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Palaeoenvironmental developments in the central Scandinavian mountains during deglaciation – a discussion
Abstract
Data from different disciplines are integrated and used to propose an alternative hypothesis regarding the Upper Weichselian environmental developments in the central Scandinavian mountains. This hypothesis, which tries to integrate new and controversial finds and explain them in a new light, is far from proven and needs much further research. It is proposed that parts of the mountains have been glacio-isostatically more depressed than previously thought and that the glacial dynamics could have been much more pronounced than traditionally assumed. As a consequence, it is proposed that Baltic-Bothnian water crossed temporarily ice-free areas with low-altitude thresholds across the Scandinavian mountain range, sporadically allowing drainage towards the Atlantic Sea, and even that Atlantic water could temporarily have entered into Sweden from the west. Such land-water scenarios could have resulted in a water transport system that steered floating tree seeds and sprouts, transported by rivers from central Europe and/or by seawater from the Atlantic, into the mountain range. There, high isostatic rebound rates during early deglaciation phases could quickly have made coastal areas become land, allowing plants to start their life cycle almost immediately.
... Following Svendsen et al. (2004), none of these locations is found in areas known to be ice-free during the LGM (25,000-10,000 years ago). However, the geometry and vertical extent of the Scandinavian ice sheet during the Weichselian have long been debated, and is thought to have been highly dynamic in space and time, intermittently exposing ice-free areas (Kolstrup & Olsen, 2012). In North America, C. s. scirpoidea is predominantly caespitose (i.e. ...
... The 24 populations are colour coded according to their structure group (K = 10; see Figure 3), and ordered geographically from east to west: Norway, East Greenland (E Grl), West Greenland (W Grl), East Canada (E Can), Minnesota, USA (MN), Michigan, USA (MI), Colorado, USA (CO), British Columbia, Canada (BC), Yukon, Canada (YU), and Alaska, USA (AL) al., 2004). However, the vertical extent of the ice at the LGM has been reconstructed in a variety of models as dynamic, thin, multidomed and asymmetric ice sheets with available refugial areas(Arnold, Andel, & Valen, 2002;Kolstrup & Olsen, 2012;Linge et al., 2006;Olsen, 1997). The hypothesis of such highly dynamic ice cover in space and time is coupled with findings of a unique and rare mitochondrial haplotype of spruce with a high frequency in western Norway, and chloroplast DNA of pine and spruce in late-glacial lake sediments from the known ice-free Andøya refugium in northwestern Norway, indicating LGM survival of boreal conifers in northern Scandinavia(Parducci et al., 2012). ...
Quaternary glaciations have played a major role in shaping the genetic diversity and distribution of plant species. Strong paleoecological and genetic evidence supports a postglacial recolonization of most plant species to northern Europe from southern, eastern, and even western glacial refugia. Although highly controversial, the existence of small in situ glacial refugia in northern Europe has recently gained molecular support. We used genomic analyses to examine the phylogeography of a species that is critical in this debate. Carex scirpoidea Michx ssp. scirpoidea is a dioecious, amphi‐Atlantic arctic‐alpine sedge that is widely distributed in North America, but absent from most of Eurasia, apart from three extremely disjunct populations in Norway, all well within the limits of the Weichselian ice sheet. Range‐wide population sampling and variation at 5307 SNPs show that the three Norwegian populations comprise unique evolutionary lineages diverged from Greenland with high between‐population divergence. The Norwegian populations have low within‐population genetic diversity consistent with having experienced genetic bottlenecks in glacial refugia, and host private alleles likely accumulated in long‐term isolated populations. Demographic analyses support one single, pre‐Weichselian colonization into Norway from East‐Greenland, and subsequent divergence of the three populations in separate refugia. Other refugial areas are identified in Northeast‐Greenland, Minnesota/Michigan, Colorado and Alaska. Admixed populations in British Columbia and West‐Greenland indicate postglacial contact. Taken together, evidence from this study strongly indicate in situ glacial survival in Scandinavia.
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... These studies of isostatic adjustment have been used to suggest that the mountains were more glacio-isostatically depressed than previously thought (Kolstrup and Olsen, 2012). If such findings are later validated, changes in subsidence and uplift in response to glacial isostasy will be important for understanding how glacial isostatic adjustment impacts buried hydrocarbons in frontier glaciated basins. ...
... On the mid-Norwegian shelf the timing of retreat is poorly constrained. Luminescence dating has been interpreted to suggest a substantial retreat of the ice margin at~22 ka (Johnsen et al., 2012;Kolstrup and Olsen, 2012), but conflicting marine geophysical and geological evidence suggest that ice was still grounded on the shelf at a similar time (Elliot et al., 2001;Dahlgren and Vorren, 2003) (Fig. 14a). However, at this time the southern and eastern margins of the Fennoscandian Ice Sheet were close to their maximum extent Lasberg and Kalm, 2013) and it thus appears unlikely such a large retreat occurred on the western margin . ...
