A new timeline for maximum glaciation?
Top image: Sampling sites were often difficult to access. Endre Før Gjermundsen is climbing down to one of the sites in Losvikfjella, east of Magdalenefjorden. Photo: Anne Hormes/UNIS.
PhD candidate Endre Før Gjermundsen studies the extension and age of the ice sheet during the last glaciation in Northwest Spitsbergen and Atomfjellet area. His research indicates that the maximum glaciation of Svalbard might have happened earlier than currently believed.
22 January 2009
Text: Eva Therese Jenssen
The objective of the ICEBOUND project is to create a detailed three-dimensional model of the ice sheet geometry in Northwest Spitsbergen and the Atomfjella area. The results from these areas can be extrapolated to the rest of Svalbard using remote sensing techniques based on satellite imagery and aerial photographs. The timing of the deglaciation of the ice sheet will be constrained by means of surface exposure dating using cosmogenic nuclides 10Be, 26Al and 14C.
The long-term goal is to reconstruct the extension of the late glacial cryosphere on Svalbard in order to deliver improved data for Ice Sheet and Earth System models that test the influence of deglaciation on the ocean circulation system, thus achieving a broader understanding of what might be expected in the future. The researchers aim to provide new data ready to be entered as boundary conditions for Earth System models.
New theory on timeline for Svalbard’s maximum glaciation
The deglaciation timing of the ice extension during the last glacial cycle also has important implications for the uplift history of Svalbard with regard to the whole Svalbard-Barents Sea region. This is potential information as boundary condition for late hydrocarbon migration models and present day leakage in the Barents Sea.
The central hypothesis is that a more comprehensive understanding of the last glaciation ice sheet geometry and the timing for its collapse might not fit into the present hypothesis that Svalbard experienced its maximum glaciation around 25-18 ka BP.
In contrast, the research team from UNIS believes that the maximum glaciation of Svalbard may have been in mid or early-Weichselian and not late Weichselian. The basis for this idea is the critical review of available geochronology data from key locations on Svalbard and increasing evidence from sites around the Svalbard-Barents Sea that the maximum glaciation of the Svalbard/Barents Sea ice sheet was probably earlier than in the late Weichselian.
In the field, by looking at the geomorphology (i.e. the shape of the mountain slopes), Gjermundsen and his UNIS supervisor Anne Hormes were sometimes able to recognize the most likely border of the last glacial ice sheet, defined as the “trimline”. This border could be recognized as a marked terrace or shoulder in the mountain slope despite otherwise homogeneous bedrock geology. In the field rocks were sampled for the age assignments both below and above the trimline.
Assuming that the interpretation of the trimline is correct, the dates achieved from the rocks collected above the trimline should be a lot older than the dates achieved from samples collected below this line.
Two field campaigns in 2008
In spring 2008, the team accomplished two field campaigns, one in Atomfjella and one in Northwest Spitsbergen. In Atomfjella, 20 erratic boulders were sampled at tors and bedrock sites along the east side of Austfjorden. In Northwest Spitsbergen, 26 samples were collected from below and above recognized trimlines and erratic boulders, as well as 9 samples from glacially transported boulders on Reinsdyrflya. Now preliminary results from the first analyses of these samples are awaited by the beginning of 2009.
In spite of the large amount of samples collected in spring 2008, a lot more samples are needed in order to achieve a thorough age constraint for the time of deglaciation in the field areas. It is also necessary to spread samples more geographically within the two field areas, in order to eliminate the risk of mapping only very local small ice caps and not grasping the broad picture for the areas.
In Northwest Spitsbergen 2008 the researchers failed to find glacial striations on the bedrock, a feature which is a secure sign of glacial erosion and thus proves the existence of glacier ice over the bedrock. Searching for glacial striations in this area will therefore be one of the main tasks for the upcoming field season in spring 2009.
In addition, the work in Atomfjella in 2009 will be concentrated on the more central areas at high altitudes, as opposed to the field campaign in 2008 when the team was based in Austfjorden and only worked at the western margin of this mountain range.
Gjermundsens proof-of-concept study demonstrates the findings of nunataks and trimlines and offers the unique possibility to test the hypothesis of the age of deglaciation from these vertical highest points of glacial erosion. ASTER satellite images were used successfully during the field campaigns in order to find potential trimline sites. The bedrock types of erratic boulders on Reinsdyrflya can be used in addition to reconstruct ice flow dynamics during their transportation towards their present location.
This study was supported by the Arctic Field Grant.
(Source: Svalbard Science Forum).