The 'Little Ice Age' – only temperature?

Understanding the climate of the last few centuries, including the 'Little Ice Age', may help us better understand modern-day natural climate variability and make climate predictions. The conventional view of the climate development during the last millennium has been that it followed the simple sequence of a 'Mediaeval Warm Period', a cool 'Little Ice Age' followed by warming in the later part of the nineteenth century and during the twentieth century. This view was mainly based on evidence from western Europe and the North Atlantic region. Recent research has, however, challenged this rather simple sequence of climate development in the recent past. Data presented here indicate that the rapid glacier advance in the early eighteenth century in southern Norway was mainly due to increased winter precipitation: mild, wet winters due to prevailing 'positive North Atlantic Oscillation (NAO) weather mode' in the first half of the eighteenth century; and not only lower summer temperatures. A comparison of recent mass-balance records and 'Little Ice Age' glacier fluctuations in southern Norway and the European Alps suggests that the asynchronous 'Little Ice Age' maxima in the two regions may be attributed to multidecadal trends in the north–south dipole NAO pattern.publishedVersio

Evidence of glacier-permafrost interactions associated with hydro-geomorphological processes and landforms at Snøhetta, Dovrefjell, Norway

Glacier-permafrost interactions are investigated to understand glacial-hydrological influence along a partly glacierised valley on the NE flank of the Snøhetta massif, Dovrefjell, southern Norway. Of particular interest is how processes are controlled by a hydrological connection between landforms. Field mapping identified an ice-marginal landsystem comprising a polythermal glacier, a proglacial lake, an ice-cored moraine complex and a river-lake with perennial frost mounds. A clear interaction between glacial and periglacial processes was observed in transitional landforms, most prominently in the ice-cored moraine which constitutes a permafrost environment that is directly reworked by glaciofluvial processes. The role of this interaction in controlling seasonal, partial drainage of the proglacial lake was assessed using remote sensing-based observations of lake surface size evolution and seasonal surface subsidence. Results suggest a two-fold threshold for lake drainage: Depending on the dynamics of glacial discharge and active layer depth, the ice-cored moraine may either act as a barrier or a pathway to meltwater exiting the glacier. This demonstrates the importance of meltwater dynamics in controlling landform evolution in a glacial-periglacial landscape. To further assess the importance of surface and subsurface hydrology in linking glacial and periglacial domains, water stable oxygen isotope ratios across the study area were studied to map the flow of meltwater from glacier to permafrost. Results include a model of the surface and subsurface hydrology in the catchment and promote a conceptual understanding of water as a thermal, hydraulic and mechanical agent of transient glacier-permafrost interaction operating at heterogeneous timescales.publishedVersio

Reconstruction of former glacier equilibrium-line altitudes based on proglacial sites: an evaluation of approaches and selection of sites

Various approaches are used to record variations in glacier activity and equilibrium-line altitudes (ELAs) based on proglacial sites (lacustrine and terrestrial). These approaches are based on a conceptual model of glacier-meltwater induced sedimentation in which the minerogenic (nonorganic) component of the sediments is related to the occurrence of a glacier in the catchment. The principal coupling to former glacier activity and ELAs is common for these approaches. However, different methods and techniques may complement each other, and both possibilities and limitations are demonstrated. Site selection for reconstructing variations in glacier activity/ELAs is evaluated and critical factors are discussed. Rerouting of glacier meltwater streams across local watersheds in combination with proglacial sites gives a distinct on/off signal for former glacier activity/ELAs. Together with representative lateral moraines of known age, local watersheds are important for calibrating reconstructed glacier activity/ELAs based on a chain of proglacial lakes. Based on the ‘modern analogue principle’, various proxies can record whenever glaciers existed in a catchment. In a chain of proglacial lakes with different sensitivity to record variations in glacier activity/ELAs, these proxies can be calibrated against independent records. For one-site approaches, however, variations in glacier activity/ELAs depend on the interpretation and sensitivity of the proxies used

Age, origin and palaeoclimatic implications of peri- and paraglacial boulder-dominated landforms in Rondane, South Norway

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.publishedVersio

A preboreal elk (Alces alces L., 1758) antler from south-eastern Norway

In 1895 a shed elk antler was found in a mire on a farm near Fluberg, in Søndre Land municipality in south-eastern Norway. The antler was first radiocarbon dated in 2008 and yielded the age 9,100 ± 50 BP (8,340 – 8,250 BC), which is the oldest dated elk remain from Norway. Elk (Alces alces L., 1758) are a pioneer colonising species; they were already established south of the ice front in Denmark and southern Sweden in the Late Glacial period. This antler shows that the species had arrived in south-eastern Norway in the late Preboreal period. This could tie in with the earliest arrival of elk once the colonizing routes from southern Sweden were established 9,300-9,200 BP. The antler is clearly of the palmate morph, and strongly resembles elk antlers found in Denmark and southern Sweden from the Late Glacial and Early Holocene periods. This find also reveals that the vegetation at the end of the Preboreal period suited large herbivores such as elkpublishedVersio

Holocene palaeoclimate reconstructions at Vanndalsvatnet, western Norway, with particular reference to the 8200 cal. yr BP event

