Search

Surface exposure–age dating was applied to rock surfaces associated with ice‐marginal moraines at elevations of ~1520–1780 m a.s.l. on the slopes of Galdhøpiggen and Glittertinden, the two highest mountains in Scandinavia located in the Jotunheimen mountains of central southern Norway. This is important for understanding the pattern and timing of wastage of the Scandinavian Ice Sheet at the Younger Dryas–Holocene transition. Cosmogenic exposure dating (here 10Be dating) of boulders from the moraine ridges yielded overall mean ages (corrected for glacio‐isostatic uplift, surface erosion and snow shielding) of ~11.6 ka from Galdhøpiggen and ~11.2 ka from Glittertinden. Similar 10Be ages were also obtained from additionally collected proximal and distal erratic boulders and bedrock samples. These enabled age calibration of Schmidt‐hammer R‐values and independent Schmidt‐hammer exposure‐age dating (SHD) of the moraine ridges, which yielded comparable mean SHD ages of ~10.8 and ~10.6 ka from the Galdhøpiggen and Glittertinden sites, respectively. Taking account of the age resolution and other limitations of both dating techniques, the results suggest that the two sets of moraines have approximately the same age but that neither technique can distinguish unambiguously between moraine formation in the late Younger Dryas or Early Holocene. Together with features of moraine‐ridge morphology and estimates of equilibrium‐line altitude depression of ~360–575 m (corrected for land uplift), the results imply moraine formation during short‐lived re‐advances of active glaciers, at least the lower reaches of which were warm‐based. It is concluded that the local glaciers remained active and advanced during deglaciation either very late in the Younger Dryas or very early in the Holocene, possibly in response to the Preboreal Oscillation at ~11.4 ka. The study supports the concept of a thin Younger Dryas ice sheet and places time constraints on the timing of final deglaciation in southern Norway. [ABSTRACT FROM AUTHOR]

In southern Norway, early-Holocene climatically induced glacier expansion episodes have been recognised at ~11.1, 10.5, 10.2, 9.7 and 8.2 ka, but the only convincingly dated, single- or doubleridged moraines are those associated with the regional Erdalen Event (i.e., ~10.2-9.7 ka). We applied three numerical-age dating techniques to sequences of up to five moraine ridges deposited by the former Sognefjell ice cap and by Styggedalsbreen, a large cirque glacier in the nearby Hurrungane massif. On inner and outer ridges and relict patterned ground proximal to the moraines, six 10Be and eight Schmidt hammer (SHD) surface exposure ages were obtained. Thirteen radiocarbon dates were obtained from stream-bank mire sediments proximal to the Sognefjell moraines. The basal date is similar to those from cores in an adjacent lake indicating disappearance of the Sognefjell ice-cap immediately following the Erdalen Event. Three of four SHD results, and one of three 10Be surface exposure ages from the Sognefjell moraines support this. At Styggedalsbreen, two of three 10Be surface exposure ages lie between the 8.2 ka (Finse) and Erdalen Event, though 1 s dating uncertainties only overlap with the former: the third is clearly affected by cosmogenic nuclide inheritance. SHD results also suggest the younger event, but this is attributed to lithological differences between the Schmidt-hammer calibration site and the sampled moraine boulders. Considering the chronological evidence as a whole, supported by equilibrium-line altitude (ELA) calculations for Styggedalsbreen, we conclude that the moraines were formed by up to five short but distinct fluctuations of these ice masses during the Erdalen Event. This indicates more complex decadal- to centennial-scale glacier variations and climatic perturbations within the Erdalen Event than previously recognised. The implied exceptional glaciological sensitivity to climate variability is attributed to local topographic factors causing glacial fluctuations in response to relatively small ELA changes. [ABSTRACT FROM AUTHOR]

