Bachelor’s thesis
Geography, 15 Credits
Department of Physical Geography
Mass balance and local
characteristics of three glaciers in southern Norway, between
1980 and 2018
An analysis of the mass balance and the local characteristics of Ålfotbreen, Storbreen and
Gråsubreen
Ida Eriksson Rehn
GG 242 2019
Preface
This Bachelor’s thesis is Ida Eriksson Rehn’s degree project in Geography at the Department of Physical Geography, Stockholm University. The Bachelor’s thesis comprises 15 credits (half a term of full-time studies).
Supervisor has been Per Holmlund at the Department of Physical Geography, Stockholm University. Examiner has been Margareta Hansson at the Department of Physical Geography, Stockholm University.
The author is responsible for the contents of this thesis.
Stockholm, 2 March 2020
Björn Gunnarson Vice Director of studies
Abstract
Glaciers are known as climate indicators because of their sensitivity towards climatic perturbations and fluctuations. A majority of the world’s glaciers are currently melting as a response to climatic perturbations. Glaciers in Norway display the same pattern, and the loss of mass have accelerated during the 1990s to this day. The glaciers of interest in this paper is situated in a west to east transect with the maritime Ålfotbreen in the west, to the continental Gråsubreen in the east, with the intermediate Storbreen in between. Differences in the local climate have a significant impact on the future state of glaciers. This paper aims to compare the mass balance, mass turnover and mass balance sensitivity of the three glaciers of interest, between the years 1980 and 2018, to demonstrate the importance of the local climate and characteristics for glacial existence. Mass balance data series of each glaciers’ mass balance was analysed. In addition, development trends of the mean annual summer air temperature for respective glaciers’ region were also conducted. A literature review of relevant reports and publications will be presented and analysed to complement the result of this paper. The results of this paper indicate that the characteristics of respective glacier vary along the increasing continentality of the west to east transect, with the mass balance sensitivity decreasing from west to east. The mass turnover displayed varying patterns, between the years 1980 and 2018.
ÅLF had the highest mass turnover for the period and GRÅ the smallest with STO in between.
It can be concluded, based on the result of this paper, that the fate of glaciers depends on geographical location and local characteristics. The resemblance between Storbreen and Storglaciären, and the existence of Helagsglaciären who seem to survive against the odds, strengthens the importance of local characteristics.
Key words
Mass balance, mass balance sensitivity, continental, maritime, topography, local characteristics
Glossary
AAR – Accumulation Area Ration ELA – Equilibrium Line Altitude GRÅ – Gråsubreen
M.w.e. – Metres water equivalent
NVE – The Norwegian Water Resources and Energy Directorate STO – Storbreen
WGMS – World Glacier Monitoring Service ÅLF – Ålfotbreen
Table of Contents
Abstract ... 1
Glossary ... 3
1. Introduction ... 7
1.1. Aims and objectives ... 9
2. Background ... 11
2.1. Glaciers ... 11
2.2. Mass balance ... 12
2.2.1. Mass balance measurements ... 15
2.3. Continentality ... 16
2.4. Glacier sensitivity ... 17
2.5. Previous research ... 21
3. Methodology ... 21
3.1. Study area ... 21
3.1.1. Ålfotbreen ... 21
3.1.2. Storbreen ... 23
3.1.3. Gråsubreen ... 24
3.1.4. Storglaciären ... 25
3.2. Data ... 28
3.3. Mass balance data ... 28
3.4. Temperature data ... 29
3.5. Delimitations and data quality ... 31
3.5.1. Delimitations ... 31
3.5.2. Data quality ... 31
4. Results ... 33
4.1. Mass balance characteristics of ÅLF, STO and GRÅ ... 33
4.2. Temperature development and linear trend analysis ... 37
5. Discussion ... 40
5.1. Mass balance sensitivity as a result of varying characteristics and continentality ... 40
5.2. Temperature development and future projections ... 43
5.3. Recommendations for future research ... 44
List of Figures
Figure 1. Cumulative net mass balances changes of reference glaciers displaying a uniform mass loss of the world’s
glaciers from the year 1945 to 2014 (WGMS, 2019). 7
Figure 2. Cumulative net mass balances of Norwegian glaciers and Storglaciären in Sweden, between 1945 and 2011
(Trachsel and Nesje, 2015). 8
Figure 3. Accumulation and ablation area of a glacier system (Willsman et al., 2015). 13
Figure 4. Changes in the mass balance of Storglaciären in 2011, where the mass increases with the altitude (Svenska Glaciärer, n.d.b.). The ELA is where the net balance is zero, which in this example is at approximately ~1580
m a.s.l. 14
Figure 5. Net annual mass balance map of Storglaciären indicating that the accumulation is more significant on the upper part of the glacier, whereas the lower part experiences higher ablation (Svenska Glaciärer, n.d.b.). The
white areas in the map indicate where the ELA is. 14
Figure 6. The net mass balance gradient explained by the slope angle indicating that maritime glaciers experience a significant mass turnover compared to continental glaciers. The gradient of a maritime glacier is steeper
compared to a continental glacier (Holmlund and Jansson, 2002). 17
Figure 7. The consequences of an upward shift of the ELA of an ice cap versus a valley glacier (Hock, 2010). 19
Figure 8. a) ÅLF in 2018 (photo by Hallgeir Elvehøy, n.d.), and b) Geological and topographical features of ÅLF
(Google Earth Pro, 11/07/2019). 23
Figure 9. East to west view of Storbreen with its ridge and distinct topography (photo by Liss M. Andreassen
29/07/2008). 24
Figure 10. Aerial image of Gråsubreen from 2014 (Photo by Liss M. Andreassen 14/08/2014). 25
Figure 11. a) Storglaciären situated east of the Kebnekaise massif (Photo by Per Holmlund, n.d.), and b) Mass balance histogram of Storglaciären between 1946 and 2019. Blue staples equal positive net balance and red is
negative net balance (Svenska Glaciärer, n.d.b.). 26
Figure 12. Map of the study area and Storglaciären with the glacierized areas of Norway *ArcGIS® software by Esri,
and *1©Kartverket. 27
Figure 13. Location for each meteorological station and the relative position for each glacier. Sandane-ÅLF, Løken- STO, and Vågå-GRÅ. *ArcGIS® software by Esri, and *1©Kartverket. 30 Figure 14. Graph showing the annual net balance of respective glacier between the years 1963 and 2018. 34
