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This is the first study to generate and analyze the climate signal in blue intensity (BI) tree-ring chronologies from Alaska yellow-cedar (Callitropsis nootkatensis (D. Don) Oerst. ex D.P. Little). The latewood BI chronology shows a much stronger temperature sensitivity than ring width and can thus provide information on past climate. The well-replicated BI chronology exhibits a positive January-August mean maximum temperature signal for 1900-1975, after which it loses temperature sensitivity following the 1976-1977 shift in northeastern Pacific climate. The positive temperature response appears to recover and remains strong for the most recent decades, but the coming years will continue to test this observation. This temporary loss of temperature sensitivity from about 1976 to 1999 is not evident in ring width or in a change in forest health but is consistent with prior work linking cedar decline to warming. A confounding factor is the uncertain influence of a shift in color variation from the heartwood-sapwood boundary. Future expansion of the yellow-cedar BI network and further investigation of the influence of the heartwood-sapwood transitions in the BI signal will lead to a better understanding of the utility of this species as a climate proxy. Key words: yellow-cedar, blue intensity, tree rings, dendroclimatology, Alaska. Cette etude est la premiere a generer et analyser le signal climatique dans des series dendrochronologiques construites a partir de l'intensite de la lumiere bleue (IB) refletee par les cernes annuels du faux-cypres de Nootka (Callitropsis nootkatensis (D. Don) Oerst. ex D.P. Little). La chronologie IB reliee a la densite maximum du bois final est beaucoup plus sensible a la temperature que la largeur des cernes annuels et fournit par consequent de l'information sur le climat passe. La chronologie IB bien repetee revele un signal positif de la temperature maximum moyenne de janvier a aout de 1900 a 1975, apres quoi la sensibilite a la temperature disparait a la suite du changement du climat dans le nord-est du Pacifique en 1976-1977. La reponse positive de la temperature semble se retablir et demeure forte pour les plus recentes decennies mais cette observation devra subir l'epreuve du temps. Cette perte temporaire de sensibilite a la temperature de 1976 a 1999 environ n'est pas evidente dans la largeur des cernes annuels ni dans un changement dans l'etat de sante de la foret, mais elle correspond aux resultats de travaux anterieurs reliant le deperissement du faux-cypres au rechauffement. L'influence incertaine d'un changement dans la variation de la couleur a la limite entre le bois de creur et le bois d'aubier est un facteur de confusion. L'expansion future du reseau IB du faux-cypres de Nootka et la poursuite de l'etude de l'influence de la transition entre le bois d'aubier et le bois de creur dans le signal IB meneront a une meilleure comprehension de l'utilite de cette espece comme indicateur indirect du climat. [Traduit par la Redaction] Mots-cles: faux-cypres de Nootka, intensite de la lumiere bleue, cernes annuels, dendroclimatologie, Alaska., 1. Introduction Climate-driven, abiotic stress is emerging as a major driver of forest decline in North America (Cohen et al. 2016; Buma et al. 2017). Forest decline is defined as [...]