The investigation of periglacial and related landforms in South Norway is of great interest for exploring the timing of deglaciation and to assess their geomorphological connectivity to palaeoclimatic changes during the Late Pleistocene and the Holocene. The ice margins of the Scandinavian Ice Sheet during the Last Glacial Maximum (LGM) are reasonably well established. Palaeo-ice thickness can, however, only be estimated by modelling and remains uncertain over large parts of Norway due to sparse field based evidence. Because of the significant influence of the former horizontal and vertical ice-sheet extent on sea-level rise, atmospheric and oceanic circulation patterns, erosive properties of glaciers and ice sheets, englacial thermal boundaries, and deglaciation dynamics, it is crucial to improve the understanding of the topographic properties of the LGM ice sheet. Despite recent progress, there is a lack of terrestrial evidence in the form of numerical age data from South Norway. In this study two high-mountain regions and their surroundings in west (Dalsnibba, 1476 m a.s.l.) and east (Blåhø, 1617 m a.s.l.) South Norway were studied to reconstruct palaeoclimatic conditions and deglaciation patterns. Terrestrial cosmogenic nuclide (10Be) and Schmidt-hammer exposure-age dating (SHD) have been utilized to determine the surface exposure age of glacially transported boulders as well as of boulder-dominated glacial, periglacial, and paraglacial landforms and bedrock outcrops. By developing calibration curves at both study sites for the first time it was possible to obtain landform-age estimates from Schmidt hammer R-(rebound) values. In addition, the formation and stabilization of those landforms and the formative processes have provided indications about the Late Pleistocene and Holocene climate variability and its connectivity to landform development. [ABSTRACT FROM AUTHOR]

The article discusses the preservation of periglacial and glacial landforms of South Island (Te Wai Pounamu) of New Zealand (Aotearoa). It cites on the studies using cosmogenic nuclide of moraines to recostruct palaeoclimatic conditions in the country. The article also discusses that the studies are used as basis for climatic analysis and interchemispheric correlations.

A sequence of Late Holocene moraines on the foreland of the Mueller Glacier, Southern Alps, New Zealand, forms part of a local moraine-age database used to establish a regional glacier chronology and subsequently to investigate potential intra-hemispheric and global climate forcing mechanisms. We present new sedimentological and geomorphological evidence that a set of these moraine ridges, previously considered to represent individual advances, constitutes a single moraine complex (the 'Mueller Memorial Moraine') formed by supraglacial transport of a large volume of landslide debris to the glacier terminus. Because a moraine formed in this way is not necessarily associated with an advance triggered by a climate event, we question the palaeoclimatic significance of the Mueller Memorial Moraine, as well as that of other moraines in comparable settings. Our findings suggest that the mode of formation and glacio-dynamical context of moraines whose ages contribute to existing palaeoclimate reconstructions need to be re-examined in order to assess the reliability of these reconstructions. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Boulder-dominated landforms of periglacial, paraglacial and related origin constitute a valuable, but often unexplored source of palaeoclimatic and morphodynamic information. The timing of landform development initiation and its subsequent stabilization can be linked to past climatic conditions offering the potential to reconstruct cold climatic periods. In this study, Schmidt-hammer exposure-age dating (SHD) was applied to a variety of boulder-dominated landforms (sorted stripes, blockfield, rock-slope failure, paraglacial alluvial fan) in Rondane, eastern South Norway for the first time. On the basis of old and young control points a regional SHD calibration curve was established and successively utilized for the calculation of surface exposure ages for individual landforms. The chronological investigation of development and stabilization of the respective landforms permitted an assessment of Holocene climate variability in Rondane and its impact on overall landform evolution. Our obtained SHD age estimates ranged from 11.44 ± 1.22 ka (ST-D2) to 4.09 ± 1.51 ka (AF1) showing their inactive and relict character. Most surface exposure ages for sorted stripes clustered between 9.88 ± 1.35 ka and 9.25 ± 1.21 ka, hence indicating stabilization during the late stage of the Erdalen Event or shortly thereafter. It is inferred that the blockfield formed prior to the Last Glacial Maximum, was protected by cold-based ice throughout glaciation and shortly reactivated during the Erdalen Event only to subsequently becoming inactive. The surface exposure age of a rock-slope failure (7.58 ± 0.73 ka) falls into the early phase of the Holocene Thermal Maximum (HTM, ~8.0–5.0 ka). This indicates permafrost degradation and/or increasing hydrological pressure negatively influencing slope stability. The paraglacial alluvial fan with its four subsites yielded ages between 8.73 ± 1.63 ka and 4.09 ± 1.51 ka. The old exposure ages point to fan aggradation following regional deglaciation due to paraglacial processes, whereas the younger ages can be explained by increasing precipitation during the onset neoglaciation at ~4.0 ka. Our results underline the importance of meltwater for the activation of periglacial landforms in a continental climate and indicate that the Erdalen Event and immediately following onset of the HTM had major impact on landscape evolution in Rondane. Our obtained surface exposure ages from boulder-dominated landforms in Rondane give important insights into the local palaeoclimatic variability during the Holocene. • Successful application of Schmidt-hammer exposure-age dating • First surface exposure ages of peri- and paraglacial landforms from Rondane • Stabilization of landforms during a late stage of the Erdalen Event • Lack of moisture due to continentality was compensated by meltwater supply. • Paraglacial alluvial fan development steered by debris flows throughout the Holocene [ABSTRACT FROM AUTHOR]

