Postglacial Changes Research Articles

California’s endemic Cornus sessilis in Ukraine

Global climate change and increased land use lead to the loss of biodiversity at all levels of the organization of living organisms – ecosystems, species, landscape population, genetic, molecular biological levels, etc. The reaction of plants to anthropogenic impact, according to experts, may be even stronger than postglacial changes. A shift in the thermal isotherm will cause the plants to either move and adapt, or disappear. Endemic species that make up “biodiversity hotspots” require special attention. Cornus sessilis Torr. ex Durand, the object of our research, is part of one of these points – the California Floristic Province. Researchers are now focusing their efforts on developing a climate change – related biodiversity management strategy. In the case of the threat of extinction of the species in nature, there is a important method of preserving it in culture (ex situ). M. M. Gryshko National Botanical Garden at the National Academy of Sciences of Ukraine (the NBG) pays great attention to the introduction of rare endemic species from the different geographical and floristic regions of the world. The gene pool of Cornus L. s. l. in the NBG consists of more than 30 species and 40 cultivars including the insufficiently researched and little-known Californian endemic C. sessilis. In Europe, it has been grown since 2017 only in Chateau Perouse Botanic Gardens (Saint-Gilles, France) and in Ukraine only the NBG has it. In this article we evaluate the life cycle of the development C. sessilis under conditions of introduction different from the conditions of its natural area. To do this, we used the classic traditional methods of the research on the process of introduction, in particular, botanical plant identification, visual observation, phenology, comparative morphology and biometrics. Morphological descriptors (life form, colour and texture of bark, leaf shape, pubescence character, structure of generative and vegetative buds, inflorescences, flowers, fruits and endocarp) of C. sessilis genotypes introduced to the NBG are identical to those of plants from their natural habitats. The weight of fruits and endocarps were determined by us for the first time. The results of biometric analysis of the size of leaves and fruits showed that the plants of C. sessilis grown in the NBG had the larger leaf blades, but the smaller fruits as compared to those in the wild. In the NBG the plants underwent a full cycle of seasonal development (from the deployment of buds to the leaf fall, inclusive) for 229 days. In general, the phenological strategy of C. sessilis genotypes introduced in the NBG corresponds to that of other species of Cornus s. str., including C. mas L. Our results indicate that C. sessilis, California’s rare endemic species new to Ukraine, has adapted to the new conditions – the plants bear fruits and produce seeds. The experience of successful introduction makes it possible to cultivate a new species to expand the diversity of food, medicinal and reclamation plants of the family Cornaceae as well as the use in synthetic breeding to obtain new cultivars with valuable biological and economic properties. Cornus sessilis compatibility test as rootstocks for other species is important for clarifying the theoretical issues of family ties of species Cornaceae and practical – for widespread reproduction of the required cultivars C. mas breeding in the NBG on a potentially compatible rootstock C. sessilis.

Early Holocene wetland succession at Lake Flixton (UK) and its implications for Mesolithic settlement

This paper reports on new research into the timing and nature of post-glacial environmental change at Lake Flixton (North Yorkshire, UK). Previous investigations indicate a succession of wetland environments during the early Holocene, ultimately infilling the basin by ca 7,000 cal bp. The expansion of wetland environments, along with early Holocene woodland development, has been linked to changes in the human occupation of this landscape during the Mesolithic (ca 11,300–6,000 cal bp). However, our understanding of the timing and nature of environmental change within the palaeolake is poor, making it difficult to correlate to known patterns of Mesolithic activity. This paper provides a new record for both the chronology and character of environmental change within Lake Flixton, and discusses the implications for the Mesolithic occupation of the surrounding landscape.

