Monitoring, a scientific background
This document details the monitoring program run by Tarfala Research Station (TRS) by providing a brief background to the station and activities there as well as a scientific rationale for the measurements. Most of the measurements made at Tarfala Research Station are strongly coupled to issues relating to global climate and environmental change. Much of the data is also important for basic research and development of new methods for monitoring.
Tarfala Research Station is located at 1130 m a.s.l. in the sub-arctic Tarfala Valley in the northern Swedish mountains (Figure 1 &amp;amp;amp; 2). The station has gradually grown to a modern research facility since monitoring activities focusing on the mass balance of Storglaciären began in spring 1946. The reason for performing monitoring activities was to study the processes and mechanisms involved in the strong reduction in glacier size that was widely observed by Prof. Hans W:son Ahlmann around the North Atlantic Ocean . Ahlmann realized the need for long-term monitoring on a specific glacier to increase our understaning of the climate-glacier mass balance relationship and sent out Prof Valter Schytt to identify a suitable object in the Swedish mountains. The choice fell on Storglaciären, a typical valley glacier located in the Kebnekaise massif.
Being the origin of activities at Tarfala, the mass balance monitoring program of Storglaciären has always been at the centre of the activities at Tarfala Research Station. The mass balance series is now the world's longest continuous series of measurements using the so-called Scandinavian method, which involves measuring both the total mass added in the form of snow during winter and the total mass lost through melt during the following summer, thus defining a mass balance year and the net change during this year (Figure 3). The method used by Tarfala on Storglaciären was largely developed as experience was gained throughout the years and is now the standard method of mass balance measurements used in most monitoring systems around the world, albeit with modifications for local conditions.
In parallel wit the mass balance measurements, measurements of meteorological parameters including temperature, humidity, wind speed and direction, as well as solar radiation have been carried out at the research station. These measurements have increased in complexity over the years from initially constituting measurements during the manned summer months to automatic measurements throughout the year. In 1995, the Swedish Meteorological and Hydrological Institute (SMHI) established an official meteorological station in Tarfala, the highest station in their network.
Through time, additional monitoring measurements have been added to the program run by Tarfala. In the early 1960s measurements of glacier fronts were initiated in an effort to record glacier size changes on a wider scale in the Scandinavian mountains from the Sarek Massif in the south to the Abisko area in the north (Figure 1). The glacier terminus location varies in response to changes in glacier size and provides a good and relatively easily measured proxy for the status of glaciers, whether they grow or shrink.
During the late 1960s and early 1970s, in conjunction with the UNESCO run International Hydrological Decade (IHD), studies of the hydrology of the Tarfala Valley catchment were started in earnest. Discharge measurements had been carried out also during the 1950s and 1960s but with the construction of a fixed gauging station called Rännan, true monitoring of hydrology could be initiated. Hydrological measurements are still carried out at Rännan as well as once additional station, defining a sub-catchment of Rännan, Lillsjön.
During the 1980s, the mass balance program was expanded by the addition of several glaciers, Rabots Glaciär (1982), Riukojietna (1985), and Mårmaglaciären (1988), which all by now have mass balance records of respectable length (Figure 1). Currently a fourth glacier, Tarfalaglaciären is also measured. This glacier was monitored for several years during the late 1980s but measurements were discontinued by the early 1990s. Measurements have been restarted on this glacier in 1999. The four glaciers now constitute a network of glaciers with different size, altitude range, aspect and location (relative to the main moisture source, the Norwegian Sea ).
During the 1990s three climate stations were established at different locations in the Swedish mountains: the Pårtetjåkko Observatory, an old meteorological observatory at 1830 m a.s.l. used during the early part of the 20th century for manual observations; Salajekna, a glacier on the water divide of the Scandinavian mountain chain; and Riukojietna, the only plateau glacier in Sweden (Figure 1).
Scientific rationale for the monitoring measurements at Tarfala
Glacier mass balance
Documented glacier changes are key elements within strategies for early detection of global climate change. Small glaciers and ice caps (defined by e.g. the Intergovernmental Panel on Climate Change, IPCC, as all masses of ice outside of Antarctic and Greenland ice sheets) constitute a large source of fresh water that, if released from storage, affects the environment in two principal ways, by contributing to sea-level change and by affecting runoff in rivers of the terrestrial environment. The glaciers also constitute important objects for tourism and contributing to the natural environment in mountainous regions. Glaciers are inherently effects of climate since their existence is determined by the balance between mass gains through e.g. snowfall (on glaciers in the Tarfala monitoring program mainly winter snow) and mass losses through e.g. melting (manly summer melting in the Tarfala case). Glacier mass balance monitoring, thus provide year by year updates to the state of glaciers as well as contribute to understanding their long-term contribution to e.g. sea-level change.