ABSTRACT Application of Schmidt-hammer exposure-age dating (SHD) to landforms has substantially increased in recent years. The original mechanical Schmidt hammer records R-(rebound) values. Although the newly introduced electronic Schmidt hammer (SilverSchmidt) facilitates greatly improved data processing, it measures surface hardness differently, recording Q-(velocity) values that are not a priori interconvertible with R-values. This study is the first to compare the performance of both instruments in the context of field-based exposure-age dating with a particular focus on the interconvertibility of R-values and Q-values. The study was conducted on glacially polished pyroxene-granulite gneiss, Jotunheimen, southern Norway. Results indicate that mean Q-values are consistently 8-10 units higher than mean R-values over the range of values normally encountered in the application of SHD to glacial and periglacial landforms. A convenient conversion factor of ±10 units may, therefore, be appropriate for all but the softest rock types close to the technical resolution of the instruments. The electronic Schmidt hammer should therefore be regarded as a useful complement and potential replacement for the mechanical Schmidt hammer. Conversion of published R-values data to Q-values requires, however, careful control and documentation of instrument calibration. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Lichenometric evidence and Schmidt hammer R-values are used to date Holocene moraine sequences in front of six high-altitude (> 1500 m) glaciers in Breheimen, central southern Norway. At three glacier forelands with southerly aspects (Høgsetbreen, Vestre Høybre and Østre Høybre), relatively small (≤ 4 m high) discrete boulder moraine ridges are shown to date from the 'Little Ice Age'. The remaining three glaciers (Østre Tundradalskyrkjabre, Nordre Tundradalskyrkjabre and Hestdalshøgdibreen), with northerly or easterly aspects and large, multiridged, rampart-like moraine complexes (15–30 m), thought to be ice-cored and of the 'push-deformation' type, lie above the local altitudinal limit of permafrost. Negatively skewed R-value distributions from these moraine complexes provide critical evidence for pre-'Little Ice Age' glacier expansion as they indicate the survival of long-weathered boulders on moraine surfaces where late-lying snow may reduce or prevent lichen growth. Formation of the moraine complexes appears to have begun in Preboreal times, most likely during the Erdalen Event, but much of their present character was determined by repeated Neoglacial glacier expansion, moraine deformation and ridge formation in the late Holocene, culminating in the 'Little Ice Age' readvance. [ABSTRACT FROM AUTHOR]

The high-altitudinal plateaus of Jotunheimen in central South Norway, the mountain region home of Norway's highest summits, create a unique and diverse natural environment. The specific gross morphology of Jotunheimen facilitates the occurrence of a variety of periglacial landforms ranging considerably in both dimension and age. The regional distribution of permafrost is one of the major controlling factors for the altitudinal distribution of these periglacial landforms. The largest individual features of patterned ground, undisputed the regionally most dominant periglacial landforms, are situated on terrain currently underlain by permafrost. They visually appear to be quite relict, despite the occurrence of permafrost, and the exact timing of their formation remains unknown. This example points to additional factors significantly influencing the periglacial landform assemblage, like topography, ground moisture availability, and the local deglaciation history. The lack of a regional overview regarding periglacial landforms in Jotunheimen exacerbates the need for a profound investigation of their altitudinal zonation and potential causal links to climate, permafrost, (de-)glaciation, and other factors.The compilation of a regional overview based on aerial imagery and a literature review aims, therefore, to reveal further insight into the controlling factors for and mechanisms of periglacial landform development in Jotunheimen. This shall be achieved by creating an altitudinal zonation for periglacial features and highlighting causal links between their spatial/altitudinal distribution and possible influencing factors. In an outlook to future studies this attempt may also provide more detailed information on the regional basal properties of the former Scandinavian ice sheet, the regional/local deglaciation patterns for the Jotunheimen region, and about the exact chronology of formation of the periglacial landforms studied. [ABSTRACT FROM AUTHOR]

