Michael Houmark-Nielsen

Glacial Survival of Boreal Trees in Northern Scandinavia

Tree Refugia Ideas of how and when boreal plants spread to the formerly glaciated parts of the world following the retreat of the glaciers 9000 years ago are long debated. Models of the postglacial spread of boreal plants argue for dispersal from southern refugia; however, Parducci et al. (p. 1083) have shown that both spruce and pine were present in small ice-free regions of Scandinavia much earlier than thought. DNA haplotyping confirmed that a remnant mitochondrial type of spruce, once unique to Scandinavia, now lives alongside the more common spruce originating from Eastern Europe. Evidence from lake cores collected from central and northern Norway indicated the survival of conifers as early as 22,000 years before the present, when apart from ice-free pockets, most of Scandinavia was covered by ice. DNA from modern and ancient spruce and pine indicate that both survived in ice-free areas during the last glaciations. It is commonly believed that trees were absent in Scandinavia during the last glaciation and first recolonized the Scandinavian Peninsula with the retreat of its ice sheet some 9000 years ago. Here, we show the presence of a rare mitochondrial DNA haplotype of spruce that appears unique to Scandinavia and with its highest frequency to the west—an area believed to sustain ice-free refugia during most of the last ice age. We further show the survival of DNA from this haplotype in lake sediments and pollen of Trøndelag in central Norway dating back ~10,300 years and chloroplast DNA of pine and spruce in lake sediments adjacent to the ice-free Andøya refugium in northwestern Norway as early as ~22,000 and 17,700 years ago, respectively. Our findings imply that conifer trees survived in ice-free refugia of Scandinavia during the last glaciation, challenging current views on survival and spread of trees as a response to climate changes.

Late Pleistocene glacial and lake history of northwestern Russia

Five regionally significant Weichselian glacial events, each separated by terrestrial and marine interstadial conditions, are described from northwestern Russia. The first glacial event took place in the Early Weichselian. An ice sheet centred in the Kara Sea area dammed up a large lake in the Pechora lowland. Water was discharged across a threshold on the Timan Ridge and via an ice-free corridor between the Scandinavian Ice Sheet and the Kara Sea Ice Sheet to the west and north into the Barents Sea. The next glaciation occurred around 75–70 kyr BP after an interstadial episode that lasted c. 15 kyr. A local ice cap developed over the Timan Ridge at the transition to the Middle Weichselian. Shortly after deglaciation of the Timan ice cap, an ice sheet centred in the Barents Sea reached the area. The configuration of this ice sheet suggests that it was confluent with the Scandinavian Ice Sheet. Consequently, around 70–65 kyr BP a huge ice-dammed lake formed in the White Sea basin (the ‘White Sea Lake’), only now the outlet across the Timan Ridge discharged water eastward into the Pechora area. The Barents Sea Ice Sheet likely suffered marine down-draw that led to its rapid collapse. The White Sea Lake drained into the Barents Sea, and marine inundation and interstadial conditions followed between 65 and 55 kyr BP. The glaciation that followed was centred in the Kara Sea area around 55–45 kyr BP. Northward directed fluvial runoff in the Arkhangelsk region indicates that the Kara Sea Ice Sheet was independent of the Scandinavian Ice Sheet and that the Barents Sea remained ice free. This glaciation was succeeded by a c. 20-kyr-long ice-free and periglacial period before the Scandinavian Ice Sheet invaded from the west, and joined with the Barents Sea Ice Sheet in the northernmost areas of northwestern Russia. The study area seems to be the only region that was invaded by all three ice sheets during the Weichselian. A general increase in ice-sheet size and the westwards migrating ice-sheet dominance with time was reversed in Middle Weichselian time to an easterly dominated ice-sheet configuration. This sequence of events resulted in a complex lake history with spillways being re-used and ice-dammed lakes appearing at different places along the ice margins at different times.