Genetic analysis reveals historical and contemporary population dynamics in the longfin squid Doryteuthis gahi: implications for cephalopod management and conservation

AbstractPopulation genetic structure of the Patagonian longfin squid Doryteuthis gahi was assessed across the Falkland Islands, central-southern Chile, and Peru. Microsatellite and mtDNA data partitioned samples into two groups: one consisting of the Peruvian samples, the other comprised the Chilean and Falklands samples, with no sub-structuring within either group. Recurrent demographic independence between groups can be linked to abrupt changes in continental shelf features between the Peruvian and central Chilean sites restricting adult dispersal. Phylogeographic analyses indicate a prolonged period of isolation between the Peruvian and Chilean–Falkland groups which may include divergence in allopatric glacial refugia. Both groups have experienced dissimilar historical population size dynamics with the Peruvian population exhibiting signals of size fluctuations, similar to other species in the area, that align with postglacial changes in the productivity of the Humboldt Current system. Genetic cohesion among central-southern Chilean and Falklands samples supports connectivity across current management boundaries and indicates that phenotypic differences between D. gahi from these areas reflect plastic responses to environmental heterogeneity. The study adds to evidence that loliginid squids typically display connected populations over large geographical areas unless specific oceanographic features restrict gene flow. Recognition of the Peruvian and Chilean–Falklands groups as distinct evolutionary significant units is recommended.

The kettle-hole mire as archives of postglacial changes in biogenic sedimentation (Tuchola Forest, north-Central Poland)

Kettle holes are a circular-shape product of ice decay, and thus are strongly linked with young glacial landscapes. Once glaciation terminates, these holes transform either into wetland and lakes or occasionally into kettle-hole mires. Since an entire sediment sequence preserve in the kettle-holes, these provide an excellent settings to exploit any sensitive paleoenvironmental changes. Here, the kettle-hole mire located onto the Brda River outwash plain (Tuchola Forest) is explored towards a better understanding of local and global environmental trends in the Late Glacial – present day time frame. To fulfill this, multi-proxy study as geochemical, palynological and macrofossils analyses along with the radiocarbon dating are used. Therefore, this study allows to distinguish five phases of steep environmental gradients in the investigated mire, as follows: (1) paludification after glaciation, when dead-ice melted and long-term permafrost was degraded, (2) lake started to disappear in the Late Glacial, followed by a rich vegetation in the first part of the Holocene, (3) vegetation encroachment onto the lake in the first part of the Holocene, which consequently turned into an peat bog, (4) the late Holocene peat bog with a limited human influence, and finally (5) the peat bog with a major human impact along with acidification as related to sandy underlying sediments, leaching of calcium carbonate, recharge from precipitation and pine monoculture. As additionally apparent from this small ecosystem, both local (character of substrate sediments, morphology of the area, rate of permafrost melting, climate conditions and human activity) and regional (climate changes and human activity) are detectable. Nevertheless, the record of these changes is sometimes unclear.

The record of postglacial environmental changes of the southern Baltic coastal zone in the sequence of fossil soils

PurposeThe studies aimed to reconstruct major phases of litho-morpho-pedogenic processes and past environmental changes in the Baltic coastal zone near Poddąbie (54°37,070′ N, 16°57,897′ E) based on physical, chemical, pollen, and fossil Cladocera analysis of the polycyclic pedocomplex.Materials and methodsThe polycyclic pedocomplex under study included seven fossil soils developed from the Early Holocene until modern times from various materials. The soils were sampled and analyzed using standard procedures in soil science to determine their physical and chemical properties. Pollen and fossil Cladocera analysis was also carried out in the examined profile. Radiocarbon dates of selected samples were also specified.Results and discussionThe studied polycyclic pedocomplex has been developed from materials of varied origin, including glaciofluvial, fluvial, aeolian, and biogenic deposits of the lake. According to the results of pollen and fossil Cladocera analysis and radiocarbon dating, this body of water has evolved from the beginning of Preboreal period to the half of Boreal. The studied soils represent various reference groups and advancement of development. They constitute relics of former geomorphological and soil-forming processes, which have taken place over the last 9500 years, including periglacial processes, wildfires, Baltic Sea shoreline changes, and aeolian activity. The last stage of the coastal relief dynamics was conditioned by the fire which took place about 1472–1637 AD. The lack of plant cover and intensive abrasion due to direct vicinity of the coastline has caused the deposition of aeolian material, which is the parent material of nutrient-poor initial soils.ConclusionsThe analysis of fossil soil development with the use of specialized research methods allowed for reconstructing the dynamics of past geomorphological processes and natural environment changes in the study area. The studied polycyclic pedocomplex constitutes a record of environmental changes taking place in the central part of the Polish Baltic coastal zone from the Early Holocene to the present day. The studied soil sequence is located within a land depression developed in place of the former water reservoir created as a result of permafrost degradation, and filled with Holocene deposits.