Our ability to understand the rates and consequences of contemporary climate change is limited by the insufficient duration of instrumental records. Thus, we are not able to fully understand the processes that provide a fundamental control in driving climate changes across different timescales. Palaeo-climate archives, like those preserved offshore Norway, provide our only real window through which to observe long-term rates and styles of climate change. This paper reviews the extensive geological and geophysical data available from the late Cenozoic Atlantic margin of Norway. Along the margin, periods of erosion and deposition have been controlled by agents including fluvial, glacial, and oceanographic processes. Current-controlled sedimentation along the margin provides insight into the connection of the Arctic and Atlantic Oceans from the Miocene onward. Plio-Pleistocene shelf edge progradation of up to 150 km can be linked to the grounding of ice sheets on the continental shelf through observations of buried grounding-zone wedges and mega-scale glacial lineations. The margin is also important for understanding the ability of glaciation to cause topographic relief changes and generate offshore geohazards such as the Storegga Slide, which mobilised some ~ 3000 km³ of sediments during the Holocene. Whilst the processes operating along the Norwegian margin are well-understood through the late Cenozoic, there is little geochronological control with which to constrain the environmental changes that have been observed. Concomitant with the wealth of knowledge and the extensive data that are currently available, we propose that the Norwegian margin is an ideal location to be considered for future ocean drilling. The observations of multiple processes, acting independently and together, means ocean drilling could yield information of global significance due to the bridging location of Norway's Atlantic margin between the Arctic and lower latitudes.
... The climatic amelioration that initiated the Bølling interstadial c. 15.3 ka in Norway lead to significant but still not well recorded ice retreat in the fjord regions. Some dates of plant remains from subtill sediments indicate that the ice retreat may have reached back to the fjord valleys of Mid-Norway during the Bølling interstadial (Kolstrup and Olsen 2012), but dates of marine shells of this age are so far only represented from the coastal zones in most parts of Norway. However, exceptions exist and one of these is found in the area around the Arctic Circle, where shell dates of Bølling age occur at several sites in the fjord region (Olsen 2002). ...
... The subsequent Younger Dryas readvance was of considerable length and reached, for example, at least 10 km west of Oslofjorden (Langesund area, Figure 23), more than 40 km in the area around Bergen (Andersen et al. 1995), from a few kilometres to at least 10-20 km in the Trondheim region (Reite et al. 1999, Kolstrup and Olsen 2012, and in northern Norway at least 50 km in the Ofotfjorden-Vestfjorden area (Olsen et al. 2001, Bergstrøm et al. 2005, more than 30 km in Astafjorden and some 20 km in Salangen, Troms Plassen 2002, Bergstrøm and. Therefore, the readvance during the Younger Dryas was generally apparently more than 10 km, but one exception is known. ...
... In central Norway the line is~350 km east of the maximum and mostcredible lines, which remain close to the Norwegian shelf edge. This minimum line is to accommodate evidence mainly from bulk radiocarbon dates but also OSL ages for a substantial retreat of the SIS during MIS 2 (Olsen & Hammer 2005;Johnsen et al. 2012;Kolstrup & Olsen 2012). This evidence clearly is in conflict and difficult to resolve with some marine evidence that places the western SIS margin advanced on the shelf (Elliot et al. 2001;Dahlgren & Vorren 2003;Rørvik et al. 2010) and the southern and eastern SIS margins close to their maximum extent at this time Lasberg & Kalm 2013). ...
We present a new time-slice reconstruction of the Eurasian ice sheets (British–Irish, Svalbard–Barents–Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time-slice maps of ice-sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice-sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice-margin lines for each time-slice; a most-credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice-sheet area. According to our compilation the westernmost limit along the British–Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 27–26 ka) than the eastern limit on the Russian Plain (at c. 20–19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm2) and volume (~24 m Sea Level Equivalent) at c. 21 ka. Our continental-scale approach highlights instances of conflicting evidence and gaps in the ice-sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time-slices (DATED-1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA (www.bcdc.no; http://doi.pangaea.de/10.1594/PANGAEA.848117).
Adds detail to early Holocene tree exclaves in ice-empty glacier niches
Birks et al. question our proposition that trees survived the Last Glacial Maximum (LGM) in Northern Scandinavia. We dispute their interpretation
of our modern genetic data but agree that more work is required. Our field and laboratory procedures were robust; contamination
is an unlikely explanation of our results. Their description of Endletvatn as ice-covered and inundated during the LGM is
inconsistent with recent geological literature.
Based on new data from the Fladen, Sleipner and Troll areas, combined with earlier published results, a glaciation curve for the Late Weichselian in the northern North Sea is constructed. The youngest data on marine sedimentation prior to the late Weichselian maximum ice extent is 29.4 ka BP. Between 29.4 and c. 22 ka BP, the northern North Sea experienced its maximum Weichselian glaciation with a coalescing British and Scandinavian ice sheet. The first recorded marine inundation is found in the Fladen area where marine sedimentation started close to 22 ka BP. After this the ice fronts receded both to the east and west. The North Sea Plateau, and possibly parts of the Norwegian Trench, were ice-free close to 19.0 ka, and after this a short readvance occurred in this area. This event is correlated with the advance recorded at Dimlington, Yorkshire, and the corresponding climatostratigraphic unit is denoted the Dimlington Stadial (18.5 ka to 15.1 ka). The Norwegian Trench was deglaciated at 15.1 ka in the Troll area. -from Authors
The earth’s response to glacial loading/unloading offers exceptional promise for the study of the physical properties of the lithosphere and mantle because aspects of the isostatic adjustment are very sensitive to mantle rheology and, to a lesser degree, lithosphere thickness. To determine these parameters the earth’s response to deglaciation in Fennoscandia is modelled using a three-dimensional viscoelastic model in which the asthenosphere viscosity, mantle viscosity and lithosphere thickness are allowed to vary so that the maximum rate of present uplift matches its observed value. The ice profile is considered to be known. Comparison of tilting at particular locations and the pattern of present uplift and subsidence using this approach indicates that the lithosphere is less than 50 km thick, the mantle viscosity is 1.0 x 1022 poise and the asthenosphere is 75 km with viscosity 1.3 x 1020 poise.
