The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show Climatic Change (2005) 72: 251-298 how the biocomplexity of the Arctic system has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and modeling.

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Declining sea ice is expected to change the Arctic's physical and biological systems in ways that are difficult to predict. This study used stable isotope compositions (δ13C and δ15N) of archaeological, historic, and modern Pacific walrus (Odobenus rosmarus divergens) bone collagen to investigate the impacts of changing sea ice conditions on walrus diet during the last ~4000 yr. An index of past sea ice conditions was generated using dinocyst-based reconstructions from three locations in the northeastern Chukchi Sea. Archaeological walrus samples were assigned to intervals of high and low sea ice, and δ13C and δ15N were compared across ice states. Mean δ13C and δ15N values were similar for archaeological walruses from intervals of high and low sea ice; however, variability among walruses was greater during low-ice intervals, possibly indicating decreased availability of preferred prey. Overall, sea ice conditions were not a primary driver of changes in walrus diet. The diet of modern walruses was not consistent with archaeological low sea ice intervals. Rather, the low average trophic position of modern walruses (primarily driven by males), with little variability among individuals, suggests that trophic changes to this Arctic ecosystem are still underway or are unprecedented in the last ~4000 yr.

This study provides an assessment of the temporal changes in ΔR, which is the local deviation from the global surface water marine reservoir effect (MRE), in the Point Barrow area of the Alaskan Arctic, a coastal archaeological area that has experienced severe erosion accelerated by global warming. A total of 26 samples were submitted for radiocarbon (14C) dating from eight secure Thule (AD 1000–1750) archaeological contexts, and specifically from archaeological features with paired processed seal and caribou bones that had been frozenin situ. This new approach towards ΔR estimation provides a best-fit local correction for the14C dating of human populations by focusing on the marine mammal (seals) predominantly consumed by the Thule (Coltrain et al. 2016). The weighted-mean ΔR value on these pairs is 450 ± 84 yr, which is about 50 years less than the weighted-mean (506 ± 69 yr) for the Point Barrow area calculated through14C measurements from four known-age bivalves collected in AD 1913 (McNeely et al. 2006). The effects of using this new ΔR value for calibration was assessed through the Bayesian chronological modeling of 5414C measurements from samples of human skeletons interred in the Nuvuk cemetery at Point Barrow, the largest ancient cemetery in northwest Alaska and traditionally thought to date to the Thule and earlier Birnirk (AD 500–1000) periods.

Festuca populations (Festuca arundinacea, Festuca pratensis, and Festuca rubra) from Italy, Spain, and Denmark were investigated for Neotyphodium infection, ergovaline production, and 14 microsatellite markers. Endophytes were detected in 57, 54, and 100% of the locations surveyed in Italy, Spain, and Denmark, respectively. This is the first report of F. arundinacea endophytes from seminatural grasslands in Denmark. Sixty‐seven percent of the F. rubra and 100% of the F. pratensis populations were infected. Ergovaline production varied, even within populations. A dendrogram based on microsatellite length polymorphisms separated endophytes of each Festuca species. In addition, Danish F. arundinacea endophytes were separate from the other F. arundinacea endophytes. Analysis of molecular variance (AMOVA) demonstrated a pronounced genetic variation of F. arundinacea endophytes between countries and within the Italian and Spanish locations. Sampling strategy of endophyte‐infected Festuca spp. was evaluated by occurrence and genetic diversity. Sampling a large number of plants within locations for each of the “European geographical subgroups” is the suggested strategy for obtaining a genetically diverse array of Neotyphodium endophytes.

This chapter covers the Late Western Thule (LWT) and precontact Iñupiat of Northern Alaska, the most recent archaeological manifestation of the Northern Maritime tradition. From a maritime-adapted, whale-hunting culture living in semisubterranean sod-covered houses, this culture expanded to include inland settlements along rivers and in caribou hunting regions. The chronology of the LWT period is refined, based on recent advances in dating and many new dates. Other topics covered include settlement patterns and demography, technology, trade, architecture, social relations, mortuary practices, and the history and effects of contact with Euro-Americans. Several unresolved questions, including climate-change effects, the existence and nature of resource stress, and factors governing interior occupation are highlighted.

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