Austre Okstindbreen Research Articles

A complete record of Holocene glacier variability at Austre Okstindbreen, northern Norway: an integrated approach

Arctic glaciers are currently undergoing major changes, but accurate knowledge about how they varied during the entire Holocene is still scarce. Here we present a new complete glacier record from Austre Okstindbreen in Nordland, northern Norway. This reconstruction is based on a number of short and long cores retrieved from several downstream basins, which have been analyzed by a suite of methods including geochemical elements (XRF), rock magnetic properties, dry bulk density (DBD) and Loss-on-ignition (LOI). Lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar (GPR). Independently lichen-dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210Pb dated lake sediment chronology. This integrated approach reveals that Austre Okstindbreen is the first known glacier in Scandinavia to possibly have survived the “Holocene Thermal Optimum”. It also brackets the four largest glacier advances to c 7400–7000, 1400–1200, 900–700 and 300–150 years before AD 2000 (b2k). In contrast to most reconstructed glaciers in Scandinavia, the largest glacier advance was not associated with the “Little Ice Age”, but rather to an earlier period centred at 1300 b2k. Both the moraine chronology and the lacustrine records document this Neoglacial advance. Compared to other glacier reconstructions from the Northern Hemisphere, we identify near-synchronous glacier advances occurring roughly at 4000 b2k; 2700 b2k; 1300 b2k and during the “Little Ice Age”. These correlative advances across the Northern Hemisphere suggest that these observed centennial-scale events are a shared feature regardless of the large geographical distances separating them. Some minor discrepancies between different geographical areas may be caused by lack of precise dating, but local climatic conditions may play a role as well.

Dating stratigraphic variations of ions and oxygen isotopes in a high-altitude snowpack by comparison with daily variations of precipitation chemistry at a low-altitude site

Daily precipitation at Tustervatn (65°83′N, 13°92′E, 439 m above sea level) was analysed for ions and oxygen isotopes. Seven-day air mass trajectories provided information about the precipitation source and history. The highest Na+ loads were associated with air masses which had crossed the Norwegian Sea and the highest non-sea-salt SO42− loads with trajectories crossing Scandinavia or the United Kingdom; high SO42− loads in late April reflected decreasing snow cover. Trajectories from the Arctic basin resulted in the lowest δ18O values. During the winter, 4.8 m of snow accumulated at 1470 m above sea level on the glacier Austre Okstindbreen, 25 km north-east of Tustervatn. Mean ionic concentrations were lower than at Tustervatn, but loads were higher, as the total precipitation was three times greater. At both sites, ionic loads were closely related to ionic concentrations but not to sample water-equivalent values/precipitation amounts. Dates could be assigned to much of the snowpack on the basis of similarities between its chemical stratigraphy and temporal variations of precipitation chemistry at Tustervatn. Examination of the influence of individual storms on δ18O variations and the relationship between those variations and atmospheric circulation patterns has potential importance in relation to understanding past, present and possible future climatic conditions.

Oxygen isotopes in glacier-river water, Austre Okstindbreen, Okstindan, Norway

AbstractThere is no discernible river discharge from Austre Okstindbreen, Norway, in winter; any water formed by basal melting is likely to be stored in isolated cavities or sediments at the bed. In summer, a baseflow component of discharge, relatively depleted of 18O, is diluted by water more enriched in 18O. Glacier ice meltwater with a high δ18O value passes rapidly through channelized systems, and emerges in the glacier river within a few hours. Headward extension of the systems in late summer may tap water stored within the glacier since the previous summer’s close-down. Stored water also is released during early melt-season events, when the low-capacity drainage systems cannot accommodate inputs. The high δ18O value indicates that the probable source of the released water is glacier ice or low-altitude snowfall. Stratigraphic variations of δ18O values, resulting from changing weather conditions, characterize the accumulating winter snowpack. During the melt season, the mean δ18O value of the residual pack rises. The water leaving it, depleted of 18O, passes slowly through the glacier, smoothing out variations of supply. δ18O values of rain vary between and within events, and their effect on glacier-river δ18O values is unpredictable.