Figure 15. Annual net balance graph with 5-year intervals from 1963 to 2018 of respective glacier coupled with a polynomial trendline. A forecast of one period was added in order to predict future development. 35
Figure 16. Mass balance histograms’ displaying the mass turnover for a) ÅLF, b) STO, and c) GRÅ (Andreassen et al.,
2012). 37
Figure 17. Mean annual summer temperature (°C) and a linear trend development for each data set with temperature
development relevant for a) ÅLF, b) STO and, c) GRÅ. 39
Figure 18. Helagsglaciären protected by the eastern ridge (Photo by Per Holmlund 29/08/2014). 43
List of Tables
Table 1. Calculated net balance gradient of ÅLF, STO and GRÅ between the years 1989 and 2003. Storglaciären is included as a reference with values 20 years before the values of ÅLF, STO and GRÅ. 17 Table 2. Mass balance terms used in this paper. References can be found in the text next to the terms in italic. 20
Table 3. An overview of respective glacier’s characteristics. 28
Table 4. Overview of the meteorological stations in this paper. 31
1. Introduction
Glaciers are defined uniformly as perennial compounds of ice, firn and snow that moves under the pressure of their own weight and the force of gravity (Christopherson and Birkeland, 2015, Benn and Evans, 2010). The world is currently experiencing glacial retreat and mass loss in unprecedented rates as a result of warming temperatures (Nesje et al., 2008; NSIDC, n.d.b.;
European Environment Agency, 2016). Projections by the World Glacier Monitoring Service (WGMS) (2019) indicates that a majority of the world’s glaciers are melting as a response to changing climatic factors and that the retreat has been accelerating since the 1980s (Figure 1).
Glaciers of the Scandinavian Peninsula are displaying the same trend as the projections of WGMS, and an overall negative net value can be observed in the reference glaciers of Scandinavia (Figure 2). Mass loss of Norwegian glaciers has followed the same development trend. However, decadal variations have been observed in the region. Notably, between the years 1980 and 1995 in southern Norway (Figure 2) (Andreassen et al., 2005).
Figure 1. Cumulative net mass balances changes of reference glaciers displaying a uniform mass loss of the world’s glaciers from the year 1945 to 2014 (WGMS, 2019).
Figure 2. Cumulative net mass balances of Norwegian glaciers and Storglaciären in Sweden, between 1945 and 2011 (Trachsel and Nesje, 2015).
Mass balance measurements are of utmost importance as current changing climatic circumstances have a direct impact on glaciers’ mass balances. If the mass balance of a glacier is continuously measured over a significant period and portrayed cumulatively, the trends in mass balance can distinguish climate change (Nesje et al., 2008). A glacier’s mass balance is linked directly to changes in the climate, particularly towards changes in temperature and precipitation. The state of a glacier after the ablation season and the accumulation season display the prevalent conditions of the atmosphere during a glaciological year. However, the response time is in a different time frame, and the adjustment of outlet glaciers in maritime environments are <10-15 years and for temperate glaciers approximately 25-50 years (Holmlund and Jansson, 2002; Nesje et al. 2008).
The glaciers of interest in this study make up an aligned west to east transect in southern Norway, with the maritime Ålfotbreen (ÅLF) in the west, to the continental Gråsubreen (GRÅ)
Differences in the local environment and the local climate have a significant impact on how glaciers will look in 100 years from now. Some glaciers, such as smaller glaciers with a limited horizontal extension, seem to survive despite the past decades’ increase in the air temperature.
One example is the Swedish glacier Helagsglaciären that seem to survive despite its areal extension of 0.48 km2 (Svenska Glaciärer, n.d.a.). This adds further interest in glacier characteristics and the importance of local factors. It is of importance to understand mass balance characteristics in order to interpret past and future climate variability.
I have chosen to compare the mass balance of three glaciers in a west to east transect in southern Norway to portrait the difference and importance of local characteristics and local climate for glacial existence. A rough distinction of maritime and continental glaciers is used as a starting point of the paper. However, leading into the importance of local characteristics of each glacier.
This paper portrait Norwegian glaciers and not Swedish glaciers as Sweden does not have a glacier of maritime character. In addition, Norway has an abundance of available data on maritime and continental environments in approximately the same latitude as measurements have been carried out for >50 consecutive years at respective glacier in the west to east transect (Andreassen et al., 2012). However, Storglaciären is an important reference when analysing mass balance and will, therefore, be used as a reference glacier to represent the Swedish circumstances in this paper. The time period of the study, 1980-2018, was chosen as significant rates of mass gain, followed by high rates of mass loss occurred during this period. Mass balance values from earlier years will be displayed as these indicate previous conditions that are relevant for discussion.
1.1. Aims and objectives
Based on existing literature relevant to this study, the author hypothesises that the mass balance characteristics and mass turnover, vary along increasing continentality of the west to east transect of Ålfotbreen, Storbreen and Gråsubreen in southern Norway. The aim of the study is, therefore, to conclude the mass balance characteristics for maritime and continental glaciers and their mass balance sensitivity towards summer air temperature. Furthermore, local features of each glacier will be accounted for with the purpose to highlight the importance of local variability. Moreover, the summer air temperature from 1960 until 2017, will be investigated as a contributing factor to the mass deficits of the glaciers in this paper. To reach this aim, an
analysis of respective glacier’s mass balance will be performed. Development trends of the mean annual summer air temperature for respective glaciers’ region will also be conducted. No in situ measurements are performed for this paper. Therefore, a literature review of relevant reports and publications will be presented and analysed to complement the result of this paper.