Yellow-cedar (Callitropsis nootkatensis (D. Don) Orsted ex D.P. Little) is in a century-long decline coinciding with the end of the Little Ice Age (LIA). The leading hypothesis explaining this decline is a decrease in insulating snowpack due to warming and increased susceptibility to damaging frosts in the root zone. A ring-width series from yellow-cedar on Excursion Ridge (260 m a.s.l.) in Glacier Bay National Park and Preserve, Alaska, and another from trees on Pleasant Island (150 m a.s.l.) in the Tongass National Forest in Icy Strait were compared with regional monthly temperature and precipitation data from Sitka, Alaska, to investigate the changing growth response to temperature at these sites. Comparisons with monthly temperatures from 1832 to 1876 during the end of the Little Ice Age show that the high-elevation Excursion Ridge and the low-elevation Pleasant Island sites strongly favored warmer January through July temperatures. Both tree populations have markedly changed their response from a positive to a strong negative correlation with January through July temperatures since 1950. This strong negative response to warming by the yellow-cedar together with a positive relationship with total March and April precipitation suggests that these yellow-cedar sites may be susceptible to decline. Furthermore, these analyses are consistent with the hypothesis that the yellow-cedar decline is linked to decreased snowpack. Resume: Le faux-cypres de Nootka (Callitropsis nootkatensis (D. Don) Orsted ex D.P. Little) connait une periode de deperissement qui dure depuis un siecle et dont le debut coincide avec la fin du Petit Age glaciaire. La principale hypothese pour expliquer ce deperissement est la reduction du couvert nival et de ses proprietes isolantes a cause du rechauffement climatique ainsi que l'augmentation de la sensibilite aux dommages causes par le gel dans la zone des racines. Une serie dendrochronologique du faux-cypres de Nootka provenant d'Excursion Ridge (260 metres au-dessus du niveau de la mer), dans le parc national de Glacier Bay, en Alaska, et une autre provenant d'arbres sur Pleasant Island (150 metres au-dessus du niveau de la mer) dans la foret nationale de Tongass a Icy Strait ont ete comparees aux donnees regionales de precipitation et de temperature mensuelles provenant de Sitka en Alaska pour etudier la variation de la reaction de la croissance a la temperature dans ces stations. Les comparaisons avec les temperatures mensuelles de 1832 a 1876, a la fin du Petit Age glaciaire, montrent que la station d'Excursion Ridge a une altitude elevee et la station de Pleasant Island a plus basse altitude etaient tres favorables aux temperatures plus chaudes de janvier a juillet. Les deux populations d'arbre ont nettement change leur reaction passant d'une correlation positive a fortement negative avec les temperatures de janvier a juillet depuis 1950. Cette forte reaction negative du faux-cypres de Nootka combinee a une relation positive avec la precipitation totale des mois de mars et avril indique que ces stations a faux-cypres de Nootka sont peut-etre sensibles au deperissement. De plus, ces analyses sont compatibles avec l'hypothese selon laquelle le deperissement du faux-cypres de Nootka serait relie a la reduction du couvert nival. [Traduit par la Redaction], Introduction Tree mortality caused by biotic and abiotic factors is among the responses of the world's forests to recent climate variations (Adams et al. 2010). The loss of forests has [...]

Recent decades of warmer climate have brought drying wetlands and falling lake levels to southern Alaska. These recent changes can be placed into a longer-term context of postglacial lake-level fluctuations that include low stands that were as much as 7 m lower than present at eight lakes on the Kenai Lowland. Closed-basin lakes on the Kenai Lowland are typically ringed with old shorelines, usually as wave-cut scarps, cut several meters above modern lake levels; the scarps formed during deglaciation at 25–19 ka in a kettle moraine topography on the western Kenai Lowland. These high-water stands were followed by millennia of low stands, when closed-basin lake levels were drawn down by 5–10 m or more. Peat cores from satellite fens near or adjoining the eight closed-basin lakes show that a regional lake level rise was underway by at least 13.4 ka. At Jigsaw Lake, a detailed study of 23 pairs of overlapping sediment cores, seismic profiling, macrofossil analysis, and 58 AMS radiocarbon dates reveal rapidly rising water levels at 9–8 ka that caused large slabs of peat to slough off and sink to the lake bottom. These slabs preserve an archive of vegetation that had accumulated on a lakeshore apron exposed during the preceding drawdown period. They also preserve evidence of a brief period of lake level rise at 4.7–4.5 ka. We examined plant succession using in situ peat sequences in nine satellite fens around Jigsaw Lake that indicated increased effective moisture between 4.6 and 2.5 ka synchronous with the lake level rise. Mid- to late-Holocene lake high stands in this area are recorded by numerous ice-shoved ramparts (ISRs) along the shores. ISRs at 15 lakes show that individual ramparts typically record several shove events, separated by hundreds or thousands of years. Most ISRs date to within the last 5200 years and it is likely that older ISRs were erased by rising lake levels during the mid- to late Holocene. This study illustrates how data on vegetation changes in hydrologically coupled satellite-fen peat records can be used to constrain the water level histories in larger adjacent lakes. We suggest that this method could be more widely utilized for paleo-lake level reconstruction. [ABSTRACT FROM AUTHOR]

Radiocarbon ages and lichen-dated moraines from 17 glaciers in coastal and near-coastal British Columbia and Alaska document a widespread glacier advance during the first millennium A.D. Glaciers at several sites began advancing ca. A.D. 200-300 based on radiocarbon-dated overridden forests. The advance is centered on A.D. 400-700, when glaciers along an ~2000 km transect of the Pacific North American cordillera overrode forests, impounded lakes, and deposited moraines. The synchroneity of this glacier advance and inferred cooling over a large area suggest a regional climate forcing and, together with other proxy evidence for late Holocene environmental change during the Medieval Warm Period and Little Ice Age, provide support for millennial-scale climate variability in the North Pacific region. Keywords: Alaska, British Columbia, glacier, Holocene, neoglaciation, paleoclimate.

