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)

The impact and significance of tephra deposition on a Holocene forest environment in the North Cascades, Washington, USA.

© 2016 Elsevier Ltd. High-resolution palaeoecological analyses (stratigraphy, tephra geochemistry, radiocarbon dating, pollen and ordination) were used to reconstruct a Holocene vegetation history of a watershed in the Pacific Northwest of America to evaluate the effects and duration of tephra deposition on a forest environment and the significance of these effects compared to long-term trends. Three tephra deposits were detected and evaluated: MLF-T158 and MLC-T324 from the climactic eruption of Mount Mazama, MLC-T480 from a Late Pleistocene eruption of Mount Mazama and MLC-T485 from a Glacier Peak eruption. Records were examined from both the centre and fringe of the basin to elucidate regional and local effects. The significance of tephra impacts independent of underlying long-term trends was confirmed using partial redundancy analysis. Tephra deposition from the climactic eruption of Mount Mazama approximately 7600 cal. years BP caused a significant local impact, reflected in the fringe location by changes to open habitat vegetation (Cyperaceae and Poaceae) and changes in aquatic macrophytes (Myriophyllum spicatum, Potamogeton, Equisetum and the alga Pediastrum). There was no significant impact of the climactic Mazama tephra or other tephras detected on the pollen record of the central core. Changes in this core are potentially climate driven. Overall, significant tephra fall was demonstrated through high resolution analyses indicating a local effect on the terrestrial and aquatic environment, but there was no significant impact on the regional forest dependent of underlying environmental changes

The impact and significance of tephra deposition on a Holocene forest environment in the North Cascades, Washington, USA

High-resolution palaeoecological analyses (stratigraphy, tephra geochemistry, radiocarbon dating, pollen and ordination) were used to reconstruct a Holocene vegetation history of a watershed in the Pacific Northwest of America to evaluate the effects and duration of tephra deposition on a forest environment and the significance of these effects compared to long-term trends. Three tephra deposits were detected and evaluated: MLF-T158 and MLC-T324 from the climactic eruption of Mount Mazama, MLC-T480 from a Late Pleistocene eruption of Mount Mazama and MLC-T485 from a Glacier Peak eruption. Records were examined from both the centre and fringe of the basin to elucidate regional and local effects. The significance of tephra impacts independent of underlying long-term trends was confirmed using partial redundancy analysis. Tephra deposition from the climactic eruption of Mount Mazama approximately 7600 cal. years BP caused a significant local impact, reflected in the fringe location by changes to open habitat vegetation (Cyperaceae and Poaceae) and changes in aquatic macrophytes (Myriophyllum spicatum, Potamogeton, Equisetum and the alga Pediastrum). There was no significant impact of the climactic Mazama tephra or other tephras detected on the pollen record of the central core. Changes in this core are potentially climate driven. Overall, significant tephra fall was demonstrated through high resolution analyses indicating a local effect on the terrestrial and aquatic environment, but there was no significant impact on the regional forest dependent of underlying environmental changes

Glacial and Postglacial History of the White Cloud Peaks-Boulder Mountains, Idaho, U.S.A.