There are more than 160 000 small glaciers and ice caps in the world that, if all melted, would contribute approximately 0.5 m to global sea level. Such glaciers have gained significant interest since they are thought to respond much quicker to global climate change since the ice volume is distributed over a large area (area to volume ratio; glaciers and ice caps: 4:1; Greenland and Antarctica: 1:2) and hence can melt a larger fraction of the total volume for a given amount of melt.
In order to assess global glacier volume change, the effects of all glaciers should ideally be considered. This is not possible with such a large number of glaciers, although advances in space-borne remote sensing provides continuously better estimates of glacier area. Developments in the future may also provide good estimates on volume change through repeated measurements of surface elevation change, which reflects changes in glacier volume. The long-term monitoring of glaciers in the world has, however, hitherto consisted of manual measurements of glaciers.
Worldwide collection of information about ongoing glacier changes was initiated in 1894 with the foundation of the International Glacier Commission at the 6th International Geological Congress in Zürich , Switzerland . It was hoped that long-term glacier observations would give insight into processes of climatic change such as the formation of ice ages. Since then, the goals of international glacier monitoring have evolved and multiplied. In 1986 the World Glacier Monitoring Service (WGMS) started to maintain and continue the collection of information on ongoing glacier changes, when the two former International Commission on Snow and Ice (ICSI, now the International Union of Geophysics and Geodesy Commission for the Cryospheric Sciences UCCS) services PSFG (Permanent Service on Fluctuations of Glaciers) and TTS/WGI (Temporal Technical Secretary/World Glacier Inventory) were combined. The Tarfala mass balance program delivers its mass balance data to the WGMS.
WGMS with its Global Terrestrial Network for Glaciers (GTN-G) recently established as part of the Global Terrestrial Observing System (GTOS/GCOS) follows a global hierarchical observing strategy (GHOST). In order to link detailed process studies at one extreme with global coverage by satellite imagery and digital terrain information at the other, it uses observations at the following levels:
- extensive glacier mass balance and flow studies within major climatic zones for improved process understanding and calibration of numerical models;
- determination of regional glacier volume change within major mountain systems using cost-saving methodologies;
- long-term observations of glacier length change data within major mountain ranges for assessing the representativity of mass balance and volume change measurement;
- glacier inventories repeated at time intervals of a few decades by using satellite remote sensing.
This integrative concept helps with integrative studies and assessments on the development of multi-component systems across environmental gradients by combining in-situ, remote and numerical-modelling components.
The Tarfala mass balance monitoring comprises five glaciers, Storglaciären (initiated 1946), Rabots Glaciär (initiated 1982), Riukojietna (initiated 1985), Mårmaglaciären initiated 1988), and Tarfalaglaciären (current active series initiated 1999) (Figure 1). Measurements on these glaciers differ in that a very detailed set of measurements are carried out on Storglaciären whereas sparser sets of measurements are carried out on the others. In essence, efforts on all glaciers except Storglaciären are limited to what is feasible for one day of work and further constrained by the logistics to reach the glacier within that time frame. This system is therefore characterised by detailed measurements on a reference glacier (Storglaciären) and supporting measurements on supporting glaciers. The role of the supporting glaciers is to provide information on the applicability of the measurements on the reference glacier and to ensure that the reference glacier measurements can be applied regionally. The detailed measurements on Storglaciären have the additional purpose of providing detailed data for process studies to aid in improving our understanding of processes and measurement techniques used in mass balance monitoring. The concept of reference and supporting glacier monitoring systems such as that run by the Tarfala Research Station is gaining support internationally and has been advocated as the preferred approach to establishing mass balance networks in regions where monitoring efforts need to be strengthened, e.g. the Himalayas and the Andes.
The mass balance monitoring program run by Tarfala Research Station has provided ground breaking developments in glacier monitoring. The data is continuously requested by researchers around the world, e.g. for making assessments of sea level change. Since the Storglaciären mass balance record is the longest including measurements of both mass gains and losses, maintaining the monitoring measurements and further developing methods is key. The use of supporting glaciers has not been fully evaluated but records are now of a length (c. 20 years) that makes evaluation of the entire glacier montoring system possible.
Climate stations in Tarfala and elsewhere
The primary reason for recording climate parameters at Tarfala Research Station and elsewhere in the mountains has been to provide a climatological framework for the mass balance measurements. As our understanding of the climate forcing on glacier mass balance has developed, the measurements of climate parameters have become more advanced.
