5. Menounos, B; Goehring, BM; Osborn, G; Margold, M; Ward, B; Bond, J; Clarke, GKC; Clague, JJ; Lakeman, T; Koch, J; Caffee, MW; Gosse, J; Stroeven, AP; Seguinot, J; Heyman, J.Cordilleran Ice Sheet mass loss preceded climate reversals near the Pleistocene Termination.Science, 2017, 358: 781-784 Cordilleran Ice Sheet mass loss preceded climate reversals near the Pleistocene Termination
The Cordilleran Ice Sheet (CIS) once covered an area comparable to that of Greenland. Previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost Canada as late as 12.5 thousand years ago (ka). New data indicate that substantial areas throughout westernmost Canada were ice free prior to 12.5 ka and some as early as 14.0 ka, with implications for climate dynamics and the timing of meltwater discharge to the Pacific and Arctic oceans. Early Bolling-Allerod warmth halved the mass of the CIS in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise. Dozens of cirque and valley glaciers, along with the southern margin of the CIS, advanced into recently deglaciated regions during the Bolling-Allerod and Younger Dryas. DOI PubMed
4. Turner, DG; Ward, BC; Bond, JD; Jensen, BJL; Froese, DG; Telka, AM; Zazula, GD; Bigelow, NH.Middle to Late Pleistocene ice extents, tephrochronology and paleoenvironments of the White River area, southwest Yukon.Quat. Sci. Rev., 2013, 75: 59-77 Middle to Late Pleistocene ice extents, tephrochronology and paleoenvironments of the White River area, southwest Yukon
Dating; Pleistocene; Beringia; Last Interglacial; Paleoenvironments; Tephrochronology; Macrofossil; Pollen
Sedimentary deposits from two Middle to Late Pleistocene glaciations and intervening non-glacial intervals exposed along the White River in southwest Yukon, Canada, provide a record of environmental change for much of the past 200 000 years. The study sites are beyond the Marine Isotope stage (MIS) 2 glacial limit, near the maximum regional extent of Pleistocene glaciation. Non-glacial deposits include up to 25 m of loess, peat and gravel with paleosols, pollen, plant and insect macrofossils, large mammal fossils and tephra beds. Finite and non-finite radiocarbon dates, and twelve different tephra beds constrain the chronology of these deposits. Tills correlated to MIS 4 and 6 represent the penultimate and maximum Pleistocene glacial limits, respectively. The proximity of these glacial limits to each other, compared to limits in central Yukon, suggests precipitation conditions were more consistent in southwest Yukon than in central Yukon during the Pleistocene. Conditions in MIS 5e and 5a are recorded by two boreal forest beds, separated by a shrub birch tundra, that indicate environments as warm or warmer than present. A dry, treeless steppe-tundra, dominated by Artemisia frigida, upland grasses and forbs existed during the transition from late MIS 3 to early MIS 2. These glacial and non-glacial deposits constrain the glacial limits and paleoenvironments during the Middle to Late Pleistocene in southwest Yukon. (c) 2013 Elsevier Ltd. All rights reserved. DOI
3. Zazula, GD; Turner, DG; Ward, BC; Bond, J.Last interglacial western camel (Camelops hesternus) from eastern Beringia.Quat. Sci. Rev., 2011, 30: 2355-2360 Last interglacial western camel (Camelops hesternus) from eastern Beringia
Western camel; C. hesternus; Beringia; Fauna; Yukon; Pleistocene; Stratigraphy; Last interglacial; Sangamonian; Rancholabrean
Western camel (C. hesternus) fossils are rare from Eastern Beringia, thus there is little available information on their chronology, paleoecology, and biogeography in this region. In August of 2010, a partial proximal phalanx of a western camel was recovered from a sedimentary exposure along the White River, in the formerly glaciated terrain of southwest Yukon, northwest Canada. The fossil specimen was recovered in situ from sediments that are correlated by stratigraphic, tephra and radiocarbon data to the Marine Isotope Stage (MIS) 5 interglacial period (Sangamonian). Associated paleoenvironmental data indicates that this western camel inhabited a shrub tundra ecosystem that did not include spruce trees or boreal forest during a relatively cold interval between MIS Se and 5a. This is the oldest reliably dated western camel fossil from Eastern Beringia and supports the model of range expansion for this species to the high latitudes of northwest North America during the last interglacial (sensu lato). Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved. DOI
2.Ward, BC; Bond, JD; Froese, D; Jensen, B.Old Crow tephra (140+/-10 ka) constrains penultimate Reid glaciation in central Yukon Territory.Quat. Sci. Rev., 2008, 27: 1909-1915 Old Crow tephra (140+/-10 ka) constrains penultimate Reid glaciation in central Yukon Territory
Old Crow tephra (140 +/- 10 ka) is closely associated with deposits from the penultimate Reid glaciation along the Pelly River in central Yukon Territory. The elevation of the tephra above present base level and association with deglacial sediments Suggests a close minimum age estimate, confirming a MIS 6 age for the Reid glaciation. This is in contrast to a MIS 4 age for the penultimate Gladstone glaciation in Southwest Yukon. This study demonstrates that the assumed synchrony of the penultimate advance of the Cordilleran Ice Sheet has little support, and regional controls on the mass balance of source regions of the ice sheet are more important than previously considered. (C) 2008 Elsevier Ltd. All rights reserved. DOI
1.Ward, BC; Wilson, MC; Nagorsen, DW; Nelson, DE; Driver, JC; Wigen, RJ.Port Eliza cave: North American West Coast interstadial environment and implications for human migrations.Quat. Sci. Rev., 2003, 22: 1383-1388 Port Eliza cave: North American West Coast interstadial environment and implications for human migrations
The timing of Late Pleistocene glacial advance, retreat, relative sea level and environmental viability between 25 and 12.5 ka (C-14 yrs BP) remain a key issue in the feasibility of a coastal migration route for the first North Americans. This is discussed on the basis of stratigraphic, radiometric and faunal data for Port Eliza cave, a raised sea cave, on the west coast of Vancouver Island, British Columbia. Ice cover is indicated by the occurrence of 2m of laminated clay, representing deposition in a subglacial take. From immediately below this clay a diverse vertebrate fauna of marmot, vote, marten, cervid and various species of birds and fish was recovered, yielding ages of 18-16 ka. These dates and others from the region show that ice cover on the outer coast was brief, from ca 15.5-14ka.. The fish species indicate that relative sea level was close to the cave and that salmon runs were likely present. The terrestrial vertebrate fauna is consistent with a cool, open parkland environment with maximum summer temperatures cooler than present; these conditions lasted until at least 16 ka. With a diverse fauna and favorable climate, humans could have survived here on a mixed marine-terrestrial diet, confirming the viability of the coastal migration hypothesis for this portion of the route. (C) 2003 Elsevier Science Ltd. All rights reserved. DOI
