Two and a half meters of sediments from Lake Heimtjønna in the Scandes Mountains reveal changes in the vegetation, climate, and sediment environment since deglaciation. The lake was deglaciated in ...the Late-Glacial (LG), perhaps as early as 16-18 ka cal BP. After deglaciation, the sediment environment at the Heimtjønna coring point was extraordinary and challenging to interpret. The genesis of the 1.7 m basal unsorted sediments including large stones is discussed concluding that the layer was rafted by lake-ice after the LG deglaciation. The Younger Dryas (YD) established a semi-perennial lake-ice that stopped the deposition of the ice-rafted stone-rich sediments. In the early Holocene, the unstratified and well-sorted clayey silt shows fluvial origin. In late Holocene, strong flood activity including the major flood disaster ‘Stor-Ofsen’ in AD 1789, caused a sediment hiatus at the coring point from ca 9.5 ka cal BP to ca 250 a cal BP. The LG interstadial warming initiated the succession from pioneer plants on mineral soils towards local dwarf-shrub heath. July temperatures reached at least 7–8 OC. In the LG and early Holocene, Papaver radicatum, Artemisia norvegica, and Campanula cf. uniflora today occurring at Dovre and with centric Scandinavian distributions, locally established. All have previously been connected to Weichselian survival on nunatak refugia. Continuous pollen curves of spruce (Picea abies) support the much-debated LG and early Holocene presence of spruce in the Scandes mountains. For the first time, it is shown that both grey alder (Alnus incana) and Armeria occurred in the Scandes in the LG and early Holocene. Due to dating errors, LG ages is exclusively based on stratigraphical correlations and considerations. The LG chronology must be thoroughly tested by future studies providing reliable AMS 14C-dates of terrestrial fossils.
The result of 344 radiocarbon-dated megafossils is here presented and discussed. This study aims at elucidating early- to mid-Holocene forest-line and climate dynamics in the southern Scandes along a ...present gradient of decreasing forest-line elevations. Around 9.5 calibrated ka before present (BP), pine suddenly established vertical belts of at least 200 m. These represent the highest pine-forests during the Holocene, ca. 210–170 m higher than today when corrected for land uplift. By this, summer temperatures at least 1–1.3°C warmer than today are indicated for the early Holocene thermal maximum around 8.5–9.5 cal. ka BP. The most pronounced warming occurred in Jotunheimen, the highest mountain range in Scandinavia, because of an amplified ‘Massenerhebung’ effect. Megafossils show the establishment of birch-forests above pine-forests already from the early Holocene. Pine-forests started their decline in the early Holocene and became replaced by the less warmth-demanding birch-forests. Pine megafossil results and pollen studies from the same areas show that cooling around 8.5 cal. ka BP caused a significant decrease in pine pollen production whereas pine-forest-lines were more or less unaffected. In the following period of about 2000 years, the high-altitudinal pine-forests could hardly be detected in pollen diagrams. This shows how strongly past temperatures influenced on the pollen production of individuals and how this might obscure pollen-based reconstructions of past vegetation. To be able to correct for this error, there is a need for establishing exact present-day relationships between temperature and pollen production of prolific pollen producers.
Precise and accurate reconstructions of past environmental parameters from high-quality palaeoenvironmental studies are critical for realistic testing of climate models. To ascertain the reliability ...of the reconstructions of the past, cross-validation from a variety of proxies and methods is essential. Mid-Scandinavia, showing a variety of palaeoecological studies, is a suitable region for comparing and validating environmental reconstructions. Here, pollen-based transfer-function reconstructions show inconsistent late-glacial temperature patterns. They also show that the Holocene Thermal Maximum (HTM) occurs at ca. 7.5—4.5 cal. ka B.P. However, thermal indicators (pollen, megafossils, plant macrofossils) place the HTM at no later than ca. 10—7.5 cal. ka B.P. It is argued that after the onset of the early Holocene warming equilibrium between vegetation and climate was established over a prolonged period; i.e. ca. 1,500 and 4,000 years in the mountains and lowlands, respectively. In the mountains, soil drought, wind and winter stress were important factors causing the lag, whereas interspecific competition and soil development delayed the succession within the species-diverse lowland forests. These lags when vegetation was not filling its thermal potential result in a distortion of the temperature signal as derived by transfer functions which assume that vegetation is essentially in equilibrium with climate. Due to widespread human impact and erosion today, many modern training set samples are unsuitable as reference material for past environmental conditions. Various recommendations are suggested towards making improvements in the pollen-transfer function approach to climate reconstructions. To overcome the difficulties resulting from vegetation lags in the early Holocene, proxies that have a faster response time to climate, such as chironomids and aquatic plants including algae, may replace terrestrial pollen.
