Mass-balance Fluctuations Research Articles

Mass-balance variability as a base for interpreting ice-core data

The spatial extrapolation of data from ice cores depends on the complexity of the glacier system where the drilling site is located. The correlation between net mass balance, b n, of a specific point and of the whole glacier is different for each point. Analysis of net mass balance of Tuyuksu glacier in the Tien Shan, central Asia, confirms that the distribution of mass balance with height is more-or-less constant from year to year except in years with extreme values b n. Two types of “similarity” are described, additive and multiplicative. The “similarity” changes gradually from additive at the peripheral parts of the Tien Shan to multiplicative in the most continental central and eastern parts. Glacier mass-balance fluctuations of the frontal ridges are connected to the oscillations of accumulation and consequently to precipitation. Where the climate is more continental the mass-balance variability depends much more on the melting conditions than on accumulation. For the spatial interpretation of ice-core drilling results, a special analysis of “similarity type” is necessary. It allows the fixing of the spatial borders of the glacier system for which the dhilling site is representative.

Mass-balance variability as a base for interpreting ice-core data

The spatial extrapolation of data from ice cores depends on the complexity of the glacier system where the drilling site is located. The correlation between net mass balance, bn, of a specific point and of the whole glacier is different for each point. Analysis of net mass balance of Tuyuksu glacier in the Tien Shan, central Asia, confirms that the distribution of mass balance with height is more-or-less constant from year to year except in years with extreme values bn. Two types of “similarity” are described, additive and multiplicative. The “similarity” changes gradually from additive at the peripheral parts of the Tien Shan to multiplicative in the most continental central and eastern parts. Glacier mass-balance fluctuations of the frontal ridges are connected to the oscillations of accumulation and consequently to precipitation. Where the climate is more continental the mass-balance variability depends much more on the melting conditions than on accumulation. For the spatial interpretation of ice-core drilling results, a special analysis of “similarity type” is necessary. It allows the fixing of the spatial borders of the glacier system for which the dhilling site is representative.

The spatial and temporal effect of cloud cover on the acquisition of high quality landsat imagery in the European Arctic sector

Cloud cover is one of several constraints on the ability of VIS / NIR sensors, such as those on board Landsat, to provide a continuing time series of data for glaciological studies in polar regions; for example, the long term observation of annual mass balance fluctuations or the short-term monitoring of surging glaciers. In order to ascertain the extent to which cloudiness prevents Landsat imagery from providing such datasets in the European Arctic, cloud cover data for all imagery acquired during April–September, 1983–1992, for 15 glaciologically significant areas (each represented by a Landsat path / row) were examined. Cloudiness values were derived from the Eurimage LEDA (onLine Earthnet Data Availability) catalogue. The results indicate that regions of the European Arctic may be classified into three groups on the basis of the frequency of availability of high quality imagery ( < 35% cloud cover). Marked seasonal differences are also evident between the groups. Comparable findings from previous cloud cover studies using ground station data illustrate that the scenes used in this study are representative of the regions in which they lie. The relative abilities of Landsat MSS / TM and ERS-1 SAR data to provide multitemporal datasets are compared; although SAR is unaffected by cloud, ERS-1 has a longer revisit interval (multidisciplinary phase) than Landsat. Only in East Greenland has Landsat generated a sufficient number of high quality scenes to provide a useful multitemporal dataset. Elsewhere in the European Arctic the prevalence of the cloud cover is such that it may prevent the effective use of VIS / NIR data for certain glaciological studies. If the required information can be derived from radar data, the utilization of SAR should prove advantageous for obtaining future multitemporal datasets in these regions of the European Arctic sector.

Hintereisferner, Austria: mass-balance reconstruction and numerical modelling of the historical length variations

AbstractIn this study, an attempt is made to simulate the historical length variations of Hintereisferner (Austria). Key elements in the model are: (1) reconstruction of the local climate (Vent); (2) multiple linear regression analysis between measured climate and mass-balance variations; (3) reconstruction of the mass balance with (1) and (2); (4) a one-dimensional numerical ice-flow model forced by the mass-balance history. Progress relative to the previous, similar studies can be summarized as two points: (1) the mass balance is reconstructed more carefully, and (2) sensitivity experiments show that uncertainties and assumptions in the flow model hardly affect the response of the glacier to climate fluctuations with a time-scale of the order of (or larger than) the response time of the glacier (around 100 year).In the regression equation, mass-balance fluctuations are determined by the temperature during the ablation season and the annual precipitation. Cloudiness has no effect. The local temperature can be reconstructed as far back as 1755 with the temperature series from Basel, but the reconstruction of precipitation is unreliable prior to 1900. Mainly due to this point, a simulation starting in 1755 failed completely. However, in a run starting in 1894, the total retreat since then (2.2 km) was reproduced within 10%.

