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Sedimentary ancient DNA (sedaDNA) has been established as a viable biomolecular proxy for tracking taxon presence through time in a local environment, even in the total absence of surviving tissues. SedaDNA is thought to survive through mineral binding, facilitating long-term biomolecular preservation, but also challenging DNA isolation. Two common limitations in sedaDNA extraction are the carryover of other substances that inhibit enzymatic reactions, and the loss of authentic sedaDNA when attempting to reduce inhibitor co-elution. Here, we present a sedaDNA extraction procedure paired with targeted enrichment intended to maximize DNA recovery. Our procedure exhibits a 7.7–19.3x increase in on-target plant and animal sedaDNA compared to a commercial soil extraction kit, and a 1.2–59.9x increase compared to a metabarcoding approach. To illustrate the effectiveness of our cold spin extraction and PalaeoChip capture enrichment approach, we present results for the diachronic presence of plants and animals from Yukon permafrost samples dating to the Pleistocene-Holocene transition, and discuss new potential evidence for the late survival (~9700 years ago) of mammoth (Mammuthus sp.) and horse (Equus sp.) in the Klondike region of Yukon, Canada. This enrichment approach translates to a more taxonomically diverse dataset and improved on-target sequencing. [ABSTRACT FROM AUTHOR]

Thermokarst lakes form following the thaw of ice‐rich permafrost and drain after a few decades to millennia. Drained thermokarst lake basins (DTLBs) become epicenters for peat accumulation and re‐aggradation of ice‐rich permafrost. This re‐aggradation of permafrost may be interrupted by subsequent thermokarst lake formation with sufficient disturbance. Thermokarst lakes and DTLBs are abundant near Old Crow, Yukon, Canada, but little is known about their evolution through the Holocene. In this study, we investigate the hydrology and drainage histories of seven DTLBs from the Old Crow Flats on the basis of cryostratigraphy, radiocarbon dating, and pore‐ice δ18O and δ2H records. Cryostratigraphic evidence implies only one of the seven studied DTLBs underwent multiple thermokarst cycles. Radiocarbon age–depth models demonstrate a slowdown in the rate of post‐drainage peat accumulation with time. Pore‐ice isotope analyses reveal a spectrum of possible post‐drainage isotopic histories resulting from spatial variability in permafrost, vegetation, and hydrology. Unlike lacustrine silt, post‐drainage peat contains relatively constant pore‐ice isotope trends. In light of our findings, we propose that syngenetic peat permafrost in DTLBs preserve a warm‐season sampling of local meteoric waters. These pore‐ice δ18O and δ2H records may aid millennial‐scale paleoclimate investigations, as we demonstrate through our reconstruction of Holocene climate change in northern Yukon. [ABSTRACT FROM AUTHOR]

The Pliocene (5.3–2.6 Ma), an epoch with periods of climatic warmth and possible analogue for the future, has been well‐characterized globally by marine geochemical proxies. However, far less is known about Pliocene warmth at continental high latitudes, where the greatest impacts of warming are expected. This study seeks to better characterize the Pliocene climate of central Alaska and Yukon based on a reconstruction of the stable hydrogen isotope composition of precipitation relative to modern (ΔδDprecip) preserved in volcanic glass shards, a proxy for mean air temperature. The studied tephras are from a regional suite of outcrops that, when assembled into a composite record of ΔδDprecip, can be used to resolve broad trends during the late Miocene (6.7–5.86 Ma, n = 5), Pliocene (5.08–2.81 Ma, n = 7), and late Pleistocene (0.74–0.03 Ma, n = 3). These trends indicate that Pliocene ΔδDprecip estimates were generally more enriched in heavy isotopes than the latest Miocene, Pleistocene, and modern intervals. ΔδDprecip is likely influenced by changes in regional boundary conditions including orographic barriers, depositional environments, and ocean‐atmospheric circulation, but ΔδDprecip trends are most consistent with reconstructed temperatures from Yukon‐Alaska and North Pacific marine records. As such, this record appears predominantly sensitive to regional climate. Furthermore, qualitative temperature inferences from branched‐chain glycerol dialkyl glycerol tetraethers (brGDGTs) from four of our sites dating between 2.91 and 6.17 Ma corroborate elevated temperatures during the early Pliocene. Overall, this study demonstrates the viability of volcanic glass δD as a proxy for ΔδDprecip and late Cenozoic climate change in this region. Key Points: The 2H/1H of hydrated volcanic glass shards in late Cenozoic ash beds in Yukon and Alaska document changes in meteoric 2H/1H ratiosThe 2H/1H glass record is most coherent with other terrestrial and marine temperature reconstructions, indicating strong climate sensitivityBranched‐chain glycerol dialkyl glycerol tetraether (brGDGT) biomarkers from some of the same deposits corroborate significantly elevated temperatures during the early Pliocene [ABSTRACT FROM AUTHOR]

