Early Weichselian (MIS 5d and 5c) temperatures and environmental changes in northern Fennoscandia as recorded by chironomids and macroremains at Sokli,northeast Finland

Engels, S., Helmens, K. F., Väliranta, M., Brooks, S. J. & Birks, H. J. B. 2010: Early Weichselian (MIS 5d and 5c) temperatures and environmental changes in northern Fennoscandia as recorded by chironomids and macroremains at Sokli, northeast Finland. Boreas, Vol. 39, pp. 689–704. 10.1111/j.1502‐3885.2010.00163.x. ISSN 0300‐9483. A 25‐m‐long sediment record spanning the time from the Eemian to the Holocene was recovered from Sokli, northeast Finland. This study focuses on a 6‐m‐long sediment interval that is dated to the Early Weichselian period (MIS 5d and 5c) and consists of lacustrine and fluvial deposits. Using chironomid remains, botanical and zoological macroremains as well as sediment lithology, we were able to reconstruct past changes in the environment, including climate. The results indicate that the site was situated on a flood‐plain during the latter stages of MIS 5d (Herning Stadial) and that summer temperatures might have been ～6 °C lower than at present. Although this value should be treated with caution, as numerical analysis shows that it has a very poor fit‐to‐temperature, this low reconstructed value concurs with several other reconstructions that are available from western Europe. During MIS 5c (Brørup interstadial), the depositional environment changed into a lake system, initially with stratification of the water and subsequently with complete mixing and a strong influence of streams. Both chironomid‐based and macroremain‐based temperature inferences indicate past July air temperatures that were significantly higher than at present. This result is in contrast to other (low‐resolution) reconstructions from northern Fennoscandia that indicate past temperatures 6–7 °C lower than present using fossil coleopteran assemblages. However, several central European sites indicate that there was a phase during the Brørup interstadial that was characterized by high summer temperatures, and a comparison between the high‐resolution reconstructions from western Europe and the results presented in this study suggests that the north–south July air temperature gradient between the mid‐ and high‐latitudes was much weaker during the Brørup interstadial than it is at present. High solar insolation values (particularly the obliquity) during the Brørup interstadial might explain the low summer temperature gradient over the European continent. A return to fluvial conditions occurred in the upper parts of the sediment sequence, and, after a brief interval of gyttja deposition under cooling conditions, the site became glaciated during MIS 5b.     

Late Pleistocene stratigraphy at Boliden, northern Sweden

Till-covered sand and silt sediments with organic material from Boliden, northern Sweden, have been resampled and reinvestigated. Texture and petrographic analyses demonstrated one till bed overlying, and one underlying the sandy sediments. Low frequencies of diatoms were noted, representing freshwater, halophilous and brackish water taxa. The diatoms may be allochthonous or autochthonous, or redeposited from older deposits. Pollen analysis revealed a new picture of the composition of the vegetation, as compared with earlier investigations. The flora consisted of an arctic-subarctic treeless shrub and herb vegetation dominated by Salix, Betula nana , Gramineae and Cyperaceae. Artemisia and several arctic-alpine herbs were important elements. The identification of Salix wood as well as fruits and fruit scales of Betula nana and Betula cf. humilis is in agreement with the pollen-analytical results, as is the occurrence of Nordicboreal species of Coleoptera. Two radiocarbon datings resulted in an age of c. 45,000 B. P. and >40,000 B.P. The Boliden till-covered sediments were most probably deposited during an Early or Middle Weichselian interstadial, but the initial or final stage of an interglacial (Eemian) is also possible.     

Ice‐free conditions in eastern Fennoscandia during early Marine Isotope Stage 3: lacustrine records

Helmens, K. F. & Engels, S. 2010: Ice‐free conditions in eastern Fennoscandia during early Marine Isotope Stage 3: lacustrine records. Boreas, 10.1111/j.1502‐3885.2010.00142.x. ISSN 0300‐9483. The traditional notion that Fennoscandia was glaciated throughout Marine Isotope Stages (MIS) 4–2, from c. 70 kyr BP to the deglaciation 15–10 kyr BP ago, has been challenged during the last decade. Recent studies have shown that climate and environmental settings during MIS 3 were more dynamic than previously assumed, and lacustrine sediment bodies indicate open‐water conditions for several sites in eastern Fennoscandia. In this study, three sediment sequences from western, eastern and northeast Finland are compared in detail with respect to their chronology, vegetation reconstruction and climatic inferences. OSL‐dating places the sediments in early MIS 3. Pollen evidence suggests the presence of isolated birch trees and open birch forest close to the retreating ice margin, in contrast to vegetation reconstructions from central Europe, which indicate tree‐less vegetation. Furthermore, reconstructions of climate using transfer functions have yielded surprising results, indicating present‐day summer temperatures in northeast Finland. The combined results suggest ice‐free and warm conditions in major parts of eastern Fennoscandia in early MIS 3, possibly during Greenland Interstadial (GIS) 14 around 53 kyr BP ago.     