Basin sediments from Bjerkreim, SW Norway, have been analyzed regarding pollen, plant macrofossils, chironomids, palaeomagnetism, elements, volcanic ash, and loss-on-ignition. The chronology is based ...on the Vedde Ash and Saksunarvatn ash layers and radiocarbon dates of plant and insect macrofossils. The records spanning the period from local deglaciation around 16 ka BP to the early Holocene ca 10.2 ka BP, have given new detailed information of the late-glacial environments. In the cold pre-Bølling (prior to 14.6 ka BP), open pioneer vegetation on unstable mineral soils was dominant. After the Bølling warming, climate became moister and reached the late-glacial thermal maximum (July mean of 12–13 °C), and dominant dwarf shrubs and snow beds established. Shallow soils, strong winds, and drought may have restricted vegetation development. Despite colder summers (July mean of 9.5–11 °C) in Allerød 13.9–12.8 ka BP, fertile humus-soils developed, and shrub vegetation and open birch-forests established. Snow beds regained dominance in Younger Dryas (July mean of 6.5–9 °C). The early Holocene warming initiated rapid establishment of early Betula/Populus-forests and the later Corylus forests around 10.7 ka BP. Three cooling events in the Bølling-Allerød interstadial (Older Dryas/GI-1d, G1-1c2, GI-1b/Gerzensee) temporarily increased open-ground vegetation showing the ecotonal position of Bjerkreim with low resistance to these changes. The Empetrum expansion was delayed (from 14.5 to 13.7 ka BP) towards the east along the coast of Rogaland. This could point to a precipitation/outwash gradient decreasing towards the east and developing the acid soils necessary for Empetrum to expand. For the first time, macrofossils show the late-glacial presence of tree-birch in Norway. Tree-birch were sparse in Bølling and formed patches of open-forests in Allerød. Several pollen taxa previously thought to reflect long-distance dispersal, such as Populus, Hippohaë, Jasione, and Sanguisorba ssp., most probably were present in Rogaland during Late-glacial. Doggerland seem to have been important for the late-glacial northwards migration of plants into South Norway.
•Bjerkreim.•After deglaciation (16 ka BP), sparse tundra vegetation of cold-adapted species developed.•Macrofossils show local tree-birch since Bølling and open forests in Allerød.•Moist coastal climate caused the early establishment of Empetrum and tree-birch.•Three cold events occurred around 14, 13.7 and 13 ka BP in the LG interstadial.•Doggerland was important for the immigration of species into South Norway.•Re submission of ms:
Detailed pollen analysis and pine megafossils from the immediate area of Rødalen in Central Norway have revealed new knowledge of Holocene alpine environments. A period of about 1,000 years ...characterised by pioneer herbs, dwarf-shrubs (Betula nana, Empetrum) and Juniperus followed the Holocene climatic amelioration. Local birch forest became established around 10.3 ka B.P., ca 150 years earlier than the local pine rise. Pine dominated at 1,100 m a.s.l. from 9.9 to 8.5 ka B.P., followed by birch forests until 1.3 ka B.P. when deforestation occurred. Slightly after 6 ka B.P., pine forests disappeared from the valley floor (930 m a.s.l.), an area that today is dominated by birch forest. Three short-lasting vegetational set-backs at ca 10.7, 10.5 and 10.3 ka B.P. may indicate climate oscillations. A temporary reduction of local forests reflects the Erdalen 2/9.7 ka B.P. event. The influence of the 8.2 event, superimposed on a cooling trend, lasted ca 400 years and involved a two-step vegetational regression: (1) A strong reduction of pine forests due to cooling and (2) reduction of alder due to cold and drought. Winter stress preventing pine regeneration may have caused scarcity of pine megafossils from the latter period. In the early Holocene, vegetation in the present alpine region was not in equilibrium with temperature development. It is suggested that the birch forest establishment lagged by about 1,000 years due to drought, whereas winter stress may have delayed the establishment of pine even longer.