Feedbacks between geomorphic and vegetation dynamics create spatial patterns of vegetation, soils and landforms in biogeomorphic ecosystems and determine their structure and functioning. In glacier forelands, it was shown that these biogeomorphic feedbacks link paraglacial adjustment and vegetation succession and control landscape development and stability over space and time (Eichel et al. 2016, 2018). However, the role of biogeomorphic feedbacks also depends on the environmental setting of the biogeomorphic ecosystem, e.g. on its geomorphic disturbance regime and the occurrence of ecosystem engineer species. In glacier forelands, previous research has primarily focussed on the European Alps and different environmental settings have not been comprehensively investigated yet. Here, we explore the coupling between paraglacial adjustment and vegetation succession in the Southern Alps, New Zealand. In comparison to previously investigated glacier forelands in the European Alps, the selected foreland of Mueller Glacier is characterized by an extraordinarily high geomorphic activity due to high amounts of precipitation (~4000 mm yr-1) and frequent storm events, a mostly continuous glacier wastage since the Little Ice Age maximum (1730/1735) and a mostly endemic flora. Our objectives are to (i) analyse linkages between paraglacial adjustment and vegetation succession in space and time, (ii) identify potential ecosystem engineer species, and (iii) determine the extent of biogeomorphic feedbacks and their role for landscape development and stability. To assess biogeomorphic feedbacks in space and time, we conducted a vegetation and environmental plot survey (55 plots) and created geomorphic and vegetation maps from field mapping, a UAV survey and deep learning algorithms (convolutional neural networks). Finally, we linked geomorphic and ecologic properties to the glacial chronology (Winkler, 2018). Analyses of plot data, geomorphic and vegetation maps show that (i) paraglacial adjustment and vegetation succession are mostly independent from terrain age but depend on material properties and are interlinked in a biogeomorphic succession. (ii) Once geomorphic activity decreases, stable patches are created by the prostate/low growing shrub species Muehlenbeckia axillaris and Coriaria spp., which are therefore potential ecosystem engineer species that promote slope stabilization and facilitate further vegetation succession. (iii) Biogeomorphic feedbacks mostly occur on a local (patch) scale, large areas of the foreland are either dominated by unvegetated highly active slopes or dense late-successional vegetation. Yet, our results indicate that vegetation colonization and ecosystem engineering are important controls for landscape stabilization, which can take substantially longer than in the European Alps. In conclusion, our study shows that similar biogeomorphic feedbacks link paraglacial adjustment and vegetation succession in the European and the Southern Alps, but feedback strength and extent depend on environmental setting.ReferencesEichel J, Corenblit D, Dikau R (2016) Conditions for feedbacks between geomorphic and vegetation dynamics on lateral moraine slopes: a biogeomorphic feedback window. Earth Surf Process Landforms 41:406–419. doi:10.1002/esp.3859Eichel J, Draebing D, Meyer N (2018) From active to stable: paraglacial transition of Alpine lateral moraine slopes. Land Degradation & Development 29:4158–4172. doi:10.1002/ldr.3140Winkler S (2018) Investigating Holocene mountain glaciations: a plea for the supremacy of glacial geomorphology when reconstructing glacier chronologies. Erdkunde 72:215–234. doi:10.3112/erdkunde.2018.03.04 [ABSTRACT FROM AUTHOR]