The research questions will, therefore, be as follows:
1. How does the glacier characteristics and mass turnover vary, between the years 1980 and 2018, along the west to east transect in southern Norway?
2. How does the mass balance sensitivity of Ålfotbreen, Storbreen and Gråsubreen vary, and what is the estimated response towards an increase of the mean annual summer temperature of each glacier?
2. Background 2.1. Glaciers
A glacier is a large and perennial accumulation and recrystallisation of snow, firn and ice that moves downslope under the pressure of its own weight and the influence of gravity (USGS, n.d.; Christopherson and Birkeland, 2015). The movement of a glacier is an important factor when distinguishing it from a snow patch. Required conditions that allow a glacier to form include annual accumulation of snow, temperatures around the freezing point and that the yearly temperature does not allow complete melting of the winter accumulation (USGS, n.d.b.).
Glaciers and ice sheets cover ~10 % of Earth’s total land area with the vast majority situated in Antarctica, the Arctic Islands, Greenland, the Canadian Arctic and central Asia. However, glaciers can be found in other areas in the world if the geographical and meteorological conditions are fulfilled (NSIDC, n.d.a.). The Scandinavian Peninsula inhabits a portion of the ice bodies, and the most significant concentrations can be found in mainland Norway.
According to the latest Inventory of Norwegian Glaciers (2012), the total glacierized area was estimated to be 2692 km2 ± 81 km2 (3 % uncertainty) in 2012, where the majority (57 %) is situated in southern Norway, ~1523 km2 (Andreassen et al., 2012). Sweden does not inhabit the same concentration as mainland Norway. Nevertheless, glaciers cover approximately 250 km2 of the land area (Svenska Glaciärer, n.d.c.).
Glaciers can be separated into different thermal regimes such as temperate, polar or polythermal. Temperate glaciers are often situated in environments with higher temperatures such as in maritime environments and are warm based. This means that they are close to the melting point from the surface to the bed. Their mass balance sensitivity is considered high as changes in temperature can affect a temperate glacier massively, resulting in a high mass turnover (USGS, n.d.a.; Holmlund and Jansson, 2002). The concept of mass balance sensitivity is further explained in section 2.4. Polar or cold-based glaciers experience the opposite and are not close to the melting point, implying that there is no liquid water at the bed of the glacier (Cogley et al., 2011). Contrary to the large mass turnover of temperate glaciers, polar glaciers have a small mass turnover. Polythermal glaciers consist of both cold and warm ice. The interior is partly cold, whereas the base is warm, much like the base of a temperate glacier (Andreassen et al., 2018; Holmlund and Jansson, 2002).
2.2. Mass balance
Glaciers are a result of the amount of mass gained and the amount of mass lost (Davies, 2018).
Consequently, the mass gain needs to be larger than or equal the mass loss for a glacier to exist.
Mass balance is a term used within glaciology that refers to the change of a glacier’s mass over a defined period (Benn and Evans, 2010). More terms used in this paper are defined in table 2.
An often-used period is the start of the accumulation season, typically with the first snowfall, to the end of the ablation season and before the new start of the accumulation season. This time span is referred to as a glaciological year (Holmlund and Jansson, 2002).
Accumulation accounts for the mass added to a glacier such as precipitation in the form of snow, avalanches from valley sides or redistribution of available snow by wind, whereas ablation refers to the mass lost such as melting (Holmlund and Jansson, 2002). The complex system of a glacier can be divided into two areas; accumulation area and ablation area (Figure 3). The zones are separated by an equilibrium line or the equilibrium line altitude (ELA), where the net balance equals null or bw= bs. The ELA is a theoretical approach that separates the two zones from each other. In other words, the ELA is the separation where either accumulation or ablation exceeds the other, and the glacier is in a balanced state (Holmlund and Jansson, 2002).
The area of accumulation is above the ELA in the upper parts of a glacier, and the ablation area is below the ELA, in the lower regions of a glacier (Andreassen et al., 2012; Holmlund and Jansson, 2002). The ELA is sensitive to meteorological factors such as precipitation and air temperature, that can cause a fluctuation of its altitude position. This fluctuation is a direct connection to the state of a glacier and, therefore, an indicator of importance regarding mass balance sensitivity towards climate change (Benn and Lehmkuhl, 2000).
Figure 3. Accumulation and ablation area of a glacier system (Willsman et al., 2015).
Mass balance is the quantitative explanation of the difference between a glacier’s accumulation balance (bw), and ablation balance (bs), during a glaciological year. The net effect of the accumulation and ablation during a year equals the net annual balance (bn) of the glacier, which is positive or negative, depending on which balance is greater (Holmlund and Jansson, 2002;
Benn and Evans, 2010). When the net annual mass balance is positive, it indicates that a glacier has gained mass and will increase in volume, which occurs when the winter balance exceeds the summer balance. Vice versa, when the net annual mass balance is negative, it indicates that a glacier has lost mass (Benn and Evans, 2010; NVE, 2019).
The net annual balance can be expressed as bn = bw + bs (Holmlund and Jansson, 2002;
Andreassen et al., 2005).
The net balance of a glacier is not uniform on the whole glacier. For example, accumulation can be greater on a glacier’s upper parts as a result of topographic circumstance and wind directions (Holmlund and Jansson, 2002). One such example is Storglaciären in the Kebnekaise Massif of northwest Sweden, where the net balance is increasing with the altitude, and the accumulation is more significant on the glacier’s upper parts compared to its lower parts (Figure 4 and 5).
Accumulation area ratio (AAR) is the accumulation area, divided by the total area of a glacier.
AAR is a measure of the net mass balance and describes the size of the accumulation area in
percentage (%) after the ablation season (Holmlund and Schneider, 1997; DeWayne et al., 2004).