Glacial and glaciofluvial deposits are mapped and differentiated to develop new local, relative-age (RD) stratigraphies for the North Fork of the Big Lost River, Slate Creek and Pole Creek drainages in the White Cloud Peaks and Boulder Mountains, Idaho. This stratigraphic model expands the areal extent of the "Idaho glacial model". Volcanic ash samples collected from the study area are petrographically characterized and correlated, on the basis of mineralogy and glass geochemistry, to reference samples of identified Cascade Range tephras. Four distinct tephras are recognized including; Mount St. Helens-Set S (13,600-13,300 yr BP), Glacier Peak-Set B (11,250 yr BP), Mount Mazama (6600 yr BP) and Mount St. Helens-Set Ye (4350 yr BP). A core of lake sediments containing two tephra units was obtained from a site called "Pole Creek kettle". Pollen and sediment analyses indicate three intervals of late Pleistocene and Holocene climatic change. Cool and wet climatic conditions prevailed in the region shortly before and immediately following the deposition of the Glacier Peak-Set B ash (11,250 yr BP). Climatic warming occurred from approximately 10,500 to 6600 yr BP after which warm, dry conditions prevailed. Sediment accumulation in the kettle ceased by 4350 yr BP. The presence of Glacier Peak-Set B tephra in the base of the Pole Creek kettle core provides a minimum age of 11,250 yr BP for the retreat of valley glaciers from their Late Wisconsinan maximum position. A radiocarbon date of 8450 + 85 yr BP (SI-5181), and the presence of Mount Mazama ash (6600 yr BP) up-core support the Glacier Peak-Set B identification.La cartographie et l'identification des dépôts glaciaires et fluvioglaciaires a permis d'établir la stratigraphie locale des bassins du North Fork de la Big Lost River, du Pole Creek et du Slate Creek. Le modèle stratigraphique établi augmente la superficie déjà couverte par le modèle glaciaire de l'Idaho. Les échantillons de cendre volcanique prélevés ont été identifiés sur le plan pétrographique et mis en corrélation avec des tephras témoins provenant du Cascade Range, en se fondant sur la composition minérale et sur la géochimie du verre. On distingue quatre types de tephras: ceux de la série S du mont St. Helen's (13 600-13 300 BP), ceux de la série B du Glacier Peak (11 250 BP), ceux de la série S du mont St. Helen's (4350 BP) et ceux du mont Mazama (6600 BP). Une carotte de sédiments lacustres prélevée dans le kettle Pole Creek renferme deux tephras. L'analyse du pollen et des sédiments révèle l'existence de trois grands changements climatiques au Pleistocene supérieur et à l'Holocène: un climat frais et humide un peu avant et immédiatement après la mise en place des cendres de la série B du Glacier Peak (11 250 BP); une période de réchauffement (10 500-6600 BP); un climat chaud et sec. L'accumulation de sédiments dans le kettle prit fin vers 4350 BP. La présence du tephra de la série B du Glacier Peak à la base de la carotte donne la date minimale du retrait des glaciers de vallée (11 250 BP) à partir de leur emplacement au Wisconsinien supérieur. La date de 8450 + 85 ans BP et la présence, dans la partie supérieure de la carotte, de cendres provenant du mont Mazama (6600 BP) confirment l'identification de la série B du Glacier Peak.Idaho, U.S.A. Glaziale und glaziofluviale Ablagerungen wurden kartographiert und identifiziert, um eine neue, lokale, relative Alters-Stratigraphie der North Fork des Big Lost River, des Slate Creek und des Pole Creek in den White Cloud Peaks und Boulder Mountains, Idaho, zu en-twickeln. Proben vulkanischer Asche, die im untersuchten Gebiet gesammelt wurden, werden petrographisch bestimmt und auf der Basis von mineralogischer Zusammensetzung und Geochemie des Glases in Wechselbe-ziehung zu Referenz-Belegen von identifi-zierten Tephras von den Cascade Ranges gesetzt. Es werden vier verschiedene Tephras identifiziert: von der Série S des Mount St. Helens (13 600-13 300 v.u.Z.), von der Série B des Glacier Peak (11 250 v.u.Z.), von der Série Ye des Mount Mazama (6600 v.u.Z.) und des Mount St. Helens (4350 v.u.z.). Eine Probe von See-Sedimenten, der vom Pole Creek Kettle gewonnen wurde, enthâlt zwei Tephra-Einheiten. Die Pollen- und Sediment-Analysen lassen drei Intervalle klimatischen Wechsels im spâten Pleistozân und im Ho-lozan erkennen. Kalte und feuchte Klimatische Bedingungen herrschten in diesem Gebiet vor, kurz vor und unmittelbar nach der Ablagerung der Asche der Série B des Glacier Peak (11 250 v.u.Z.). Eine klimatische Erwàrmung trat zwischen ungefàhr 10 500 bis 6600 v.u.Z. auf, nach welcher warme, trockene Bedingungen vorherrschten. Die Sediment-An-hàufung in dem Kettel endete ungefàhr um 4350 v.u.Z. Das Vorkommen von Tephra der Série B des Glacier Peak in der Basis der Probe des Pole Creek Kettle ergibt ein Minimum-Alter von 11 250 v.u.Z. fur den Ruckzug der Gletscher des TaIs von ihrer maximalen Position im spâten Wisconsin. Ein Radiokar-bon-Datum von 8450 + 85 v.u.Z. (SI-5181) und das Vorkommen von Asche des Mount Mazama (6600 v.u.Z.) im oberen Teil der Probe stutzen die Identifizierung der Série B des Glacier Peak