Ice‐flow patterns and dispersal of erratics at the southwestern margin of the last Scandinavian Ice Sheet: signature of palaeo‐ice streams

An extensive set of proxy-data was acquired from eastern and central Denmark in order to study the dynamic behaviour of the southwestern margin of the last Scandinavian Ice Sheet. We examine the last three glacier advances of the Late Weichselian: the Main advance from central Sweden, representing the maximum ice extent at this time (c. 21-20 ka BP), and the two succeeding Baltic advances (c. 18-15 ka BP). Directional properties from tills and glaciotectonic overprints are used to reveal large-scale flowline patterns. Together with the geomorphological outline of ice margins, flowlines were successively more fan-shaped, indicating that the dependence of the subglacial topography increases as ice advances become younger. It is suggested that while the ice thickness decreases. more lobate configurations of ice margins are created as a result. Clast-compositional data derived from the fine-gravel fraction in tills are used to reconstruct dispersal patterns of erratic material. The dispersal patterns during the three advances show a gradually diminishing influence of local Pre-Quaternary bedrocks and older glacial deposits, and progressively longer transport distances of far-travelled erratics. We speculate that the principal factor governing this development is a successively decreasing interaction between the ice and its bed, which influences the concentration of erratics. debris comminution processes and the basal ice velocity. We envisage the Main advance from central Sweden as a slow-flowing inter-stream ice body with high bed interaction compared to the succeeding Baltic advances, which we regard to have been rapid flowing ice streams with limited bed interaction.

Early and Middle Valdaian glaciations, ice-dammed lakes and periglacial interstadials in northwest Russia: new evidence from the Pyoza River area

The Pyoza River area in the Arkhangelsk district exposes sedimentary sequences suitable for study of the interaction between consecutive Valdaian ice sheets in Northern Russia. Lithostratigraphic investigations combined with luminescence dating have revealed new evidence on the Late Pleistocene history of the area. Overlying glacigenic deposits of the Moscowian (Saalian) glaciation marine deposits previously confined to three separate transgression phases have all been connected to the Mikulinian (Eemian) interglacial. Early Valdaian (E. Weichselian) proglacial, lacustrine and fluvial deposits indicate glaciation to the east or north and consequently glacier damming and meltwater run-off in the Pyoza area around 90–110 ka BP. Interstadial conditions with forest-steppe tundra vegetation and lacustrine and fluvial deposition prevailed at the end of the Early Valdaian around 75–95 ka BP. A terrestrial-based glaciation from easterly uplands reached the Pyoza area at the Early to Middle Valdaian transition around 65–75 ka BP and deposited glaciofluvial strata and subglacial till (Yolkino Till). During deglaciation, laterally extensive glaciolacustrine sediments were deposited in ice-dammed lakes in the early Middle Valdaian around 55–75 ka BP. The Barents–Kara Sea ice sheet deposited the Viryuga Till on the lower Pyoza from northerly directions. The ice sheet formed the Pyoza marginal moraines, which can be correlated with the Markhida moraines further east, and proglacial lacustrine deposition persisted in the area during the first part of the Middle Valdaian. Glacio-isostatic uplift caused erosion followed by pedogenesis and the formation of a deflation horizon in the Middle Valdaian. Widely dispersed periglacial river plains were formed during the Late Valdaian around 10–20 ka BP. Thus, the evidence of a terrestrial-based ice sheet from easterly uplands in the Pyoza area suggests that local piedmont glaciers situated in highlands such as the Timan Ridge or the Urals could have developed into larger, regionally confined ice sheets. Two phases of ice damming and development of proglacial lakes occurred during the Early and Middle Valdaian. The region did not experience glaciation during the Late Valdaian.