We describe glaci-lacustrine sediments buried under thick tills in Folldalen, south-east Norway, a site located close to the former centre of the Scandinavian Ice Sheet. Thus, the location implies ...that the ice sheet had melted when the sediments were deposited. The exposed ground was occupied by arctic vegetation. The best age estimate from 20 quartz luminescence dates is 55.6 ± 4.6 ka. Due to possible incomplete bleaching, an age in the younger part of the time range is most probable. We conclude that the Scandinavian Ice Sheet melted almost completely away early in Marine Isotope Stage (MIS) 3. Our review shows that the other Eurasian ice sheets also disappeared in that period. In north-western Germany, there were forests, containing warmth-demanding trees early in MIS 3, indicating a summer climate only slightly cooler than at present, thus supporting the evidence that the adjacent ice sheets had melted. The melting of the Eurasian ice sheets contributed to 50–100% of the sea-level rise from MIS 4 to MIS 3, implying that the much larger North American ice sheets did not melt much. In contrast, the Eurasian ice sheets contributed only about 30% to the sea-level drop from MIS 3 to MIS 2, meaning that the North American ice sheets during that period expanded strongly.
•The Scandinavian Ice Sheet melted away 55,000 years ago in MIS 3.•This caused most of the global sea-level rise at that time.•The necessary mild climate is supported by contemporary vegetation development in Germany.
By using heavy coring equipment in two high-altitudinal lakes (1253 and 1316 m a.s.l.) at Dovre, Central Norway, 1–1.5 m of unsorted coarsely minerogenic sediments were retrieved below the Holocene ...organic sediments. The minerogenic sequence contained well-preserved pollen and chironomid remains, revealing new and detailed palaeoenvironmental knowledge of the mountains in Central Norway during the last 5–6000 years of the Lateglacial (LG) period. However, the LG chronology is based on biostratigraphical correlations and not on
14C-dates, due to low organic content in the minerogenic sediments. The emerging LG nunataks, probably indicating a thin and multi-domed Scandinavian ice-sheet, was rapidly inhabited by immigrating species which could explain the present centric distributions of certain arctic-alpine plants. The LG vegetation development included a pre-interstadial dominated by mineral-soil pioneers, an interstadial dominated by shrubs and dwarf-shrubs, and the Younger Dryas cold period with recurring dominance of pioneers. Pollen and stomata of
Pinus and
Picea indicate their local LG presence at Dovre. LG climate oscillations are indicated by pollen stratigraphy and for the later part of LG also by chironomids. These oscillations could correspond to Heinrich event 1, GI-1d, GI-1b, and the Younger Dryas cold events. The LG interstadial reached July mean temperatures of more than 7–8 °C, similar to the present. Chironomids colonized the lake already during the onset of the interstadial, albeit at very low richness and abundances. Starting from YD, there are sufficient chironomid head capsules to perform a temperature reconstruction. The Holocene warming of about 2 °C initiated a vegetation closure from snow beds and dwarf-shrub tundra to shrubs and forests. Birch-forests established about 10 ka cal BP, slightly earlier than pine forests.
Alnus expanded ca 9.2 ka cal BP and a thinning of the local forests occurred from ca 7 ka cal BP. Two short-lasting climate deteriorations found in the pollen record and the chironomid record may represent the Preboreal Oscillation and the 8.2 event. The Holocene Thermal Maximum is indicated around ca 7.8–7.3 ka cal BP showing a chironomid-inferred July mean of at least 11 °C. This is ca 3 °C warmer than today.