Four intervals of late Holocene glacier advance are recognized from study of nine valley glaciers in the Wrangell and westernmost St. Elias Mountains of Alaska. The oldest glacial advance is recognized at the Nabesna and Barnard Glaciers where five radiocarbon ages suggest advance as early as 2700 cal. (calibrated) yr B.P. Two additional radiocarbon-dated advances are centered on cal. yr A.D. 300 and the beginning of the Little Ice Age about A.D. 1200. The best-documented Little Ice Age advances occurred during the mid-1600s through the 1800s and are recognized at all nine glaciers. These latter advances are dated by tree rings of trees overrun by glaciers in five glacier valley, by 17 radiocarbon dates, and by tree-ring and lichen ages from 20 moraines that were deposited during the culmination of these advances. The glacial chronology is broadly similar to chronologies from adjoining Alaskan mountain ranges, at both coastal and interior sites for the past 3000 yr. There are, however, differences in timing of advances during the first millennium A.D. The glacial history for the past 2000 yr is also consistent with temperature-sensitive proxy records from interior Alaska and Yukon Territory. Keywords: Alaska, glaciers, Holocene, tree rings, Wrangell-St. Elias Mountains.

Stratigraphic and geomorphic data defined by radiocarbon ages, tree-ring dates, and historical observations provide evidence of three major Holocene expansions of Hubbard Glacier. Early in each advance the Hubbard Glacier margin blocked Russell Fiord to create Russell lake, raising base level and causing stream beds and fan deltas throughout the Russell drainage basin to aggrade. Each Hubbard Glacier expansion continued with an ice lobe advancing through Disenchantment and Yakutat Bays in the west, and an eastern lobe advancing into Russell Fiord. The earlier two Holocene expansions were, respectively, under way at 7690 and 5600 calibrated yr B.P., and each advance culminated more than 1 k.y. later. The late Holocene advance was under way by 3100 yr ago and reached ~13 km farther south in Russell Fiord than the preceding two expansions. Late Holocene deglaciation of Yakutat and Disenchantment Bays was complete before A.D. 1791; Nunatak Glacier flowing from neves east of Russell Fiord became the primary ice source to the Russell Fiord lobe at or before this date. Ice retreat from the southern end of Russell Fiord began in the late eighteenth century and the penultimate Russell lake drained ca. A.D. 1860. The relatively slow advances and more rapid retreats of Hubbard Glacier are consistent with the model of the iceberg-calving glacier cycle. Hubbard Glacier is currently advancing and will likely reestablish Russell lake in the near future, affecting local fisheries. However, glacier lobes are unlikely to reach the area of the town of Yakutat, built on late Holocene glacial deposits, in the next 1 k.y. Keywords: Fan deltas, glacial geology, glacial lakes, tidewater glaciers, Yakutat Bay.

Recent retreat of outlet glaciers from the Harding and Grewingk-Yalik Icefields has revealed a vast array of deposits on the eastern and western flanks of the Kenai Mountains that records multiple glacier advances into coastal forests during late Holocene time. Tree-ring dating, together with radiocarbon and lichenometric analyses, allows for the reconstruction of these glacial fluctuations to decadal precision over the past two thousand years. The records of fluctuations are derived from 16 land-terminating and seven tidewater glaciers in three fjord systems, as well as two cirque glaciers. Three major intervals of Holocene glacier expansions are evident; they occurred about 3600 yr B.P., 600 A.D., and during the Little Ice Age, from 1300 to 1850 A.D. The earliest expansion beyond present ice margins is known only from the McCarty tidewater glacier. The 600 A.D. event involved the simultaneous advance of land-terminating and tidewater glaciers. During the Little Ice Age, however, tidewater glaciers were advancing several centuries prior to their land-terminating neighbors. Those land-terminating glaciers on the western mountain flank retreated from their Little Ice Age maxima as much as two centuries before those on the eastern mountain flank. Land-terminating tongues on the eastern, more maritime, mountain flank have shown more sensitivity to variations in winter precipitation during the Little Ice Age and within recent decades than the more continental glaciers on the western flank that are affected more by summer temperatures. The glacial and climatic records suggest that advances of the ice tongues from about 1420 to 1460 A.D., between 1640 and 1670 A.D., at about 1750 A.D., and from 1880 to 1910 A.D. reflected times of increased winter precipitation. Advances between 1440 to 1460 A.D., from 1650 to 1710 A.D., and from 1830 to 1860 A.D. followed intervals of lower summer temperatures.

