bs_bs_banner Sedimentary biomarkers reaffirm human impacts on northern Beringian ecosystems during the Last Glacial period RICHARD S. VACHULA , YONGSONG HUANG, JAMES M. RUSSELL, MARK B. ABBOTT, MATTHEW S. FINKENBINDER AND JONATHAN A. O’DONNELL Vachula, R. S., Huang, Y. , Russell, J. M., Abbott, M. B., Finkenbinder, M. S. & O’Donnell, J. A.: Sedimentary biomarkers reaffirm human impacts on northern Beringian ecosystems during the Last Glacial period. Boreas. https://doi.org/10.1111/bor.12449. ISSN 0300-9483. Our understanding of the timing of human arrival to the Americas remains fragmented, despite decades of active research and debate. Genetic research has recently led to the ‘Beringian standstill hypothesis’ (BSH), which suggests an isolated group of humans lived somewhere in Beringia for millennia during the Last Glacial, before a subgroup migrated southward into the American continents about 14 ka. Recently published organic geochemical data suggest human presence around Lake E5 on the Alaskan North Slope during the Last Glacial; however, these biomarker proxies, namely faecal sterols and polycyclic aromatic hydrocarbons (PAHs), are relatively novel and require replication to bolster their support of the BSH. Wepresent newanalyses of thesebiomarkers in the sediment archive of Burial Lake (latitude 68°260N, longitude 159°100W m a.s.l.) in northwestern Alaska. Our analyses corroborate that humans were present in Beringia during the Last Glacial and that they likely promoted fire activity. Our data also suggest that humans coexistedwith Ice Age megafauna for millenniaprior to theireventual extinction at the end of the Last Glacial. Lastly, we identify fire as an overlooked ecological component of the mammoth steppe ecosystem. Richard S. Vachula ([email protected])(present address: Department of Geography and Environmental Science, UniversityofReading,Reading,UK),YongsongHuangandJamesM.Russell,DepartmentofEarth,Environmental,and Planetary Sciences, Institute at Brown for Environment and Society, Brown University, Providence, RI, USA; Mark B. Abbott, Department of Geologyand Environmental Science, Universityof Pittsburgh, Pittsburgh, PA,USA; Matthew S. Finkenbinder, Department of Environmental Engineering and Earth Sciences, Wilkes University, Wilkes-Barre, PA, USA; Jonathan A. O’Donnell, Arctic Network, National Park Service, Anchorage, AK, USA; received 1st February 2020, accepted 17th April 2020. Human arrival to the American continents remains one Cinq-Mars & Morlan 1999; Morlan 2003), but have of the most debated topics in our understanding the been controversial for decades. More recently, stone global dispersal and proliferation of Homo sapiens artifacts in the Bluefish Caves that had remained (Goebel et al. 2008; Waters 2019). Most researchers overlooked for decades were reexamined and found to agree that Beringia, the landmass that spanned north- indicate human presence during the Last Glacial eastern Asia and northwest North America during the (Bourgeon et al. 2017; Waters 2019). These findings, Last Glacial period (herein referring to Marine Isotope combined with genetic data, stimulated the proposal of Stages 2 and 3), was the initial entrywayof this migration the ‘Beringian standstill’ hypothesis (BSH), which to the Americas (West 1996; Hoffecker et al. 2014, suggests a small group diverged from East Asians 2016), but genetic data and archaeological artifacts c. 36 000 years ago, moving to isolation in Beringia provide a fragmented history of human populations in before eventually moving south into the continent the region. Despite assumptions that human popula- (Tamm et al. 2007; Skoglund & Reich 2016; Mulligan tions could not survive the cold climate of the Glacial & Szathmary 2017; Moreno-Mayar et al. 2018; Waters Arctic, cut-marked bones found at the Bunge Toll site 2019). Importantly, the BSH is built upon earlier genetic (Pitulko et al. 2016), and stone tools found at the Yana analyses that detected differences between Native site complex (Pitulko et al. 2017), in Siberia place Americans north and south of the Laurentide Ice Sheet humans in western Beringia c. 48 thousand calibrated (Szathmary 1993; Bonatto & Salzano 1997) and anthro- years before present (cal. ka BP) and 32 cal. ka BP pological inferences from linguistic analyses (Nichols (Pitulko et al. 2016), respectively. In contrast, the 1990, 2008). It has also been bolstered by dental analyses earliest unequivocal archaeological evidence in eastern (Scott et al. 2018) and further genetic analyses of ancient Beringia dates to 14 cal. ka BP (Swan Point; Potter et al. DNA and whole genomes (Moreno-Mayar et al. 2018; 2013), roughly contemporaneous with the earliest finds