Late Pleistocene yedoma in south-western Yukon (Canada): a remnant of Eastern Beringia?

Yedoma deposits developed from the syngenetic accumulation and freezing of organic-rich and ice-rich sediments during the Late Pleistocene over vast portions of Siberia, Alaska and Yukon Territory. Cryostratigraphic investigations revealed the presence of a yedoma deposit in the Beaver Creek area of south-western Yukon. The Beaver Creek area was not glaciated during the last glacial advance and the cryostratigraphic record comprises Middle Wisconsinian up to Holocene deposits covering the Mirror Creek disintegration moraine. Reworking of glacial deposits by alluvial and solifluction processes and peat accumulation in the depression of the hummocky moraine likely occurred during the Middle Wisconsinian period and was followed during the Late Wisconsinian by the yedoma build-up. A major thaw event interrupted the syngenetic permafrost aggradation which eventually resumed as attested by the upward growth of ice wedges

Plant Macrofossils Associated with an Early Holocene Beaver Dam in Interior Alaska

Dynamic climate changes and expansion of new biomes characterize the late Pleistocene–early Holocene of eastern Beringia. Analysis of plant macrofossils from an early Holocene (ca. 9300 14C yrs BP) beaver dam in central Alaska provides insight into the local environment and vegetation. The plant macrofossil assemblage comprises remains of trees and shrubs, graminoids, and forbs, including Betula sp., Carex sp., Rubus sp., Eleocharis sp., Scirpus sp., Potamogeton sp., Najas flexilis and Typha latifolia, indicative of standing water of a beaver pond. Bryophytes from the beaver dam include Warnstorfia spp. and Drepanocladus aduncus, suggesting shallow, stagnant, or slow-moving water. The presence of Najas flexilis, Typha latifolia, and modern beaver (Castor canadensis) suggest that central Alaska had a warmer climate during the early Holocene.Changements climatiques dynamiques et expansion de nouveaux biomes caractérisent la période du Pléistocène supérieur et de l’Holocène inférieur de la Béringie de l’Est. L’analyse des macrofossiles de plantes provenant d’une digue de castor du centre de l’Alaska datant de l’Holocène inférieur (env. 9300 14C années BP) donne des indices sur l’environnement et la végétation de la région. L’assemblage de macrofossiles de plantes est composé d’arbres et d’arbustes, de graminoïdes et d’herbes non graminéennes, dont Betula sp., Carex sp., Rubus sp., Eleocharis sp., Scirpus sp., Potamogeton sp., Najas flexilis et Typha latifolia, ce qui signale la présence d’eau stagnante dans un étang de castor. Parmi les bryophytes de la digue de castor, notons Warnstorfia spp. et Drepanocladus aduncus, ce qui laisse supposer la présence d’eau peu profonde stagnante ou se déplaçant lentement. Par ailleurs, la présence de Najas flexilis, Typha latifolia et du castor contemporain (Castor canadensis) laissent croire que le climat du centre de l’Alaska était plus chaud pendant l’Holocène inférieur

Dynamical response of the southwestern Laurentide Ice Sheet to rapid Bølling–Allerød warming

The shift in climate that occurred between the Last Glacial Maximum (LGM) and the Early Holocene (ca. 18–12 kyr BP) displayed rates of temperature increase similar to present-day warming trends. The most rapid recorded changes in temperature occurred during the abrupt climate oscillations known as the Bølling–Allerød interstadial (14.7–12.9 kyr BP) and the Younger Dryas stadial (12.9–11.7 kyr BP). Reconstructing ice sheet dynamics during these climate oscillations provides the opportunity to assess long-term ice sheet evolution in reaction to a rapidly changing climate. Here, we use glacial geomorphological inversion methods (flowsets) to reconstruct the ice flow dynamics and the marginal retreat pattern of the southwestern sector of the Laurentide Ice Sheet (SWLIS). We combine our reconstruction with a recently compiled regional deglaciation chronology to depict ice flow dynamics that encompass the time period from pre-LGM to the Early Holocene. Our reconstruction portrays three macroscale reorganizations in the orientation and dynamics of ice streaming followed by regional deglaciation associated with rapid warming during the Bølling–Allerød interstadial. Initial westward flow is documented, likely associated with an early set of ice streams that formed during the advance to the LGM. During the LGM ice streaming displays a dominant north to south orientation. Ice sheet thinning at ∼15 ka is associated with a macroscale reorganization in ice stream flow, with a complex of ice streams recording south-eastward flow. A second macroscale reorganization in ice flow is then observed at ∼14 ka, in which southwestern ice flow is restricted to the Hay, Peace, Athabasca, and Churchill river lowlands. Rates of ice sheet retreat then slowed considerably during the Younger Dryas stadial; at this time, the ice margin was situated north of the Canadian Shield boundary and ice flow continued to be sourced from the northeast. Resulting from these changes in ice sheet dynamics, we recognize a three-part pattern of deglacial landform zonation within the SWLIS characterized by active ice margin recession, stagnation and downwasting punctuated by local surging (terrestrial ice sheet collapse): the outer deglacial zone contains large recessional moraines aligned with the direction of active ice margin retreat; the intermediate deglacial zone contains large regions of hummocky and stagnation terrain, in some areas crosscut by the signature of local surges, reflecting punctuated stagnation and downwasting; and the inner deglacial zone contains inset recessional moraines demarcating progressive regional ice margin retreat. We attribute these macroscale changes in ice flow geometry and associated deglacial behaviour to external climatic controls during the Bølling–Allerød and Younger Dryas but also recognize the role of internal (glaciological, lithological and topographic) controls in SWLIS dynamics