Flora, vegetation and climate at Sokli, northeastern Fennoscandia, during the Weichselian Middle Pleniglacial

A 2 m thick laminated lacustrine deposit of silt and clay recovered from the high-latitudinal site at Sokli (northern Finland) provides a unique mid-Weichselian fossil record for Fennoscandia. High-resolution botanical and zoological analyses of the lacustrine deposit allow detailed reconstruction of the regional vegetational development and of the history of the lake and the wetland ecosystem within the Sokli basin during the early part of the Weichselian Middle Pleniglacial (=equivalent to Marine Isotope Stage (MIS) 3). The inferred terrestrial vegetation represented by the Sokli MIS 3 sequence (so-called Tulppio Interstadial) was probably low-arctic tundra, treeless but with shrub elements including juniper, willow, dwarf birch, ericoids, lycopods and a rich herb flora with a variety of arctic–alpine taxa and heliophilous, pioneer elements. The presence of herbs such as Rubus chamaemorus, Epilobium palustre, Potentilla palustris and Sphagnum, Drepanocladus and other mosses suggests that the lake was fringed by wet meadows and peatlands or peaty telmatic communities. The distributional ranges of pine and tree birch were probably only a few hundred kilometres south or southeast of Sokli. This is concordant with evidence for the presence of boreal tree taxa during the MIS 3 in the Baltic countries and further east in Europe, but contradicts with the commonly inferred treeless tundra or grass-dominated steppe conditions in central Europe.     

The Petrology and Geochemistry of Mafic Igneous Rocks in the Anorthosite-Bearing Adirondack Highlands, New York

Igneous rocks of broadly basaltic composition are widely distributedin the anorthosite-bearing Adirondack Highlands of New York.They constitute a mafic series of rocks that occurs on the marginsof the anorthosite series and up to 50 km away from the anorthosite.On an Sr reference diagram, the mafic series has an apparentinitial ⁸⁷Sr/⁸⁶Sr value of 0.7036, which is consistent with1100 Ma subcontinental mantle. The series was probably emplacedin the interval 1150–1100 Ma, during which time anorthositeand granitic magmas were also emplaced. The rocks were metamorphosedshortly thereafter ({small tilde} 1088 Ma) under upper-amphiboliteand granulite facies conditions. Individual bodies of maficrocks range in thickness from small enclaves and layers >>1 m thick to large lensoid masses several tens of meters thick.Despite deformation and metamorphic recrystallization, manyof the rocks retain chiHed margins, cross-cutting relationships,and relict igneous textures. Selected samples of the mafic series have been analyzed fortheir major and trace element compositions. Metamorphism didnot significantly alter the igneous geochemical relationships,and the rocks retain mantle-like values for Zr/Nb, K/Zr, K/Rb,Rb/Sr, and ⁸⁷Sr/⁸⁶Sr. The most primitive rocks of the seriesare silica-undersaturated gabbroic troctolites, and the moreevolved rocks are basaltic in composition. The mafic seriesas a whole has high abundances of A1₂O₃, FeO, the light rareearth elements (LREE), and other incompatible trace elements.Even the most geochemically primitive compositions have highFeO contents. The Fe enrichment and Si depletion that are shownby chemically evolved compositions are consistent with a Fennertrend of fractionation. Low levels of normative di indicatethat high Fe is not a result of the extensive fractionationof cpx. The geochemical trends that are defined by the traceelements, including the REE, suggest the basaltic rocks maybe differentiates of a parental magma of gabbroic troctolitecomposition. The main compositional trend of the mafic seriescan be simulated by 61% crystallization of olivine and plagioclaseof a gabbroic troctolite, followed by 13% crystallization ofolivine, plagioclase, clinopyroxene, and titanomagnetite atthe final stages. The modelled ratio of olivine to plagioclasecrystallization changes from 1–8: 1 to 0–64: 1.These non-cotectic ratios may reflect a delay in the crystallizationof plagioclase relative to olivine, possibly as a result oflow nucleation rates. At later stages of differentiation, plagioclasewas more important in the crystallization of the series. Delayedcrystallization of plagioclase may also have resulted in thehigh A1₂O₃ contents and enhancement of Eu and Sr relative toother trace elements at early stages of differentiation. The mafic series and the silica-saturated anorthosite seriestogether form an anorthosite-norite-troctolite (ANT) suite.More than one mantle composition may have been involved in generatingthe Adirondack mafic magmas. The rocks retain geochemical evidenceof a source that was depleted in basaltic components (cpx) butenriched in Fe, Ti, K, and the LREE. Previously documented evidenceof anticlockwise cooling paths (Bohlen, 1987) and of a regionalgravity high centered beneath the Adirondack region (Simmons,1964) suggests that of the continental crust by basaltic magmasmay have underplating of the continental crust by basaltic magmasmay have been an important feature of the tectonic evolutionofthe region. A model of mantle upwelling beneath thinning continentalcrust explains the geochemically hybrid nature of the maficseries magmas. It is also consistent with a tectonic settingof incipient or failed continental rifting, to which the generationof the anorthosites is commonly attributed.     