The last interglacial-glacial cycle in Denmark

Abstract The stratigraphy of Late Pleistocene interglacial, interstadial and stadial deposits in Denmark shows radical alternation of marine and terrestrial environments within the last interglacial-glacial cycle (Isotope Stages 6-2). Climatically dependent environmental changes, eustatic and isostatic responses, combined with the advance and retreat of glaciers, are elements in a chronostratigraphic model for SW Scandinavia. The Late Saalian Borglum-Margreteberg interstade (Isotope Stage 6) was characterized by arctic to boreo-arctic marine conditions and tundra vegetation. The Eemian interglaciation (Isotope Substage 5e) reflects high sea levels with boreo-lusitanian marine faunas and dense temperate forests. In the Early Weichselian Brorup interstade (Isotope Substage 5c), boreal to boreo-arctic seas with relatively low water level prevailed along with open forest vegetation. The Middle Weichselian commenced with arctic seas accompanied by ice-rafting and followed by major glacier cover possibly reaching eastern Denmark (Karmoy-Ristinge-Goteborg I stade, Isotope Stage 4). The Bo-Older Dosebacka-Hirtshals interstade (Isotope Stage 3) witnessed boreo-arctic conditions with ice-rafting and the establishment of a park tundra vegetation. During the later Jaeren-Goteborg II-Vennebjerg stade (Isotope Stage 3) shelf-ice appeared in high arctic Kattegat and Skagerrak along with surging glaciers in the Baltic. The Middle Weichselian Isotope Stage 3 ended with the Sandnes-Mon-Gardslov interstade. Park tundra and boreo-arctic seas prevailed. The Late Weichselian, Jylland stade (Isotope Stage 2), comprises complex stadial conditions with glacier advance and retreat. The Jylland stade peaked with the maximum extension of Weichselian glaciers along the Main Stationary Line, equivalent to the Frankfurt-Poznan glacial stage on the north European continent.

The last Scandinavian Ice Sheet in northwestern Russia: ice flow patterns and decay dynamics

Advance of the Late Weichselian (Valdaian) Scandinavian Ice Sheet (SIS) in northwestern Russia took place after a period of periglacial conditions. Till of the last SIS, Bobrovo till, overlies glacial deposits from the previous Barents and Kara Sea ice sheets and marine deposits of the Last Interglacial. The till is identified by its contents of Scandinavian erratics and it has directional properties of westerly provenance. Above the deglaciation sediments, and extra marginally, it is replaced by glaciofluvial and glaciolacustrine deposits. At its maximum extent, the last SIS was more restricted in Russia than previously outlined and the time of termination at 18 16 cal. kyr BP was almost 10 kyr delayed compared to the southwestern part of the ice sheet. We argue that the lithology of the ice sheets’ substrate, and especially the location of former proglacial lake basins, influenced the dynamics of the ice sheet and guided the direction of flow. We advocate that, while reaching the maximum extent, lobe-shaped glaciers protruded eastward from SIS and moved along the path of water-filled lowland basins. Ice-sheet collapse and deglaciation in the region commenced when ice lobes were detached from the main ice sheet. During the Lateglacial warming, disintegration and melting took place in a 200 600 km wide zone along the northeastern rim of SIS associated with thick Quaternary accumulations. Deglaciation occurred through aerial downwasting within large fields of dead ice developed during successively detached ice lobes. Deglaciation led to the development of hummocky moraine landscapes with scattered periglacial and ice-dammed lakes, while a subarctic flora invaded the region.