First evidence of cryptotephra in palaeoenvironmental records associated with Norse occupation sites in Greenland

The Norse/Viking occupation of Greenland is part of a dispersal of communities across the North Atlantic coincident with the supposed Medieval Warm Period of the late 1st millennium AD. The abandonment of the Greenland settlements has been linked to climatic deterioration in the Little Ice Age as well as other possible explanations. There are significant dating uncertainties over the time of European abandonment of Greenland and the potential influence of climatic deterioration. Dating issues largely revolve around radiocarbon chronologies for Norse settlements and associated mire sequences close to settlement sites. Here we show the potential for moving this situation forward by a combination of palynological, radiocarbon and cryptotephra analyses of environmental records close to three ‘iconic’ Norse sites in the former Eastern Settlement of Greenland – Herjolfsnes, Hvalsey and Garðar (the modern Igaliku). While much work remains to be undertaken, our results show that palynological evidence can provide a useful marker for both the onset and end of Norse occupation in the region, while the radiocarbon chronologies for these sequences remain difficult. Significantly, we here demonstrate the potential for cryptotephra to become a useful tool in resolving the chronology of Norse occupation, when coupled with palynology. For the first time, we show that cryptotephra are present within palaeoenvironmental sequences located within or close to Norse settlement ruin-groups, with tephra horizons detected at all three sites. While shard concentrations were small at Herjolfsnes, concentrations sufficient for geochemical analyses were detected at Igaliku and Hvalsey. WDS-EPMA analyses of these tephra indicate that, unlike the predominantly Icelandic tephra sources reported in the Greenland ice core records, the tephra associated with the Norse sites correlate more closely with volcanic centres in the Aleutians and Cascades. Recent investigations of cryptotephra dispersal from North American centres, along with our new findings, point to the potential for cryptotephra to facilitate hypothesis testing, providing a key chronological tool for refining the timing of Norse activities in Greenland (e.g. abandonment) and of environmental contexts and drivers (e.g. climate forcing)

Ice Cores from the St. Elias Mountains, Yukon, Canada: Their Significance for Climate, Atmospheric Composition and Volcanism in the North Pacific Region

A major achievement in research supported by the Kluane Lake Research Station was the recovery, in 2001 –02, of a suite of cores from the icefields of the central St. Elias Mountains, Yukon, by teams of researchers from Canada, the United States, and Japan. This project led to the development of parallel, long (103 – 104 year) ice-core records of climate and atmospheric change over an altitudinal range of more than 2 km, from the Eclipse Icefield (3017 m) to the ice-covered plateau of Mt. Logan (5340 m). These efforts built on earlier work recovering single ice cores in this region. Comparison of these records has allowed for variations in climate and atmospheric composition to be linked with changes in the vertical structure and dynamics of the North Pacific atmosphere, providing a unique perspective on these changes over the Holocene. Owing to their privileged location, cores from the St. Elias Icefields also contain a remarkably detailed record of aerosols from various sources around or across the North Pacific. In this paper we review major scientific findings from the study of St. Elias Mountain ice cores, focusing on five main themes: (1) The record of stable water isotopes (δ18O, δD), which has unique characteristics that differ from those of Greenland, other Arctic ice cores, and even among sites in the St. Elias; (2) the snow accumulation history; (3) the record of pollen, biomass burning aerosol, and desert dust deposition; (4) the record of long-range air pollutant deposition (sulphate and lead); and (5) the record of paleo-volcanism. Our discussion draws on studies published since 2000, but based on older ice cores from the St. Elias Mountains obtained in 1980 and 1996

