The Rhone Glacier was smaller than today for most of the Holocene

Understanding and interpretation of 'numbers' produced about the depositional age of an erratic boulder by cosmogenic nuclide surface-exposure dating is important in the construction of glacial chronology. We have sampled three 'Findlinge' (glacially transported boulders) located on the right-lateral margin of the Aare glacier at Möschberg, Grosshöchstetten, southeast of Bern, with the aim of shedding light on this topic. The boulders have the same depositional, but different post-depositional histories: simple exposure; exhumation; and human impact. This sampling is specially selected for this study, since the boulders showing exhumation and human impact would not have been sampled in a regular surface-exposure dating application. We measured cosmogenic 10 Be concentrations and calculated apparent exposure ages that are 13.6 ± 0.5, 18.1 ± 0.8, and 7.5 ± 0.4 ka, respectively. The exposure age of the first boulder reflects exhumation. The apparent exposure age of 18.1 ± 0.8 ka (erosion-corrected exposure age 19.0 ± 0.9 ka) from the second boulder correlates well with the end of the Alpine and global last glacial maximum. The third boulder shows evidence of quarrying as it is surrounded by a rim of excavation material, which is also reflected by the 7.5 ± 0.4 ka apparent exposure age. We modeled the variation of 10 Be concentrations with depth down into the sediment in which the first (exhumed) boulder was once buried in, and down into the third (quarried) boulder. According to our modeling, we determined that the exhumed 'Findling' was buried in sediment at a depth of around 0.5 m, and around 2 m of rock was quarried from the third 'Findling'. Our results reveal the importance of sampling for surface-exposure dating within a well defined field context, as post-depositional impacts can easily hinder exposure-dating of surfaces.

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“…10 Be and 14 C), for instance, can help to determine complex exposure histories (e.g. Goehring et al 2011).…”

Section: Implications For Surface-exposure Datingmentioning

confidence: 99%

Post-depositional impacts on ‘Findlinge’ (erratic boulders) and their implications for surface-exposure dating

Akçar

Ivy‐Ochs

Kubik³

et al. 2011

Swiss J Geosci

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“…For some of them, as the ones driven by the IPSL and MPI models, the minimum is clearly reached in the late 20th century while many glaciers were smaller during the period 1000-1150 CE in the simulations driven by CESM and GISS outputs. It is difficult to estimate from observations when glaciers were smaller than presently as the evidence may still be buried under the ice (Goehring et al, 2011;Luthi et al, 2014;Solomina et al, 2016). For the Alps, this might have occurred before 1000 CE or in the periods 1200-1280 and 1400-1550 CE, but there is currently no direct evidence that this was actually the case during the past millennium (Luthi et al, 2014).…”

Section: Simulated Glacier Changesmentioning

confidence: 99%

Testing the consistency between changes in simulated climate and Alpine glacier length over the past millennium

et al. 2018

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Abstract.It is standard to compare climate model results covering the past millennium and reconstructions based on various archives in order to test the ability of models to reproduce the observed climate variability. Up to now, glacier length fluctuations have not been used systematically in this framework even though they offer information on multidecadal to centennial variations complementary to other records. One reason is that glacier length depends on several complex factors and so cannot be directly linked to the simulated climate. However, climate model skill can be measured by comparing the glacier length computed by a glacier model driven by simulated temperature and precipitation to observed glacier length variations. This is done here using the version 1.0 of the Open Global Glacier Model (OGGM) forced by fields derived from a range of simulations performed with global climate models over the past millennium. The glacier model is applied to a set of Alpine glaciers for which observations cover at least the 20th century. The observed glacier length fluctuations are generally well within the range of the simulations driven by the various climate model results, showing a general consistency with this ensemble of simulations. Sensitivity experiments indicate that the results are much more sensitive to the simulated climate than to OGGM parameters. This confirms that the simulations of glacier length can be used to evaluate the climate model performance, in particular the simulated summer temperatures that largely control the glacier changes in our region of interest. Simulated glacier length is strongly influenced by the internal variability in the system, putting limitations on the model-data comparison for some variables like the trends over the 20th century in the Alps. Nevertheless, comparison of glacier length fluctuations on longer timescales, for instance between the 18th century and the late 20th century, appear less influenced by the natural variability and indicate clear differences in the behaviour of the various climate models.

