ALBERT

Description: Two lacustrine sediment cores from Oldevatnet in western Norway have been studied in order to produce a record of floods, mass-wasting events and glacier fluctuations during the last 7300 years. River floods, density currents and snow-avalanches have deposited distinct ‘event layers’ at the lake floor throughout this time interval. In this study, a novel approach has been applied to distinguish event layers from the continuous background sedimentation, using Rb/Sr-ratios from X-Ray Fluorescence data. Grain-size distribution and the sedimentological parameters ‘mean’ and ‘sorting’ were used to further infer the depositional processes behind each layer. Our data suggest a record dominated by snow-avalanches, with the largest activity occurring during the ‘Little Ice Age’ (LIA). This increase in snow-avalanche activity observed during the LIA was probably caused by a combination of generally increasing winter precipitation and the advance of local glaciers towards the steep valley sides. Several fluctuations in snow-avalanche activity are also recognized prior to the LIA. Proxies of glacial activity from the background sediments indicate a similar development as earlier palaeoclimatic reconstructions from the area. It differs from previous reconstructions, however, by suggesting a lower glacial activity in the period from 2200 to 1000 cal. yr BP.

Description: Glaciers are sensitive indicators of past climate and thus valuable sources of climate history. Unfortunately, direct determinations of glacier changes (variations in length and mass balance) did not start with increasing accuracy before the end of the nineteenth century. Therefore, historical and geomorphological evidence has to be used to reconstruct glacier variability for preceding time periods. Here we present new glacier length reconstructions for selected outlet glaciers of Jostedalsbreen and Folgefonna (two ice caps in southern Norway). A wealth of different historical sources (drawings, paintings, prints, photographs, maps, written accounts; about 400 documents) allows reconstruction of glacier length variations for the last 300 (Jostedalsbreen), and 200 years (Folgefonna), respectively. We present historical material newly collected for Briksdalsbreen, Bøyabreen, Store Supphellebreen, Bergsetbreen, Nigardsbreen, Lodalsbreen (all Jostedalsbreen), and Bondhusbrea, Buerbreen (both southern Folgefonna). At Jostedalsbreen, glaciers reached their ‘Little Ice Age’ (LIA) maximum extent around AD 1750. Nigardsbreen is best documented, where also the advance in the mid-eighteenth century can be quantified. However, the nearby Bergsetbreen shows more distinct glacier advances and retreats since the LIA maximum extent. A minor peak is documented in the 1870s for all outlet glaciers of Jostedalsbreen studied. At southern Folgefonna, the LIA maximum was attained in the late 1870s (second peak around 1890). So far, there is no direct historical evidence for the time before AD 1800.

Description: The main aim of this study is to describe consequences of climate change in the mountain region of southern Norway with respect to recently exposed finds of archaeological remains associated with reindeer hunting and trapping at and around ice patches in central southern Norway. In the early years of the twenty-first century, warm summers caused negative glacier mass balance and significant glacier retreat and melting of ice patches in central southern Norway. As a result, prehistoric remains lost and/or left by past reindeer hunters appeared at ice patches in mountain areas of southern Norway. In the warm summer and autumn of 2006 the number of artefact recoveries at ice patches increased significantly because of melting of snow and ice patches and more than 100 objects were recovered in the Oppland county alone. In 2009, detailed multidisciplinary investigations were carried out at the Juvfonne ice patch in Jotunheimen at an elevation of c . 1850 metres. A well-preserved Iron Age hunting station was discovered and in total c . 600 artefacts have been documented at the Juvfonne site alone. Most of the objects were recovered and brought to the Museum of Cultural History at the University of Oslo for conservation, exhibition and storing. Thirteen so called ‘scaring sticks’ recovered from the recently exposed foreland of Juvfonne were radiocarbon dated, yielding ages that group in two separate time intervals, ad 246–534 and ad 804–898 (±1 sigma). By putting the temporal distribution of the radiocarbon-dated artefacts into the context of late-Holocene glacier-size variations in the Jotunheimen and Jostedalsbreen regions, we conclude that the most extensive reindeer hunting and trapping associated with snow/ice patches was related to periods with prevailing warm summers when the reindeer herds gathered on high-altitude, contracted glaciers and ice patches to avoid insect plagues. The ‘freshness’ of the fragile organic finds strongly indicates that at least some of the artefacts were rapidly covered by snow and ice and that they may have been more-or-less continuously covered by snow and ice since they were first buried.