Winter-Season Climatic Signals in the Recently Deposited Snowpack on a Norwegian Alpine Glacier

Vertical variations of oxygen isotopes in the snow which accumulates during the winter at the Norwegian glacier Austre Okstindbreen are not entirely eliminated after 1-2 months of ablation in the following summer. Survival of isotopic signals closely relates to the re-freezing capacity of snow accumulated in winter when its temperature was below 0°C. The meltwater re-freezes in layers formed in winter hindered subsequent meltwater percolation in summer when snow temperature was at melting point and, therefore, varied isotopic record was reserved between these ice layers. The isotopic record in snowpack can provide an estimate of the approximate trend of the most recent winter season temperatures. The relationship between regional temperature changes and б18O values in the snowpack is affected by many natural factors, but 1989-90 (a glacier balance year) winter air temperatures were reflected in the snow which remained on the glacier Austre Okstindbreen at an altitude of 1,350 m in July 1990. There was larger amplitude of variations of б 18O values in the 4.1 m of snow above the 1989 summer surface, but variations in the underlying firn were relatively small. Meltwater percolation modifies the initial variations of б 18O values in the snowpack. At a site below the mean equilibrium line altitude on Austre Okstindbreen, increased isotopic homogenization within a ten-day period in July accompanied an increase of the mean б 18O value. Although the isotopic record at a temperate glacier is likely to be influenced by more factors than is that at polar glaciers, it can provide an estimate of the approximate trend of recent local temperature variations.

Firn-line detection on Austre Okstindbreen, Norway, with airborne multipolarization SAR

AbstractWe examine the ability of synthetic aperture radar (SAR) to detect the equilibrium line on the glacier Austre Okstindbreen, Norway, using multipolarization SAR images in C- and L-band acquired with the Electromagnetic Institute of the Technical University of Denmark’s airborne EMISAR sensor during the European Multisensor Airborne Campaign EMAC ’95. The late-summer snowline, approximating the equilibrium line, cannot be seen on the SAR images. Instead, photographs from Austre Okstind-breen show that a distinct boundary visible on the C-band SAR images corresponds to the firn line created by old snow from many previous years. This is better seen on the cross-polarized SAR images (HV and VH), which in general reveal more detail than the HH- and VV-polarized images. We model the stratigraphy from net balance and glacier velocity data to calculate the firn-line altitude (FLA). Modelled FLA and the observed boundary are separated by 50 m in elevation, but considering errors during co-registration and modelling we conclude that the observed boundary on Austre Okstindbreen is the firn line. Monitoring FLA rather than equilibrium-line altitude (ELA) for mass-balance studies with remote sensing is therefore suggested.

The isotopic record at an alpine glacier and its implications for local climatic changes and isotopic homogenization processes

AbstractStratigraphic variations of oxygen isotopes in the snow which accumulates during the winter at the Norwegian glacier Austre Okstindbreen are not entirely eliminated after 1–2 months of ablation in the following summer. The relationship between regional temperature changes and δ18O values in the snowpack is affected by many natural factors, but 1989/90 winter air temperatures were reflected in the snow which remained on Austre Okstindbreen at 1350 m a.s.l. in July 1990. There were many variations of δ18O values in the 4.1m of snow above the 1989 summer surface, but variations in the underlying firn were relatively small. Meltwater percolation modifies the initial variations of δ18O values in the snowpack. At a site below the mean equilibrium-line altitude on Austre Okstindbreen, increased isotopic homogenization within a 10 day period in July accompanied an increase of the mean δ18O value. Although the isotopic record at a temperate glacier is likely to be influenced by more factors than is that at polar glaciers, it can provide an estimate of the approximate trend of local temperature variations.

Relations between Winter Climate and Ionic Variations in a Seven-Meter-Deep Snowpack at Okstindan, Norway

Seven meters of snow accumulated at 1470 m above sea level on the Norwegian glacier Austre Okstindbreen during the 1994–95 winter. Fifty samples, together representing the entire snowpack, were collected in a continuous column downwards from the surface on 29 April 1995, before the onset of melting. The water-equivalent thickness of each sample was calculated from density measurements. Concentrations of Na+ and non-sea-salt (nss) SO42– in the samples were measured and the ionic loads determined. In an attempt to date some of the stratigraphic variations of ionic concentrations, use was made of precipitation data from the monitoring site Tustervatn (439 m asl), 25 km southwest of the glacier. Synoptic conditions associated with heavy precipitation, extended periods of dry weather, high Na+ loading, and high nss SO42– loading were identified. Daily values for precipitation amount, Na+ load, and nss SO42– load for the 115 d on which more than 1 mm of precipitation was recorded were recalculated as percentages of the winter totals. Comparison of data from Tustervatn and the 1470 m site indicates that about 2.5 m of the 1470 m snowpack had accumulated by the end of November 1994, 4 m by the middle of January, and 5 m by mid-February.