The Pleistocene of Denmark: a review of stratigraphy and glaciation history

Abstract Climatically dependent environmental changes and the advance and retreat of glaciers have controlled the development of sedimentary successions in Denmark during the Middle and Late Pleistocene. Over the last four glacial-interglacial cycles radical alternations of marine and terrestrial environments, combined with eustatic and isostatic response to glaciation, has lead to the following geological history. The first Quaternary glaciation reached the country during the Menapien or the early Cromerian. The Cromerian II interglacial is represented by single finds of lacustrine deposits. During the Elsterian glaciation three major glacial advances from different parts of Scandinavia are recognized. By the end of the Elsterian and during the Holsteinian interglacial infilling of incised valleys took place. In local lake basins, the Holsteinian is characterised by calcareous gyttja and diatomite with a flora characteristic of leached soils. The Drenthe phase of the Saalian glaciation began with an ice advance from southern Norway, it culminated with glaciation from Middle Sweden and terminated during the Warthe stadial with ice flow from the Baltic depression. During deglaciation, arctic to boreo-arctic marine conditions and tundra vegetation was restored. The Eemian interglacial includes high sea levels with boreo-lusitanian marine faunas and dense temperate forests. In the Early Weichselian shallow and boreal to boreo-arctic seas prevailed along with open forest and tundra vegetation. The Middle Weichselian began with arctic seas accompanied by ice rafting and followed by major glacier cover from the Baltic and possibly preceded by glaciation from southern Norway. Most of the remaining Middle Weichselian witnessed boreo-arctic conditions with ice rafting and the establishment of a shrub tundra vegetation. Glaciers calved in high arctic Kattegat and Skagerrak accompanied by surging glaciers in the Baltic. The Middle Weichselian ended with ameliorated interstadial environments. Shrub tundra and boreo-arctic seas prevailed. The Late Weichselian, Jylland stadial comprises complex conditions with several glacier advances and retreats. An ice stream from southern Norway was followed by glaciation from central Sweden during the maximum extension of Weichselian glaciers and the glaciations were terminated by ice streaming from the Baltic while arctic marine conditions were restored in Skagerrak and Kattegat.

Pleistocene Glaciations in Denmark: A Closer Look at Chronology, Ice Dynamics and Landforms

Abstract Increasingly better preserved glacial landscapes from the Mid Pleistocene and onwards expose intimate relationships between super imposed landforms, stratigraphy and glacial tectonic architecture. The extent and flow pattern of glaciations are shown in digital base maps and palaeogeographical reconstructions.

Late Pleistocene stratigraphy and sedimentary environment of the Arkhangelsk area, northwest Russia

The Arkhangelsk area lies in the region that was reached by the northeastern flank of the Scandinavian ice sheet during the last glaciation. Investigations of Late Pleistocene sediments show interglacial terrestrial and marine conditions with sea level up to 52 m above the present level. An unconformity in the stratigraphy suggests a hiatus representing the Early Valdaian (Weichselian) and the beginning of the Middle Valdaian. This unconformity could be related to a low base level and isostatic depression of the area north of Arkhangelsk, either caused by ice masses advancing from the Kara and Barents ice sheets and/or to Scandinavian ice over the Kola Peninsula. During Middle Valdaian, from c. 66 ka BP, until the advance of the Late Valdaian glacier, c. 17–16 ka BP, peat formation, and northward fluvial sedimentation occurred coexisting with permafrost conditions in a later phase. Before the glacier advance, the base level rose and thick vertical accumulations of fluvial sediments were formed. Associated with this glacier advance from the north–northwest, ice damming occurred. Fluvial drainage was opposite to the present drainage pattern and deposition appeared in glaciolacustrine ponds in the area outside the limit of the glaciation. After the deglaciation that started c. 15 ka BP, permafrost conditions and downwasting of buried stagnant glacier ice prevailed until at least 10.7 ka BP.

A multi-disciplinary macrofossil study of Middle Weichselian sediments at Kobbelgård, Møn, Denmark

Abstract Multi-proxy studies of radiocarbon and luminescence dated Middle Weichselian sediments and allochthonous plant and animal macrofossils from Kobbelgaard, Mon, point to a lacustrine environment with shallow mesotrophic fresh water. The lake was surrounded by mires rich in mosses and Carex , while the vegetation on the uplands was tree-less and herb dominated but with scattered shrubs. The climate was considerably colder than at the present day with average July temperatures around 11°C, about 6°C below those for the region today—probably normal for the later part of the Middle Weichselian. The sediments contain the first remains of lemmings ( Dicrostonyx torquatus and Lemmus lemmus ) found in Denmark.