies, which are a precondition for com- parisons across records and proxies. In this study we present a refined chronology of the Velay pollen sequence (0–423 ka) from south-central France by tuning it to the recently published Lake Ohrid pollen sequence from the southern Balkans, which itself has a vegetation-independent, numerical chronology. Furthermore, we use ordi- nation techniques in combination with independent palaeo-temperature proxies and seasonality as explanatory variables for both sites. This allows us to infer climatic responses of interglacial vegetation over a broad ecological gradient, i.e., from a cool-temperate to a submediterranean site. Our analysis shows that temperature is a significant determinant for interglacial vegetation composition at both sites but explains slightly more variance at cool-temperate Velay compared to submediterranean Lake Ohrid, where precessional-driven mois- ture availability might have had a greater influence. Temperate oceanic taxa such as Abies and Taxus were most affected by comparably cool or warm interglacials at Velay, whereas at Lake Ohrid, the same accounts for Mediterranean taxa such as Quercus ilex, Q. cerris, or Ostrya/Carpinus orientalis. Responses of single taxa and vegetation groups to seasonality changes over the last five interglacials suggest that species-specific niche preferences have remained stable since 423 ka. Additionally, we suggest that unless a future climate exceeds the MIS 5e anomaly of c. +1.3 ◦C (if compared to the Holocene), evergreen Mediterranean taxa such as Quercus ilex will not expand into temperate biomes north of the Alps. However, even temperature rises below +1.3 ◦C will cause a restructuring of the current vegetation in both areas

Three-dimensional gravity modelling of a Quaternary overdeepening fill in the Bern area of Switzerland discloses two stages of glacial carving

The geometry of glacial overdeepenings on the Swiss Plateau close to Bern was inferred through a combination of gravity data with a 3D gravity modelling software. The target overdeepenings have depths between 155 and > 270 m and widths between 860 and 2400 m. The models show incisions characterized by U-shaped cross-sectional geometries and steep to over-steepened lateral flanks. Existing stratigraphic data reveals that the overdeepenings were formed and then filled during at least two glacial stages, which occurred during the Last Glacial Maximum (LGM) within the Marine Isotope Stage (MIS) 2, and possibly MIS 6 or before. The U-shaped cross-sectional geometries point towards glacial erosion as the main driver for the shaping of the overdeepenings. The combination of the geometries with stratigraphic data suggests that the MIS 6 (or older) glaciers deeply carved the bedrock, whereas the LGM ice sheet only widened the existing valleys but did not further deepen them. We relate this pattern to the different ice thicknesses, where a thicker MIS 6 ice was likely more powerful for wearing down the bedrock than a thinner LGM glacier. Gravity data in combination with forward modelling thus offers robust information on the development of a landscape formed through glaciers.ISSN:2045-232

Overdeepening or tunnel valley of the Aare glacier on the northern margin of the European Alps: Basins, riegels, and slot canyons

This work summarizes the results of an interdisciplinary project where we aimed to explore the origin of overdeepenings or tunnel valleys through a combination of a gravimetry survey, drillings, dating and a synthesis of previously published work. To this end, we focused on the Bern area, Switzerland, situated on the northern margin of the European Alps. In this region, multiple advances of piedmont glaciers during the Quaternary glaciations resulted in the carving of the main overdeepening of the Aare River valley (referred to as Aare main overdeepening). This bedrock depression is tens of km long and up to several hundreds of meters to a few kilometers wide. We found that in the Bern area, this main overdeepening is made up of two >200 m-deep troughs that are separated by a c. 5 km-long and up to 150 m-high transverse rocky ridge, interpreted as a riegel. The basins and the riegel are overlain by a >200 m- and 100 m-thick succession of Quaternary sediments, respectively. The bedrock itself is made up of a Late Oligocene to Early Miocene suite of consolidated clastic deposits, which are part of the Molasse foreland basin, whereas the Quaternary suite comprises a middle Pleistocene to Holocene succession of glacio-lacustrine gravel, sand and mud. A synthesis of published gravimetry data revealed that the upstream stoss side of the bedrock riegel is c. 50 % flatter than the downstream lee side. In addition, information from >100 deep drillings reaching depths >50 m suggests that the bedrock riegel is dissected by an anastomosing network of slot canyons. We propose that these canyons established the hydrological connection between the upstream and downstream basins during their formation. Based on published modelling results, we interpret that the riegels and canyons were formed through incision of subglacial meltwater during a glacier’s decay state, when large volumes of meltwater were released. Such a situation has repeatedly occurred since the Middle Pleistocene Transition approximately 800 ka ago, when large and erosive piedmont glaciers began to advance far into the foreland. This resulted in the deep carving of the inner-Alpine valleys, and additionally in the formation of overdeepenings on the plateau on the northern margin of the Alps

