Final Report Summary - EX-GLACIER (A record of rapid climate change from the Pyrenees, Spain)
The modern extent of glaciation in the Pyrenees is currently very limited. Only a small number of the highest peaks host small cirque glaciers. These glaciers are currently retreating very rapidly as a response to global warming. However, during the last Ice Age, the Pyrenees were extensively glaciated with large piedmont lobes extending out onto the French and Spanish hinterlands.
The Pyrenees contain one of the best records in Europe of past changes in ice extent. On the dry side of the Pyrenees in Spain, a lack of erosion has preserved multiple glacial moraines along the trunk valleys. Glaciers are a sensitive indicator of climate change, mostly temperature and precipitation; therefore their fluctuations record past periods of climate change. These records are invaluable for determining the sensitivity of an area to climate change through comparison with records from other areas and climate forcing mechanisms.
The Gallego valley in the south-western Pyrenees contains one of the best records of moraines in the Pyrenees. This catchment hosts the modern small Glaciar de l'Inferno which terminates at 2750 m. This glacier has halved in size since the end of the Little Ice Age and is still rapidly retreating. However, moraines mark the former extent of ice down the main valley to surprisingly low levels of 780 m. This project's aim was to quantify the climate change responsible for such large fluctuations.
The second aim of this project was to establish a cosmogenic nuclide clean lab facility for Cl-36. This isotope is not presently as commonly used as isotopes such as Be-10. However, the technique has excellent potential in lithologies where quartz is not present. In the Gallego catchment, half the valley is comprised of rock where quartz is rare (marl) or completely absent (limestone). Therefore we needed this capacity to carry out the project.
The project centred on the Gallego valley system and the neighbouring Aragon valley to the west. The second valley was chosen because of exceptional preservation of moraines at low altitudes, whereas the Gallego valley had the best preservation in the mid and upper altitudes.
Glacier reconstruction depends on being able to identify ice marginal features. During the course of the project we found that mapping was difficult because of the complex topography of the upper catchment. To compensate for this we used two separate approaches. The first relied on 2-dimensional modelling of the glacier profile. This method uses well known characteristics of ice to determine the extent of ice with distance. The second approach was to use a more sophisticated 2-dimensional model of accumulation and ablation coupled with an ice flow model to determine resultant glacier shape. The advantage of this model is that climate inputs can be adjusted iteratively to determine the most likely combination of temperature and precipitation that matches the geological evidence.
Reconstructions of flowlines revealed that the glacier was a maximum of 480 m thick in the trunk of the valley during the maximum extent of glaciation when the glacier was 40 km long and 119 km2. The equilibrium line altitude (ELA), where accumulation of ice equals ablation, was 1500 m. This is a long way down the valley compared to the modern ELA of 2850 m, ~1350 m lower in elevation and more than the global average by some 30%. The results of the glacier modelling were exciting and indicate a new field of investigation in this region. A validation model was run for the modern Glaciar de l'Inferno which produced an excellent match using modern climate fields. When run for the mapped past glacial extents, the cooling was much larger than expected. A cooling of the global average (6 °C) resulted in only a small glacier restricted to the eastern side of the catchment. A cooling of 7 °C was needed to reach the first moraine whereas 8 and 10 °C was needed to reach the two lowest moraines.
Dating of the moraines produced mixed success. Firstly, more quartz was available than originally estimated in some rock types as a very fine detrital component. We designed a new chemical separation protocol to separate this quartz, which was time consuming but produced satisfactory results. However, the amount of chemical erosion on the limestone surfaces was much greater than expected. To account for this, a model of recent erosion has been created and is being used to correct the results.
The dating constrained the fluctuations of the main trunk glacier over three advances. In the western catchment, ice was near its limits during the last glacial maximum at approximately 18 ka, consistent with previous age constraints. Ice persisted in the catchment longer than previously thought, probably to the early Holocene. Debris was still being added to a moraine in the Holocene, but this is likely to have been debris sliding over snow, not ice. A larger number of samples was available than originally estimated in the application and this has provided a more detailed chronology. The results are being finalised and will represent the largest data set from the Pyrenees.
Results from the project can eventually be used to address the climate sensitivity of this area of Spain. As part of larger datasets we can look at causes of climate change over long timescales.
The cosmogenic nuclide clean lab was commissioned in a very short period of time which allowed the facility to be used jointly for other projects. Two other successful grant applications were funded as a result of the availability of the lab and a third application has been submitted. The first grant looked at the timing of climate change derived from glaciers compared to carbon dioxide changes at the end of the last Ice Age. The second grant looked at the pattern of climate change during the last Ice Age in Australia. Evidence is often contradictory and enigmatic and our contribution to the grant was to clarify the timing of change using exposure dating on periglacial landscapes.