High-resolution age modelling of peat bogs from northern Alberta, Canada, using pre- and post-bomb 14 C, 210 Pb and historical cryptotephra

High-resolution studies of peat profiles are frequently undertaken to investigate natural and anthropogenic disturbances over time. However, overlapping profiles of the most commonly applied age-dating techniques, including 14C and 210Pb, often show significant offsets (>decadal) and biases that can be difficult to resolve. Here we investigate variations in the chronometers and individual site histories from six ombrotrophic peat bogs in central and northern Alberta. Dates produced using pre- and post-bomb 14C, 210Pb (corroborated with 137Cs and 241Am), and cryptotephra peaks, are compared and then integrated using OxCal's P_Sequence function to produce a single Bayesian age model. Environmental histories for each site obtained using physical and chemical characteristics of the peat cores, e.g. plant macrofossils, humification, ash content and dry density, provide important constraints for the models by highlighting periods with significant changes in accumulation rate, e.g. fire events, permafrost development, and prolonged surficial drying. Despite variable environmental histories, it is possible to produce high-resolution age-depth models for each core sequence. Consistent offsets between 14C and 210Pb dates pre-1960s are seen at five of the six sites, but tephra-corrected 210Pb data can be used to produce more coherent models at three of these sites. Processes such as permafrost development and thaw, surficial drying and local fires can disrupt the normal processes by which chronological markers and environmental records are incorporated in the peat record. In consequence, applying standard dating methodologies to these records will result in even greater uncertainties and discrepancies between the different dating tools. These results show that using any single method to accurately date peat profiles where accumulation has not been uniform over time may be unreliable, but a comprehensive multi-method investigation paired with the application of Bayesian statistics can produce more robust chronologies. New cryptotephra data for the Alberta region are also reported here, including the historical Novarupta-Katmai 1912 eruption, White River Ash (East), and glass from Mt. St. Helens, Mt. Churchill, and probable Aleutian sources

Ice Cores from the St. Elias Mountains, Yukon, Canada: Their Significance for Climate, Atmospheric Composition and Volcanism in the North Pacific Region

A major achievement in research supported by the Kluane Lake Research Station was the recovery, in 2001 –02, of a suite of cores from the icefields of the central St. Elias Mountains, Yukon, by teams of researchers from Canada, the United States, and Japan. This project led to the development of parallel, long (103 – 104 year) ice-core records of climate and atmospheric change over an altitudinal range of more than 2 km, from the Eclipse Icefield (3017 m) to the ice-covered plateau of Mt. Logan (5340 m). These efforts built on earlier work recovering single ice cores in this region. Comparison of these records has allowed for variations in climate and atmospheric composition to be linked with changes in the vertical structure and dynamics of the North Pacific atmosphere, providing a unique perspective on these changes over the Holocene. Owing to their privileged location, cores from the St. Elias Icefields also contain a remarkably detailed record of aerosols from various sources around or across the North Pacific. In this paper we review major scientific findings from the study of St. Elias Mountain ice cores, focusing on five main themes: (1) The record of stable water isotopes (δ18O, δD), which has unique characteristics that differ from those of Greenland, other Arctic ice cores, and even among sites in the St. Elias; (2) the snow accumulation history; (3) the record of pollen, biomass burning aerosol, and desert dust deposition; (4) the record of long-range air pollutant deposition (sulphate and lead); and (5) the record of paleo-volcanism. Our discussion draws on studies published since 2000, but based on older ice cores from the St. Elias Mountains obtained in 1980 and 1996

Permafrost Deep Organic Matter: The IPA Yedoma Action Group

Die Action Group "The Yedoma Region: A Synthesis of Circum-Arctic Distribution and Thickness" der Internationalen Permafrost Assoziation (IPA) hat es zum Ziel die Verbreitung und Mächtigkeit von Yedoma Permafrost, einem spätpleitozänen sehr eisreichem Permafrost, zu quantifizieren. Yedoma ist durch Eisgehalte von bis zu 80vol% sehr anfällig gegenüber Erwärmung. Denn wenn das Bodeneis schmilzt und abgeführt wird sind Absenkungen der Bodenoberflächen von mehr als 30 Metern möglich, was deutliche Auswirkungen hat auf die Landschaft, samt Infrastruktur und menschlicher Landnutzung. Als Produkt dieses Projektes möchten wir hier eine circum-arktische Karte präsentieren. Diese Daten werden als Grundlage dazu dienen, den Kohlenstoffpool von Yedoma Ablagerungen realistisch in computergestützte Modelle zu implementieren und die zukünftigen Auswirkungen von Thermokarst und Thermoerosion auf die Treibhausgasemissionen abzuschätzen