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- Goodfellow, Bradley W., et al.
(författare)
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Last ice sheet recession and landscape emergence above sea level in east-central Sweden, evaluated using in situ cosmogenic 14C from quartz
- 2024
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Ingår i: GEOCHRONOLOGY. - 2628-3719. ; 6:2, s. 291-302
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Tidskriftsartikel (refereegranskat)abstract
- In situ cosmogenic C-14 (in situ C-14) in quartz provides a recently developed tool to date exposure of bedrock surfaces of up to similar to 25 000 years. From outcrops located in east-central Sweden, we tested the accuracy of in situ C-14 dating against (i) a relative sea level (RSL) curve constructed from radiocarbon dating of organic material in isolation basins and (ii) the timing of local deglaciation constructed from a clay varve chronology complemented with traditional radiocarbon dating. Five samples of granitoid bedrock were taken along an elevation transect extending southwestwards from the coast of the Baltic Sea near Forsmark. Because these samples derive from bedrock outcrops positioned below the highest postglacial shoreline, they target the timing of progressive landscape emergence above sea level. In contrast, in situ C-14 concentrations in an additional five samples taken from granitoid outcrops above the highest postglacial shoreline, located 100 km west of Forsmark, should reflect local deglaciation ages. The 10 in situ C-14 measurements provide robust age constraints that, within uncertainties, compare favourably with the RSL curve and the local deglaciation chronology. These data demonstrate the utility of in situ C-14 to accurately date ice sheet deglaciation, and durations of postglacial exposure, in regions where cosmogenic Be-10 and Al-26 routinely return complex exposure results.
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| 2. |
- Ruskeeniemi, Timo, et al.
(författare)
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Subglacial permafrost evidencing re-advance of the Greenland Ice Sheet over frozen ground
- 2018
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 199, s. 174-187
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Tidskriftsartikel (refereegranskat)abstract
- Greenland Ice Sheet (GrIS) covers an area of 1.7 million km(2). It has been an important source of climate information and the air temperature history of Greenland is well known. However, the thermal history and temperature conditions of the Greenland bedrock are poorly known. There are only few records on the temperature of the proglacial bedrock and no records on bedrock temperature underneath the ice sheet. The Greenland Analogue Project (GAP) recently investigated hydrological, hydrogeological and geochemical processes in Kangerlussuaq, West Greenland. Because permafrost has a major hydrological impact in Arctic regions, the cryogenic structure of the bedrock was an important research topic. From previous studies it was already known that Kangerlussuaq is located within the zone of continuous permafrost. Temperature profiling in a new research borehole, extending horizontally 30 m underneath the ice sheet, revealed that permafrost is 350 m deep at the ice margin. This result raised the question how far the permafrost extends under the ice sheet? In order to investigate the thermal properties, we made a series of electromagnetic (EM) soundings at the ice margin area - on proglacial area and on the ice sheet - and detected, that subglacial permafrost extends at least 2 km from the ice margin to inland. We also observed a patchy unfrozen sediment layer between the ice and the frozen bedrock. Possible existence of subglacial sediments and their role in ice dynamics has been debated in many recent papers. Our successful campaign shows that geophysics can be used for bedrock investigations through thick ice, which is known to be challenging for electromagnetic methods. Our results provide the first direct evidence supporting the proposed Holocene ice re-advance over frozen ground, and contribute to the discussion on the rapid climate changes in past, to the future of the ice sheet under warming climate and hydrogeology at the ice margin.
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