Oxygen-isotope record of Late-Glacial climatic change in western Ireland

Oxygen-isotope profiles for the Late-Glacial carbonate sediments from Red Bog and adjacent Lough Gur in County Limerick in western Ireland are readily correlated with the classical hiozones delineated on pollen diagrams for the same cores. The estimated summer temperatures of the Bølling/Allerød were as high as those in the early Holocene and are correlated with increasing Milankovitch summer insolation. This warm phase was abruptly terminated in the Younger Dryas cold episode by a depletion of 4% in δ¹⁸O, suggesting a summer atmospheric temperature decrease of about 12°C, comparable to that inferred from fossil beetle data. The Younger Dryas phase is attributed to a major cooling of the sea-surface temperature by a postulated discharge of icebergs similar to that of the Heinrich events, for the icebergs were much more effective than simple meltwater in cooling the sea surface and thus the climate over Europe. Shorter-term cool phases (Older Dryas. Gerzensee. Preboreal oscillation) are also recognized.     

ASSESSING THE PALAEOCLIMATE POTENTIAL OF CAVE GLACIERS: THE EXAMPLE OF THE SČRIŞOARA ICE CAVE (ROMANIA)

ABSTRACT. The ice block in Scarisoara Cave, NW Romania, is preserved due to unusual climate and permafrost conditions within the cave. The air temperature in the cave is governed by the winter cold, the cooling effect of the ice block, and only to a minor extent influenced by summer temperatures. At present, the ice block is slowly thinning, but the present-day climate is sufficiently cold to preserve the permafrost conditions caused by the cold air trapped in the cave. In February 2003 a 22.5 m long ice core was recovered from the ice block. Approximately 200 ice layers have been identified by visual examination. Ice crystallographic analyses indicate a steady growth of ice crystals with depth and there is no sign of deformation. Carbon-14 dates on wood-related samples collected from a natural vertical exposure of the ice block indicate that the ice spans more than 1000 years. Observations on the exposure indicate that a basal melting phase may have occurred in the past.     

Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years

Sundqvist, H. S., Holmgren, K., Moberg, A., Spötl, C. & Mangini, A. 2009: Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years. Boreas, 10.1111/j.1502‐3885.2009.00099.x. ISSN 0300‐9483. This study of a 4000‐year‐old stalagmite from Korallgrottan in northwestern Sweden highlights the potentials and challenges when using stable isotopes in stalagmites as climate proxies, as well as the fact that the relationship between climate and proxy may change through time. Both the oxygen and the carbon isotopes display an overall trend of enrichment together with decreasing growth rates over the time period covered by the stalagmite, which is considered a generally cooling period according to current palaeoclimate understanding. The stable isotope records show enriched isotopic values during the, for Scandinavia, comparatively cold period AD 1300–1700 and depleted values during the warmer period AD 800–1000. The indication of a negative relationship between measured δ¹⁸O and surface temperature concurs with earlier reported stalagmite records from regions with a seasonal snow cover and is further supported by the fact that the stalagmite δ¹⁸O record shows general similarities with both regional and hemispheric temperature reconstructions available for the past 500 and 2000 years, respectively. Compared with a stable isotope record of lacustrine carbonates from northern Sweden, however, shifting correlations over time between the two records indicate that a local hydrological change may have taken place at Korallgrottan, or at the lake, compared with around 1000 years ago. The earlier part of the stalagmite δ¹⁸O might thus be influenced, to some extent, by another process than the later part, which means that a negative relationship between δ¹⁸O and surface temperature might not hold for the entire 4000‐year‐old record.