Post-glacial climate forcing of surface processes in the Ganges–Brahmaputra river basin and implications for carbon sequestration

Climate has been proposed to control both the rate of terrestrial silicate weathering and the export rate of associated sediments and terrestrial organic carbon to river-dominated margins – and thus the rate of sequestration of atmospheric CO2 in the coastal ocean – over glacial–interglacial timescales. Focused on the Ganges–Brahmaputra rivers, this study presents records of post-glacial changes in basin-scale Indian summer monsoon intensity and vegetation composition based on stable hydrogen (δD) and carbon (δ13C) isotopic compositions of terrestrial plant wax compounds preserved in the channel–levee system of the Bengal Fan. It then explores the role of these changes in controlling the provenance and degree of chemical weathering of sediments exported by these rivers, and the potential climate feedbacks through organic-carbon burial in the Bengal Fan. An observed 40‰ shift in δD and a 3–4‰ shift in both bulk organic-carbon and plant-wax δ13C values between the late glacial and mid-Holocene, followed by a return to more intermediate values during the late Holocene, correlates well with regional post-glacial paleoclimate records. Sediment provenance proxies (Sr, Nd isotopic compositions) reveal that these changes likely coincided with a subtle focusing of erosion on the southern flank of the Himalayan range during periods of greater monsoon strength and enhanced sediment discharge. However, grain-size-normalized organic-carbon concentrations in the Bengal Fan remained constant through time, despite order-of-magnitude level changes in catchment-scale monsoon precipitation and enhanced chemical weathering (recorded as a gradual increase in K/Si⁎ and detrital carbonate content, and decrease in H2O+/Si⁎, proxies) throughout the study period. These findings demonstrate a partial decoupling of climate change and silicate weathering during the Holocene and that marine organic-carbon sequestration rates primary reflect rates of physical erosion and sediment export as modulated by climatic changes. Together, these results reveal the magnitude of climate changes within the Ganges–Brahmaputra basin following deglaciation and a closer coupling of monsoon strength with OC burial than with silicate weathering on millennial timescales.

Late-Glacial Vegetational History of the Edmund Niles Huyck Bog, Rensselaerville, New York

Abstract Pollen analysis of a 10-m core from the Niles Huyck Bog in Rensselaerville, NY, yields a history of late-glacial and postglacial vegetational change from the beginning of sediment deposition into the bog basin following ice withdrawal to the present. A radio-carbon-dated sequence is provided as time control for the upper 6 m. Late-glacial pollen assemblages seen near the base of the core consist of Abies spp. (fir) and Picea spp. (spruce) as the principal tree genera and grasses and sedges as the main herbaceous components, and resemble pollen assemblages elsewhere in New York and New England. These assemblages were replaced by ones consisting primarily of Pinus spp. (pine), which became dominant ca. 9000 years before present (YBP). By 8000 YBP, pine gave way to Tsuga canadensis (Eastern Hemlock), Quercus spp. (oak), and Fagus grandifolia (American Beech), denoting a more mesic climate. Thereafter, the replacement of oak by beech is a notable trend that continues throughout the pollen profile and...

Postglacial relative sea level change at Fildes Peninsula, King George Island (West Antarctic)