Mangerud, J.: Late Weichselian marine sediments containing shells, foramitli-fera, and pollen, at Agotnes, western Norway. Norsk Geologisk Tidsskrift, Vol. 57, pp.23-54. Oslo 1977. Marine sediments, mainly clay' and silt, deposited at a water depth of 20-30 m are describeil. The base of the succession is radiocarbon dated to 12.220 + 150 B.P., the upper part to 10,230 + 180. The shells indicate water tempera-tures similar to those of northern Norrvay today. These shells and shells from other localities suggest that warm Atlantic water entered the Norrvegian Sea prior to 12,600 B.P. The pollen diagram from the sediments has the same main trends as in cliagrams from limnic sediments covering the same period, except for high percentages of Alnus. The age and correlation of several Late Weichselian events are discttsscd. J. Mangerud, Geologisk instittttt, Avd.B, Olal Ryesvei 19' N-5014 Bergett-U niv ersitetet, N orw aY. Large areas of Hordaland were deglaciated during the A11er0d Chronozone (Figs. I and l4) (Mangerud 1910,1912 b, Aarseth & Mangerud 1974). LaIer' during the Younger Dryas Chronozone, the ice front re-advanced by at least 40 km. The maximum extent of the inland ice during this re-advance is marked by the Herdla moraines (Aarseth & Mangerud 1974). The Agotnes locality discussed in the present paper lies 2 3 km outside the Herdla moraines (Fig. 1), and includes sediments of both Allerpd and Younger Dryas age. The stratigraphical terminology used here is in accordance with the pro-posals of Mangerud et a]l. (1974). The boundaries of the chronozones (Younger Dryas, Allerod, etc.) are defined in conventional radiocarbon years.
1992: Subglacially formed clastic dikes. Sueriges Geologisha Undersdhning, Ser. Ca 81, pp. 163-170. ISBN 91-7158-518-4. Clastic dikes formed by downward injection or infilling of sediments from the sole of glaciers are reported from many sites around the world. They are of two main types: till dikes consisting of material from the overlying till; and sorted dikes consisting of clay to gravel that can be massive or laminated parallel to the walls. Dikes have been reported to be as much as 2.5 m wide and up to 20 m long. Subglacial dikes can form by crack and fill, by squeeze-in of till (or other plastic material), or by injec-tion of a water/sediment mixture. All these processes require that the base of the glacier is at the pressure-melting point. However, the substrate could be either frozen or unfrozen, the latter situation probably being most common. Crack and fill is obvious in cases where dikes were formed in hard bedrock, but this mechanism can also operate in unlithified and unfrozen substrate. Squeeze-in of till or other plastic material is driven by the weight and movement of the overlying glacier. Injection of a water/sediment mixture into the underlying host sediment takes place as several successive pulses, with widening ofthe fissure and simultaneous depo-sition of each lamina. The latter mechanism requires a steep hydraulic gradient into the subglacial sedi-ments. This may be obtained under different glaciohydrological situations. However, near-margin posi-tion with pore pressure in the subglacier sediments controlled by low water level outside the terminus may perhaps be the most common situation where such gradients are established.
Satellite images provide unique means of identifying large-scale flow-generated lineations produced by former ice sheets. They can be interpreted to reconstruct the major elements which make up the integrated, large-scale structure of ice sheets: ice divides; ice streams; interstream ridges; ice shelves; calving bays. The evolving palaeoglaciological structure of the European ice sheet during its decay from the Last Glacial Maximum (LGM) is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat. During the retreat phase in particular the time-dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed. Crossing lineations are widespread. The older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum, particularly in areas which lay, during deglaciation, beneath ice divides and inter-ice stream ridges, both areas of slow flow and possibly frozen bed conditions. Four phases of growth (A1 to A4) and five phases of decay (R1 to R5) are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle. The growth and decay patterns are quite different and associated with major shifts in the ice divide, reflecting growth from the Fennoscandian mountains and decay away from marine influenced margins. These patterns were determined by the locations of nucleation areas; spatial patterns of climate; and calving at marine margins.The prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming, and that this might reconcile glaciological models and earth rheology models which infer paleao-ice sheet thickness by inverting sea level data.
Widespread glacier acceleration has been observed in Greenland in the past few years associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean. These glaciers thin both at the surface, from warm air temperatures, and along their submerged faces in contact with warm ocean waters. Little is known about the rates of submarine melting and how they may affect glacier dynamics. Here we present measurements of ocean currents, temperature and salinity near the calving fronts of the Eqip Sermia, Kangilerngata Sermia, Sermeq Kujatdleq and Sermeq Avangnardleq glaciers in central West Greenland, as well as ice-front bathymetry and geographical positions. We calculate water-mass and heat budgets that reveal summer submarine melt rates ranging from 0.7+/-0.2 to 3.9+/-0.8md-1. These rates of submarine melting are two orders of magnitude larger than surface melt rates, but comparable to rates of iceberg discharge. We conclude that ocean waters melt a considerable, but highly variable, fraction of the calving fronts of glaciers before they disintegrate into icebergs, and suggest that submarine melting must have a profound influence on grounding-line stability and ice-flow dynamics. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
When a force is applied to the Earth's surface, there is an immediate elastic deformation, proportional to the stress. This paper reports the calculations of the elastic deflections caused by the unloading of the Late Weichselian ice sheets in Fennoscandia. The deflections caused by the unloading of the maximum Late Weichselian ice sheet are calculated to be 76 m in the central parts of the former glaciated area. This is less than 8% of the isostatic response in the same area. When taking into consideration that this displacement is gradually recovered as the Earth readjusts towards isostatic equilibrium, the elastic mechanism can be assumed to be of little importance for the overall postglacial uplift. Maximum elastic deflection in Fennoscandia is calculated to be a subsidence of 12 m in the central parts of the former glaciated area, and 4-5 m along the Norwegian coast, over the last 10,000 years.