Hintereisferner, Austria: mass-balance reconstruction and numerical modelling of the historical length variations

AbstractIn this study, an attempt is made to simulate the historical length variations of Hintereisferner (Austria). Key elements in the model are: (1) reconstruction of the local climate (Vent); (2) multiple linear regression analysis between measured climate and mass-balance variations; (3) reconstruction of the mass balance with (1) and (2); (4) a one-dimensional numerical ice-flow model forced by the mass-balance history. Progress relative to the previous, similar studies can be summarized as two points: (1) the mass balance is reconstructed more carefully, and (2) sensitivity experiments show that uncertainties and assumptions in the flow model hardly affect the response of the glacier to climate fluctuations with a time-scale of the order of (or larger than) the response time of the glacier (around 100 year).In the regression equation, mass-balance fluctuations are determined by the temperature during the ablation season and the annual precipitation. Cloudiness has no effect. The local temperature can be reconstructed as far back as 1755 with the temperature series from Basel, but the reconstruction of precipitation is unreliable prior to 1900. Mainly due to this point, a simulation starting in 1755 failed completely. However, in a run starting in 1894, the total retreat since then (2.2 km) was reproduced within 10%.

Simultaneous monitoring of mass balance fluctuations of and runoff from Tien Shan glaciers

Simultaneous monitoring of mass balance fluctuations of and runoff from Tien Shan glaciers

Simultaneous monitoring of mass balance fluctuations of and runoff from Tien Shan glaciers

Simultaneous monitoring of mass balance fluctuations of and runoff from Tien Shan glaciers

Climate Sensitivity: The Significance of the Altitude-mass-balance Feedback on Glaciers and Ice Sheets

An ice mass increasing its extent will generally also increase its mean surface elevation (anything else being unchanged). Since temperature drops rapidly with height this often implies a more positive mass balance and thus further growth. This powerful feedback loop is at least as important as the temperature-albedo feedback. In this work, we present a general study of the nature of the altitude-mass-balance feedback, with special attention for the role of differences in the bedrock geometry. One- and two-dimensional experiments on various bedrock topographies are run, using a numerical ice-sheet model based on plane shear flow of ice. Different climates are simulated by lowering or raising uniformly the mass-balance distribution over the ice sheet.These studies were first done on steady state ice sheets. They show that some geometries can largely enhance this altitude mass-balance feedback. On an island, for instance, it is possible to have two different stable steady states under the same climatic environment: no ice sheet, or a large one over the whole island. When the geometry of the island becomes more complex, for instance with two hills of unequal heights, four different equilibria can be found for the same climatic conditions: no ice sheet, one small one, two small ones or a very large one. Which will develop depends entirely on the history of the mass-balance fluctuations.

Climate Sensitivity: The Significance of the Altitude-mass-balance Feedback on Glaciers and Ice Sheets

An ice mass increasing its extent will generally also increase its mean surface elevation (anything else being unchanged). Since temperature drops rapidly with height this often implies a more positive mass balance and thus further growth. This powerful feedback loop is at least as important as the temperature-albedo feedback. In this work, we present a general study of the nature of the altitude-mass-balance feedback, with special attention for the role of differences in the bedrock geometry. One- and two-dimensional experiments on various bedrock topographies are run, using a numerical ice-sheet model based on plane shear flow of ice. Different climates are simulated by lowering or raising uniformly the mass-balance distribution over the ice sheet. These studies were first done on steady state ice sheets. They show that some geometries can largely enhance this altitude mass-balance feedback. On an island, for instance, it is possible to have two different stable steady states under the same climatic environment: no ice sheet, or a large one over the whole island. When the geometry of the island becomes more complex, for instance with two hills of unequal heights, four different equilibria can be found for the same climatic conditions: no ice sheet, one small one, two small ones or a very large one. Which will develop depends entirely on the history of the mass-balance fluctuations.

Recent glacial history and climatic change, Bergsfjord, Troms-Finnmark, Norway

Systematic documentation of climatic change using historical records of glacier fluctuations in North Norway is complicated by the strong topographic control exerted on glacier and ice-cap development in plateau regions. Ice avalanches from high plateaux maintain valley glaciers up to 600 m below in the surrounding valleys. Ice-marginal recession due to changing mass balance on the plateau ice caps has reduced ice avalanching and contributed to the subsequent decline of outlet and valley glaciers. The plateau ice caps on the Bergsfjord Peninsula occupy a critical altitudinal threshold between 900 and 1200 m which is particularly sensitive to recent climatic change. Patterns of glacier response are recorded with the aid of historical records and field mapping. The changes in ice distribution are linked to both fluctuations in mass balance and to important topographic controls on summit ice caps.