Tephrochronology is one of the most effective ways to correlate and date Quaternary deposits across large distances. However, it can be challenging to obtain direct ages on tephra beds when they are beyond the limit of radiocarbon dating, do not contain mineral phases suitable for 40K-40Ar (or 40Ar/39Ar) dating, or suitable glass shards for fission-track dating are not available. Zircon U-Pb dating by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging technique for dating young (<1 Ma) tephra. Here, we demonstrate that LA-ICP-MS zircon U-Pb dating can produce reliable ages for key tephra beds found in Yukon and Alaska. We assessed five different techniques for calculating tephra maximum depositional ages from zircon U-Pb ages for eight tephra beds. Our preferred zircon U-Pb ages (reported with 2σ uncertainties), based on a Bayesian model for calculating maximum depositional ages, are broadly consistent with previously established chronology constructed from stratigraphy, paleomagnetism, and/or glass fission track and 40Ar/39Ar ages: Biederman tephra (178 ± 17 ka), HP tephra (680 ± 47 ka), Gold Run tephra (688 ± 44 ka), Flat Creek tephra (708 ± 43 ka), PA tephra (1.92 ± 0.06 Ma), Quartz Creek tephra (2.62 ± 0.08 Ma), Lost Chicken tephra (3.14 ± 0.07 Ma), and GI tephra (542 ± 64 ka). We also present newly revised glass fission-track and 40Ar/39Ar ages recalculated from previous determinations using updated ages for the Moldavite tektite and Fish Canyon Tuff standards, and updated K decay constants. For Pleistocene age zircon crystals, corrections for 230Th disequilibrium and common-Pb are significant and must be treated with caution. Similarly, apparent tephra ages are sensitive to the choice of method used to calculate a maximum depositional age from the assemblage of individual crystallization ages. This study demonstrates that LA-ICP-MS zircon U-Pb dating can be successfully applied to numerous Pliocene-Pleistocene Alaskan-Yukon tephra, providing confidence in applying this method to other stratigraphically important tephra in the region. • LA-ICP-MS method is well suited for rapid dating of very young zircon crystals. • Eight key tephra beds from Eastern Beringia were dated by zircon U-Pb method. • Young U-Pb ages are particularly sensitive to common-Pb and 230Th corrections. • Bayesian modeling reduces subjectivity in calculating ages. [ABSTRACT FROM AUTHOR]

The Old Crow basin, northern Yukon, provides a key record of environmental change in northwestern North America from the late-Middle Pleistocene through the Early Holocene. Site chronologies are based on the presence of the Old Crow tephra (OCt: 124 ± 10 ka) at three sites, and provide a stratigraphic framework for observations. Ecological affinities of fossil insects indicate that Pleistocene environments were dominated by dry tundra and steppe-tundra. Forest insect species are relatively rare even during the last interglaciation (MIS 5e), and it is only by considering the total insect assemblages that interglacial beds can be recognized. Last interglacial insects from these sites indicate a relatively wet and warm tundra environment with evidence for sparse forest vegetation. Rare taxa with strong affinities to warmer temperatures are present and could suggest a warmer than modern climate. Early Holocene deposits yield a greater abundance of forest insects relative to MIS 5 or 7 interglacial deposits. Fossil insect assemblages reflect the position of the sites above the Arctic Circle, and in contrast to central Yukon sites, steppe insects are less common during cold stages and forest insects are less common during warm stages. These data suggest overall that the contrast between cold and warm stages was less pronounced than in other regions of Yukon and Alaska, and may indicate influence of persistent large regional lakes during the Pleistocene. [ABSTRACT FROM AUTHOR]