Figure 4. Changes in the mass balance of Storglaciären in 2011, where the mass increases with the altitude (Svenska Glaciärer, n.d.b.). The ELA is where the net balance is zero, which in this example is at approximately ~1580 m a.s.l.
−4 −3 −2 −1 0 1 2 3 4
1100 1200 1300 1400 1500 1600 1700 1800
Mass balance (m w.e.)
Elevation (m a.s.l.)
Winter balance Summer balance Net balance
7.537 7.5375 7.538
x 106
−2 0 2 4 6
7.537 7.5375 7.538
x 106
−2 0 2 4 6
2.2.1. Mass balance measurements
Detailed measurements are often time-consuming and expensive. Therefore, measurements must be surveyed on multiple decided points on the glacier surface to get as representative information as possible as efficiently as possible (Holmlund and Jansson, 2002; Kjøllmoen et al., 2019). The amount of measured points depends on local characteristics. For instance, Storglaciären has a predefined grid-system on its surface with a 100-meter distance in between each point that allows consistent measurements with accurate values (Holmlund and Jansson, 2002).
The winter mass balance measurements in Norway are generally surveyed in April or May and is decided by measuring the bulk snow density in addition to probing the snow depth to the previous year’s summer surface (Kjøllmoen et al., 2019; Engelhardt et al., 2013). The procedure is performed in different profiles along the surface to capture the intricate and non- homogenous accumulation patterns of a glacier. The summer mass balance measurements are usually surveyed in September or October with the help of a point mass balance system that uses ablation stakes (Kjøllmoen et al., 2019; Engelhardt et al., 2013; Cogley et al., 2011).
The transformation of a glacier’s snow depth into its equivalent of water is through the density.
A glacier consists of compressed ice, firn and snow that have different densities. Metres water equivalent (m w.e.), transform the multiple densities of a glacier into an easier measurement by explaining the volume of water that would be retrieved if ice and snow melted in one place.
This unit allows for comparisons between different glaciers mass balances, and comparisons of different mass balance years (Hock, 2010; Holmlund and Jansson, 2002).
The m w.e. equation is expressed as follows: snow depth (ds) multiplied with snow density (𝜌s) and divided with the density of water (1000 kg/m3) or dv = ds 𝜌s/𝜌v (Hock, 2010; Holmlund and Jansson, 2002).
If mass balance measurements are performed over a long period of time, trends in the previous climate can be visualised, and that is why glaciers are considered to be climate archives.
Further, it gives a direct indication of the weather during a glaciological year based on the records of the ablation and accumulation season (WGMS, 2019; Nesje et al., 2008). Mass balance measurements are further of importance as glaciers serve a vital role in the environment and to societies. Norway is dependent on glacial meltwater runoff for energy purposes, and
approximately half of Norway’s 3143 glaciers drain to catchments that are regulated for hydropower energy (Andreassen et al., 2012). Hence, it is of importance to record glacial mass balance in order to understand development patterns and project future scenarios.
2.3. Continentality
As explained in section 2.2., accumulation and ablation changes with the altitude. Nesje et al.
(2000) explain that the rates which annual accumulation and ablation change are called accumulation gradient and ablation gradient respectively. Together, they define the net balance gradient (Nesje et al. (2000). Holmlund explains it further as “the annual change of a glacier’s mass as a function of the altitude” (1993) (Figure 6). The net mass balance gradient is determined by the hypsometry, glacier size, geographical location and the glacier slope (Davies, 2017). The mentioned example of Storglaciären (Figure 4 and 5), is an example where the net balance changes with altitude.
Moreover, the net balance gradient describes a glacier’s mass turnover determined by the local conditions and varies depending on the local climate of a glacier. A maritime glacier is an example of a type of glacier with high mass turnover as it has a large mass surplus in the accumulation zone. In contrast, a continental glacier typically has a smaller mass turnover and experiences the opposite (Holmlund and Jansson, 2002) (Figure 6).
Maritime glaciers have a steeper gradient than continental glaciers as a result of the high rates of solid precipitation in maritime regions (Davies, 2017). Intermediate glaciers are not as easily characterised as a maritime or a continental glacier, but they are often defined somewhere in between the values of maritime and continental glaciers. See the gradient values of the intermediate STO and Storglaciären compared to the continental GRÅ (Table 1).
The net mass balance gradient for ÅLF, STO and GRÅ was calculated to get a continentality
The distinction of maritime and continental glaciers roughly indicates characteristics in terms of possible rates of precipitation and temperature. However, local circumstances such as topography and hypsometry are also of importance as they influence the climatic conditions and, therefore, the survival potential of a glacier (Imhof et al., 2011).
Figure 6. The net mass balance gradient explained by the slope angle indicating that maritime glaciers experience a significant mass turnover compared to continental glaciers. The gradient of a maritime glacier is steeper compared to a continental glacier (Holmlund and Jansson, 2002).
Table 1. Calculated net balance gradient of ÅLF, STO and GRÅ between the years 1989 and 2003. Storglaciären is included as a reference with values 20 years before the values of ÅLF, STO and GRÅ.
Glacier Gradient
Ålfotbreen 0.0066
Storbreen 0.0058
Gråsubreen 0.0019
Storglaciären 0.0072
2.4. Glacier sensitivity
Glaciers are known as climate indicators because of their sensitivity towards climatic perturbations and fluctuations (Engelhardt et al., 2013; Imhof et al., 2011). Glaciers change their size in response to changes in the climate (Holmlund and Jansson, 2002). Meteorological components such as air temperature and precipitation have a significant impact on mass
balance and, changes in either result in a response and an adjustment of a glacier to meet the new circumstances (Benn and Evans, 2010). Mass balance sensitivity can be defined in several ways such as the percentage of precipitation required to add up for a +1 K warming (Oerlemans, 1997; Engelhardt et al., 2015). In this paper, sensitivity is defined, more generally, as the change in the mass balance of a glacial system in response to a changing climate, particularly temperature change, and will be referred to as mass balance sensitivity.