Winter is a critical season for land‐surface feedbacks and ecosystem processes; however, most high‐latitude paleo‐environmental reconstructions are blind to cold season conditions. Here we introduce a winter‐sensitive, paleo‐proxy record that is based on the relative frequency of tangential rows of traumatic resin ducts (TRDs) in the annual growth rings of mountain hemlocks (Tsuga mertensiana) growing near treeline in Southeast Alaska. Hemlocks produce a row of TRDs in the earlywood portion of their annual rings in response to cambial damage incurred during winter. Multidecadal bouts of TRD production were followed by growth‐leader replacement, reaction wood formation, and divergence in radial growth between storm‐damaged trees and less exposed mountain hemlock forests. These patterns are consistent with TRDs being a response to tree damage caused by ice and snowstorms, a conclusion supported by the krummholz tree architecture at these sites. This relationship is further corroborated by significant correlations between our TRD record and the strength of the wintertime Aleutian Low (AL) pressure system that is linked to tree‐damaging agents like wind, precipitation, and ice storm strength in Southeast Alaska. The combined TRD/krummholz architecture record indicates that abrupt shifts between strong and weak AL phases occurred every several decades since CE 1700 and that the 1800s had relatively long AL phases with heavy snowpacks. In addition to describing the magnitude and tempo of wintertime climate change in Northwestern North America, these results suggest that North Pacific Decadal Variability underlies the long‐term dynamics of treeline ecosystems along the northeast Pacific coast. Key Points: Traumatic resin ducts in the cross‐dated tree rings of subalpine mountain hemlocks record tree damage during winter storms in Southeast AlaskaWarmer, windier winters that accompany strong Aleutian Low pressure systems result in more tree damageDecadal‐scale variability in North Pacific climate has impacted treeline ecosystems throughout this region [ABSTRACT FROM AUTHOR]

A 1200-year-long tree-ring width record from living and subfossil mountain hemlock wood is used to reconstruct February through August temperatures for the Gulf of Alaska, providing a record of past climate variability for the Northeast Pacific sector that captures interannual to centennial timescales. The moderate elevation at the tree-ring sites has allowed these trees to retain their temperature signal without evidence of the so-called divergence effect, or underestimation of tree-ring inferred temperature trends, which is observed at many northern latitude forest locations. This ‘divergence-free’ reconstruction reveals centennial trends that include a warm interval centered on ad 950 for coastal Alaska that occurs around the time of the ‘Medieval Warm Period’, a warming that is only rivaled by recent decades. Spectral analysis of this reconstruction supports the centennial pacing identified as a 170–220-year cadence consistent with solar variability. On the decadal to bidecadal scale, the reconstruction reveals ~10- and 18-year cycles, which have been observed elsewhere in climate records for western North America and are linked to solar and lunar tidal forcing, respectively. Temperature minima that occur at ad 969–970 and 1698–1700 correspond with the timing of major volcanic events. This tree-ring reconstruction supports centennial modes of solar forcing as a driver of surface air temperatures in the Gulf of Alaska, with lunar tidal, solar variability, internal variability, and volcanism, impacting climate on annual to decadal timescales. [ABSTRACT FROM PUBLISHER]