The AvrPm3-Pm3 effector-NLR interactions control both race-specific resistance and host-specificity of cereal mildews on wheat

The wheat Pm3 resistance gene against the powdery mildew pathogen occurs as an allelic series encoding functionally different immune receptors which induce resistance upon recognition of isolate-specific avirulence (AVR) effectors from the pathogen. Here, we describe the identification of five effector proteins from the mildew pathogens of wheat, rye, and the wild grass Dactylis glomerata, specifically recognized by the PM3B, PM3C and PM3D receptors. Together with the earlier identified AVRPM3A2/F2, the recognized AVRs of PM3B/C, (AVRPM3B2/C2), and PM3D (AVRPM3D3) belong to a large group of proteins with low sequence homology but predicted structural similarities. AvrPm3b2/c2 and AvrPm3d3 are conserved in all tested isolates of wheat and rye mildew, and non-host infection assays demonstrate that Pm3b, Pm3c, and Pm3d are also restricting the growth of rye mildew on wheat. Furthermore, divergent AVR homologues from non-adapted rye and Dactylis mildews are recognized by PM3B, PM3C, or PM3D, demonstrating their involvement in host specificity

Vitamin C is dispensable for oxygen sensing in vivo

Prolyl-4-hydroxylation is necessary for proper structural assembly of collagens and oxygen-dependent protein stability of hypoxia-inducible transcription factors (HIFs). In vitro function of HIF prolyl-4-hydroxylase domain (PHD) enzymes requires oxygen and 2-oxoglutarate as cosubstrates with iron(II) and vitamin C serving as cofactors. Although vitamin C deficiency is known to cause the collagen-disassembly disease scurvy, it is unclear whether cellular oxygen sensing is similarly affected. Here, we report that vitamin C–deprived Gulo−/− knockout mice show normal HIF-dependent gene expression. The systemic response of Gulo−/− animals to inspiratory hypoxia, as measured by plasma erythropoietin levels, was similar to that of animals supplemented with vitamin C. Hypoxic HIF induction was also essentially normal under serum- and vitamin C–free cell-culture conditions, suggesting that vitamin C is not required for oxygen sensing in vivo. Glutathione was found to fully substitute for vitamin C requirement of all 3 PHD isoforms in vitro. Consistently, glutathione also reduced HIF-1α protein levels, transactivation activity, and endogenous target gene expression in cells exposed to CoCl2. A Cys201Ser mutation in PHD2 increased basal hydroxylation rates and conferred resistance to oxidative damage in vitro, suggesting that this surface-accessible PHD2 cysteine residue is a target of antioxidative protection by vitamin C and glutathione

Substantial light woodland and open vegetation characterized the temperate forest biome before Homo sapiens

The extent of vegetation openness in past European landscapes is widely debated. In particular, the temperate forest biome has traditionally been defined as dense, closed-canopy forest; however, some argue that large herbivores maintained greater openness or even wood-pasture conditions. Here, we address this question for the Last Interglacial period (129,000–116,000 years ago), before Homo sapiens–linked megafauna declines and anthropogenic landscape transformation. We applied the vegetation reconstruction method REVEALS to 96 Last Interglacial pollen records. We found that light woodland and open vegetation represented, on average, more than 50% cover during this period. The degree of openness was highly variable and only partially linked to climatic factors, indicating the importance of natural disturbance regimes. Our results show that the temperate forest biome was historically heterogeneous rather than uniformly dense, which is consistent with the dependency of much of contemporary European biodiversity on open vegetation and light woodland.Peer reviewe