Analysis and integration of data obtained in our field and laboratory investigations of 2008–2012 together with results of previous paleogeographic studies were conducted to reveal parameters and factors of the post-glacial changes in the relative sea-level on the Fildes Peninsula and the King George Island. Results of dating of organic material taken from cross-sections of Quaternary deposits, data on morphology of marine landforms as well as on bottom sediments in lakes were used to construct a curve of changes in the relative sea-level. Our research has shown that the rapid rise of relative sea level in the area (since the beginning of the Holocene) decelerated about 8000 years BP, achieving its maximum about 7000 years BP. This was followed by the fall of relative sea-level (the land elevation) by 18–20 m in total, and it was characterized by relatively high rate of fall during periods of 6000– 5000 years BP, 4000–2500 years BP, and during the last 1500 years; the rate decreased in 5000–4000 years BP and 2500– 1600 years BP. The changes in relative sea level in this region were determined by the following factors: the eustatic component of the global changes in sea-level and, possibly, oscillations in the global sea level of another nature; local parameters of the Last glacial maximum; a course of the Peninsula deglaciation; regional physical characteristics of the Earth's crust and the mantle substances; local tectonic processes, including the isostatic rebound. Since the beginning of the Holocene up to about 7000 years BP, the main contribution to changes of the relative sea-level in this area was made by the global eustatic factor. The subsequent fall of the relative sea-level (elevation of the Peninsula surface) proceeded under condition of reduced role of the eustatic factor and predominance of other factors.

Mineral and elemental indicators of post-glacial changes in sediment delivery and deposition under a western boundary upwelling system (Cabo Frio, southeastern Brazil)

Minerals and elements are important proxies that can provide information about variations in the delivery and deposition of coastal ocean sediments associated with past climate changes. In this study, postglacial changes in the accumulation of sediments on the upper shelf of southeastern Brazil are linked to the evolution of regional paleoceanographic and continental paleoclimatic conditions during the last 14.4kyr CAL BP. Mineralogical and major and trace element analyses of a 14C-dated sediment core identify three main lithostratigraphic units of this core that reveal a succession of changes in sediment delivery and accumulation as postglacial sea level rose and Holocene climate on land evolved. The depositional setting has transitioned in response to the large sea level rise prior to 9.9kyr CAL BP from being a shallow water high energy environment to a deeper water one. This location has since then been a lower energy environment that has persisted into modern times. Due to the high marine productivity associated with the Cabo Frio upwelling system in an oxygenated water column, the sediments have shown a complex and dynamic redox condition, making variations in redox-sensitive trace elements indicative of changes in primary production and organic matter diagenesis at this location. After sea level stabilized ~9kyr CAL BP, variations in fluxes of Al, Fe, Ca, and minerals were small, indicating that climate driven changes had only secondary controls on delivery of detrital sediment components to the Cabo Frio shelf. Modern coastal upwelling conditions and the onset of mid-shelf organic-rich sediment deposition were established after 9.9CAL kyr BP.

Late Quaternary evolution of Lago Castor (Chile, 45.6°S): Timing of the deglaciation in northern Patagonia and evolution of the southern westerlies during the last 17 kyr

Even though Patagonia is ideally located to study climate of the southern mid-latitudes, many questions on the late Quaternary climate evolution remain unresolved. The timing of maximum glacier extent is still uncertain in vast areas, and the postglacial evolution of the Southern Westerly Wind Belt (SWWB) remains highly debated. Here, we study the sedimentary infill of a glacigenic lake (Lago Castor; 45.6°S, 71.8°W) located at the leeside of the Andes in Chilean Patagonia to i) reconstruct the deglacial evolution of the eastern flank of the Patagonian Ice Sheet (PIS), and ii) discuss postglacial changes in wind strength at a critical location where westerly wind records are critically lacking. A dense grid of high-resolution reflection-seismic data was used to reconstruct the large-scale infill history of the lake, and a radiocarbon dated sediment core penetrating all lacustrine seismic units, was retrieved. Results indicate that the deglaciation of the lake basin and its catchment occurred no later than ∼28 cal kyr BP (i.e. an early LGM), but possibly even already after MIS 4. Afterwards, the Lago Castor area was covered by a large proglacial lake that drained – possibly through an outburst flood – when the PIS outlet glaciers retreated to a critical location. Subsequently, very dry conditions caused the lake to desiccate, as evidenced by an unconformity visible on the seismic profiles and in the sediment core. This dry period likely resulted from the increased orographic effect of the PIS-covered Andes, accompanied by weaker westerlies. From ∼20 kyr BP onwards, the combination of a shrinking PIS and a southward shift of the SWWB resulted in increased precipitation, which caused the lake level to rise. After ∼17 cal kyr BP, lake sedimentation was more directly influenced by the southern westerlies, with the formation of sediment drifts resulting from strong bottom current during periods of intense westerly winds. Our results suggest a progressive increase in wind strength at 46°S from 11.2 to 4.5 cal kyr BP, which supports the hypothesis that the SWWB broadened during the early and middle Holocene.