Timing and Paleoclimatic Significance of Latest Pleistocene and Holocene Cirque Glaciation in the Enchantment Lakes Basin, North Cascades, WA

The Enchantment Lakes Basin in the Alpine Lakes Wilderness, Washington, preserves two sets of moraines that record distinct post-Wisconsin maximum advances of cirque glaciers in the eastern North Cascades. Cores collected from five lakes adjacent to the moraines indicate that there were two Neoglacial advances, culminating with the Little Ice Age, and one slightly larger advance that ended coincident with the termination of the North Atlantic Younger Dryas event. The cores show no evidence for an early Holocene advance, in contrast to some other studies in the North Cascades, (e.g., Heine, 1998; Thomas, 1997; Thomas et al., 2000). Upstream glacier activity, as indicated by rock-flour production, is recorded in the lake sediments as fluctuations in magnetic susceptibility, organic content, and sediment particle size. Tephra identification, AMS 14C dating, and paleomagnetic secular variation of the sediments provide detailed age constraints for the lake cores. The presence of the 475 cal yr B.P. Mount St. Helens Wn tephra within outwash associated with the inner (Brynhild) moraines indicates that they are Little Ice Age (LIA) equivalent. The age constraints on the lake sediments show that this advance began between ~ 1000-800 cal yr B.P. and culminated after the Wn tephra was deposited. The age of the outer (Brisingamen) moraines, previously reported as early Holocene (Waitt et al.,1982), are instead latest Pleistocene; close limiting 14C dates demonstrate that this advance ended shortly before ~11,300 cal yr B.P., suggesting temporal equivalence with the North Atlantic Younger Dryas climatic reversal (12,940 ± 260 - 11,640 ± 250 cal yr B.P; Alley et al., 1993). A ~500-yr interval of high rock-flour flux in the cores records an early Neoglacial advance between ~3300 and ~2800 cal yr B.P. that was less extensive than the subsequent LIA advance. Steady-state equilibrium-line altitudes (ELAs) for Brynhild and Brisingamen advances estimated with accumulation-area ratio and balance-ratio methods are distinct but nearly indistinguishable at ~2355 m, roughly 200 m below the modern ELA. Conditions required to form and sustain the Brisingamen and Brynhild paleoglaciers include a summer temperature depression of ~3° C, an increase of ~90 cm water-equivalent in winter precipitation, or, more likely, some lesser combination of the two. These constraints imply a local climate that could support only small-scale advances in both the latest Pleistocene and late Holocene, and warmer as well as drier conditions throughout the early Holocene

Mineralogy and Phase Chemistry of Mount St. Helens Tephra Sets W and Y as Keys to Their Identification

Voluminous and widespread tephras were produced frequently during the last 36,000 yr of volcanic activity at Mount St. Helens. Numerous tephra sets have been defined by D. R. Mullineaux, J. H. Hyde, and M. Rubin (1975, U.S. Geological Survey Journal of Research, 3, 329–335) on the basis of field relations, Fe-Mg phenocryst assemblage, and 14C chronology and are valuable marker beds for regional stratigraphic studies. In this study modal abundances and mineral compositions were determined (via petrographic and electron microprobe techniques) for numerous samples of individual layers within tephra sets W and Y to evaluate the degree of compositional variability within and between tephra layers and criteria by which to distinguish among Mount St. Helens and other Pacific Northwest tephras. Although individual layers within a set (e.g., We, Wn) cannot be distinguished from each other on the basis of mineralogic characteristics examined, mineral compositions allow distinction among layers W and Y and other Pacific Northwest tephras (e.g., Mazama, Glacier Peak). Fe-Ti oxide compositions and T-ƒO2 estimates derived using coexisting magnetite-ilmenite are especially useful due to the compositional homogeneity of these minerals both within and between samples of a given unit over a wide geographic area. The silicates show more compositional variability than the oxides, but SiO2/Al2O3 contents in hornblende and Fe/Mg ratios in hypersthene aid in distinguishing among Pacific Northwest tephras