Abstract: Two interstadial tree ring-width chronologies from Geikie Inlet, Glacier Bay Southeast, Alaska were built from 40 logs. One of these chronologies has been calendar dated to AD 224–999 (775yr) crossdating with a living ring-width chronology from Prince William Sound, Alaska. Trees in this chronology were likely killed through inundation by sediments and meltwater from the advancing Geikie Glacier and its tributaries ca. AD 850. The earlier tree-ring chronology spans 545yr and is a floating ring-width series tied to radiocarbon ages of about 3000calyr BP. This tree-ring work indicates two intervals of glacial expansion by the Geikie Glacier system toward the main trunk glacier in Glacier Bay between 3400 and 3000calyr BP and again about AD 850. The timing of both expansions is consistent with patterns of ice advance at tidewater glaciers in other parts of Alaska and British Columbia about the same time, and with a relative sea-level history from just outside Glacier Bay in Icy Strait. This emerging tree-ring dated history builds on previous radiocarbon-based glacial histories and is the first study to use tree-ring dating to assign calendar dates to glacial activity for Glacier Bay. [Copyright &y& Elsevier]

We utilized dendrochronology and precise elevation-constrained mapping to date glacially overridden and drowned trees at the margin of Brady Glacier in southeast Alaska. This technique allowed determination of the timing of the former tidewater glacier’s last advance and consequent formation and filling of two marginal lakes. The subfossil tree-ring chronology spans the interval from AD 1370 to 1861. Brady Glacier impounded Spur Lake to an elevation of 83 m a.s.l. around 1830 and 121 m a.s.l. around 1839. Soon after, Spur Lake reached 125 m a.s.l. and began to overflow a stable bedrock sill. The glacier continued to advance, thickening by at least 77 m between c. 1844 and 1859 at a site down-glacier of Spur Lake on the opposite glacier margin. Farther down-glacier, North Trick Lake began to form by 1861 and reached its highest elevation at approximately 130 m a.s.l. when Brady Glacier reached its maximum extent around 1880. Our findings add precision to the chronology of the last advance of Brady Glacier and provide insight into the evolution of glacier-dammed lakes and calving glaciers. [ABSTRACT FROM AUTHOR]

Abstract: Tree-ring crossdates from glacially killed logs show that Tebenkof Glacier advanced into a forefield forest in the AD 710s and 720s. Recession from this First Millennium AD (FMA) advance occurred before the 950s, after which the ice margin readvanced in the 1280s to 1320s at the start of the Little Ice Age (LIA). A more extensive LIA advance was underway from the 1640s to 1670s, and the terminus stayed at or near its LIA maximum until the 1890s. These are the first absolute tree-ring crossdates for a FMA glacier advance in North America and support growing evidence from northwestern North America and Europe for a significant cool interval in the centuries around AD 500. [Copyright &y& Elsevier]

Tree-ring studies at 13 glacier forefields in western Prince William Sound show ‘Little Ice Age’ glacial fluctuations were strongly synchronous on decadal timescales. Cross-dated glacially overrun trees at eight sites indicate ice margins advanced in the early (late twelfth through thirteenth centuries) and middle (seventeenth to early eighteenth centuries) ‘Little Ice Age’. Tree-ring dates of 22 moraines at 13 glaciers show two main periods of stabilization. The earlier of these, in the first decades of the eighteenth century, overlaps with the second period of glaciers overrunning trees and marks culmination of this middle ‘Little Ice Age’ expansion. Stabilization of moraines on nine of the study forefields in the latter part of the nineteenth century delineates a third interval of ‘Little Ice Age’ glacial advance. The detailed ‘Little Ice Age’ record from land-terminating glaciers in western Prince William Sound is consistent on a timescale of decades with four other tree-ring-dated glacial histories from across the northern Gulf of Alaska. This coastal northeastern Pacific glacial record reveals the structure of the ‘Little Ice Age’ in the region and provides a strong basis for comparison with other proxy climate records spanning the past 1000 years. [ABSTRACT FROM AUTHOR]

Few paleoclimatic records exist for Hokkaido, the northernmost, coldest and least environmentally disturbed of Japan's main islands. Here, we present a chronology for kashiwa oak (Quercus dentata Thunb.) atLake Saroma on the north central coast of Hokkaido. This record (1710--1993) was compared with the meteorological data from Abashiri, thelongest existing station (1899--1989) near the site. Growth correlates positively with current June-July temperatures, but negatively with prior-year August temperatures. Growth also correlates positively with prior November, December, and March temperatures and with prior February precipitation. Results suggest that these oaks grow best during warm, early summers, or after warm, snowy winters. The lowest growth year is 1784, following the 'year without a summer' elsewhere in Japan. This record contributes to a growing tree-ring network for the North Pacific rim, including sites in Japan, Kamchatka, Korea, Alaska, and Canada. It also adds a new species to those considered useful for dendroclimatology. [ABSTRACT FROM AUTHOR]