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“…BP, respectively (Wanner et al, 2014). The hypothesis of increased rainfall and river runoff, in the Rhône watershed, during the cooler late Holocene is supported, at least for the LIA, by the observed advance of the Rhône Glacier (Goehring et al, 2011), the high level in Lake Bourget (France) (Arnaud et al, 2012), higher soil erosion in the French Pre-Alps , increased detritism in the Rhône delta plain (Bruneton et al, 2001;Provansal et al, 2003), and increased Rhône River floods (Pichard, 1995). In contrast, CR5, the so-called Migration Period Cooling, is not characterized by any increase in Leptocythere, suggesting drier conditions in the Rhône watershed compared to CR4 and CR6.…”

Section: Record Of Holocene Cold Events (Crs)mentioning

confidence: 97%

“…CR0, or the so-called 8.2 ka event (Alley et al, 1997), is indeed marked by high lake levels generated by more intense rainfall (Magny and Begeot, 2004;Magny et al, 2003). The LIA (CR6), which is well documented in the Rhône watershed, is marked by a period of significant Alpine glacier advance (Goehring et al, 2011;Ivy-Ochs et al, 2009), high lake levels (Magny et al, 2010), and an increase in Rhône River floods (Pichard, 1995;Pichard and Roucaute, 2014).…”

Section: Holocene Climate and Its Regional Characteristicsmentioning

confidence: 99%

Sedimentary archives of climate and sea-level changes during the Holocene in the Rhône prodelta (NW Mediterranean Sea)

et al. 2016

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Abstract. A 7.38 m long sediment core was collected from the eastern section of the Rhône prodelta (NW Mediterranean) at 67 m water depth. A multi-proxy study (including sedimentary facies, benthic foraminifera, ostracods, and clay mineralogy) provides a multi-decadal to century-scale record of climate and sea-level changes during the Holocene. The early Holocene is marked by alternative silt and clay layers interpreted as distal tempestites deposited in a context of rising sea level. This interval contains shallow infra-littoral benthic meiofauna (e.g., Pontocythere elongata, Elphidium spp., Quinqueloculina lata) and formed between ca. 20 and 50 m water depth. The middle Holocene (ca. 8.3 to 4.5 ka cal. BP) is characterized, at the core site, by a period of sediment starvation (accumulation rate of ca. 0.01 cm yr −1 ) resulting from the maximum landward shift of the shoreline and the Rhône outlet(s). From a sequence stratigraphic point of view, this condensed section, about 35 cm thick, can be identified on seismic profiles as a maximum flooding surface that marks the transition between delta retrogradation and delta progradation. The transition between the early Holocene deposits and the middle Holocene condensed section is marked by a gradual change in all proxy records. Following the stabilization of sea level at a global scale, the late Holocene is marked by the establishment of prodeltaic conditions at the core site, as shown by the lithofacies and by the presence of benthic meiofauna typical of the modern Rhône prodelta (e.g., Valvulineria bradyana, Cassidulina carinata, Bulimina marginata). Several periods of increased fluvial discharge are also emphasized by the presence of species commonly found in brackish and shallow-water environments (e.g., Leptocythere spp.

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The Rhone Glacier was smaller than today for most of the Holocene

Cited by 101 publications

References 25 publications

Post-depositional impacts on ‘Findlinge’ (erratic boulders) and their implications for surface-exposure dating

Post-depositional impacts on ‘Findlinge’ (erratic boulders) and their implications for surface-exposure dating

Testing the consistency between changes in simulated climate and Alpine glacier length over the past millennium

Sedimentary archives of climate and sea-level changes during the Holocene in the Rhône prodelta (NW Mediterranean Sea)

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