The Eigebakken, Jæren, pollen diagram shows a tripartite division of the Late Weichselian into three main climatic periods. The pleniglacial, from local deglaciation c. 14,000 B.P. to c. 13,000 B.P., reflects an Artemisia-dominated pioneer vegetation on disturbed mineral-soil, prevented from further development by cold winters and katabatic winds. The Bøilling amelioration opens the Late Weichselian Interstadial (13,000-11,000 B.P.) and initiates soil development and vegetational closure into a Salix-shrub consolidation phase (to c. 12,650 B.P.). Thereafter an open birch vegetation phase (to c. 12,200 B.P.) follows. The subsequent birch-forest phase (c. 12,200-11,000 B.P.) reflects the interstadial vegetational and edaphical optimum. In this phase July mean temperature reached at least 14°C. In contrast to late-glacial studies from N Rogaland, the Eigebakken diagram gives no biostratigraphical indications of climatic deteriorations such as "Older Dryas" within the interstadial. This is probably explained by denser local birch forests with higher ecological inertia on Jæren. Furthermore, no traces of Fægri's "Brøndymyra interstadial" are recorded. The Younger Dryas Stadial (11,000-c. 10,500 B.P.) shows a two-step regressional succession. In the first step (to 10,600 B.P.) the birch forests degraded into open birch woodland. The second phase (10,600- c. 10,500 B.P.) involved the maximum extent of open-ground vegetation and possibly temporary local deforestation. Critical climatic factors included cold winters and strong winds. The first vegetational responses of the Holoecene climatic amelioration are recorded locally as early as c. 10,500 B.P. Tree-birches re-established, finally developing into dense forests c. 10,000 B.P. Boreal-circumpolar, eurasiatic and arctic-alpine plants dominated the late-glacial flora. For the majority of the late-glacial taxa a northward migration into SW Norway is suggested.
The earth's response to deglaciation in Fennoscandia is modelled using a three-dimensional viscoelastic model in which the asthenosphere viscosity, mantle viscosity and lithosphere thickness are allowed to vary so that the maximum rate of present uplift matches its observed value. The ice profile is considered to be known. Comparison of tilting at particular locations and the pattern of present uplift and subsidence using this approach indicates that the lithosphere is less than 50 m thick, the mantle viscosity is 1.0 × 10²² poise and the asthenosphere is 75 km with viscosity 1.3 × 10²⁰ poise. -from Authors
The ice sheet in the accumulation zone on the northern Jostedal Plateau was relatively thin during the peak of the Late Weichselian glaciation, due mainly to effective ice-drainage through the deep fjords and valleys. A longitudinal profile for the surface of the ice sheet from the northern Jostedal Plateau through More to the edge of the continental shelf has been reconstructed for the Late Weichselian glacial maximum. -from Authors
Based on fourteen radiocarbon datings, mainly of marine molluscs, a shoreline displacement curve has been constructed. The curve is compared to curves based on datings of gyttja, especially the curve from Frosta 30 km further SW. Radiocarbon datings and morphological features at Verdal point to a slow regression during the time interval 7000-8000 BP. A preliminary equidistant shoreline diagram is presented. -from Authors
Frost-shattered bedrock and venifacts interpreted to be abraded by drifting snow or ice particles occur frequently in the wooded areas of northernmost Sweden. Ice-wedge casts and periglacial involutions are encountered more sporadically. The phenomena cannot be explained by the present or the Holocene climate and demonstrably pre-date last deglaciation. The periglacial activity dates from the local Tarendo Interstadial, tentatively correlated with Odderade. A similar situation appears to prevail in northernmost Dalecarlia and parts of Harjedalen and Jamtland in central Sweden. -from Author
Seven localities with fossil-bearing tills were found in the Alesund area. Fifteen radiocarbon dates of marine shells in the tills all gave ages between 28 000 and 38 000 yr BP. The ice-free period is named the Alesund Interstadial, and its Middle Weichselian age is also suggested by amino acid D/L ratios in shells, compared with Late Weichselian and Eemian ratios.-from Authors
Regional Quaternary stratigraphy, fossil content (marine mollusc shells, dinocysts, pollen, etc.), some palaeomagnetic data, and more than 200 datings, mostly AMS-14C datings of organic-bearing tills and sub-till waterlain sediments from the northern, central and southern parts of Norway are the basis for construction of nine glaciation curves from the inland to the coast and shelf, and for interpretation of the palaeoclimate. The results show rapid shifts between glacial and interstadial conditions in semi-cycles of five thousand to seven thousand years in the interval from c. 40-45 ka to 10 ka (14C) BP. We describe these glacial variations in a new model which reflects rapid and rythmic glacier fluctuations. The conclusions with regard to number and size (extent) of the glacial and interstadial events are based on stratigraphy, whereas the timing and rapidity of events are based on dates. All these basis data are presented more thoroughly in an accompanying paper (this volume). The interstadials are named the Hattfjelldal interstadial I (30-39 ka BP) and II (24-27 ka BP), and the Trofors interstadial (17-21 ka BP). Previously reported interstadials are extended in this study to include larger inland areas, indicating extreme fluctuations several times both in the extent and volume of the ice. Considerable ice retreat with very extensive ice-free areas in several parts of Norway during the last two interstadials (c. 24-27 and c. 17-21 ka BP) have not been reported before, except for preliminary short notices from our studies. The stratigraphical record includes many indications of high pre-Holocene relative sea-levels, suggesting a considerable glacial isostatic depression of western Scandinavia during the interstadials. We suggest that, in addition to precipitation, the mountainous fjord and valley topography, glacial isostasy and relative sea-level changes were probably more important for the size of the glacial fluctuations than the air-temperature changes.