Highlights • Major plant wax sources were compared to bog sediments in a forested catchment. • All plants had similar n- acid abundance; n -alkanes were notably abundant in trees. • Wax δ2H and δ13C indicate a sediment bias toward trees and other woody plants. • δ2H fractionation from precipitation to wax was −133‰ (n -alkanes) & −103‰ (n -acids) • Bog sediment wax reflects proximate plants rather than regionally integrated signal. Abstract Sedimentary plant waxes and their hydrogen and carbon (δ2H and δ13C) isotopes are important proxies for past hydrologic and vegetation change. However sedimentary waxes accumulate from diverse sources, integrating uncertainties from: (i) variable isotope fractionation among plant species, and (ii) unresolved processes controlling the transport of waxes from plants to sediments. We address these uncertainties by comparing the molecular and isotopic composition of n -alkanes and n -alkanoic acids in recent bog sediments with all major plant species growing in the catchment of Browns Lake Bog (BLB) in Ohio, USA. There are two distinct plant assemblages at BLB, including a forest dominated by trees and a bog shoreline composed of shrubs, woody groundcover, herbs and graminoids. n -Alkane concentrations in trees were 10–300 times higher than in shoreline plants, while n -alkanoic acid concentrations were generally lower and comparable across all species. The overall range of wax δ2H values among individual plants (77‰ for n -C 29 alkane and 84‰ for n -C 28 alkanoic acid) was likely driven by interspecies differences in biosynthetic δ2H fractionation as well as source water differences between forest and shoreline plants. A considerably smaller range of δ2H wax values in the bog sediments (9‰ for n -C 29 alkane and 11‰ for n -C 28 alkanoic acid) suggests that sediments are either biased toward specific plants, or that signal averaging processes during or after deposition are constant. The combined δ2H and δ13C signatures of plant sources and sediments indicate a sediment bias mainly toward trees, with contributions from woody shrubs and groundcover growing in the bog shoreline. Within trees and woody shrubs, we observed δ2H wax –δ13C wax relationships of opposite sign for n -C 29 alkane and n -C 28 alkanoic acid, which we speculate may reflect contrasting seasonal timing of synthesis and plant metabolic status between compound classes. The net apparent δ2H fractionation between precipitation and wax (ε app) was approximately 30‰ larger for n -alkanes (−133‰) than for n -alkanoic acids (−103‰), both at the plant level and in sediments. These results demonstrate the sensitivity of sediments in a hydrologically closed basin to woody plants growing in the associated catchment and can guide ε app estimates for sedimentary records from similar depositional settings. [ABSTRACT FROM AUTHOR]