Regional patterns of postglacial changes in the Palearctic mammalian diversity indicate retreat to Siberian steppes rather than extinction.

We examined the presence of possible Recent refugia of Pleistocene mammalian faunas in Eurasia by analysing regional differences in the mammalian species composition, occurrence and extinction rates between Recent and Last Glacial faunas. Our analyses revealed that most of the widespread Last Glacial species have survived in the central Palearctic continental regions, most prominently in Altai–Sayan (followed by Kazakhstan and East European Plain). The Recent Altai–Sayan and Kazakhstan regions show species compositions very similar to their Pleistocene counterparts. The Palearctic regions have lost 12% of their mammalian species during the last 109,000 years. The major patterns of the postglacial changes in Palearctic mammalian diversity were not extinctions but rather radical shifts of species distribution ranges. Most of the Pleistocene mammalian fauna retreated eastwards, to the central Eurasian steppes, instead of northwards to the Arctic regions, considered Holocene refugia of Pleistocene megafauna. The central Eurasian Altai and Sayan mountains could thus be considered a present-day refugium of the Last Glacial biota, including mammals.

Late Glacial and Holocene Vegetation Changes in the Wigry National Park, Ne Poland – New Pollen Data from Three Small Dystrophic Lakes

Abstract The main phases of the Late Glacial and Holocene development of vegetation in the Wigry National Park were reconstructed based on the pollen analysis of sediments from three small dystrophic lakes (Lake Suchar Wielki, Lake Suchar II and Lake Ślepe). At the current stage of research, the age of the studied deposits was determined by AMS radiocarbon dating of few samples only. This meant that the chronology of the investigated sections had to be estimated also indirectly using their palynological correlation with the radiometrically well-dated section from Lake Wigry. The obtained pollen data confirmed the picture of the postglacial vegetation changes of the Wigry National Park, which was based on earlier studies of Lake Wigry. Furthermore, it documented the existence, mainly in the Preboreal and Atlantic chronozones, of temporary changes in vegetation, which might be a reaction to a short-lived cold fluctuations of climate.

Palynological records of the Early Permian postglacial climate amelioration (Karoo Basin, South Africa)

The Permian coal-bearing formations of the South African Karoo Basin play a crucial role in the study and interpretation of Gondwana’s climate history and biodiversity in this time of major global changes in terrestrial and marine ecosystems. Here, we report on new palynological data from the No. 2 coal seam of the Witbank coalfield, documenting the switch from icehouse to greenhouse conditions in the Early Permian. The studied postglacial fluvio-deltaic deposits of a highly proximal setting comprise coarse-grained to pebbly sandstones, partially with an abrupt upward transition into fine-grained sediments and coal, trough cross-stratified medium- to coarse-grained sandstones and horizontally laminated fine- to medium-grained sandstones and siltstones. The sedimentary organic matter content clearly documents stratal changes in the palynomorph assemblage and variations in the amount and in the type, size and shape of plant debris. Generally, palynofacies is characterized by a high amount of opaque phytoclasts. Amorphous organic matter is characteristic of laminated siltstones and coals. The palynological record indicates a cold climate, fern wetland community, characteristic of lowland alluvial plains, and an upland conifer community in the lower part of the coal seam. Up section, these communities are replaced by a cool-temperate cycad-like lowland vegetation and gymnospermous upland flora. The data presented herein, provide important information for (1) reconstructing palaeoenvironmental and climate change within the Lower Permian of the NE part of the South African Karoo, (2) intercontinental comparison of palaeofloral diversity patterns in adjacent sub-basins and (3) intra-Gondwanic correlations of coal-bearing basins (e.g. Australia), recording a major postglacial change associated with climate amelioration.