Relations between Winter Climate and Ionic Variations in a Seven-meter-deep Snowpack at Okstindan, Norway

Seven meters of snow accumulated at 1470 m above sea level on the Norwegian glacier Austre Okstindbreen during the 1994–95 winter. Fifty samples, together representing the entire snowpack, were collected in a continuous column downwards from the surface on 29 April 1995, before the onset of melting. The water-equivalent thickness of each sample was calculated from density measurements. Concentrations of Na+ and non-sea-salt (nss) SO42– in the samples were measured and the ionic loads determined. In an attempt to date some of the stratigraphic variations of ionic concentrations, use was made of precipitation data from the monitoring site Tustervatn (439 m asl), 25 km southwest of the glacier. Synoptic conditions associated with heavy precipitation, extended periods of dry weather, high Na+ loading, and high nss SO42– loading were identified. Daily values for precipitation amount, Na+ load, and nss SO42– load for the 115 d on which more than 1 mm of precipitation was recorded were recalculated as percentages of the winter totals. Comparison of data from Tustervatn and the 1470 m site indicates that about 2.5 m of the 1470 m snowpack had accumulated by the end of November 1994, 4 m by the middle of January, and 5 m by mid-February.

Changes of snow cover thickness measured by conventional mass balance methods and by global positioning system surveying

The most labour‐intensive and time‐consuming part of many mass balance programmes is the acquisition of snow depth data. The standard technique, which involves probing the snow cover at intervals along a series of profiles, generally by an individual on skis, may involve more than 300 discrete measurements along a total of more than 20 km of profiling at a single glacier. Kinematic surveying with a global positioning system (GPS) in differential mode provides much more information about changes of glacier surface level and snow thickness between surveys. The positions of a large number of points can be fixed in a relatively short time by GPS surveying, and the technique is usable in adverse weather conditions. With real‐time kinematic GPS surveying, it is possible to return to the same positions (longitude, latitude) during successive field programmes, and a previously followed route can be retraced precisely. GPS surveying facilitates the production of accurate glacier maps for mass balance programmes. Data obtained by snow depth probing and GPS surveying in 1995 at Austre Okstindbreen, the largest glacier of the Okstindan area, Norway (66°N), indicate that repeated GPS surveys are likely to provide a large amount of information on withinyear and between‐year changes of surface topography and are not subject to the errors in mass balance calculations which arise from probing snow depths along selected profiles. Kinematic GPS surveying of several glaciers within an area would overcome the difficulties arising when mass balance studies are confined to a single glacier within a particular area.

Changes of Ionic and Oxygen Isotopic Composition of the Snowpack at the Glacier Austre Okstindbreen, Norway, 1995

Marked vertical variations of ions and oxygen isotopes were present in the snowpack at the glacier Austre Okstindbreen during the pre-melting phase in 1995 at sites between 825 m and 1,470 m above sea level. As the first meltwater percolated from the top of the pack, ions were moved to a greater depth, but the isotopic composition remained relatively unchanged. Ions continued to move downwards through the pack during the melting phase, even when there was little surface melting and no addition of liquid precipitation. The at-a-depth correlation between ionic concentrations and isotopic ratios, strong in the pre-melting phase, weakened during melting. In August, concentrations of Na+ and Mg2+ ions in the residual pack were low and vertical variations were slight; 18O enrichment had occurred. The difference of the time at which melting of the snowpack starts at different altitudes influences the input of ions and isotopes to the underlying glacier.

Digital terrain modelling of the surface and bed topography of the glacier austre okstindbreen, okstindan, norway

Twentieth‐century changes in Norwegian glaciers have been pronounced, but the different geometries and dynamics of the glaciers have caused different responses to similar climatic changes. Close to the Arctic Circle, all the glaciers of Svartisen, the largest ice‐covered area of northern Scandinavia, have retreated since the beginning of the century. However, several of the smaller glaciers which end at relatively high altitude have experienced both periods of advance and periods of retreat since the mid‐1960s. The mass balance of Engabreen, the largest of the West Svartisen glaciers, was positive in 21 of the 27 years to 1995–96. The sizes of most of the glaciers of the Okstindan area, 60 km south‐east of Svartisen, have also decreased throughout the twentieth century, but Corneliussens Bre, a small glacier at the eastern side of the massif, has been advancing since 1970. The areas supplying some of the southern glaciers of Okstindan have been reduced as a result of changes in ice thickness at high altitude. Studies of glacier change are aided by the use of digital terrain models (DTMs). Triangular irregular network DTMs of the surface and bed topography of the largest of the Okstindan glaciers, Austre Okstindbreen, have been used in studies of mass‐balance variations and changing surface flow patterns between 1976 and 1995.