Radiocarbon datings of a 4.10 m long lacustrine sequence from Lake Ovre AErasvatn reveal continuous sediment accumulation during most of the Late Weichselian, starting before 21 800 BP. The pollen record for the period 21 800 to 12 800 BP is uniform and is strongly dominated by Poaceae. Pollen influx variations suggest a succession of climatic ameliorations and deteriorations which are described. -after Author
[1] Project BIFROST (Baseline Inferences for Fennoscandian Rebound Observations, Sea-level, and Tectonics) combines networks of continuously operating GPS receivers in Sweden and Finland to measure ongoing crustal deformation due to glacial isostatic adjustment (GIA). We present an analysis of data collected between August 1993 and May 2000. We compare the GPS determinations of three-dimensional crustal motion to predictions calculated using the high-resolution Fennoscandian deglaciation model recently proposed by Lambeck et al. [1998a, 1998b]. We find that the maximum observed uplift rate (∼10 mm yr−1) and the maximum predicted uplift rate agree to better than 1 mm yr−1. The patterns of uplift also agree quite well, although significant systematic differences are evident. The root-mean-square residual rate for a linear error model yields estimates of rate accuracy of 0.4 mm yr−1 for east, 0.3 mm yr−1 for north, and 1.3 mm yr−1 for up; these figures incorporate model errors, however. We have also compared the values for the observed radial deformation rates to those based on sea level rates from Baltic tide gauges. The observational error for the vertical GPS rates required to give a reduced χ2 of unity is 0.8 mm yr−1. The time series do exhibit temporal variations at seasonal frequencies, as well as apparent low-frequency noise. An empirical orthogonal function analysis indicates that the temporal variations are highly correlated among the sites. The correlation appears to be regional and falls off only slightly with distance. Some of this correlated noise is associated with snow accumulation on the antennas or, for those antennas with radomes, on the radomes. This problem has caused us to modify the radomes used several times, leading to one of our more significant sources of uncertainty.
For the first time, Holocene macroremains (cones and wood) of Larix sibirica Ledeb., radiocarbon dated between 8700 and 7500 BP, have been recovered from two sites in the Scandes Mountains of Sweden. The sites are separated by >300 km and lie in the present subalpine and low alpine belts, respectively. Existing pollen-stratigraphical records have not suggested the presence of Larix in the Holocene beyond its present range, i.e. >1000 km to the east in Russia. Hence, the pollen analytical method should be used more cautiously when inferring subcontinental-continental biogeographical dynamics. It appears that Larix immigrated rapidly by longdistance jump dispersal soon after the deglaciation. The same pattern has emerged for Picea abies (L.) Karst. and some thermophilous broadleaved tree species. This might be a more general mechanism for tree spread during the early Holocene. Step-wise migration and migrational lags could be quite unimportant elements within tree palaeobiogeography. This increases the prospects for interpretation of longterm and large-scale changes in plant cover performance in terms of expansion/decline relative to climatic change. Today, Larix sibirica prospers in continental climates with extremely cold winters, thus it is reasonable to infer that early-Holocene winters in western Fennoscandia could have been similar to, or slightly colder than those of today. This contention conflicts with previously published simulations using General Circulation Models, pollen-climate response surfaces and other retrospective devices, which suggest a strongly oceanic climate with winters >2<sup>⚬</sup>C warmer than present.
The evolution of ice-sheet configuration and flow pattern in Fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model, i.e. a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets. The model uses mapped flow traces and deglacial melt-water landforms, as well as relative chronologies derived from cross-cutting striae and till lineations, as input data. Flow-trace systems were classified into four types: (i) time-transgressive wet-bed deglacial fans, (ii) time-transgressive frozen-bed deglacial fans, (iii) surge fans, and (iv) synchronous non-deglacial (event) fans. Using relative chronologies and aggregation of fans into glaciologically plausible patterns, a series of ice-sheet configurations at different time slices was erected. A chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume. Geological evidence exists for several discrete ice-sheet configurations centred over the Scandinavian mountain range during the early Weichselian. The build-up of the main Weichselian Fennoscandian ice sheet started at approximately 70 ka, and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern Norway. This configuration had a flow pattern which is poorly reproduced by current numerical models of the Fennoscandian ice sheet. At the Last Glacial Maximum the main ice divide was located over the Gulf of Bothnia. A major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the Scandinavian mountain chain. Widespread areas of preserved pre-late-Weichselian landscapes indicate that the ice sheet had a frozen-bed core area, which was only partly diminished in size by inward-transgressive wet-bed zones during the decay phase.