A 3-D coupled ice sheet – sea level model applied to Antarctica through the last 40 ky

We present results from a three-dimensional ice sheet-shelf model of Antarctica, coupled to a gravitationally self-consistent global sea-level model that incorporates (Maxwell) viscoelastic deformation of the solid Earth. The coupled model captures complex post-glacial changes in sea level associated with the gravitational, deformational and rotational effects of the evolving surface mass (ice plus ocean) load over the global ocean, including at the grounding lines of marine-based ice. The simulations are initiated at 40 ka and we focus on ice distributions and sea levels from the Last Glacial Maximum to present. Our results extend and confirm the key conclusions of earlier work using a simplified, 1-D ice-sheet model, by demonstrating that the sea-level coupling has a significant stabilizing influence on marine ice-sheet grounding lines. The feedback of sea-level changes into the ice-sheet model acts to slow down the retreat and advance of the grounding line relative to simulations in which the full coupling is not incorporated. Differences in ice thickness between these simulations can reach ∼1 km close to the grounding line. Finally, we perform preliminary comparisons of our results to relative sea level (RSL) histories and GPS-derived present-day uplift rates at sites near the margins of Antarctica. We find that the coupling improves fits to uplift rates in several regions, and that the RSL predictions of the coupled model yield a fit to the observations that is comparable to recent, uncoupled simulations in which the underlying Earth model was varied to obtain a best-fit to the RSL histories.

Postglacial RSL changes of White Sea according the lithological data and sporo-pollen proxy (Kandalaksha Bay, NW Russia)

Postglacial RSL changes of White Sea according the lithological data and sporo-pollen proxy (Kandalaksha Bay, NW Russia)

Christian Theodor Vaupell, a Danish 19th century naturalist and a pioneering developer of the Quaternary geoscience

Abstract. Christian Theodor Vaupell (1821–1862) was a Danish scholar with pioneering investigations particularly on the late Quaternary development of bog forests, but also microscopy of plant anatomy and vegetative reproduction. His studies contributed to the early scientific thinking of the Quaternary environmental changes. Before his academic efforts, he had already survived the war between Prussia and Denmark albeit he became severely wounded and his left arm was amputated. The drama of his academic efforts, on the other hand, lies in the more or less suspicious dispute of his first doctoral thesis and his dismissal from the academic world during the following years. At the same time, he earned praise for his first thesis (never accepted as thesis but published as a regular book) from abroad; he was also able to attract private foundations for financial support of his scientific work. Following the enthusiasm of his time, Vaupell became attracted to the pine megafossils known to have been preserved in the bogs in north-west Europe. The megafossils led him to study not only the life systems of the ancient and modern bog forests but also their associations with Earth processes. As an interesting detail of his research, Vaupell made compound interpretations on the occurrence of megafossil stumps and their tree-ring growth patterns. In the course of the 20th century, Vaupell's studies have been cited as a general reference of post-glacial vegetation change and plant succession rather than clearly pioneering investigations of palaeoecology, an angle that we would like put into a contrasting perspective. To do so, we provide a brief portrait of Christian Vaupell and his research career. In conclusion, we wish to emphasize the comprehensiveness of Vaupell's views on the late Quaternary vegetation changes and the role of plant succession in that development.

Plant Diversity Changes during the Postglacial in East Asia: Insights from Forest Refugia on Halla Volcano, Jeju Island

Understanding how past climate changes affected biodiversity is a key issue in contemporary ecology and conservation biology. These diversity changes are, however, difficult to reconstruct from paleoecological sources alone, because macrofossil and pollen records do not provide complete information about species assemblages. Ecologists therefore use information from modern analogues of past communities in order to get a better understanding of past diversity changes. Here we compare plant diversity, species traits and environment between late-glacial Abies, early-Holocene Quercus, and mid-Holocene warm-temperate Carpinus forest refugia on Jeju Island, Korea in order to provide insights into postglacial changes associated with their replacement. Based on detailed study of relict communities, we propose that the late-glacial open-canopy conifer forests in southern part of Korean Peninsula were rich in vascular plants, in particular of heliophilous herbs, whose dramatic decline was caused by the early Holocene invasion of dwarf bamboo into the understory of Quercus forests, followed by mid-Holocene expansion of strongly shading trees such as maple and hornbeam. This diversity loss was partly compensated in the Carpinus forests by an increase in shade-tolerant evergreen trees, shrubs and lianas. However, the pool of these species is much smaller than that of light-demanding herbs, and hence the total species richness is lower, both locally and in the whole area of the Carpinus and Quercus forests. The strongly shading tree species dominating in the hornbeam forests have higher leaf tissue N and P concentrations and smaller leaf dry matter content, which enhances litter decomposition and nutrient cycling and in turn favored the selection of highly competitive species in the shrub layer. This further reduced available light and caused almost complete disappearance of understory herbs, including dwarf bamboo.