Research on mountain glaciations has a long history and in the light of current global change, they are increasingly recognised as highly important palaeoclimatic archives for the immediate and more distant geological past. One of the most important leaps forward with the investigation of mountain glaciations during the past 2 decades was substantial improvement achieved within the field of numerical age dating techniques, in particular progress of surface exposure dating using cosmogenic radionuclides (CRN). This development has definitely given the entire research field new momentum. Unfortunately, this methodological progress is in many cases not matched by the recommended necessary level of precautions regarding the interpretative steps with the reconstruction of Holocene glacier chronologies. Improved precision and accuracy with numerical dating techniques comes often with an increasing lack of attention with the geomorphological analysis of the dated landforms. With recent studies it has subsequently become more popular to outline moraines primarily based on individual CRN boulder age clusters without detailed geomorphological mapping or examination. Such an attempt has also been conducted on Holocene glacier forelands in Aoraki/Mt.Cook National Park where a substantial number of CRN boulders ages have been employed to identify and label numerous "moraines". Subsequently, arithmetic means of CRN ages for these apparent "moraines" were linked to individual glacier advances and palaeoclimatically interpreted accordingly. A sound geomorphological analysis of the studied glacier foreland does, however, reveal that this procedure is actually erroneous. Among the problems identified are (a) inclusion of hugely overprinted moraine remnants that lack proper characterisation, (b) wrong subdivision of moraine segments belonging to one defined individual moraines, and (c) mismatching of apparent CRN ages for moraine segments that morphologically need to correspond for any meaningful reconstruction of former marginal positions. A revision of this particular glacier chronology provides major implications for any subsequent palaeoclimatic interpretation as the number of reliably documented neoglacial events decrease from 9 to 5.The value of geomorphological analysis in the context of investigating mountain glaciations is, however, not primarily restricted to chronological approaches. It may also provide assistance with the conceptual context for mechanisms of deglaciation patterns or long-term landscape evolution. In the upper Waimakariri River catchment following a Late Glacial readvance dated to c. 17.5 ka ago, a lake dammed by the related moraine system and debris-covered dead ice should have existed for many centuries before it subsequently drained. That lake would naturally have influenced both the immediate deglaciation mechanism and landform evolution post-LGM. Despite introduced during the 1950s, the concept of this particular palaeo-lake has never been exposed to any detailed geomorphological analysis yet. Whereas the existence of a post-LGM palaeo-lake itself remains out of question, the proposed link to glacier retreat following a Late Glacial re-advance is unrealistic in light of a logical time sequence for individual elements of the local landform assemblage. The lake needs to be younger and postdate Deglaciation in this section of the Waimakariri River.Summarising, detailed geomorphological analysis is indispensable with any attempt to investigate mountain glaciations. [ABSTRACT FROM AUTHOR]

Growth and decay of Quaternary glaciers and ice sheets had fundamental implications for environmental changes worldwide. The chronology of the last deglaciation following the Last Glacial Maximum (LGM, 26.5-20 ka) and its ice marginal positions in Norway are generally perceived as being well constrained. The detailed vertical extent in Norway remains, however, still uncertain over large areas. The knowledge of the vertical dimension of the LGM ice sheet can provide crucial information on palaeo-environmental factors like sea-level changes, atmospheric and oceanic circulation, (de-)glaciation patterns, which are important variables for climate modelling. The interpretation of differently weathered bedrock in mountain areas affected by Quaternary glaciation can be crucial for determining ice-sheet behaviour and thickness. Based on 10Be terrestrial cosmogenic nuclide dating and Schmidt-hammer exposure age-dating (SHD) performed in eastern and western South Norway, we provide new insights in (de)glaciation patterns, landform evolution and estimate ice thickness during and following the LGM. We present the first numerical dates from the western study area showing that deglaciation started ~4 ka earlier and ice sheet downwasting lasted longer than assumed. SHD ages obtained from periglacial and related landforms (e.g. rock-slope failures, pronival ramparts) in this area point to their stabilization during the Holocene Thermal Maximum (~8-5 ka). The rock-slope failures investigated did not occur shortly after local deglaciation, it appears that they cluster around warm periods due to climate-driven factors, like decreasing permafrost depth or increasing cleft-water pressure. Exposed bedrock at the summit in the eastern study area yields a 10Be exposure age predating the Late Weichselian Maximum of 43.7 ± 1.9 ka, possibly indicating ice free areas during the LGM. Instead of the inferred ice coverage at ~15 ka, our SHD ages from blockfields suggest ice-free and severe periglacial conditions occurred earlier. Landforms above 1450 m a.s.l. (e.g. sorted stone polygons, blockstreams) do not show any form of reactivation during cold periods within the Late Glacial or the Holocene. Our results have wider implications on the glaciation history of the area. The results point to a more complex ice sheet behaviour than previously expected. Therefore, we suggest a more complex and topographically controlled configuration of the LGM ice sheet in relation to previous reconstructions. [ABSTRACT FROM AUTHOR]