Digital Terrain Modelling of the Surface and Bed Topography of the Glacier Austre Okstindbreen, Okstindan, Norway

Digital Terrain Modelling of the Surface and Bed Topography of the Glacier Austre Okstindbreen, Okstindan, Norway

Use of the total input and output of ions to measure meltwater runoff time through a glacier’s accumulation area

Ionic analyses of snow samples collected from snow pits and cores, and samples of meltwater collected from the only river draining the Norwegian glacier Austre Okstindbreen during the 1995 summer, showed that the input/output relations of sodium and chloride were nearly identical. Sampling at the pits revealed that some 72% of the Na+ and Cl– ions which accumulated in winter drained from the snowpack in early June with the first 12% of the meltwater. Concentrations and loads of the two ions in the first meltwater draining from the glacier in late May were relatively high. There then followed a slight decrease in both the concentrations and the loads of the two ions in samples of the river water, and more-or-less steady levels were present for a long period. In late July, concentrations decreased. Loads decreased in early August, indicating that most of the winter-accumulated ions had drained from the catchment. Input and output calculations for Na+ and C1– indicate a total drainage time for the first meltwater from the uppermost part of the accumulation area of 6–7 weeks, equivalent to an average drainage velocity of 100 md–1.

Surface-velocity and strain-rate variations at the glacier Austre Okstindbreen, Okstindan, Norway, 1976–95

Long-term observations of surface velocities and strain rates at the Norwegian glacier Austre Okstindbreen revealed both temporal and spatial variations. During a period of 6 years, the amount of ice passing through a cross-section slightly below the mean equilibrium-line altitude (1250 m) was some 30% less than the amount which accumulated above the equilibrium line. The mean horizontal component of surface velocity at the centre of the cross-section was of the order of 45–50 m a−1, whilst the thinner marginal ice moved less rapidly. At an altitude of about 1230–1200 m, surface velocities generally increased as the ice entered a steep icefall. In the lower part of the icefall, mean surface velocities again were of the order of 50 m a−1. From there, a general decrease down-glacier was evident, and longitudinal compression along the curving centre line of flow was accompanied by lateral extension. The contribution of internal deformation to surface flow at the lower part of the glacier, which was less than 150 m thick, is likely to have been relatively small, and between-year variations of the horizontal component of surface flow which affected a large area probably were a response to changes of basal sliding rates, reflecting variations of mass balance and water availability.

Surface-velocity and strain-rate variations at the glacier Austre Okstindbreen, Okstindan, Norway, 1976–95

Long-term observations of surface velocities and strain rates at the Norwegian glacier Austre Okstindbreen revealed both temporal and spatial variations. During a period of 6 years, the amount of ice passing through a cross-section slightly below the mean equilibrium-line altitude (1250 m) was some 30% less than the amount which accumulated above the equilibrium line. The mean horizontal component of surface velocity at the centre of the cross-section was of the order of 45–50 m a−1, whilst the thinner marginal ice moved less rapidly. At an altitude of about 1230–1200 m, surface velocities generally increased as the ice entered a steep icefall. In the lower part of the icefall, mean surface velocities again were of the order of 50 m a−1. From there, a general decrease down-glacier was evident, and longitudinal compression along the curving centre line of flow was accompanied by lateral extension. The contribution of internal deformation to surface flow at the lower part of the glacier, which was less than 150 m thick, is likely to have been relatively small, and between-year variations of the horizontal component of surface flow which affected a large area probably were a response to changes of basal sliding rates, reflecting variations of mass balance and water availability.

Use of the total input and output of ions to measure meltwater runoff time through a glacier’s accumulation area

Ionic analyses of snow samples collected from snow pits and cores, and samples of meltwater collected from the only river draining the Norwegian glacier Austre Okstindbreen during the 1995 summer, showed that the input/output relations of sodium and chloride were nearly identical. Sampling at the pits revealed that some 72% of the Na+ and Cl– ions which accumulated in winter drained from the snowpack in early June with the first 12% of the meltwater. Concentrations and loads of the two ions in the first meltwater draining from the glacier in late May were relatively high. There then followed a slight decrease in both the concentrations and the loads of the two ions in samples of the river water, and more-or-less steady levels were present for a long period. In late July, concentrations decreased. Loads decreased in early August, indicating that most of the winter-accumulated ions had drained from the catchment. Input and output calculations for Na+ and C1– indicate a total drainage time for the first meltwater from the uppermost part of the accumulation area of 6–7 weeks, equivalent to an average drainage velocity of 100 md–1.