The Origin of Dark Mats at the Sunrise Ridge Borrow Pit Site (45PI408) Mount Rainier National Park, Washington

The Sunrise Ridge Borrow Pit Site is a precontact archaeological site located in the upland forest soils of Mount Rainier National Park. Site stratigraphy is complicated, consisting of tephra deposits from mostly known origins that are intercalated with dark sediments of unknown origin, referred to here as dark mats. Precontact occupation has been split previously into two components based on the ambiguous depositional history of the dark mats, notably their unknown parent material, depositional environment, and relationship with adjacent tephra strata. Stratigraphic samples from excavation units, features, and one off-site excavation unit was used to investigate these data gaps. Grain size, chemistry, organic content, pH, and calcium carbonate content are characterized to document parent material and depositional environment of adjacent strata. Dark mats typically had higher organic content and similar chemistry and grain-size properties compared to underlying tephra strata, and interpreted as buried A horizons that formed in tephra of known regional origin. However, a few dark mats were reworked, and at times the product of multiple or unknown parent material. These determinations are used to revise a depositional history model of the Sunrise Ridge Borrow Pit Site that places the main occupation at 471 years BP to 2,200 cal years BP yet supports previous site assemblage organization into two precontact components

Environmental and Hunter-Gatherer Responses to the White River Ash East Volcanic Eruption in the Late Holocene Canadian Subarctic

The eastern lobe of the Alaskan White River Ash volcanic event of AD 846 – 848 blanketed portions of Yukon and Northwest Territories, Canada, in 5 to 50 cm of tephra. The eruption has been linked to concurrent changes among hunter- gatherers, including the spread of new technologies and the continent-wide migration of a group of Dene ancestors from Subarctic Canada to the United States. We use published palaeoenvironmental data (primarily pollen and charcoal profiles) as well as studies of modern ash fall ecology and human health hazards associated with eruptions to reconstruct effects of the White River Ash east event on northern hunter-gatherer subsistence. While many components of local ecosystems appear to have rebounded quickly from ash deposition, we deduce a more pronounced impact on the important game species of caribou and salmon, the seasonal migration paths of which were intersected by thick deposits of ash. A trophic model informed by palaeoenvironmental data and ethnohistoric records suggests that negative biological effects of the ash temporarily pushed hunter-gatherer populations to neighbouring and less affected kin groups for up to 100 years. This synthesis contextualises archaeological theories of human responses to ecological disturbance events in circumpolar landscapes.Le lobe occidental du dépôt de cendres volcaniques White River Ash, en Alaska, remontant aux années 846 – 848 A.D., a recouvert certaines parties du Yukon et des Territoires du Nord-Ouest, au Canada, d’une couche de téphra de 5 à 50 cm. Cette éruption a été liée à des changements simultanés chez les chasseurs-cueilleurs, dont l’adoption de nouvelles technologies et la migration à l’échelle du continent d’un groupe d’ancêtres dénés, de la zone subarctique canadienne jusqu’aux États-Unis. Nous avons publié des données paléoenvironnementales (principalement des profils de pollen et de charbon de bois) ainsi que des études d’écologie moderne de chutes de cendres et de dangers pour la santé des êtres humains découlant d’éruptions afin de reconstituer les effets du dépôt occidental White River Ash sur la subsistance des chasseurs-cueilleurs nordiques. Même si de nombreuses composantes des écosystèmes locaux semblent s’être remises rapidement des dépôts de cendres, nous déduisons que les répercussions ont été plus prononcées sur les espèces de gibier de caribou et sur le saumon, dont les voies de migration saisonnière croisaient les épais dépôts de cendres. Un modèle trophique établi à l’aide de données paléoenvironnementales et d’enregistrements ethnohistoriques suggère que les effets biologiques négatifs des cendres ont poussé temporairement les populations de chasseurs-cueilleurs chez des groupes apparentés avoisinants et moins touchés pendant une centaine d’années. Cette synthèse met en contexte les théories archéologiques se rapportant aux réactions humaines vis-à-vis d’événements de perturbation écologique dans les paysages circumpolaires