Sikora et al. 2019). Though the inferences drawn from in the American continents. This coincidence of timing linguistic and dental analyses support early divergence supports the hypothesis of a ‘swift peopling’ of eastern of the Native American founder group from its Asian Beringia and the American continents c. 14 000 years ancestors, these analyses do not place humans in ago (Goebel et al. 2008). However, cut-marks on animal Beringia during the Last Glacial. At present, the bones found in the Bluefish Caves equivocally support Bluefish Caves provide the only archaeological site human presence in eastern Beringia during the Last supporting a human population in eastern Beringia Glacial (Morlan & Cinq-Mars 1982; Cinq-Mars 1990; during the Last Glacial, although lack of more estab- DOI 10.1111/bor.12449 © 2020 The Authors. Boreas published by John Wiley & Sons Ltd on behalf of The Boreas Collegium This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 2 Richard S. Vachula et al. BOREAS lished forms of archaeological evidence, such as stone fire in the mammoth steppe biome that spanned Beringia tools and fire pits, still cast uncertainties on the during the Last Glacial. attribution of cut-marks on bones to humans. The BSH also has important implications for our Study site understanding of Beringian ecosystem dynamics in the Last Glacial and the role of humans in the Burial Lake (68°260N, 159°100W; 460 m a.s.l.; Fig. 1) is extinction of Pleistocene megafauna. During the Last located in the Noatak River Basin in the Brooks Range in Glacial, Beringia was home to the mammoth steppe northwestern Alaska (Kurek et al. 2009; Abbott et al. ecosystem, a productive, diverse grassland that sup- 2010; Dorfman et al. 2015; Finkenbinderet al. 2015). The ported and was in turn enhanced by megafauna lake is deep (21.5 m) and small (0.8 km2), with a relatively herbivores including mammoths, bison, horses, cari- small watershed (3.3 km2), one outlet stream, and several bou, woolly rhinoceros, saiga and muskoxen (Guthrie seasonally ephemeral inlets (Finkenbinder et al. 2015). 2001; Mann et al. 2013). The ecosystem dynamics Like Lake E5 in north-central Alaska (Vachula et al. and demise of the Beringian mammoth steppe and 2019), Burial Lake is one of a small number of lakes that its megafauna are debated (Guthrie 2001; Yurtsev persisted during the cold and arid Last Glacial period 2001; Zimov et al. 2012; Mann et al. 2013, 2015; (Finkenbinder et al. 2015). As such, sediments from E5 Sandom et al. 2014). To date, little research has and Burial are valuable environmental archives. characterized the role that a Standstill population of humans might have had in the demise of this Material and methods ecosystem without modern counterparts. Recent palaeolimnological analyses from Lake E5, Sediment core and chronology located in northern Alaska, provide additional bio- geochemical evidence supporting the presence of Sediment cores were collected from several water depths humans in Beringia during the Last Glacial (Vachula in Burial Lake (5.0, 7.9, 13.2 and 21.5 m), but sedimen- et al. 2019). Measurements of charcoal and polycyclic tary hiatuses associated with the drier glacial period aromatic hydrocarbons (PAHs) in the E5 sediment interrupt all of these archives with the exception of the record indicate increased fire activity from 32 to 19 cal. core from the deepest water (Abbott et al. 2010; Finken- ka BP, despite natural lightning ignitions being binder et al. 2015). The sediments preserved in this core suppressed by a cold glacial climate (Vachula et al. span the last 37 000 years. The age-depth chronology of 2019). In many ignition-limited regions, evidence of this core was established by Finkenbinder et al. (2015, increased burning has been observed to coincide with 2018) using the CLAM age modelling package (Blaauw human arrival (Mann et al. 2008; Pinter et al. 2011; 2010). The chronology is informed by 15 radiocarbon- Argiriadis et al. 2018). Similarly, the arrival of humans dated terrestrial macrofossils (Fig. 2). In this paper, we to Australiawas accompanied by increased fire activity refer to sedimentological ages as thousands of calibrated (Rule et al. 2019). This circumstantial evidence for years before present (1950 CE = 0cal.kaBP). human presence is further supported by faecal sterol data suggesting human faecal contamination at E5. Organic geochemical analyses Thus, the Lake E5 record provides evidence of a sustained human presence in eastern Beringia during Following Vachula et al. (2019), we quantified polycyclic the Last Glacial (Vachula et al. 2019). The Lake E5 aromatic hydrocarbons (PAHs) and faecal sterols in the analyses support the BSH but