We present a detailed cryostratigraphic reconstruction of the degradation and recovery of near-surface permafrost in the southern Klondike goldfields, central Yukon Territory. Two ice-rich layers are recognized in near-surface permafrost and attributed to thermal impacts following vegetation disturbance. At an undisturbed forest site, the base of the modern active layer is stable. At an adjacent site, where a late twentieth century disturbance of surface vegetation and permafrost degradation occurred, there is evidence of recovery in the form of aggradation (upward shift) of the permafrost table following limited vegetation succession. Underlying both the undisturbed forest and the late twentieth century disturbance is an older thaw unconformity corresponding to a thaw depth of ∼2 m, likely associated with early twentieth century (gold rush era) impacts. Field and air photo surveys allow identification of the nature of the disturbances, while a chronology of the surface disturbance has been established using age estimates from tree rings, and the presence of tritium and post-bomb 14C from organic samples within aggradational ice. Collectively, these data underscore the importance of vegetation cover in maintaining ground temperatures in the discontinuous permafrost zone and suggest that, at least at the study site in recent decades, permafrost shows the potential to recover from disturbance in the modern climatic regime of the region. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: We synthesize pollen spectra from eleven dated stratigraphic sections from central and northern Yukon. Palaeomagnetic and tephra dating indicates the earliest assemblages, representing closed canopy Pinus and Picea forest, are middle-late Pliocene age. More open forest conditions, indicated by increased Poaceae and with evidence of permafrost, are dated at ca 3 Ma. While Pinus pollen is abundant at 3 Ma, it is reduced in records after 2.6 Ma, and subsequent Pleistocene interglacial forest records are repeatedly dominated by Picea, along with Alnus and small but significant amounts of Abies. Surface sample comparisons indicate that Abies was more widespread and abundant in past interglaciations than at present and that Middle-Pleistocene Picea–Abies forest grew in the northern Yukon Porcupine Basin, 500 km beyond modern Abies limits. In contrast, Pinus, which occurs today in southern and central Yukon, was not a significant component of these Pleistocene interglacial forests. Late-Holocene pollen assemblages with rare Abies and high Pinus are the most distinct in the past 2.6 Ma. Possible factors driving Holocene difference are paleoclimate, paludification, changes in megafaunal herbivory and an unusual fire regime. Anthropogenic burning is a factor unique to the Holocene, and if it is shown to be important in this case, it would challenge our notion of what constitutes boreal wilderness. [Copyright &y& Elsevier]

Abstract: Radiocarbon dating of soils and sediments is notoriously problematic for the purposes of dating a specific event due to their heterogeneous mix of multiple organic fractions, each of which may have a different radiocarbon age. Numerous studies have failed to agree on which sedimentary fraction or radiocarbon pre-treatment method, if any, provides the closest agreement between the age of a sedimentary fraction and that of associated plant macrofossils or charcoal. We tested the stepped-combustion method of , as well as standard radiocarbon humin and humic extraction techniques, using samples from a chronologically well-constrained perennially-frozen site at Quartz Creek, Yukon Territory, Canada. The ages in closest agreement with associated radiocarbon-dated plant macrofossils and with the overlying Dawson tephra were given by the humic and humin fractions, but even these were still older than the macrofossil ages by up to 4195 ± 260 radiocarbon years. The low temperature (LT) humin method recommended by yielded ages older than the macrofossils by up to nearly 4425 ± 240 radiocarbon years. These fractions, while still providing information on the mobility and potential residence times of carbon in soils and sediments, should not be relied upon to provide consistently accurate site chronologies. [ABSTRACT FROM AUTHOR]