As mentioned, glaciers change their mass balance as a response to perturbations in the climate.
Researchers agree on the importance of understanding the response of glaciers in order to predict future states of the ice bodies (Jóhannesson et al., 1989; Nesje et al., 2008; Lie., 2003).
According to Jóhannesson et al. (1989), response time is one of the more fundamental features to evaluate when analysing mass balance characteristics. Response time and reaction time are characteristic features of a glacier and consequently, relevant to the concept of mass balance sensitivity. The former is a theoretical explanation of the total time required for a glacier to adjust its volume between two balanced states after a disturbance in the mass balance (Jóhannesson et al., 1989; Holmlund and Jansson, 2002). The latter is the physical change when a glacier adjusts to the new circumstances. To exemplify, maritime glaciers with high mass turnovers react faster towards climate perturbations compared to continental glaciers. Hence, their response time is shorter compared to a continental glacier. The response time for outlet glaciers in maritime environments is <10-15 years and for temperate glaciers approximately 25-50 years (Holmlund and Jansson, 2002; Nesje et al. 2008).
The mass balance sensitivity can be demonstrated in the position of the ELA, as the ELA of a glacier shifts its altitude position as a response towards changing climatic circumstances. A temperature rise could lead to an upward shift of the ELA, that would increase the ablation area and increase the net mass loss of a glacier (Benn and Evans, 2010; DeWayne, 2004).
Temperature generally decreases with altitude, and when a glacier moves downslope, it reaches a warmer local climate. Consequently, this results in a glacier with a higher mass balance sensitivity in the lower parts of a glacier compared to its higher parts (Davies, 2018). Small glaciers have a particularly sensitive mass balance and have a shorter response time compared to larger glaciers (Holmlund and Schneider, 1993). The geographical extension is, therefore, of importance when discussing mass balance sensitivity.
Figure 7. The consequences of an upward shift of the ELA of an ice cap versus a valley glacier (Hock, 2010).
Table 2. Mass balance terms used in this paper. References can be found in the text next to the terms in italic.
Term Definition
Ablation Output of mass from a glacier
Ablation area Area below the ELA where the greater
ablation occurs
Accumulation Input of mass to a glacier
Accumulation area Area above the ELA where the greater
accumulation occurs
Accumulation Area Ratio (AAR) Measurement of the net mass balance.
Describe the size of the accumulation area after the ablation season
Equilibrium Line Altitude (ELA) Line that separates the ablation and
accumulation zone. Net annual balance equals null or bw= b. Measurement of a glacier’s state in correlation to the climate
Glaciological year Start of the accumulation season, e.g.
when the first snow fall, to the end of the ablation season and before the new start of the accumulation season
Mass balance The change of a glacier’s mass over a
defined period
Metre water equivalent (M w.e.) Unit that represents the density of
snow, firn and ice in water volume
Net annual balance The sum of ablation and accumulation
during a glaciological year
Net balance gradient The annual change of a glacier’s mass
as a function of the altitude
Mass balance sensitivity The change in the mass balance of a
glacial system in response to a
2.5. Previous research
Hans W. Ahlmann and Valter Schytt first initiated continuous mass balance measurements in 1946 on Storglaciären, which, to the day have the most extensive mass balance series in the world (Holmlund and Jansson, 1992). Norway followed Sweden’s example and initiated mass balance measurements three years later on Storbreen (NVE, 2017; DeWayne et al., 2004).
Mass balance measurements have been surveyed since the 1940s and are continuously surveyed globally to the day. The measurements constitute a vital part in understanding climate change that is of importance when discussing the anthropogenic impact on the atmosphere. The quantitative data of mass balance allow researchers to analyse the relationship between climate perturbations and the possible consequences of the ongoing loss of the world’s glaciers (WGMS, 2013). WGMS inhabits a worldwide collection of information and data on the world’s glaciers to provide long-term observations on glacier change (WGMS, 2013).
There is an abundance of research available in the study region concerning mass balance characteristics of glaciers. Norway has extensive records of glacial monitoring as the country is dependent on runoff for hydropower purposes. Many glaciers in Norway are situated in regions with hydropower potential and a change in glacial mass balance could affect the runoff, and the total annual volume discharge vital for hydropower (Kjøllmoen et al., 2019;
Andreassen et al., 2005; Engelhardt et al., 2013).
The Norwegian Water Resources and Energy Directorate (NVE), is responsible for the management of energy and water resources in Norway and produce a large quantity of the available research, material and data regarding glacial research in Norway. Hence, an abundance of the literature and data in this paper is retrieved from NVE.
3. Methodology 3.1. Study area 3.1.1. Ålfotbreen
Ålfotbreen ice cap (61°45'N, 5°40'E), is part of a glacier complex and consists of two north- facing outlet glaciers; Ålfotbreen to the west and Hansebreen to the east (Kjøllmoen et al., 2019; NVE, 2016a). In this study, the outlet glacier of Ålfotbreen (Figure 8a and figure 8b) is of interest as it is one of the westernmost situated glaciers and the most maritime glacier of Norway and in the west to east transect (Kjøllmoen et al., 2019; NVE, 2016a; WGMS, 2018a).
When mentioned, “Ålfotbreen” will refer to the outlet glacier of the ice cap and not the ice cap itself (Figure 8b).
The glacier is of temperate regime as a result of its location in a maritime environment (Holmlund and Jansson, 2002). Ålfotbreen has an area of approximately 4.0 km2 (2010) (Kjøllmoen, 2016; Gjerde et al., 2016). Annual mass balance measurements have been surveyed since 1963 (Kjøllmoen, 2016; NVE, 2016a; Andreassen et al., 2005).