The Swedish Meteorological and Hydrological Institute (SMHI) have stations at numerous locations in or near the mountain chain but most are located at low elevation sites along roads and railways, i.e. in logistically beneficial locations and, at least in the past, where human habitation allowed them to recruit manual observers. Despite that SMHI established an automatic station at the Tarfala Research Station in 1995; which is the highest located station in their monitoring network this has resulted in that large areas of the northern Scandinavian mountains are void of climate stations. This inhomogeneous distribution of stations is problematic as local climate is highly variable in mountain environments.
Historically, mountain meteorology gained the interest of Prof. Axel Hamberg in the early 20th century. He established the Pårte Observatory on Pårtetjåkka (1830 m a.s.l.) in 1915 and four other observation posts at lower elevation in the surroundings, the river stage recorder at Litnok still in operation. The meteorological observations at Pårte were discontinued in 1917. In 1992, Tarfala Research Station established an automatic temperature recorder at the Pårte observatory to collect data for comparison with the Hamberg records. Pårteglaciären, which is also monitored by the Tarfala Research Station on a semi-annual basis, is located just below the observatory. This glacier has, like all glaciers in the Scandinavian mountains, undergone extensive volume decrease since the early 20th century.
In order to better quantify the glacier volume changes measured around the mountains, (and also part of a PhD project on glacier volume change), two climate stations were established at Salajekna (1994) and Riukojietna (1997) (Figure 1) in addition to maintaining the station at Pårtetjåkko.
Measurement of climate parameters at different elevation (e.g. to establish local and spatial variations in lapse rates) and at different locations in the mountain area where glacier monitoring is performed is an integral part of a complete system for monitoring global climate change in such an environment. Tarfala Research Station will maintain the stations initiated in this study and if possible also establish stations in closer proximity to the supporting glaciers in the glacier monitoring network.
Glacier terminus mapping
Measurements of glacier mass balance is labor intensive and also involves logistical problems since successful measurements involve two visits annually to each glacier by as much as four persons in order to collect reliable data. Since glacier volume change essentially involves both changes in surface elevation and a change in glacier surface area, both can be used as a proxy measurement of the true volume change. This is however not straight forward since the change in surface typically occurs with some delay once the volume has changed, that is to say the surface elevation changes more rapidly than the surface area. The surface area, however, is a much easier quantity to measure (represented by the terminus of the glacier). For valley glaciers, the most common type of glacier in the Scandinavian mountains, the surface area change is equivalent to a change in length of the glacier. Traditionally this has been accomplished by traditional surveying by either triangulation methods or, more recently, differential global positioning systems (dGPS) of the terminus of glaciers. Surface elevation changes can also be surveyed but involve additional difficulties, including the safety aspects of traveling on the glacier surface, that makes area measurements much more cost effective. It seems likely that satellite measurements of surface elevation changes may become available in the future but presently area measurements seem to be the only measurements that can be made with sufficient accuracy. Satellite measurements of glacier area have also become available and are used to provide regional inventories. The resolution of satellite images, and the difficulties involved in defining the actual glacier area from such images (e.g. due to marginal snow fields that obscure the true glacier outline), enables monitoring of areal changes with time resolution of 5-10 years, depending on the rate of change in area of the individual glaciers. Measurements of changes in glacier surface area thus contribute important information that provides regional estimates of volume change and also provides a wider framework for interpreting the detailed volume change measurements provided by the glacier mass balance monitoring program. Glacier terminus measurements thus constitute the end member in a three-pronged approach including glacier mass balance measurements on the reference glacier, supporting glaciers.
Tarfala Research Station maintains a glacier terminus position monitoring program comprising 18 glaciers from the Kårsaglaciären, located near Abisko in the north to Pårtglaciären in the southern part of Sarek (Figure 1). These measurements were initiated in 1965 by Prof. Valter Schytt and measurements are maintained on a semi-annual basis.
Tarfala Research Station will maintain glacier terminus measurements at relevant time intervals of 3-5 years. Results show that since the start of measurements in the early 1960s, significant retreat has occurred. In some cases glacier termini have become difficult to asses, e.g. through the melting out of bedrock undulations causing abrupt topographically forced retreat and remnants of stagnant ice left downstream from such undulations. As with the glacier mass balance measurements Tarfala Research Station can perform critical assessment of such measurements to provide standards for other programs run elsewhere.