Description: Glacier length, though an indirect and delayed signal of climate conditions, can be used to determine the relationship between climate and glacier response. This study discusses glacier length change of eight outlet glaciers of Jostedalsbreen and Folgefonna (southern Norway), from the ‘Little Ice Age’ (LIA) until the present. A climate index was calculated from meteorological data from Bergen to determine the specific frontal time lags of the individual glaciers. Short and steep outlet glaciers, such as Briksdalsbreen, react rapidly to changes in climatic conditions, whereas long and gently descending glaciers, such as Nigardsbreen, need longer time to adjust to changes in temperature and/or precipitation. The time lag of Briksdalsbreen was about twice as long during the LIA as today. The correlations between North Atlantic Oscillation (NAO) and climate conditions and glacier fluctuations in Norway and the European western Alps were analysed. As the influence of the NAO on glacier fluctuations is most pronounced during winter, only the winter NAO index was considered. Fluctuations of maritime Norwegian glaciers are highly correlated with the NAO, whereas variations of more continental glaciers in the European western Alps are only partly influenced by the NAO and tend to be anti-correlated. However, the (anti-)correlation with the NAO is not constant during the record, and significantly weaker or even inversed during some periods. A comparison of the LIA glacier fluctuations in southern Norway and the European western Alps suggests that the asynchronous LIA maxima in the two regions may partly be attributed to multidecadal trends in the NAO.

Description: In the ad 1990s maritime glaciers in Scandinavia started to advance as a response to positive net mass balance in the preceding years, invoking annual advance rates in the order of ~50–60 m and a total frontal advance of 285 m (at Briksdalsbreen) in less than a decade. Records from six south Norwegian glaciers with continuous, annual front measurements are used to evaluate the magnitude, duration, climatic causes, and frontal time lags involved in this mass balance perturbation and the following frontal response of glaciers in southern Norway. A climate index based on meteorological data from Bergen unequivocally demonstrates that the main cause for the large glacier advances in Scandinavia in the 1990s was high winter precipitation linked to positive NAO index in the winters of 1988/1989, 1989/1990, 1992/1993, 1994/1995, 1997/1998, and 1999/2000. Less positive (or negative) glacier mass balance years were 1990/1991, 1993/1994, 1995/1997, and 1998/1999. Between 1996/1997 and 2009, Briksdalsbreen retreated 486 m (maximum annual retreat of 145 m in 2005/2006). The main cause of the significant glacier retreat in the early twenty-first century was a combined effect of reduced winter precipitation and higher summer temperatures. The glacier advance and following retreat phase back to the pre-advance position was completed in ~20 years, and is here termed the Briksdalsbre Event. This event has relevance for the identification and interpretation of decadal to centennial Holocene glacial events recorded in lacustrine and terrestrial sequences.

Description: Omnsbreen is a small (〈0.5 km 2 ) and degrading glacier situated at the regional lower limit of present-day permafrost distribution and glaciation. At present, the existence of Omnsbreen is mainly dependent on wind-borne snow redistributed by the prevailing westerly winter-wind, and lies in an area of marginal permafrost occurrence. During the ‘Little Ice Age’ (LIA) both the glacier and the distribution of permafrost in the area reached their maximum late-Holocene areal extents. The first occurrence of Omnsbreen is recorded in sediment cores retrieved from a proglacial lake and dated at ad 1425, and marks the onset of the local LIA. Reconstruction of the maximum LIA extent by means of geomorphic indicators revealed a size of 7.1 km 2 , a volume of more than 0.25 km 3 and a maximum glacier thickness of 110 m. Since the LIA Omnsbreen has been reduced by more than 90% in area. Omnsbreen retreated rapidly from its LIA maximum, which we suggest was determined by the shape of the glacier, filling up the valley, and hence being unable to accumulate wind-borne snow. Prominent glacier marginal landforms are absent along the maximum LIA extent of Omnsbreen. We propose that the lack of glacier marginal landforms in this case is indicative of a cold glacier margin, and that the landscape evolution in maritime and marginal permafrost regions is characterised as being closely connected with glacial activity.

Description: Glaciated passive margins display dramatic fjord coasts, but also commonly retain plateau fragments inland. It has been proposed recently that such elevated, low-relief surfaces on the Norwegian margin are products of highly efficient and extensive glacial and periglacial erosion (the glacial buzzsaw) operating at equilibrium line altitudes (ELAs). We demonstrate here that glacial erosion has acted instead to dissect plateaus in western Norway. Low-relief surfaces are not generally spatially associated with cirques, and do not correlate regionally with modern and Last Glacial Maximum ELAs. Glacier dynamics require instead that glacial erosion is selective, with low-relief surfaces representing islands of limited Pleistocene erosion. Deep glacial erosion of the coast and inner shelf has provided huge volumes of sediment (70,000 km 3 ), largely resolving apparent mismatches (65–100,000 km 3 ) between fjord and valley volumes and Pliocene–Pleistocene sediment wedges offshore. Nonetheless, as Pleistocene glacial valleys and cirques are cut into preexisting mountain relief, tectonics rather than isostatic compensation for glacial erosion have been the main driver for late Cenozoic uplift on the Norwegian passive margin.