Abstract: We present stratigraphic observations from three sites in eastern Beringia – Ch’ijee’s Bluff in northern Yukon and nearby exposures on the Old Crow River, the Palisades on the Yukon River in Alaska, and placer mining exposures at Thistle Creek in west-central Yukon – which provide insight into the response of permafrost to regional warming during the last interglaciation. Chronology is based on the presence of Old Crow tephra, an important regional stratigraphic marker that dates to late Marine Isotope Stage 6, supplemented by paleoecology and non-finite 14C ages on wood-rich organic silts. Old Crow tephra overlies several relict ice wedges at the Palisades and Thistle Creek, indicating that permafrost at these sites did not thaw completely during the last interglaciation. Prominent deposits of last interglacial wood-rich organic silt are present at multiple sites in eastern Beringia, and probably represent accumulations of reworked forest vegetation due to thaw slumping or deposition into thermokarst ponds or depressions. Consistent stratigraphic relations between these deposits, Old Crow tephra, and ice wedge pseudomorphs at our three study sites, and at least six other sites in eastern Beringia, suggest that thaw of shallow permafrost was widespread during the last interglaciation. Limited stratigraphic evidence suggests that thaw was probably on the order of meters, rather than 10s of meters. The ubiquity of shallow permafrost degradation during the last interglaciation suggests that current ground warming may foreshadow widespread near-surface thaw under even modest future warming scenarios. However, the persistence of relict pre-last interglacial ice wedges highlights the potential for the regional antiquity of discontinuous permafrost, and provides compelling field evidence for the long-term resilience of deep permafrost during sustained periods of warmer-than-present climate. [ABSTRACT FROM AUTHOR]

Abstract: The Eagle River spillway and braid delta complex provide a record of the maximum extent of the northwest Laurentide Ice Sheet and diversion of meltwater from Bonnet Plume Basin into the interior basins of non-glaciated northern Yukon. Development of the spillway can be characterized in three distinct zones based on the distribution of erosion and deposition along each reach: erosion-dominated channel initiation and incision; followed by channelization and coarse clastic deposition along channel margins and into tributary valleys; and lastly, fine-grained deltaic and lacustrine sedimentation in the lower channel reach. Deltaic sedimentation within the spillway is crudely-coarsening upward from alternating beds of massive clay and silt to ripple-cross-bedded sand. All sediments occur in rapidly-aggrading forms with no evidence for a significant hiatus in deposition. Radiocarbon ages on woody plant macrofossils and spruce needles are non-finite, while radiocarbon ages on macrofossils from herbaceous plant taxa and insects with ‘steppe-tundra’ ecological affinity from the upper part of the delta range from 15 840±90 to 21 600±1300 14CyrBP. These ages, coupled with the rapidly-aggrading nature of the delta sediments and landform, suggest an age of ca 15–16 000 14CyrBP. Non-finite and mixed ages underscore the significant problem of reworked, well-preserved macrofossils in Arctic environments and the need for careful selection of both fragile and ecologically-representative macrofossils to establish reliable chronologies. [Copyright &y& Elsevier]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article discusses a study on the use of floodplain stratigraphy as a method in assessing ice jam flood frequency in Yukon River, which stretches from Yukon Territory to Alaska. The study focuses on the development of an ice jam flood record for northern rivers for the last 2000 years based on three study locations at the river as well as investigates natural variability and the changes of flood frequency in response to climactic factors. The benefit of the sedimentary record for future studies on flood frequency monitoring is also discussed.

Dawson tephra, recently recognized in the Klondike area of Yukon Territory, records one of the largest Quaternary volcanic eruptions in Beringia. Its composition is similar to that of Old Crow tephra, indicating a source in the Aleutian arc-Alaska Peninsula region of southwestern Alaska. Its primary thickness in central Yukon is nearly twice that of Old Crow tephra, which has an estimated eruption volume of >50 km3. The distribution of Dawson tephra is still poorly known, but based on its source area and occurrence in central Yukon, it should be widespread across southern Alaska, Yukon and the Gulf of Alaska. New radiocarbon ages indicate the eruption occurred at about 24,000 14C yr BP (ca 27,000 cal yr BP). The Dawson tephra is a valuable marker bed for correlating late Pleistocene records across large areas of eastern Beringia and adjacent marine records. [Copyright &y& Elsevier]

The article discusses a study on the areas of permafrost. Vulnerability to climate change of permafrost because of its nearness in melting point of the earth is explained. It mentions that prediction of numerical models suggest a permafrost degradation on twenty-first century climate. It investigates ground ice within the discontinuous permafrost zone of central Yukon Territory, Canada. Ice composing the wedge of ice through thermal contraction cracking and infilling surface water are also discussed.