Spatial Patterns of Mass-balance Fluctuations of North American Glaciers

AbstractLong-term records (10–30 years of measurements) of North American glaciers are compared using Lliboutry’s simplified linear model. This model separates the mass balance into two additive terms, one dependent on the location of the glacier and the other on time. The time-dependent term provides a common signal for the variations of different glaciers. Principal-component analysis indicates that these similarities amount to between 65 and 70% of the total variance for glaciers up to about 500 km apart. Within this distance, similar variations of mass balance and, therefore the same yearly climatic variations, can be observed.

Spatio Temporal Distribution of the Glacial Mass Balance in the Alpine, Scandinavian and Tien Shan Areas

In order to find some regional climatic significance of glaciers mass balanse a statistical examination is made of the four longest published data series in the Alps: one located in France, two in Switzerland, and one in Austria. It is clear that much of the balance fluctuations for the different glaciers along the 500 km alpine chain can be explained by temporal correlation, to about 80% of the variance, while only 10% is explained by the geographical (spatial) distribution. This homogeneity in the mass balance fluctuations facilitates an analysis of glacier variations from the same climatic signal. The available data for Norway and Sweden indicate a regional variation similar to the alpine mechanism but with a more marked spatial dependence due clearly to the different distances inland from the coast. An other data set, 9 Russian glaciers for 16 years, gives us a very good test of the spatio temporal balance distribution. Finally two balance reconstructions are examined in order to find similarities between the Alps and Scandinavia on a century.

Variations climatiques et fluctuations glaciaires au cours du siècle écoulé

A linear regression analysis between annual mass balances of Glacier de Sarennes 1948-75 (Massif des Grandes Rousses, France) and corresponding meteorological data from Lyon-Bron station (precipitation and temperature) has been developed. The faithful regression (77 % of variance explained) is obtained in using : -total precipitation from october to may, -total precipitation of june, -july and august mean monthly maximum temperature. According to this relation, mass balances of Glacier de Sarennes have been reconstituted since 1882 and they show a 46 m average decrease of the whole surface. There is a good correlation between the annual variations of previously reconstituted values and annual variations of mass balances measured on other alpine glaciers (Mer de Glace, 1969-75, Aletsch Glacier, 1922-75). Using a series of transverse surface profiles mealace (France) since 1905, it is possible to study the correlation between annual mass balance fluctuation and glacier reactions. The results suggest a very simple model in which the climatic fluctuations produce an uniform variation of the whole glacier surface with an amplification below ice-falls. These local perturbations are then the origin of kinematic waves travelling downith four or more times the surface ice velocity.

The Wisconsin Laurentide Ice Sheet: Dispersal Centers, Problems of Rates of Retreat, and Climatic Implications

Isochrone maps on the late Wisconsin deglaciation of the Laurentide ice sheet enable estimates to be made of changes in the volume and area of the ice sheet. The average marginal recession between 12,000 and 7,000 BP is estimated as 260 m year-1 and varies little between the northwest and southern margins. The northeastern margin retreated at 20 m year-1 and the overall tendency was for the Laurentide ice sheet to migrate toward Baffin Island. Vertical mass loss required to produce marginal retreat of over 200 m year-1 indicates values between 10 and 50 m of vertical ice wastage per year. Consideration of atmospheric energy sources provides approximate ablation season inputs of 60, 14, and 6 kcal · cm-2 · year-1 for the south, northwest, and northeast margins compared to required totals of 72 to 360, 72 to 360, and 8 to 16 kcal · cm-2 · year-1, a deficiency in the energy sources by a factor of between 1 and 17.Attention is directed to the great extent of lacustrine and marine environments during deglaciation so that extensive sectors of the Laurentide ice sheet terminated in water; calving is considered the most likely additional ablation process that would explain both the high rates of marginal retreat and the lack of difference in retreat rates of margins at 72°N and 45°N.Large end moraines are commonly interpreted as the response of an ice sheet to climatic change; however, the ice sheet responds to climate through the associated mass balance fluctuations. Major end moraines within the borders of the Laurentide ice sheet are frequently preserved immediately above the local marine limit or glacial lake level, suggesting that moraines may be caused by a lag in response of the ice sheet to the reduction in frontal calving, thus resulting in a limited re-advance or stillstand. Such moraines are not associated with climatic change.