► The Scandinavian ice-sheet during LGM was thin and multi-domed. ► The Dovre Mountains in Central Norway were deglaciated during early Lateglacial. ► The Dovre LG interstadial vegetation was similar to the present alpine vegetation. ► The Dovre summers in the LG interstadial were as warm as today. ► Pollen and chironomids show a highly unstable climate during LG and early Holocene.
We found strong signals of two cooling events around 9700 and 8200 cal yrs. BP in lakes Store Finnsjøen and Flåfattjønna at Dovre, mid-Norway. Analyses included pollen in both lakes, and C/N-ratio, ...biomarkers (e.g. alkanes and br-GDGTs), and XRF scanning in Finnsjøen. The positions of these lakes close to ecotones (upper forest-lines of birch and pine, respectively) reduced their resilience to cold events causing vegetation regression at both sites. The global 8.2 event reflects the collapse of the Laurentide Ice Sheet. The 9.7 event with impact restricted to Scandinavia and traced by pollen at Dovre only, reflects the drainage of the Baltic Ancylus Lake. More detailed analysis in Finnsjøen shows that the events also caused increased allochtonous input (K, Ca), increased sedimentation rate, and decreased sediment density and aquatic production. br-GDGT-based temperatures indicate gradual cooling through the early Holocene. In Finnsjøen, ca. 3100 maxima-minima couplets in sediment density along the analysed sequence of ca. 3100 calibrated years show the presence of varves for the first time in Norway. Impact of the 9.7 and 8.2 events lasted ca. 60 and 370 years, respectively. Pine pollen percentages were halved and re-established in less than 60 years, indicating the reduction of pine pollen production and not vegetative growth during the 9.7 event. The local impact of the 8.2 event sensu lato (ca. 8420–8050 cal yrs. BP) divides the event into a precursor, an erosional phase, and a recovery phase. At the onset of the erosional phase, summer temperatures increased.
•Sediments in two alpine Dovre lakes show distinct traces of the 9.7 and 8.2 events.•The ecotonal position of the sites reduced their resilience to climate fluctuations.•Sediment density and elements in Finnsjøen show annually varved sediments.•The local impact of the 9.7 and 8.2 events lasted 60 and 370 years, respectively.•Pine pollen production was severely reduced during the 9.7 cold event.
A 24,000-year record of plant community dynamics, based on pollen and ancient DNA from the sediments (sedaDNA) of Lake Bolshoye Shchuchye in the Polar Ural Mountains, provides detailed information on ...the flora of the Last Glacial Maximum (LGM) and also changes in plant community composition and dominance. It greatly improves on incomplete records from short and fragmented stratigraphic sequences found in exposed sedimentary sections in the western Russian Arctic. In total, 162 plant taxa were detected by sedaDNA and 115 by pollen analysis. Several shifts in dominance between and within plant functional groups occurred over the studied period, but most taxa appear to have survived in situ. A diverse arctic-alpine herb flora characterised the interval ca. 24,000–17,000 cal years BP and persisted into the Holocene. Around 17,000 cal years BP, sedges (e.g. Carex) and bryophytes (e.g. Bryum, Aulacomnium) increased. The establishment of shrub-tundra communities of Dryas and Vaccinium sp., with potentially some Betula pubescens trees (influx ∼290 grains cm2 year−1), followed at ca. 15,000 cal years BP. Forest taxa such as Picea and ferns (e.g. Dryopteris fragrans, Gymnocarpium dryopteris) established near the lake from ca. 10,000 cal years BP, followed by the establishment of Larix trees from ca. 9000 cal years BP. Picea began to decline from ca. 7000 cal years BP. A complete withdrawal of forest tree taxa occurred by ca. 4000 cal years BP, presumably due to decreasing growing-season temperatures, allowing the expansion of dwarf-shrub tundra and a diverse herb community similar to the present-day vegetation mosaic. Contrary to some earlier comparative studies, sedaDNA and pollen from Lake Bolshoye Shchuchye showed high similarity in the timing of compositional changes and the occurrence of key plant taxa. The sedaDNA record revealed several features that the pollen stratigraphy and earlier palaeorecords in the region failed to detect; a sustained, long-term increase in floristic richness since the LGM until the early Holocene, turnover in grass and forb genera over the Pleistocene-Holocene transition, persistence of a diverse arctic-alpine flora over the late Quaternary, and a variable bryophyte flora through time. As pollen records are often limited by taxonomic resolution, differential productivity and dispersal, sedaDNA can provide improved estimates of floristic richness and is better able to distinguish between different plant assemblages. However, pollen remains superior at providing quantitative estimates of plant abundance changes and detecting several diverse groups (e.g. Poaceae, Cyperaceae, Asteraceae) which may be underreported in the sedaDNA. Joint use of the two proxies provided unprecedented floristic detail of past plant communities and helped to distinguish between long-distance transport of pollen and local presence, particularly for woody plant taxa.