Description: Long-term records of glacier mass changes are important for improving our understanding of glacier dynamics and for predicting the response of glaciers to future climate change. In contrast to moraine sequences that only record isolated stages of glacier status, proglacial lake sediments may record long-term continuous glacier activities. The melt of old glacier ice releases old pollen that may affect the radiocarbon ages of pollen in proglacial lake sediments. We define the offset between the calibrated pollen 14 C ages and the sediment depositional age as the "old pollen effect" (OPE). In small catchments dominated by glaciers, the OPE may record variations in glacier melt intensity and extent, even though complex processes (e.g., modern pollen flux to a glacier or a proglacial lake, glacier flow velocities) may also impact the OPE. Using the sediments of a small proglacial lake on the southern Tibetan Plateau, we found that over the past 2.5 k.y., a weakened OPE occurred during three historical cool periods that coincided with regional glacier advances defined by moraine ages. Thus, we interpret the OPE as a new indicator of glacier melt intensity and its fluctuations. Our reconstructed glacier variability agrees well with glacier fluctuations in the European Alps and the global average temperature record, suggesting that hemispheric-scale temperature variations and/or mid-latitude Westerlies may have controlled the late Holocene glacier variability in monsoonal High Asia. We also show that the 20 th century glacier melt intensity has exceeded that of two historical warm periods and is unprecedented over the past 2.5 k.y. This implies that current anthropogenic warming poses a serious threat to the survival of glaciers in monsoonal High Asia.

Description: A two-dimensional shallow ice-flow model, yielding the glacier geometry at selected time intervals, is used to simulate the development of Spørteggbreen (1) from 8000 cal. yr BP to the present, (2) from ad 2011 to 2050, and (3) extending forward in time to ad 2100 and 2200. Glacier-surface geometry, subglacial topography, mass-balance data, internal deformation, and subglacial sliding are used as input data for the model runs. To force the model from 8000 cal. yr BP to the present, a mass-balance series based on the equilibrium-line altitude (ELA) variations on Jostedalsbreen to the west of Spørteggbreen is applied. A 50% reduction of the ELA amplitude at Jostedalsbreen is used to construct a new mass-balance series, and it was found that this gives a reasonably good coherence between the modelled and the real glacier. The modelled time series for ELA and length changes indicate that the glacier melted away c. 7300 cal. yr BP and was absent for c. 1700 years. It reformed c. 5400 cal. yr BP because of a modest lowering of the ELA and continued to grow in areal extent after c. 4000 cal. yr BP, apart from a small retreat episode c. ad 500. Simulations of the extent and geometry of Spørteggbreen in the future are carried out using different climate scenarios, involving summer temperature and winter precipitation. The model simulation from ad 2011 to 2050 gives relatively minor changes for glacier-surface profiles and glacier-surface geometry, mainly because of the short duration of the model run and because the increase of 12% in winter precipitation compensates for about 25% of the temperature increase of 1.3°C. The simulations from ad 2011 to 2100, and further extended to ad 2200, show, however, significant changes in the glacier volume. This is reasonable because a summer temperature rise of 2.3°C, which is used in this simulation, must be compensated for by an increase in winter precipitation of about 70% to maintain equilibrium.

Description: The melting of perennial ice patches globally is uncovering a fragile record of alpine activity, especially hunting and the use of mountain passes. When rescued by systematic fieldwork (glacial archaeology), this evidence opens an unprecedented window on the chronology of high-elevation activity. Recent research in Jotunheimen and surrounding mountain areas of Norway has recovered over 2000 finds—many associated with reindeer hunting (e.g. arrows). We report the radiocarbon dates of 153 objects and use a kernel density estimation (KDE) method to determine the distribution of dated events from ca 4000 BCE to the present. Interpreted in light of shifting environmental, preservation and socio-economic factors, these new data show counterintuitive trends in the intensity of reindeer hunting and other high-elevation activity. Cold temperatures may sometimes have kept humans from Norway's highest elevations, as expected based on accessibility, exposure and reindeer distributions. In times of increasing demand for mountain resources, however, activity probably continued in the face of adverse or variable climatic conditions. The use of KDE modelling makes it possible to observe this patterning without the spurious effects of noise introduced by the discrete nature of the finds and the radiocarbon calibration process.