Ålfotbreen is situated in a topographical with low topography (Figure 8b). The elevation extends from ~890 meters above sea level to ~1370 meters above sea level, and the ELA is
~1160 meters above sea level (NVE, 2016a; Andreassen et al., 2005). The hypsometry is considered narrow, according to Gjerde et al. (2016) and Kjøllmoen. (2016).
a)
Figure 8. a) ÅLF in 2018 (photo by Hallgeir Elvehøy, n.d.), and b) Geological and topographical features of ÅLF (Google Earth Pro, 11/07/2019).
3.1.2. Storbreen
Storbreen (61°34’N, 8°8’E), is defined as a polythermal cirque glacier or a short valley glacier and is situated in a leeward position in western part of the Jotunheimen massif (Figure 9a) (NVE, 2018; Lie et al., 2003). The glacier is east facing and considered as an intermediate glacier with a total area of approximately 5.1 km2 (2009) (Lie et al., 2003; NVE, 2018).
Storbreen is surrounded by distinct topography and a subglacial ridge divide the glacier in the centre (Figure 9b). The altitude of the glacier ranges from approximately 1390 meters above sea level to 2090 meters above sea level with the ELA situated around 1760 meters above sea level (NVE, 2018).
Storbreen is the second most documented glacier in the world after Storglaciären and inhabits the longest mass balance record in Norway. Mass balance observations were first initiated in 1949 and have been measured regularly since the start of the observations (NVE, 2018).
b)
Figure 9. East to west view of Storbreen with its ridge and distinct topography (photo by Liss M. Andreassen 29/07/2008).
3.1.3. Gråsubreen
Gråsubreen (61°39'N, 8°37'E), is a polythermal glacier situated in the north-eastern part of the Glittertind mountain in Jotunheimen massif and is one of the most continental glaciers in Norway (NVE, 2016b; WGMS, 2018b). GRÅ has a total area of approximately 2.1 km2 (2009) and its extension ranges from ~1830 meters above sea level to ~2280 meters above sea level, making it a high-altitude glacier (NVE, 2016b; Lie et al., 2003). The ELA of GRÅ is estimated to be around 2130 meters above sea level (Andreassen et al., 2005). Mass balance measurements were initiated in 1962 and have been monitored out continuously ever since as a result of its continental character (WGMS, 2018b).
Figure 10. Aerial image of Gråsubreen from 2014 (Photo by Liss M. Andreassen 14/08/2014).
3.1.4. Storglaciären
Storglaciären (67°54'N, 18°34'E), is an east-facing polythermal, valley glacier in the Kebnekaise massif of the Tarfala valley in northern Sweden. The glacier is situated considerably further north compared to ÅLF, STO and GRÅ (Figure 12), but the interest lies in the local characteristics such as topography and hypsometry. Storglaciären is ~3.0 km2 with an elevation range of approximately from 1140 m a.s.l. to 1700 m a.s.l (Svenska Glaciärer, n.d.b.; Holmlund and Holmlund, 2019). Storglaciären is surrounded by distinct topography and situates east of a ridge originating from Kebnekaise. The resulting leeward position allows for snow to accumulate in its upper parts (Holmlund and Jansson, 2002). Winds generally originate from the west in Sweden, which means that the glacier is protected from wind abrasion and instead accumulate the snow received (Holmlund and Jansson, 2002). The mass turnover of Storglaciären can be observed in the mass balance histogram Storglaciären (Figure 11b). The annual net values have generally been negative since the mid 1980s until 2019.
Figure 11. a) Storglaciären situated east of the Kebnekaise massif (Photo by Per Holmlund, n.d.), and b) Mass balance histogram of Storglaciären between 1946 and 2019. Blue staples equal positive net balance and red is negative net balance (Svenska Glaciärer, n.d.b.).
a)
b)
Figure 12. Map of the study area and Storglaciären with the glacierized areas of Norway
*ArcGIS® software by Esri, and *1©Kartverket.
Table 3. An overview of respective glacier’s characteristics.
3.2. Data
3.3. Mass balance data
The mass balance data used in this paper was retrieved from the NVEs “Climate Indicator Products” data portal that provides official data from the NVEs database. Winter balance, summer balance and annual balance for respective glacier were obtained and exported to Microsoft Excel 2016.
Firstly, a graph was developed in order to demonstrate the annual net balance values for each year of the chosen time period. This enabled an overview of the glacier’s annual net mass balance patterns and further, the patterns in relation to one another.
Secondly, a 5-year interval graph was developed to get a simplified overview of the annual mass balance of each glacier. A polynomial regression analysis was conducted on the 5-year interval graph in order to display a trend of the annual balance values. The polynomial regression analysis was considered suitable as the data set is fluctuating and represent both loss and gains (Microsoft, n.d.). Since the dataset used was relatively large and fluctuating, an Order 4 polynomial trendline was chosen in order to get a development trend as valid as possible (Microsoft, n.d.). The order of the polynomial, which is the highest possible order, was chosen as a result of the number of hills and valleys in the graph (Microsoft, n.d.). A forecast was
Name Location Type Area
(km2)
Elevation (m a.s.l.)
Mass balance records
Ålfotbreen 61°45'N, 5°4'E Maritime ~4.0 (2010) ~890-1370 m 1963-ongoing
Storbreen 61°36'N, 8°8'E Intermediate ~5.1 (2009) ~1390-2090 m 1949-ongoing
Gråsubreen 61°39'N, 8°37'E Continental ~2.1 (2009) ~1830-2280 m 1962-ongoing
Storglaciären 67°54'N, 18°34'E Intermediate ~3.0 (2018) ~1140-1700 m 1946-ongoing
No in situ measurements were carried out by the author for this paper. However, mass balance histograms from the latest Glaciological Investigations in Norway (2018) written by the principal investigators of the mass balance measurements in Norway will be included in order to complement the retrieved result by the author. This will allow further analysing and discussion of the result.