•The proxies show high overlap in the pattern of occurrence of key plant taxa.•In contrast to pollen, sedaDNA shows increasing richness from LGM until early Holocene.•SedaDNA is superior at identifying floristic richness changes and distinguishing between plant assemblages.•Pollen remains superior at quantitative estimates of plant abundance changes.•Joint use of the proxies provides unprecedented floristic detail of past plant communities.
The Lateglacial (LG) deglaciation and vegetation development in the Scandes Mountains has been debated for a century. Here we present new evidence from microfossils, radiocarbon dated plant ...macrofossils and sedimentary ancient DNA from laminated sediments in Lake Store Finnsjøen (1260 m a.s.l.) at Dovre, Central Norway. Combined with previous results from three other Dovre lakes, this allows for new interpretations of events during and immediately after the LG deglaciation. The Finnsjøen sediments present the first uninterrupted record of local vegetation development in the Scandes Mountains from the late Younger Dryas (YD), ca 12,000 cal years BP, to the early Holocene around 9700 cal years BP. The local vegetation in late YD/early Holocene was extremely sparse with pioneer herbs (e.g. Artemisia norvegica, Beckwithia, Campanula cf. uniflora, Koenigia, Oxyria, Papaver, Saxifraga spp.) and dwarf-shrubs (Betula nana, Salix including Salix polaris). From 11,300 cal years BP, local vegetation rapidly closed with dominant Dryas, Saxifraga spp., and Silene acaulis. From ca 10,700 cal years BP, open birch-forests with juniper, Empetrum nigrum and other dwarf-shrubs developed. Pine forests established within the area from 10,300 cal years BP. We identified the cold Preboreal Oscillation (PBO), not earlier described from pollen data in South Norway, around 11,400 cal years BP by a regional pollen signal. Distinct local vegetation changes were not detected until the post-PBO warming around 11,300 cal years BP. Apparently, the earlier warming at the YD/Holocene transition at 11,650 cal years BP was too weak and short-lived for vegetation closure at high altitudes at Dovre. For the first time, we demonstrate a regional glacier readvance and local ice cap formations during the YD in the Scandes Mountains. In two of the deep lakes with small catchments, YD glaciation blocked sedimentation without removing old sediments and caused a hiatus separating sediments of the ice-free LG interstadial (LGI) from those of the ice-free Holocene period. Both regional glaciers and local ice caps caused hiati. Ice-free pre-YD conditions at Dovre followed by a YD readvance point to a scenario that is intermediate between the maximum ice model postulating a thick glacier during the entire LG, and the minimum ice model postulating thin and multi-domed early LG ice.
•Detailed DNA and pollen analysis were performed in well-dated alpine lake deposits.•These laminated lake deposits show uninterrupted records from late YD to Holocene.•The post-PBO warming was the first Holocene event causing local vegetation closure.•Sediment hiati separate LG interstadial from late YD/Holocene in deep lakes.•The hiati reflect none-erosive glacier advances and local ice-cap formations in YD.
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