039 Postglacial change in the vegetation and climate of western Siberia and mountains of southern Siberia based on palaeopalynological data

039 Postglacial change in the vegetation and climate of western Siberia and mountains of southern Siberia based on palaeopalynological data

Deglaciation, basin formation and post-glacial climate change from a regional network of sediment core sites in Ohio and eastern Indiana

Many paleoclimate and landscape change studies in the American Midwest have focused on the Late Glacial and early Holocene time periods (~ 16–11 ka), but little work has addressed landscape change in this area between the Last Glacial Maximum and the Late Glacial (~ 22–16 ka). Sediment cores were collected from 29 new lake and bog sites in Ohio and Indiana to address this gap. The basal radiocarbon dates from these cores show that initial ice retreat from the maximal last-glacial ice extent occurred by 22 ka, and numerous sites that are ~ 100 km inside this limit were exposed by 18.9 ka. Post-glacial environmental changes were identified as stratigraphic or biologic changes in select cores. The strongest signal occurs between 18.5 and 14.6 ka. These Midwestern events correspond with evidence to the northeast, suggesting that initial deglaciation of the ice sheet, and ensuing environmental changes, were episodic and rapid. Significantly, these changes predate the onset of the Bølling postglacial warming (14.8 ka) as recorded by the Greenland ice cores. Thus, deglaciation and landscape change around the southern margins of the Laurentide Ice Sheet happened ~ 7 ka before postglacial changes were felt in central Greenland.

A 16 000‐year record of vegetational change in south‐western Alaska as inferred from plant macrofossils and pollen

AbstractPollen and macrofossil analyses of a sediment core from Beaver Pond (60° 37′ 14″ N, 154° 19′ W, 579 m a.s.l.) reveal a record of regional and local postglacial vegetation change in south‐western Alaska. The chronology is based on five AMS (accelerator mass spectrometry) 14C ages obtained from terrestrial plant macrofossils. Pollen and macrofossil records suggest that open herb and shrub tundra with e.g. Poaceae, Cyperaceae, Artemisia, Vaccinium and Salix prevailed on the landscape before ca. 14 000 cal a BP. The shift from herb‐ to shrub‐dominated tundra (Salix, subsequent Betula expansion) possibly reflects climatic warming at the beginning of the Bølling period at ca. 14 700–14 500 and around 13 500 cal a BP. Vegetation (Betula shrub tundra) remained relatively stable until the early Holocene. Macrofossil influx estimates provide evidence for greater biomass in Betula shrub tundra during the early postglacial period than today. Charcoal accumulation rates suggest tundra fire activity was probably greater from ca. 12 500 to 10 500 cal a BP, similar to results from elsewhere in Alaska. The pollen and macrofossil records of Beaver Pond suggest the prevalence of low shrub tundra (shrub Betula, Betula nana, Vaccinium, Ledum palustre, Ericaceae) and tall shrub tundra (Alnus viridis ssp. crispa, Salix) between 10 000 and 4000 cal a BP. This Holocene vegetation type is comparable with that of the modern treeless wet and moist tundra in south‐western Alaska. The expansion of Picea glauca occurred ∼4000 cal a BP, much later than that of A. viridis (ssp. crispa), whereas in central and eastern Alaska Picea glauca expanded prior to or coincident with Alnus (viridis). At sites located only 200–400 km north‐east of Beaver Pond (Farewell and Wien lakes), Picea glauca and Betula forests expanded 8000–6000 cal a BP. Unfavourable climatic conditions and soil properties may have inhibited the expansion and establishment of Picea across south‐west Alaska during the mid and late Holocene. Copyright © 2011 John Wiley & Sons, Ltd.