3.4. Temperature data
Summer air temperature and winter precipitation are two factors of importance when analysing mass balance changes since the existence of a glacier depend on the balance of the two. The goal was to compare the mean annual summer air temperature data to the mass deficits of each glacier and further, to predict possible future temperature development in each region. Mass balance sensitivity to changing climatic circumstances vary depending on the type of glacier as well its location. However, the response time is approximately >10-15 years for outlet glaciers in maritime environments and 25-50 years for glaciers in coastal and temperate regions (Holmlund and Jansson, 2002). Therefore, data outside assessment period for this paper, 1980- 2018, is included.
Mean monthly air temperature data for each glacier was obtained from the Norwegian Meteorological Institute (MET), the equivalent to the Swedish Meteorological Hydrological Institute (SMHI). MET offers free access to meteorological data through several self-download services. For this paper the Norwegian Centre for Climate Services (NCCS) was chosen as it provided with historical temperature data.
Temperature data was retrieved from the three closest meteorological stations with sufficient data for respective glacier and the chosen stations were consequently: Sandane, Vågå - Klones and Løken in Volbu (Table 4) (Figure 13). Temperature data from the meteorological station Sandane (50 m a.s.l.) roughly 30 km east of ÅLF was obtained from the year 1960 to 2017.
The closeness is favourable as it demonstrates the local climate for ÅLF. Temperature data for STO was collected from Løken meteorological station (521 m a.s.l.) situated approximately 70 km southeast from STO. Records from the year 1962-2017 were retrieved. Lastly, data for the years 1960-2004 was obtained from the adjacent station Vågå (371 m a.s.l.), approximately 35 km northeast from the glacier, in order to represent temperature data relevant for GRÅ.
A graph with the mean annual summer air temperature of June, July and August was developed in Microsoft Excel 2016. As a result of the lacking data of Vågå station from 2004 and onwards and in order to predict future temperature development trend, a linear regression analysis with four periods, was conducted on each temperature data set in order to make up for the non- existent data and in order to receive a future development trend for each region. The linear analysis is considered suitable for the data set as the purpose was to display the temperature trend (Microsoft, n.d.).
Table 4. Overview of the meteorological stations in this paper.
Meteorological station
Responding glacier
Coordinates
Altitude m (a.s.l.)
Time- period
Total mean (°C)
Sandane Ålfotbreen 61°86'N, 9°08'E 50 1960–2017 14.0
Løken Storbreen 61°78'N, 9°18'E 521 1962–2017 12.5
Vågå Gråsubreen 61°12'N, 9°06'E 371 1960–2004 13.2
3.5. Delimitations and data quality 3.5.1. Delimitations
Mass balance is particularly sensitive to summer temperatures. The selected months for the temperature data (June, July and August) was chosen as ablation rates is at the peak during these months and, therefore, determine the state of a glacier (Imhof et al., 2011). Exceptions must be kept in mind, but the general rule is that the ablation rates at their peak during the summer. The temperature data for each glacier are not obtained from the same periods, 1960- 2017, 1962- 2017 and 1960-2004 respectively. This resulted in some limitation when analysing and comparing the data. Historical temperature data was only accessible from the year 1960.
However, the time period is considered sufficient enough for this purpose as a result of glaciers response time to air temperature change.
Moreover, it would have been favourable to have an adjacent meteorological station to STO as Løken is situated in a remote distance. More adjacent meteorological stations did not inhabit consistent data or sufficiently long time series. Even though the lack of values and the remote location, the meteorological station provided with data sufficient enough for this purpose.
Furthermore, precipitation data would have contributed to the overall result and discussion.
However, no accessible data was obtained as no adjacent, or remotely adjacent meteorological station could provide with sufficiently long time series. This limits the discussion and analysis further and leaves parts of the result to be based on other researchers’ findings.
3.5.2. Data quality
The mass balance data retrieved from NVE are official values that are produced and used by the NVE itself. The measurement methods and field work in Norway has reduced over time as detailed measurements are expensive and time consuming. Mass balance measurements have been performed in Norway since the 1949 and since then upgrades of mass balance procedures
have occurred (Kjøllmoen, 2016). Number of stakes, position of stakes and the amount of snow depth measurement has varied as a result of limited resources and poor weather conditions throughout the years (Kjøllmoen, 2016). As always with field measurements, possible human errors can occur and should be taken into consideration.
The mass balance data retrieved and processed in Microsoft Excel 2016 did not indicate any errors while analysing it. However, the validity of mass balance values is reliant on the accuracy of the point observations made in the field and the conversion of the values to a spatial extension of the glacier (Kjøllmoen et al., 2019). According to Andreassen et al. (2013), the raw data is calibrated and interpolated to avoid misrepresentation. In situ errors can occur as a result of unexpected circumstances that cannot be avoided. For instance, aluminium stakes used to measure snow accumulation or melting of a glacier are prone to be destroyed or disappear if a glacier experience heavy snowfall (Kjøllmoen et al., 2019). This can result in systematic errors as the equipment used fail to deliver accurate data.
Sandane temperature data are missing June and July values from the year 1969. The temperature data from the meteorological station Løken lack of yearly values from 1987-1989, 1991-1993, 2001, 2003 and 2004. Furthermore, monthly values for June in 1968, 1997, 1999, 2000, and August values from 2002, are non-existent. Data from Vågå is close to consistent, however, 1980 and 1990 are lacking data for August and 1999 lacks data for June. The last measurement year is 2004 as the station was discontinued1, which is considered to be a delimitation, however, accurate enough for this purpose.
The lack of data from the meteorological station Løken lowers the reliability of the results. The reason for lacking data is systematic errors with damaged equipment and technical errors. In order to reduce these errors, MET have set up automatic checks that inform the station owners if there is a problem with missing data2. Nevertheless, the data is the most reliable for this study
The majority of the missing data is between the years 1990-2000 and with the response time of glaciers in maritime and temperate climate in mind, the time-period of the temperature data is considered to be representative enough.