One of the main effects of climate change on the mountain environment involves a redistribution of runoff by changing the length of the warm and cold seasons as well as possibly changing the amount of precipitation. Redistribution thus occurs because snow fall is replaced by rainfall and because storage characteristics of the catchment may change. In the cases where the catchments harbor glaciers, changes in both the average discharge and the variability (amplitude) of discharge variations can be expected. Since very few catchment located in alpine mountainous environments are gauged, combined records of snow accumulation and melt and runoff are very rare. Through the construction of a permanent gauging station, Rännan, in the Tarfala valley in response to the International Hydrological Decade (IHD, 1965-1975) and the participation of the Tarfala Research Station in the IHD activities, Tarfala constitutes the only gauged alpine catchment in Sweden . In addition, the IHD activities provided base line data with which continued monitoring data can be compared.
Runoff measurements in the Tarfala catchment are strongly coupled to the presence of glaciers. Combined measurements of glacier mass balance and runoff from alpine catchments are very few. The Glaciology commission of the Bavarian Academy of Sciences runs a combined hydrology and mass balance program at Vernagtferner in the Austrian Alps which is probably the best in the world. The program in the Tarfala basin has the prerequisites to become a parallel program for the sub-arctic environment. Thus, measurements of runoff will be maintained by the Tarfala Research Station.
Permafrost (permanently frozen ground) is a core feature of the arctic and sub-arctic environments. Since permafrost owes its existence to a negative energy balance at the Earth's surface, changes in the energy balance also greatly affects the permafrost, through more extensive thawing of the surface and in a longer perspective changing the geographical area harboring permafrost. The ongoing global climate changes already visibly affects areas with permafrost such as the Alps region where thawed soils in high mountains are mobilized resulting in increased hazards for structural damage and loss of life, as well as causing permanent change in the natural environment essential for e.g. tourism and agriculture.
Permafrost (permanently frozen ground) at higher altitudes in European mountains make them potentially sensitive to climate warming. This is because the presence of frozen ground may be a vital factor in the stability of steeper slopes, and where buildings and other installations are underlain by permafrost, their foundations may be adversely affected by ground thawing. The combination of ground temperatures only slightly below zero, high ice contents and steep slopes, makes mountain permafrost vulnerable to even small climate changes.
In Scandinavia , the extent of permafrost has not generally been known, and, therefore, any changes in permafrost extent are even less known. The EU Permafrost and Climate in Europe (PACE) project was a 3-year collaborative research project which commenced in December 1997, funded under the European Union Environment and Climate Research Programme 4th Framework and the Swiss Government. The project improved on permafrost monitoring by
- The establishment of a European Permafrost Monitoring Network by drilling a series of 7 instrumented boreholes forming a north-south transect from Svalbard to the Sierra Nevada .
- Developing new methods for geophysical mapping of ice-rich frozen ground
- Integration of field-based microclimate measurements to calibrate physically-based numerical modelling of the distribution of thermally sensitive mountain permafrost.
- New applications of geotechnical centrifuge modelling to investigate the potential instability of thawing ice-rich soil and rock slopes.
- Integration of research outcomes into GIS-based approaches to terrain evaluation in the context of permafrost hazard assessment in a changing global climate.
A critical and on-going outcome of the PACE project was the permafrost borehole monitoring network, consisting of a series of 100 m deep instrumented permafrost boreholes, providing the major European contribution to the Global Climate Observing System (GCOS) Global Terrestrial Network for Permafrost (GTN-P). There remains a major need to coordinate data collection, and to establish further international collaboration so that similar systems, for instance in the Ural Mountains and in arctic regions, can be established to provide data for inter-regional and global synthesis. Associated with this is a requirement for international networking programs to coordinate regional monitoring systems, interface these with global data banks such as GTN-P, and provide large-scale analysis of regional patterns of climatically forced change.
The continuous measurement of ground temperature through the 100 m bore hole is the main thrust of permafrost monitoring at Tarfala. Data indicate a 100 m temperature of -2.7°C and a possible permafrost depth of ~300 m. Through the connection to global observation networks, data is made available to researchers and contributing to our increased understanding of the effects of global climate change on the cryosphere.
The monitoring performed by Tarfala Research Station comprises glacier mass balance and volume change, alpine meteorology, alpine hydrology, and permafrost. This program constitutes a well balanced program for monitoring of central themes of the alpine environment. It is, however, obvious that additional types of monitoring measurements such as geochemical (e.g. pollutants and nutrients) variations and content and vegetation changes may be areas of expansion in the future. This will involve expanding the support basis for Tarfala in order to design and maintain such monitoring systems.
This document has been assembled and reviewed by the staff and researchers associated with Tarfala Research Station (Peter Jansson, Gunhild Rosqvist, Per Holmlund)
14 november 2011
Webbredaktör: Gunhild Rosqvist
Sidansvarig: Institutionen för naturgeografi och kvartärgeologi