The Aleutian Arc-Alaska Peninsula and Wrangell volcanic field are the main source areas for tephra deposits found across Alaska and northern Canada, and increasingly, tephra from these eruptions have been found further afield in North America, Greenland, and Europe. However, there have been no broad scale reviews of the Late Pleistocene and Holocene tephrostratigraphy for this region since the 1980s, and this lack of data is hindering progress in identifying these tephra both locally and regionally. To address this gap and the variable quality of associated geochemical and chronological data, we undertake a detailed review of the latest Pleistocene to Holocene tephra found in interior Alaska and Yukon. This paper discusses nineteen tephra that have distributions beyond southwest Alaska and that have the potential to become, or already are, important regional markers. This includes three ‘modern’ events from the 20th century, ten with limited data availability but potentially broad distributions, and six that are widely reported in interior Alaska and Yukon. Each tephra is assessed in terms of chronology, geochemistry and distribution, with new Bayesian age estimates and geochemical data when possible. This includes new major-element geochemical data for Crater Peak 1992, Redoubt 1989–90, and two andesitic tephra from St Michael Island (Tephra D), as well as revised age estimates for Dawson tephra, Oshetna, Hayes set H, Aniakchak CFE II, and the White River Ashes, northern and eastern lobes. [ABSTRACT FROM AUTHOR]

Abstract: The Palisades, in central Alaska, is one of the most prominent exposures of Quaternary sediments on the Yukon River. Perennially-frozen silt and sand at the Palisades are presently thought to preserve paleoenvironmental records from the Holocene to ∼Marine Isotope Stage (MIS) 8 and, beneath a major unconformity, the earliest Pleistocene (∼2 Ma). We present new paleomagnetic and tephrochronologic constraints that substantially revise the age of the sediments at the Palisades. We describe 15 new tephra beds, including five beds below the prominent PAL tephra that correlate to known tephra with independent age control from other sites in eastern Beringia. These five known tephra include Chester Bluff tephra, which is present in east-central Alaska and the Yukon, and the newly named Alyeska Pipeline and Taylor Highway tephra from central Alaska; all are constrained to the middle Pleistocene. Paleomagnetic transects from the base of the bluff to the MIS 5e forest bed yield normal polarity, with the exception of a brief reversal event between Old Crow tephra (124 ± 10 ka) and the MIS 5e forest bed that is likely the first documentation of the Blake paleomagnetic event in Alaskan loess. The detailed tephrostratigraphy and paleomagnetic data collectively suggest that most of the sedimentary record at the Palisades is middle Pleistocene in age. The Palisades thus preserves a rare record of late to middle Pleistocene paleoenvironments with multiple regionally distributed tephra beds. [Copyright &y& Elsevier]

The increased use of radiocarbon analyses for archeological, paleontological, and paleoclimate research has created a demand for robust and well characterized procedural blanks. Currently, blanks are distributed ad hoc throughout the radiocarbon community in limited quantities and are depleted quickly by high throughput labs. This forces AMS facilities to regularly seek out suitable blanks from other facilities, and the switch to different blank material inhibits assessment of long term procedural blank performance. An excellent source for well-preserved radiocarbon "dead" organic material is the permafrost-rich region of unglaciated Yukon and Alaska. Extensive placer mining operations and river bluffs expose Middle Pleistocene sediments that regularly yield pristine organic material. Here, we present an assessment of laboratory precision and overall measure of performance of two processing blanks from the region. The AVR-07-PAL-37 wood and Hollis Mammoth pelvis bone collected from Alaska and Yukon, respectively. Both are independently dated to the Middle Pleistocene and have been verified by 14C-AMS to be radiocarbon "dead", with mean FmC of 0.0054 ± 0.0002 (n = 714) and 0.0031 ± 0.0002, (n = 219), respectively. Preliminary use at several AMS and stable isotope facilities in the U.S.A., Canada, United Kingdom, and China confirms that AVR-07-PAL-37 and Hollis Mammoth are suitable blanks for radiocarbon analyses. Both materials are available for wide distribution to other interested AMS labs. [ABSTRACT FROM AUTHOR]