4. Results
4.1. Mass balance characteristics of ÅLF, STO and GRÅ
The net mass balance gradient of ÅLF (0.0066) indicates that the glacier has an abundant mass gain in the accumulation area and a large mass loss in the ablation area that result in a significant mass turnover (Table 1). The net balance gradient for ÅLF is not as steep as expected (Table 1). The gradient of STO (0.0058) and GRÅ (0.0019) is as expected. The mass balance sensitivity decreases along the transect. ÅLF as a maritime glacier with high rates of precipitation and a low continentality have a high mass balance sensitivity compared to STO and GRÅ that situates in a drier and more continental climate (Anderson and Mackintosh, 2012).
ÅLF, STO and GRÅ all have different topographic and hypsometric circumstances. ÅLF have a low-lying, stair-like hypsometry and is not surrounded with distinct topography or a headwall that catches the snow for accumulation (Figure 8a). STO is surrounded by distinct topography on a mid-altitude, much like Storglaciären (Figure 9 and 11). GRÅ is situated on high altitude with modest topography (Figure 10). ÅLF is situated in the path of the westerly winds that bring significant precipitation and winds that redistribute or remove the snow on the glacier.
The winds decrease when moving inland towards STO and GRÅ.
During the observation period (1980-2018), ÅLF has had 23 out of 38 years with negative values. The glacier was close to a balanced state in 1972 (0.04 m w.e.) and 1982 (-0.01 m w.e.).
The glacier volume of ÅLF increased between 1987 and 1995 as a result of a significant increase in winter precipitation. STO and GRÅ had the same increase in mass between the years 1980 and 1995, (except for the year 1988). The total annual mean of ÅLF between 1980 and 2018 was 0.19 m w.e. (Figure 14).
Storbreen have had constant negative net values since 1963 and, consequently, during the observation period as well (Figure 14). The most significant deficit occurred in 2018 (-3.24 m w.e.). The total annual mean of STO was -1.90 m w.e. between the years 1980 and 2018. On average, the mass balance has been below its annual mean since the start of the observation
period. STO experienced a decrease in mass from the year 1989 and 1996, the same period ÅLF experienced a considerable gain in mass.
The majority of the glaciological years of GRÅ are negative (Figure 14), although, a few years display a positive net value. This occurred from the mid-1980s to the mid-1990s. The total annual mean of GRÅ between 1980 and 2018 was -0.47 m w.e. with most years being below the mean. GRÅ display the greatest stability of the observation period.
The majority of the mass balance years for each glacier was below their mean, indicating a continuous mass loss that has been exceeding the normal. All three display a substantial mass loss after the 1990s and onward indicating that mass loss rates have been increasing. The year 2012 and 2015 display a significant increase in the mass balance for all three glaciers (Figure 14). The polynomial analysis with the included forecast (Figure 15) indicates that the future mass balance of each glacier will continue to be negative.
-4,00 -3,00 -2,00 -1,00 0,00 1,00 2,00 3,00
1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017
M.w.e
Year
Annual net balance between 1963 and 2018
ÅLF STO GRÅ
Figure 15. Annual net balance graph with 5-year intervals from 1963 to 2018 of respective glacier coupled with a polynomial trendline. A forecast of one period was added in order to predict future development.
Figure 16 represent the net values for the winter balance and the summer balance, which display the mass turnover of each glacier. The histograms are a courtesy of NVE and published in the Latest Inventory of Norwegian Glaciers (Andreassen et al., 2012). ÅLF display the lowest stability of the observation period represented in the high mass gain and high mass losses of ÅLF (Figure 16a). The mass gain during the accumulation season is typically ~3.0 m w.e and the mass deficit during the ablation season is ~ -3.0. The years 1989-1995 had the largest mass gain since mass balance measurements started. The period, 1995-onward, had almost continuous mass deficits after the period with high mas gain large mass gain.
The mass turnover of STO is displaying a more stable pattern with a smaller mass turnover (Figure 16b). The mass gain during the accumulation season is typically ~1.5 m w.e and the mass deficit during the ablation season is ~ -2.0. The cumulative line indicates that STO has experienced net values since start of the measurements with the highest loss rates after the 1990s.
GRÅ have the smallest mass turnover of the glaciers in this paper. The mass gain is generally small, ~0.5-1 m w.e. The mass loss displays more fluctuating values. The cumulative net values
-4,00 -3,00 -2,00 -1,00 0,00 1,00 2,00 3,00
1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013 2018
M w.e.
Year
Annual net balance with a 5 year-interval with trendline
ÅLF STO GRÅ
have been negative from 1969 to 2018 (Figure 16c). It can be observed that the accumulation values are more stable than the values of the ablation season (Figure 16c).
a)
b)
Figure 16. Mass balance histograms’ displaying the mass turnover for a) ÅLF, b) STO, and c) GRÅ (Andreassen et al., 2012).
4.2. Temperature development and linear trend analysis
Sandane displays the highest annual summer temperature of the three stations, indicating that ÅLF is situated in the region with the highest temperatures of the transect. The highest recorded mean of Sandane is 16.7 °C in 1997, with the lowest mean of 12.1 °C in 1964 (Figure 17a).
The peak of 1969 is representing the mean August temperature solely as a result of the lack of data from June and July and is, therefore, not considered as the highest mean of the period. The highest observed record in the region representing STO is 14.9 °C in 2006 followed by 13.6
°C in 1969, with the lowest recorded mean value being 11.4 °C in 1993 (Figure 17c).
Løken meteorological station display annual fluctuations of the temperature between 10 °C and 15 °C. The highest record was in 2006 with 14.9 °C. The lack of data from the station Løken can be observed in the graph between the years 1987-1989, 1991-1993, 2001, 2003 and 2004 (Figure 17c). The mean summer temperature most relevant for this paper is the period between 1962 and 1986. However, the linear trend analysis was conducted in order to make up for the non-existent values. The result of the analysis is based on the available data and indicates a positive development trend for the periods with missing data.
Vågå station experiences a general fluctuation between 11 °C and 14 °C with a few extremities (for the region) exceeding the average value in 1969 and 1997. The linear trendline was
c)