A number of joint projects have also resulted, including looking at landslides in Malta on limestone, landscape evolution of Hong Kong, the glacial history of Britain, and the timing of climate change in east Africa, including sites in Ethiopia, Kilimanjaro, Lesotho, and South Africa. These projects are in various stages of pilot work, grant application and publication.
The Pyrenees contain one of the best records in Europe of past changes in ice extent. On the dry side of the Pyrenees in Spain, a lack of erosion has preserved multiple glacial moraines along the trunk valleys. Glaciers are a sensitive indicator of climate change, mostly temperature and precipitation; therefore their fluctuations record past periods of climate change. These records are invaluable for determining the sensitivity of an area to climate change through comparison with records from other areas and climate forcing mechanisms.
The Gallego valley in the south-western Pyrenees contains one of the best records of moraines in the Pyrenees. This catchment hosts the modern small Glaciar de l'Inferno which terminates at 2750 m. This glacier has halved in size since the end of the Little Ice Age and is still rapidly retreating. However, moraines mark the former extent of ice down the main valley to surprisingly low levels of 780 m. This project's aim was to quantify the climate change responsible for such large fluctuations.
The second aim of this project was to establish a cosmogenic nuclide clean lab facility for Cl-36. This isotope is not presently as commonly used as isotopes such as Be-10. However, the technique has excellent potential in lithologies where quartz is not present. In the Gallego catchment, half the valley is comprised of rock where quartz is rare (marl) or completely absent (limestone). Therefore we needed this capacity to carry out the project.
The project centred on the Gallego valley system and the neighbouring Aragon valley to the west. The second valley was chosen because of exceptional preservation of moraines at low altitudes, whereas the Gallego valley had the best preservation in the mid and upper altitudes.
Glacier reconstruction depends on being able to identify ice marginal features. During the course of the project we found that mapping was difficult because of the complex topography of the upper catchment. To compensate for this we used two separate approaches. The first relied on 2-dimensional modelling of the glacier profile. This method uses well known characteristics of ice to determine the extent of ice with distance. The second approach was to use a more sophisticated 2-dimensional model of accumulation and ablation coupled with an ice flow model to determine resultant glacier shape. The advantage of this model is that climate inputs can be adjusted iteratively to determine the most likely combination of temperature and precipitation that matches the geological evidence.
Reconstructions of flowlines revealed that the glacier was a maximum of 480 m thick in the trunk of the valley during the maximum extent of glaciation when the glacier was 40 km long and 119 km2. The equilibrium line altitude (ELA), where accumulation of ice equals ablation, was 1500 m. This is a long way down the valley compared to the modern ELA of 2850 m, ~1350 m lower in elevation and more than the global average by some 30%. The results of the glacier modelling were exciting and indicate a new field of investigation in this region. A validation model was run for the modern Glaciar de l'Inferno which produced an excellent match using modern climate fields. When run for the mapped past glacial extents, the cooling was much larger than expected. A cooling of the global average (6 °C) resulted in only a small glacier restricted to the eastern side of the catchment. A cooling of 7 °C was needed to reach the first moraine whereas 8 and 10 °C was needed to reach the two lowest moraines.
Dating of the moraines produced mixed success. Firstly, more quartz was available than originally estimated in some rock types as a very fine detrital component. We designed a new chemical separation protocol to separate this quartz, which was time consuming but produced satisfactory results. However, the amount of chemical erosion on the limestone surfaces was much greater than expected. To account for this, a model of recent erosion has been created and is being used to correct the results.
The dating constrained the fluctuations of the main trunk glacier over three advances. In the western catchment, ice was near its limits during the last glacial maximum at approximately 18 ka, consistent with previous age constraints. Ice persisted in the catchment longer than previously thought, probably to the early Holocene. Debris was still being added to a moraine in the Holocene, but this is likely to have been debris sliding over snow, not ice. A larger number of samples was available than originally estimated in the application and this has provided a more detailed chronology. The results are being finalised and will represent the largest data set from the Pyrenees.
Results from the project can eventually be used to address the climate sensitivity of this area of Spain. As part of larger datasets we can look at causes of climate change over long timescales.
The cosmogenic nuclide clean lab was commissioned in a very short period of time which allowed the facility to be used jointly for other projects. Two other successful grant applications were funded as a result of the availability of the lab and a third application has been submitted. The first grant looked at the timing of climate change derived from glaciers compared to carbon dioxide changes at the end of the last Ice Age. The second grant looked at the pattern of climate change during the last Ice Age in Australia. Evidence is often contradictory and enigmatic and our contribution to the grant was to clarify the timing of change using exposure dating on periglacial landscapes.
A number of joint projects have also resulted, including looking at landslides in Malta on limestone, landscape evolution of Hong Kong, the glacial history of Britain, and the timing of climate change in east Africa, including sites in Ethiopia, Kilimanjaro, Lesotho, and South Africa. These projects are in various stages of pilot work, grant application and publication.