Recent work has suggested that the Scandinavian ice sheet was much more dynamic than previously believed, and its western marine-based margin can provide an analogue to the rapid-paced fluctuations and deglaciation observed at the margins of the Antarctic and Greenland ice sheets.In this study we used a complimentary dating technique, OSL (Optically Stimulated Luminescence dating), to support the existence of the Trofors interstadial in central Norway; an ice-free period that existed from ∼25 to 20 ka recorded at multiple sites throughout Norway (cf. Andøya interstadial) and that divides the Last Glacial Maximum (LGM) into two stadials. OSL signal component analysis was used to optimize data analysis, and internal (methodological) tests show the results to be of good quality. Both large and small aliquots gave consistent OSL ages (22.3 ± 1.7 ka, n = 7) for sub-till glaciofluvial/fluvial sediments at the Langsmoen stratigraphic site, and an apparent old age (∼100 ka) for a poorly-bleached sample of glaciolacustrine sediment at the nearby stratigraphically-related Flora site. Eight radiocarbon ages of sediment from the Flora site gave consistent ages (20.9 ± 1.6 cal ka BP) that overlap within 1σ with OSL ages from the nearby Langsmoen site.The similarity in age within and between these stratigraphically-related sites and using different geochronological techniques strongly suggests that this area was ice-free around ∼21 or 22 ka. The existence of the Trofors interstadial along with other interstadials during the Middle and Late Weichselian (MIS 3 and MIS 2) indicates that not only the western margin, but the whole western part of the Scandinavian ice sheet, from the ice divide to the ice margin was very dynamic. These large changes in the ice margin and accompanying drawdown of the ice surface would have affected the eastern part of the ice sheet as well.
Megafossil wood remnants (trunks and roots) of mountain birch (Betula pubescens ssp. tortuosa) were retrieved from the alpine tundra of the southern Swedish Scandes (the Sylarna Mountains). The samples have recently become exposed by rapid recession of glaciers and snow patches at three sites located 630 to 350 m higher than the present-day birch tree-limit and 350 to 80 m higher than the early Holocene pine limit. Radiocarbon dating yielded ages ranging between 8700 and 6200 B.P. (9700–7000 cal B.P.). This is the first direct evidence of past tree growth at such high elevations in the Scandes, relative to the modern tree-limit. The overall situation with uniquely high tree-limits and absence of glaciers suggests a climate with generally drier and warmer summers than during any later part (secular-millennial scale) of the Holocene. Corrected for glacioisostatic land-uplift, summers around 8700 B.P. may have been about 3°C warmer than at present. This inference is compatible with the Milankovitch model of orbital climate forcing during the course of the Holocene, implying a gradually increasing maritime climate (less seasonal), with a heavier snowpack. As a consequence, alpine snowfields started to develop over the period 8700–6200 B.P., causing demise and burial of the highest metapopulations of mountain birch. At lower elevations, where snow accumulation had previously been suboptimal for birch, this species could now benefit from a deeper and more persistent snow cover. Since about 7000 B.P., a distinct mountain birch belt has been a characteristic feature in this part of the Scandes. The exposure of mountain birch megafossils relates to substantial 20th-century warming, reaching a peak in the past few years. Evidently, this is an exceptional occurrence in the context of several past millennia.
The glacigenic sequence on the continental shelf and shelf break in the Barents Sea has been mapped seismostratigraphically. The outer shelf units increase in thickness towards the shelf break, except for the youngest one. The two youngest units also have a blanketing character. The geometry of the younger units gives indications of source areas, as well as of ice movement direction of subsequent eroding ice sheets. The palaeoenvironment and palaeogeography during the mid-late Weichselian in the Barents Sea is reconstructed. -from Authors
The onshore record of Middle to Late Weichselian sediments and glacial history in Norway indicates a succession of four major ice advances alternating with rapid, considerable ice recessions and interstadial conditions. During all the glacial advances the ice sheet expanded from onshore/inland positions to the shelf areas. The basis for visualizing these variations in glaciation curves constructed along nine transects from inland to shelf, and for interpretation of the palaeoclimatic history, is the regional Quaternary stratigraphy, more than 300 datings, fossil content and some palaeomagnetic data. The methods applied in recent years for AMS radiocarbon dating of glacial sediments with low organic carbon content have given promising results with respect to accuracy and precision, and the results of such datings were an important tool for our reconstructions and for timing of the ice oscillations. The rapid and rhythmic ice fluctuations, as reconstructed in our new model, have been fairly synchronous in most parts of Norway. Ice advances commenced and culminated at 40, 30-28, 24-21 and 18-15 (14C) Kya. We describe three intervening interstadials from inland sites: Hattfjelldal I, Hattfjelldal II and Trofors. Our stratigraphical record also includes many indications of high, pre-Holocene, relative sea levels, suggesting a considerable glacioisostatic depression of western Scandinavia during the interstadials. In our glaciation model we suggest that, in addition to precipitation, the mountainous fjord and valley topography, glacial isostasy and relative sea level changes were probably more important for the size of the glacial fluctuations than were air temperature changes.
Shore-level displacement and glacio-isostatic uplift in the area affected by the Scandinavian ice is calculated from empirical data. Besides 79 shore-level curves from Scandinavia the calculations are also based on some detailed lake-tilting investigations and information concerning present relative uplift recorded by precision levelling and tide gauge data. The course of glacio-isostatic uplift is expressed in solely mathematical terms. The model is transformed to a GIS-application using levelling data. Maps showing the distribution between land, lakes and sea at different times are produced by this application. These maps can also be designed to show changes of the hydrography through time including changes in lakes, glacial lakes, rivers and drainage basins. The accuracy of the calculated shore-levels is generally very high. A result of the calculation is that the existence of the Baltic Ice Lake is questioned as both the calculations and an analysis of the earlier used proofs of the Baltic Ice Lake show that the Baltic basin was most probably at sea level.
