@article {2913,
	title = {Insolation and greenhouse gases drove Holocene winter and spring warming in Arctic Alaska},
	journal = {Quaternary Science Reviews},
	volume = {242},
	year = {2020},
	month = {Jan-08-2020},
	pages = {106438},
	abstract = {Global surface temperature changes and their drivers during the Holocene Epoch remain controversial. Syntheses of proxy data indicate that global mean annual temperature declined from the mid-Holocene until the Pre-industrial Era, a trend linked to decreasing Northern Hemisphere summer insolation. In contrast, global climate models simulate increasing mean annual temperatures driven by retreating ice sheets and increasing greenhouse gas concentrations. This proxy-model disagreement may originate from a warm season bias in Northern Hemisphere proxy reconstructions, highlighting the need for new proxies that quantify cold season temperature, especially in Arctic regions that were devoid of continental ice sheets during the Holocene. Here, we present a new 16,000-year winter-spring temperature reconstruction derived from the unsaturation ratio of alkenones (U-3(7)K) in a continuous sedimentary sequence from Lake E5, northern Alaska. We employ a thermodynamic lake model to convert alkenone-inferred lake temperatures into winter-spring air temperature anomalies and we contextualize our proxy reconstruction with climate model output from the region. Our reconstruction shows that winter-spring temperatures warmed rapidly during the deglaciation at 16 and 14 thousand years before present and continued to warm gradually throughout the middle and late Holocene (0.12-0.28 degrees C/thousand years) in concert with regional sea surface temperature and sea ice records. Our results are consistent with climate model simulations and we attribute Holocene warming to rising winter-spring insolation, radiative forcing from rising greenhouse gas concentrations and regional feedbacks. Our reconstructed cold season warming equaled or exceeded summer cooling according to a regional synthesis of temperature records, suggesting that seasonal biases in temperature reconstructions may account for proxy-model disagreements in Holocene temperature trends from Eastern Beringia. (C) 2020 Elsevier Ltd. All rights reserved.},
	keywords = {Alkenone, Beringia, Continental biomarkers, Holocene, North America, paleoclimatology, paleolimnology, Proxy data-model comparison, seasonality, Temperature reconstruction},
	issn = {02773791},
	doi = {10.1016/j.quascirev.2020.106438},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0277379120304005},
	author = {Longo, William M. and Huang, Yongsong and Russell, James M. and Morrill, Carrie and Daniels, William C. and Giblin, Anne E. and Crowther, Josue}
}
@article {2637,
	title = {Evidence of Ice Age humans in eastern Beringia suggests early migration to North America},
	journal = {Quaternary Science Reviews},
	volume = {205},
	year = {2019},
	month = {Jan-02-2019},
	pages = {35 - 44},
	abstract = {Our understanding of the timing and pathway of human arrival to the Americas remains an important and polarizing topic of debate in archaeology and anthropology. Traditional consensus, supported by archaeological and paleoenvironmental data, favors a {\textquoteright}swift peopling{\textquoteright} of the Americas from Asia via the Bering Land Bridge during the last Glacial termination. More recent genetic data and archaeological finds have challenged this view, proposing the {\textquoteright}Beringian standstill hypothesis{\textquoteright} (BSH), wherein a population of proto-Americans migrated from Asia during, or even prior to the Last Glacial Maximum (LGM) and lived in Beringia for thousands of years before their eventual spread across the American continents. Using a sediment archive from Lake E5 (68.641667 degrees N, 149.457706 degrees W), located on Alaska{\textquoteright}s North Slope, we present new data supporting the BSH and shedding new light on the environmental impact of these early American populations. Fecal biomarkers support human presence in the environs of the lake, and our data demonstrate elevated biomass burning in this region during the last Glacial. Elevated burning defies the expectation that natural fires would be less frequent in the Arctic during the last Glacial, thereby suggesting human ignition as the likely culprit. Our data shed new light on the pathway and timing of human migration to the Americas and demonstrate the possibility of the sustainable coexistence of humans and the Ice Age megafauna in Beringia prior to their extinction. (C) 2018 Elsevier Ltd. All rights reserved.},
	keywords = {Beringia, charcoal, Fecal sterols, Last Glacial, Paleofire, Polycyclic aromatic hydrocarbons (PAHs)},
	issn = {02773791},
	doi = {10.1016/j.quascirev.2018.12.003},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0277379118307716https://api.elsevier.com/content/article/PII:S0277379118307716?httpAccept=text/xmlhttps://api.elsevier.com/content/article/PII:S0277379118307716?httpAccept=text/plain},
	author = {Vachula, Richard S. and Huang, Yongsong and Longo, William M. and Dee, Sylvia G. and Daniels, William C. and Russell, James M.}
}
