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Investigating Holocene glacier chronologies constitutes a valuable approach within palaeoclimatic research. Recent progress of numerical dating techniques, in particular terrestrial cosmogenic nuclide dating (TCND), has given it new momentum. Highly increased precision and improved methodological procedures of data calibration seem, however, to have gradually pushed previous rigorous geomorphological analysis of the investigated glacier forelands aside. By using a well-known key site in the Southern Alps/New Zealand it is demonstrated that even alleged benchmark studies are not immune to geomorphological uncertainties. Considerable potential misinterpretations are alerting and reinforce the demand for an unaltered ‘supremacy' of geomorphology in this context. Especially with global compilations aiming at wider palaeoclimatic conclusions critical re-assessment of glacier chronologies may occasionally seem necessary. [ABSTRACT FROM AUTHOR]

Schmidt-hammer exposure-age dating (SHD) is a numerical, calibrated-age dating technique based on the degree of weathering of rock surfaces. The Schmidt hammer measures the hardness or strength of a rock surface by means of R-values (rebound values), which are produced as the hammer impacts the surface. Age calibration is carried out with reference to at least two surfaces of known age (control surfaces). Mean R-values then yield numerical estimates of the time elapsed since exposure of rock surfaces to subaerial weathering. Under favourable circumstances with a sufficiently large number of impacts, SHD has an age resolution of 300–500 years for rock surfaces exposed during the Holocene and Late Pleistocene, and a current age range of ~25 ka. Accurate independent dating of control surfaces and careful selection of sites to reduce the effects of lithological variability are essential. R-value distributions are an important aid in the interpretation of SHD ages from active and relict, synchronous and diachronous, single and multiple-event surfaces. Important research applications have been made within the fields of Quaternary geochronology, palaeoenvironmental reconstruction, geomorphology and subaerial processes, and landscape dynamics. SHD has been found particularly useful in relation to boulder deposits and bedrock surfaces in glacial and periglacial environments. There is much untapped potential in coastal, temperate and tropical landscapes wherever rock surfaces are exposed to undisturbed rock weathering. The advantages and limitations of SHD compare favourably with the complementary exposure-age technique of terrestrial cosmogenic nuclide dating (TCND). The capability to provide a large number of exposure ages at low cost, and non-destructively in sensitive natural and artefactual settings, are special strengths of SHD. [ABSTRACT FROM AUTHOR]

Chronological studies applying Schmidt-hammer exposure-age dating (SHD) were performed on six glacier forelands in the western part of the Southern Alps, New Zealand. Although lithological heterogeneity prevented a regional age-calibration curve to be established, local age-calibration curves for La Perouse Glacier and Strauchon Glacier could be derived. They show similar linear equations and trends/slopes and enabled a preliminary assessment of the representativeness of individual 10Be terrestrial cosmogenic nuclide dating (TCND)-ages obtained from the other forelands. No mid- and early-Holocene advance periods were detected. Clusters of moraine ages date around 2800, 1850–1450, and 1100–900 years ago, followed by the ‘Little Ice Age’ commencing c. 500 years ago. There is no good agreement with earlier radiocarbon-based studies and recently published TCND-chronologies. As it will be outlined, this partly could be the result of different approaches to the palaeoclimatic interpretation of the dated samples. The results obtained from this recent study do not support an elsewhere proposed general asynchronous glacier behaviour between the mid-latitudinal Northern and Southern hemispheres. [ABSTRACT FROM AUTHOR]

Matthews, J. A. & Winkler, S. 2010: Schmidt-hammer exposure-age dating (SHD): application to early Holocene moraines and a reappraisal of the reliability of terrestrial cosmogenic-nuclide dating (TCND) at Austanbotnbreen, Jotunheimen, Norway. Boreas, 10.1111/j.1502-3885.2010.00178.x. ISSN 0300-9483. Schmidt-hammer exposure-age dating (SHD) and terrestrial cosmogenic-nuclide dating (TCND) are complementary techniques that can be used for mutual testing. SHD is low-cost but requires local control points of known age and may be affected by local geological variation and other environmental factors that influence weathering rates. TCND is vulnerable to the occurrence of anomalous boulders, other geomorphological uncertainties and the effects of snow-shielding at high altitudes. Both techniques are sensitive to post-depositional disturbances if other than solid bedrock is sampled. SHD was applied to two moraine ridges beyond the Little Ice Age limit of Austanbotnbreen in the Hurrungane massif, southern Norway. Independent regional and experimental local age-calibration curves were used to reappraise previous TCND results. Neither the two boulder surfaces nor their proximal bedrock surfaces could be differentiated statistically in terms of SHD exposure ages or their mean R-values (±95% confidence intervals), which ranged from 40.73±1.72 to 43.34±0.69. The best of the independent regional-calibration curves produced SHD exposure ages of 9413±723 and 9304±602 years, which are consistent with moraine formation early ( c. 10.2 ka) and late ( c. 9.7 ka) within the late-Preboreal Erdalen Event. The current precision of SHD, as reflected in 95% confidence intervals of ±500-900 years, enables rejection of a Finse Event ( c. 8.2 ka) age for either moraine. Results are consistent with a retracted Austanbotnbreen between the Erdalen Event and the Little Ice Age, and a modified model of Neoglaciation. [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]

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 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.