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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 [...]

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.