In eastern Beringia (unglaciated Alaska and western Yukon), the Pleistocene-Holocene transition was characterised by rapid changes in plant, insect and mammal communities as the mammoth steppe ecosystem was replaced, first by shrub tundra and later boreal forest. These changes indicate a transition from well drained terrain with deep active layers to wetter, cooler soils, to which steppe-tundra vegetation was poorly adapted. The nature and precise timing of these events is not well resolved, particularly in central Yukon where regional climate may have been strongly affected by the retreating Cordilleran-Laurentide ice sheet complex. Resolving this uncertainty is not only important for understanding past ecosystems, but also provides a long-term perspective for contemporary environmental change and shrub expansion that affects large areas of northern high-latitudes today. Here, we report chronology (41 radiocarbon dates), stratigraphy, pore-ice δ2H/δ18O measurements, pollen data, megafauna remains and fossil insect assemblages from a permafrost-preserved loessal sequence in central Yukon, named Lucky Lady. The site spans the interval from ca. 17,000 to 8000 cal yr BP (calibrated years before C.E. 1950) and records the Pleistocene-Holocene transition in exceptional resolution. Full glacial environments (ca. 16,500 cal yr BP) supported elements of steppe-tundra vegetation and an insect fauna dominated by Connatichela artemisiae - an endemic weevil indicating warm soil temperatures. The collapse of the mammoth steppe ecosystem began with slowing of loess accumulation and development of paleosol ca. 13,480 cal yr BP. At this time, C. artemisiae remains become infrequent and Artemisia pollen decline to be replaced by Cyperaceae (ca. 13,220), before mesic, shrub taxa (likely dwarf Betula and Salix) becomes dominant ca. 13,210 cal yr BP. The establishment of shrub tundra is associated with rapid changes in δ2H/δ18O measurements, suggesting that ecological turnover coincided with a shift in atmospheric conditions and moisture availability. Finally, boreal vegetation communities became established ca. 10,680 cal yr BP. The replacement of steppe-tundra vegetation in central Yukon lagged other areas of eastern Beringia by as much as 1000 years and coincided with rapid deglaciation during the Bølling–Allerød time-period (14,600–12,900 cal yr BP). Turnover in insect and vegetation communities took place in ca. 40 years as shrub tundra became dominant. This rapid turnover has parallels with contemporary Arctic greening and re-emphasises the sensitivity of high-latitude environments to climate change. • High-resolution environmental data spans the Pleistocene-Holocene transition. • Chronology of mammoth steppe collapse in central Yukon. • Evidence for warm soils during full glacial. • Delayed onset of shrub expansion in easternmost Beringia. • Rapid vegetation change coincides with atmospheric shift. [ABSTRACT FROM AUTHOR]

Abstract: The Variegated (VT) tephra, likely sourced from the eastern Aleutian arc, has a geographic distribution that places it amongst the most widespread tephra beds in eastern Beringia. First identified in the Fairbanks area of interior Alaska, it has been identified at eight additional sites ranging from Togiak Bay in southwestern Alaska, to the Klondike area of west-central Yukon. Correlation of these occurrences is established through the equivalence of glass major and trace-element geochemistry, Fe-Ti oxide geochemistry, stratigraphy, and independent age data. In Yukon and Alaska, VT tephra has a minimum bulk tephra volume estimate of ∼32 km3. Previous age estimates for VT tephra have varied, ranging from a glass fission-track age of 125 ± 30 ka to a weighted mean thermoluminescence (TL) age of 77.8 ± 4.1 ka from bracketing ages on loess. A new infrared stimulated luminescence (IRSL) age of 106 ± 10 ka, paleoenvironmental data, and several TL and IRSL ages from Togiak Bay suggest that the time of deposition is more likely between these previous age estimates: post-marine isotope stage (MIS) 5e but underlying a prominent soil likely associated with MIS 5c, placing it within late MIS 5d. [Copyright &y& Elsevier]