Monitoring glacier changes using a global positioning system in differential mode

Recent developments of global positioning systems (GPS) have provided opportunities for rapid and frequent glacier mapping. The speed and accuracy of GPS techniques make them particularly suitable for repeated glacier mapping. Using two receivers in differential mode provides very high accuracy. In July 1995, a kinematic differential GPS survey of Austre Okstindbreen, one of the glaciers in the Norwegian national programme of mass-balance studies, provided three-dimensional positions of 2228 points in less than 6.5 h. Handling the data in a geographic information system permitted construction of a triangular irregular network digital terrain model (TIN DTM), which could be compared with TIN DTMs constructed from 1981 and 1993 surveys based on aerial photogrammetry and electronic distance measurement, respectively. A TIN DTM has advantages over the more usual grid-based DTM, which incorporates many interpolated values, although interpolation also is necessary if contours are to be derived from a TIN model. The aspect and gradient of triangular facets in the 1995 DTM have been used to produce a map which has considerable potential for detailed energy-balance studies of the glacier’s accumulation area.

Monitoring glacier changes using a global positioning system in differential mode

Recent developments of global positioning systems (GPS) have provided opportunities for rapid and frequent glacier mapping. The speed and accuracy of GPS techniques make them particularly suitable for repeated glacier mapping. Using two receivers in differential mode provides very high accuracy. In July 1995, a kinematic differential GPS survey of Austre Okstindbreen, one of the glaciers in the Norwegian national programme of mass-balance studies, provided three-dimensional positions of 2228 points in less than 6.5 h. Handling the data in a geographic information system permitted construction of a triangular irregular network digital terrain model (TIN DTM), which could be compared with TIN DTMs constructed from 1981 and 1993 surveys based on aerial photogrammetry and electronic distance measurement, respectively. A TIN DTM has advantages over the more usual grid-based DTM, which incorporates many interpolated values, although interpolation also is necessary if contours are to be derived from a TIN model. The aspect and gradient of triangular facets in the 1995 DTM have been used to produce a map which has considerable potential for detailed energy-balance studies of the glacier’s accumulation area.

ISOTOPIC AND IONIC VARIATIONS IN GLACIER RIVER WATER DURING THREE CONTRASTING ABLATION SEASONS

The significance of the baseflow component of glacier river discharge in summer varies with geographical location, altitude, glacier geometry and glacier size. Baseflow is maintained by meltwater generated above the transient equilibrium line and by water released from temporary storage on, in or beneath the glacier. At the Norwegian glacier Austre Okstindbreen, where precipitation is generally high throughout the year and the summers are cool and wet, observations in three successive, but contrasting, years have shown that Na+ ion concentrations in the glacier river water are influenced strongly by the amount of snowmelt. This itself depends on the preceding winter conditions, which determine the amount of accumulation, and on the current summer's weather. The efficiency of the glacier's drainage systems depends on the general progress of summer ablation. The speed with which the systems develop influences ion provision from subglacial sources. Ca2+ ion concentrations are largely determined by subglacial conditions. Oxygen isotope variations in glacier river water reflect the relative contributions made to total discharge by snow meltwater and other sources; the composition of the snow cover, which is a function of winter temperatures, has a strong influence. Ice meltwater has low isotopic variability, but the isotopic composition of rainfall varies markedly. A simple model of mixing of englacial and subglacial waters, each of a constant composition, cannot be applied to a high-latitude glacier of the size and altitudinal range of Austre Okstindbreen.

Oxygen Isotope and Ionic Concentrations in Glacier River Water: Multi-Year Observations in the Austre Okstindbreen Basin, Norway

Austre Okstindbreen, the largest glacier of the Okstindan area, Norway, covers about 14 km2 within a drainage basin of 22.5 km2. Each year, about one third of the discharge of the glacier river results from snowmelt outside the glacier margins. Snow melting on the glacier contributes about twice as much water to the river as does glacier ice. Early in the melt season, the glacier river is supplied almost entirely by snow meltwater. Na+ ion concentrations in the snow are much higher than those of Ca2+; percolation of meltwater from the surface results in chemical changes. Water entering the body of the glacier from the melting snow cover is relatively depleted of 18O, whilst the residual snow is more enriched. As the ablation season proceeds and the transient equilibrium line rises up-glacier, an increasing amount of ice meltwater is mixed with snow meltwater, diluting the overall concentration of ions in the river. Ice meltwater is 18O-rich, and the δl8O value of glacier river water rises at times of high ice ablation. Water which percolates through the snow cover above the transient equilibrium line during the melt season may maintain river discharge in late summer. Mean concentrations of the principal cations in the river water vary between years; after winters with above-average snow accumulation, Na+ values tend to be high. Ca2+ concentrations are determined largely by subglacial conditions.