Analyses of organic content, magnetic susceptibility, grain size and pollen in sediments from the proglacial lake Vanndalsvatnet in western Norway provide a high-resolution terrestrial record and pollenbased quantitative estimates of mean July and January temperatures and annual precipitation across the /8200 cal. yr BP event. Glaciers in the catchment melted away at approximately 8600 cal. yr BP. Immediately following deglaciation, a series of thin minerogenic layers indicate several abrupt, short-lived glacial episodes peaking at /8550, 8450, 8350, 8250, 8200, 7900, 7300 and 7150 cal. yr BP. A single, mid- Holocene glacial episode occurred at 4900 4800 cal. yr BP. Between 2000 and 1400 cal. yr BP, six shortlived glacial episodes occurred /2000, 1900, 1800, 1700, 1600, and 1500 cal. yr BP. The part of Spørteggbreen that drains to Vanndalsvatnet has existed continuously since /1400 cal. yr BP. Just prior to a first loss-on-ignition minimum reflecting a glacial episode centred at 8200 cal. yr BP, pollen-inferred July temperatures were relatively high, January temperatures were low, and annual precipitation was relatively low. During the period 8200 7900 cal. yr BP, July temperatures showed a falling trend. Both January temperature and annual precipitation, however, were relatively high. After 7900 cal. yr BP, July temperatures increased, but both January temperatures and annual precipitation were lower than in the preceding period. The pollen analytical and sedimentary data suggest that the glacial advance during the Finse event seems not to have been a response to cooler summers, but to milder winters and increasing precipitation (similar to a positive North Atlantic Oscillation weather mode)

Palaeoclimatic and regional implications of Older Dryas and Younger Dryas local glacier activity in the low-Arctic valley Finnkongdalen, Andøya, northern Norway

Continuous glacier margin and equilibrium-line altitude fluctuations of a former glacier on central Andøya, northern Norway, are reconstructed during the Lateglacial based on moraines and AMS 14C-dated sediments from the distal glacier-fed lake Ner-Finnkongdalsvatnet. The results indicate that a valley glacier occupied the entire valley during the Last Glacial Maximum (before 21 970±620 cal. a BP). The glacier remained large throughout the early Lateglacial until a significant glacier retreat took place about 14 300±330 cal. a BP. Major advances occurred during the Older Dryas (OD) and during the Younger Dryas (YD), while minor advances are suggested to have taken place during the Intra Allerød Cold Period and the Late Allerød Cooling. Additionally, three smaller glacier retreats/re-advances within the YD are suggested to have taken place, the latter being the largest. The glacier re-formations/advances during the Lateglacial are consistent with increases in temperature, and they are thus suggested to be the result of increased winter precipitation. Comparing the results with relevant glacier and sea-surface temperature records, a south–north migration of storm tracks may have occurred between 12 100–11 810±220 cal. a BP. The high temporal resolution of local glacier activity in Finnkongdalen improves our understanding of the climate forcing of the regional glacier fluctuations of the northwestern sector of the Scandinavian Ice Sheet during the Skarpnes- (OD) and Tromsø-Lyngen (YD) re-advances.publishedVersio

A theoretical approach to glacier equilibrium-line altitudes using meteorological data and glacier massbalance

Based on a close exponential relationship between mean ablation-season temperature and winter precipitation at the equilibrium-line altitude (ELA) of 10 Norwegian glaciers, three equations are derived. The first equation enables calculation of the minimum altitude of areas climatically suited for glacier formation, and is termed the altitude of instantaneous glacierization (AIG). Equation (2) is derived based on the ‘principle of terrain adaptation’, enabling quantification of the glacial buildup sensitivity (GBS) in presently non-glaciated areas. The theoretical climatic temperature-precipitation ELA (CTP-ELA) in presently non-glaciated areas is calculated in equation three by combining GBS with terrain altitude. Mass-balance records from four modern glaciers (Ålfotbreen, Nigardsbreen, Storbreen and Gråsubreen) situated in maritime to continental climate regimes in southern Norway are used to test these equations. Correlation between AIG and net balance measurements (bn) yielded correlation coefficients of r = –0.80 to r = –0.84. Calculated AIGs correspond well with observed ELAs on Ålfotbreen, Nigardsbreen and Gråsubreen, while it deviates from the observed ELA on Storbreen; the latter is probably due to leeward accumulation of wind-blown snow on this cirque glacier. Based on this approach, regional representative climatic ELAs can be calculated for non-glaciated areas with instrumental records of ablation-season temperature and winter precipitation

Theoretical equilibrium-line altitudes and glacier buildup sensitivity in southern Norway based on meteorological data in a geographical information system

Three equations derived from a close exponential glacier-climate relationship at the equilibrium-line altitude (ELA) of Norwegian glaciers have been utilized and implemented in a geographical information system (GIS). The first equation enables calculation of the minimum altitude of areas climatically suited for glacier formation at present, and is termed the altitude of instantaneous glacierization (AIG). Equation (2) is based on the ‘principle of terrain adaptation’, enabling quantification of the glacial buildup sensitivity (GBS) in an area. The third equation calculates the theoretical climatic (instrumental) temperature-precipitation ELA (CTPELA) in presently non-glaciated areas by combining GBS with terrain altitude. The presented approach is primarily intended for palaeoclimatic analyses of former glacial records, and is tested here based on a plot of 122 temperature stations and 197 precipitation stations during the climate normal period 1961–1990 which has been recalculated to sea level using empirical vertical climatic gradients. These data were interpolated in the GIS using an ‘inverse square interpolation’ routine. Subsequently, the interpolated climatic data were recalculated to the terrain surface using vertical climatic gradients and a digital elevation model (DEM) of southern Norway (resolution 5 3 5 degree minutes/c. 1 km2). The present glacier distribution in southern Norway is reproduced in great detail, and maps showing the modern GBS and CTP-ELA in non-glacierized areas of southern Norway are presented. Based on the GBS analysis, four scenarios with ELA depressions of 150 m (average ‘Little Ice Age’ conditions), 500 m (average coastal Younger Dryas conditions), 1000 m (suggested late Weichselian maximum coastal conditions) and 1500 m are shown