Based on grain-size distribution and sea floor photographs, the sea bed sediments between Bergen and Måløy have been divided into four groups: (A) sand with coarse material on the northern part of the North Sea Plateau and the Måløy Plateau; (B) very well sorted sand on the southern part of the North Sea Plateau and the upper part of the western slope of the Norwegian Trench; (C) silty, clayey sand in lower part of the slopes; (D) silty, sandy clay in the central part of the Norwegian Trench. Large local variations are found in the group A sediments, on the Måløy Plateau partly caused by relict iceberg plough marks. The net deposition after the transition to boreal conditions with Atlantic water about 10,000 yrs ago is mostly between 0 and 30 cm on the northern part of the North Sea Plateau and exceeds 200 cm in the deepest parts of the Norwegian Trench. The total thickness of sediments above assumed overconsolidated material has been mapped based on sparker records. On the northern part of the North Sea Plateau the sediment cover above a supposed wavecut platform is less than 1 m over large areas, while a Late Weichselian coastal unit fringing the plateau consists of up to 40 m of sand and gravel. On the southern part of the plateau and the upper part of the western slope of the Norwegian Trench up to 10–30 m of sediments are found, probably dominated by sand formed by wave and tidal current action during a period of low sea level. In the central part of the trench a total thickness of up to 40 m of clay deposited during varying environments is found. Most of the investigated area is believed to be underlain by a till deposited by a north-northwestward moving ice sheet.
As recently as 7 years ago Quaternary geologists believed that there were no Pleistocene paleosols represented by non-peaty soil horizons (A, B, etc.) in Norway. However, several buried soils of this type have recently been reported and studied by stratigraphic, magnetic and chemical methods. Magnetic susceptibility is a useful method for identifying and correlating paleosols, even in areas of complex glacial stratigraphy such as the Nordic countries. At Sargejohka in Finnmark, up to seven different buried pedocomplexes are separated by tills and glaciotectonic deformation structures. They represent different periods of land surface stability and, with two possible exceptions, are not pseudosoils formed by a fluctuating groundwater table. The most important from stratigraphic and paleoclimatic points of view is a well-developed red–yellow paleosol numbered p3 counting down from the top. It is thought to be a podzol of the last interglacial. Later cryoturbation of pre-Mid Weichselian age has greatly altered its upper part, indicating a dramatic change in climate after development of the soil. At Lillehammer in southeastern Norway, remains of the oxidised zone of a buried paleosol, also thought to have formed mainly in the last interglacial, occur in an inferred Saalian till. The presence of buried Pleistocene paleosols in the interior of Norway (central part of the Fennoscandian glaciations) indicates that glacial erosion was locally less during several glacial cycles than previously thought.
Palaeoclimate changes in the North Atlantic region during the last glacial–interglacial transition (LGIT) were not only abrupt but were also spatially complex: the major climate shifts appear to have been time transgressive, with some areas experiencing cooling at the same time as others were experiencing warming. The construction of the data bases of palaeoclimatic information for this period is therefore far from straightforward, and requires exacting procedures for quantitative climate reconstruction, as well for the dating and correlation of site records. High-precision correlations of events that occurred within the LGIT are, however, difficult to effect using conventional methods of radiocarbon dating, biostratigraphy and lithostratigraphy. One method that offers considerable potential for solving issues of chronology and correlation, as well as for testing ideas about non-synchronous responses to climate variations during the LGIT, is tephrochronology. Recent discoveries of high concentrations of micro-tephra particles in LGIT sequences in northern Europe extend the region over which high-precision correlations will be possible.
A major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment transport efficacy. Here we present the first well-constrained data on sediment flux from a paleoice stream. This has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet of the Norwegian Channel ice stream, and converting to a flux measurement by accounting for the duration of streaming in this episode (between 20 and 19 ka during the last glacial stage). In this period the ice stream delivered an average 1.1 Gt of sediment per year, equivalent to 8000 m3yr-1 per meter width of ice stream front. The calculated flux is an order of magnitude higher than most previous estimates for other paleoice streams and is comparable to the present sediment flux from the world's largest rivers. The short period of debris-flow deposition suggests that the Norwegian Channel ice stream underwent rapid on-off switching, with punctuated iceberg delivery to the North Atlantic as a consequence.
This paper reviews megafossil evidence for the first postglacial records of different tree species in northern Scandinavia. Betula pubescens coll. appeared at the Arctic coast of northern Norway by 16, 900yrBP. In addition, Betula pubescens (14, 000yrBP), Pinus sylvestris (11, 700yrBP) and Picea abies (11, 000yrBP) existed on early ice- free mountain peaks (nunataks) at different locations in the Scandes during the Lateglacial. Larix sibirica, currently not native to Fennoscandia, and several thermophilous broadleaved tree species were recorded in the earliest part of the Holocene. The conventional interpretation of pollen and macrofossil records from peat and sediment stratigraphies do not consider the occurrence of the species mentioned above that early at these northern and high altitude sites. This very rapid arrival after the local deglaciation implies that the traditional model of far distant glacial refugial areas for tree species has to be challenged. The current results are more compatible with a situation involving scattered “cryptic” refugia quite close to margin of the ice sheet at its full-glacial extension. This fits a more general pattern currently emerging on different continents. In general, “cryptic” refugia should be considered in connection with modelling extinction risks related to modern and possible future “climatic crises”.