Declining sea-ice extent is currently amplifying climate warming in the Arctic. Instrumental records at high latitudes are too short-term to provide sufficient historical context for these trends, so paleoclimate archives are needed to better understand the functioning of the sea ice-albedo feedback. Here we use the oxygen isotope values of wood cellulose in living and sub-fossil willow shrubs (δ 18 O wc ) ( Salix spp.) that have been radiocarbon-dated ( 14 C) to produce a multi-millennial record of climatic change on Alaska's North Slope during the Pleistocene-Holocene transition (13,500–7500 calibrated 14 C years before present; 13.5–7.5 ka). We first analyzed the spatial and temporal patterns of δ 18 O wc in living willows growing at upland sites and found that over the last 30 years δ 18 O wc values in individual growth rings correlate with local summer temperature and inter-annual variations in summer sea-ice extent. Deglacial δ 18 O wc values from 145 samples of subfossil willows clearly record the Allerød warm period (∼13.2 ka), the Younger Dryas cold period (12.9–11.7 ka), and the Holocene Thermal Maximum (11.7–9.0 ka). The magnitudes of isotopic changes over these rapid climate oscillations were ∼4.5‰, which is about 60% of the differences in δ 18 O wc between those willows growing during the last glacial period and today. Modeling of isotope-precipitation relationships based on Rayleigh distillation processes suggests that during the Younger Dryas these large shifts in δ 18 O wc values were caused by interactions between local temperature and changes in evaporative moisture sources, the latter controlled by sea ice extent in the Arctic Ocean and Bering Sea. Based on these results and on the effects that sea-ice have on climate today, we infer that ocean-derived feedbacks amplified temperature changes and enhanced precipitation in coastal regions of Arctic Alaska during warm times in the past. Today, isotope values in willows on the North Slope of Alaska are similar to those growing during the warmest times of the Pleistocene-Holocene transition, which were times of widespread permafrost thaw and striking ecological changes. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the history of stream erosion and changes in channel morphology is important for managing and restoring unstable streams. One of the significant challenges in this type of research is establishing accurate dating of late Holocene and historic alluvium. Here we evaluate the potential of using 14C dating and amino acid racemization (AAR) to date large terrestrial gastropod shells that are often preserved within alluvial sediments. Many terrestrial gastropods incorporate old carbon from limestone or other carbonate rocks into their shells and therefore are unsuitable for radiocarbon dating. Recent studies, however, have shown that some taxa avoid this ‘limestone problem’ and can yield reliable 14C ages. In this study, we measured the 14C activity of specimens for the genera Mesodon, Ventridens, and Allogona collected live and from alluvial sequences dated independently by dendrochronology, 14C dating of wood, and/or 137Cs analyses. Mesodon zaletus contained old carbon in similar concentrations (up to ~30%) found in previous studies of other large taxa and should be avoided for 14C dating when possible. In contrast, shells of Ventridens ligera and Allogona profunda showed minimal limestone effects and therefore may be suitable for dating late Holocene alluvium. These results highlight the importance of taxonomic identification of gastropod taxa prior to their use for 14C dating and demonstrate that shell fragments that are not identifiable should be avoided. We also measured d/l ratios (n =17) of aspartic and glutamic acid from eight different taxa of terrestrial gastropods recovered from four late Holocene and historic stratigraphic sequences. Average d/l ratios of aspartic and glutamic acid from historic sediments <300years old are lower in shells from younger stratigraphic units, indicating that AAR can be used to differentiate between multiple historic stratigraphic units. [Copyright &y& Elsevier]

A dendrochemical study of cottonwood trees (Populus deltoides) was conducted across a childhood cancer cluster in eastern Sandusky County (Ohio, USA). The justification for this study was that no satisfactory explanation has yet been put forward, despite extensive local surveys of aerosols, groundwater, and soil. Concentrations of eight trace metals were measured by ICP-MS in microwave-digested 5-year sections of increment cores, collected during 2012 and 2013. To determine whether the onset of the first cancer cases could be connected to an emergence of any of these contaminants, cores spanning the period 1970–2009 were taken from 51 trees of similar age, inside the cluster and in a control area to the west. The abundance of metals in cottonwood tree annual rings served as a proxy for their long-term, low-level accumulation from the same sources whereby exposure of the children may have occurred. A spatial analysis of cumulative metal burdens (lifetime accumulation in the tree) was performed to search for significant 'hotspots', employing a scan statistic with a mask of variable radius and center. For Cd, Cr, and Ni, circular hotspots were found that nearly coincide with the cancer cluster and are similar in size. No hotspots were found for Co, Cu, and Pb, while As and V were largely below method detection limits. Whereas our results do not implicate exposure to metals as a causative factor, we conclude that, after 1970, cottonwood trees have accumulated more Cd, Cr, and Ni, inside the childhood cancer cluster than elsewhere in Sandusky County. Image 1 • A childhood cancer cluster exists around the City of Clyde, Sandusky County, OH. • Dendrochemistry was used as a proxy for the long-term deposition of eight metals. • Cottonwood inside the cancer cluster have taken up more Cd, Cr, and Ni since 1970. • As, Co, Cu, Pb, and V burdens are similar for the cancer cluster and a control area. • Our study does not link etiology to higher metal burdens inside the cancer cluster. [ABSTRACT FROM AUTHOR]

Presents evidence for thicker ice in interior West Antarctica. Factors which suggest that coastal interior portions of the west antarctic ice sheet were on the order of several hundred meters or more thicker during the Late Pleistocene glacial maximum than they are now; General level of the ice sheet at Mount Waesche; Indication of an ice-sheet surface that was higher than present at Mount Waesche.