The stratigraphy in Hamnsundhelleren is as follows. A basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the Laschamp excursion (43–47 000 yr BP). Angular blocks, bones and clay above this are 14C dated to the Ålesund Interstadial (28–38 000 yr BP). Another stadial laminated clay following the Ålesund Interstadial includes a palaeomagnetic excursion correlated with Lake Mungo (28 000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost-weathered clay and scattered angular blocks. It is 14C dated to 24 500 yr BP on bones mixed into the Ålesund Interstadial. The Hamnsund Interstadial is succeeded by another stadial laminated clay and then a Late-glacial–Holocene mixture of bones and blocks.In Hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice-free–ice-covered cycle have been identified: (i) ice-free phase (deposition of bones and frost-weathered blocks); (ii) subaerial ice-dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice-dammed lake phase (cave closed by ice, deposition of till, debris flows and laminated clay); (d) ice-plugged phase (cave is plugged by frozen lake water and/or glacial ice, no deposition).
Reconstruction of the ice extent and glacier chronology on the continental shelf off mid-Norway has been severely hampered by the lack of dates from the glacial deposits. Seismic interpretation and new accelerator mass spectrometer radiocarbon dates show that the ice sheet extended to the edge of the continental shelf at the last glacial maximum. The two youngest till units near the shelf edge were deposited about 15,000 and 13,500 BP. The results indicate that the ice sheet partly reached the shelf break as late as 13,000 BP, followed by a deglaciation of most of the continental shelf in less than 1000 years.
After the first emergence following deglaciation, relative sea level rose by 10 m in western Norway and culminated late in the Younger Dryas (YD). The relative sea-level history, reconstructed by dating deposits in isolation basins, shows a sea-level low-stand between $13 640 and 13 080 cal yr BP, a 10 m sea-level rise between $13 080 and 11 790 cal yr BP and a sea-level high-stand between $11 790 and 11 550 cal yr BP. Shortly after the YD/Holocene boundary, sea level fell abruptly by $37 m. The shorelines formed during the sea-level low-stand in the mid-Allerød and during the sea-level high-stand in the YD have almost parallel tilts with a gradient of $1.3 m km À1 , indicating that hardly any isostatic movement has taken place during this period of sea-level rise. We conclude that the transgression was caused by the major re-advance of the Scandinavian Ice Sheet that took place in western Norway during the Lateglacial. The extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea. Our results show that the crust responded to the increased load well before the YD (starting $12 900 cal yr BP), with a sea-level low-stand at 13 640 cal yr BP and the subsequent YD transgression starting at 13 080 cal yr BP. Thus, we conclude that the so-called YD ice-sheet advance in western Norway started during the Allerød, possibly more than 600 years before the Allerød/YD transition.
Altitude relationships between shore forms and their sea levels are investigated. Raised shore lines are measured in a large number of localities. Equidistant shore-line diagrams are constructed and used for relative dating purposes. Late Glacial shore lines older than the Main line (Younger Dryas time) seem to have larger gradients than assumed in previous studies. Selected glacial landforms are mapped and interpreted. In the investigated area, the ice reached beyond the coast of Finnmark during the last Glacial maximum. Distinct end moraines mark numerous halts during the subsequent ice recession. Margins of sub-stages are traced, and local glaciers and accumulation centres are located. The Main sub-stage moraines are best developed regionally. Important aspects of deglaciation patterns and ice-directed drainage are described. Streamlined forms are analysed in relation to topography, and axes of fossil inland dunes measured.
Based on diatom analysis, pollen analysis and radiocarbon dating, a shore-level displacement curve has been constructed for Nord-Jæren, south-west Norway. The upper marine limit on Nord-Jæren, 25–26 m above sea level, must be older than 13 100 ± 190 years B.P. A regression throughout B⊘lling and Older Dryas times reached down to 11–14 m a.s.l. in Aller⊘d time before a short-lived transgression to approximately 21 m a.s.l. occurred in the transition between Aller⊘d and Younger Dryas. The curve then falls quickly through Younger Dryas.
This paper presents a new hypothesis on spreading and immigration of pioneer plants. It is speculated that during phases of sudden climate warming, seeds and other parts of plants were transported by rivers from central Europe into the North Sea and the Baltic areas and drifted on to surrounding shores. Some parts have remained in the records as macrofossils, while in other cases the plants are proposed to have continued their life cycle in the new areas. The principle is illustrated by examples from different areas and times: Weichselian Lateglacial finds in NW Germany suggest that tree trunks were brought northward. For central and northern Sweden exceptionally strong glacio-isostatic rebound could have followed pronounced land surface depression after the ice-sheet meltings. This would have transformed coasts to land quickly, promoting the growth of seeds and plants in areas that are now far inland. If this hypothesis is valid it can explain the presence of anomalously early, warm vegetations in newly deglaciated areas. The rapidity of water-borne immigration following a climatic warming can also open up for a possibility of quick immigration to other former near-coast areas and river banks in Europe. Based on an example of a warmth requiring palaeovegetation at Vrøgum in Denmark and the fact that trees survived in central Europe during the coldest part of the Weichselian it is suggested that short-lived, palaeobotanically hitherto unknown warm phases might be worth looking for in the terrestric records.
It is a reply to: “Cosmogenic dating of the Pomeranian Moraine: adding a regional perspective” by Michael Houmark-Nielsen, Svante Björck and Barbara Wohlfarth