GLACIATIONS/Late Pleistocene Events in Beringia 1057 Espizu´a, L. (2004). Pleistocene glaciations in the Mendoza Extent and Chronology, Part III (J. Ehlers and P. Gibbard, Andes, Argentina. In Quaternary Glaciations – Extent Eds.), pp. 285–291. Elsevier. and Chronology, Part III (J. Ehlers and P. Gibbard, Eds.), Ton-That, T., Singer, B., Mo¨ rner, N., and Rabassa, J. (1999). pp. 69–73. Elsevier. Datacio´n de lavas basa´lticas por 40Ar/39Ar y geologı´a glacial Espizu´a, L., and Bigazzi, G. (1998). Fission-track dating of the de la regio´n del Lago Buenos Aires. Revista de la Asociacio´n Punta de Vacas glaciation in the Rı´o Mendoza valley, Geolo´ gica Argentina 54(4), 333–352. Argentina. Quaternary Science Reviews 17, 755–760. Hall, K. (2004). Quaternary glaciation of the sub-Antarctic Islands. In Quaternary Glaciations – Extent and Chronology, Part III (J. Ehlers and P. Gibbard, Eds.), pp. 339–345. Elsevier. Heine, J. (1995). Late Quaternary glacier advances in the Late Pleistocene Events in Ecuadorian Andes: a preliminary report. Quaternary of South Beringia America and Antarctic Peninsula 9, 1–22. Heine, J. (2004). Late Quaternary glaciations of Ecuador. In S A Elias, Royal Holloway, University of London, Quaternary Glaciations – Extent and Chronology, Part III Surrey, UK (J. Ehlers and P. Gibbard, Eds.), pp. 165–169. Elsevier. J Brigham-Grette, University of Massachusetts, Ingo´lfsson, O. (2004). Quaternary glacial and climate history MA, USA of Antarctica. In Quaternary Glaciations – Extent and Chronology, Part III (J. Ehlers and P. Gibbard, Eds.), ª 2007 Elsevier B.V. All rights reserved. pp. 3–44. Elsevier. Kaplan, M., Douglass, D., Singer, B., Ackert, R., and Caffe, M. (2005). Cosmogenic nuclide chronology of Pre-last glacial maximum moraines at Lago Buenos Aires, 46 S, Argentina. Introduction Quaternary Research 63, 301–315. Mahaney, W. (2004). Quaternary glacial chronology of The region of the western Arctic stretching from the Mount Kenya massif. In Quaternary Glaciations – Extent and Lena River in northeast Russia to the Mackenzie Chronology, Part III (J. Ehlers and P. Gibbard, Eds.), pp. 227– River in Canada, is geographically know as 231. Elsevier. Beringia. From a glaciological standpoint, Beringia, Mark, B., Seltzer, G., and Rodbell, D. (2004). Late Quaternary glaciations of Ecuador, Peru and Bolivia. In Quaternary including the vast continental shelves of the Bering Glaciations – Extent and Chronology, Part III (J. Ehlers and and Chukchi Sea, has presented a great anomaly P. Gibbard, Eds.), pp. 151–163. Elsevier. throughout the Cenozoic. While nearly all other Meglioli, A. (1992). Glacial geology of Southernmost Patagonia, high latitude regions of the Northern Hemisphere the Strait of Magellan and Northern Tierra del Fuego. PhD Dissertation, Lehigh University, Bethlehem, USA. were covered by ice sheets during each glaciation, Unpublished. the lowlands of Beringia remained ice-free, thus pro- Mercer, J. H. (1976). Glacial history of Southernmost South viding a refuge for high-latitude flora and fauna. Due America. Quaternary Research 6, 125–166. to the build up of continental-sized ice sheets over Osmaston, H. (2004). Quaternary glaciations in the east African North American, Greenland, parts of Eurasia, and mountains. In Quaternary Glaciations – Extent and Chronology, Part III (J. Ehlers and P. Gibbard, Eds.), pp. 139– other regional mountain ranges during Pleistocene 149. Elsevier. glaciations, global sea level repeatedly dropped sig- Porter, S. (1981). Pleistocene glaciations in the Southern Lake nificantly exposing large portions of the continental District of Chile. Quaternary Research 16, 263–292. shelves. For instance, during the last glaciation, glo- Rabassa, J., and Clapperton, C. (1990). Quaternary glaciations of bal sea level dropped by 120–130 m (Lambeck et al., the Southern Andes. Quaternary Science Reviews 9, 153–174. Rabassa, J., Coronato, A., and Salemme, M. (2005). Chronology 2002) exposing the continental shelf regions of the of the Late Cenozoic Patagonian glaciations and their correla- Bering and Chukchi seas between Siberia and Alaska. tion with biostratigraphic units of the Pampean region These vast shelves lie only about 30–110 m below (Argentina). Journal of South American Earth Sciences 20, modern sea level. Therefore, as continental ice sheets 81–103. grew, sea level dropped, and the shelf regions Rodbell, D. (1993). Subdivision of Late Pleistocene moraines in Cordillera Blanca, Peru, based on rock-weathering features, between northeast Russia and Alaska became dry soils and radiocarbon dates. Quaternary Research 39, land forming the Bering land bridge. By mapping 133–143. the 120 m contour of the sea floors for the Bering Schubert, C., and Clapperton, C. (1990). Quaternary glaciations in and Chukchi seas, it is possible to roughly trace the the Northern Andes (Venezuela, Colombia and Ecuador). outline of the former land bridge region (Fig. 1). Quaternary Science Reviews 9, 123–135. Shanahan, T., and Zreda, M. (2000). Chronology of Quaternary This land bridge was no narrow isthmus between glaciations in East Africa. Earth and Planetary Science Letters two continents. Rather, from north to south, the 177, 23–42. land bridge extended more than 1,000 km and may 40 39 Singer, B., Ackert, R., and Guillou, H. (2004). Ar/ Ar and K-Ar have existed for nearly 10,000 years (from 30,000 to chronology of Pleistocene glaciations in Patagonia. Geological Society of America Bulletin 116, 434–450. 20,000 years ago) during the last glacial advance. Suggate, R. (2004). South Island, New Zealand; ice From east to west, the land bridge was narrow at advances and marine shorelines. In Quaternary Glaciations – the center (in the Bering Strait region) but broad at 1058 GLACIATIONS/Late Pleistocene Events in Beringia Figure 1 Map of northeast Asia and northwestern North America, showing the regions of western and eastern Beringia, and the Bering Land Bridge. both the north and south ends. The area of the land Western Beringia is comprised of the regions of bridge was larger than the state of Texas. northeast Russia, from the Verkhoyansk Mountains When it existed, the Bering Land Bridge cut off in the west, to the Bering and Chukchi Sea coasts in circulation between the waters of the North Pacific the east, and the Sea of Okhotsk in the south. The and Arctic oceans. This in turn greatly increased Verkhoyansk Mountains lie along the eastern margin continentality and diminished the in-land flow of of the lower Lena River Basin, and form the western relatively warm, moist air masses from the North limit of some characteristic Beringian plant taxa. The Pacific. Beringia was also influenced by being down- central sector of Beringia is that area of the Bering wind of large ice sheets in Scandinavia and the Land Bridge that is now submerged beneath the Eurasian north, themselves creating widespread arid- Bering and Chukchi seas, forming what was once a ity during full glacial conditions (Siegert et al., 2001). broad, relatively flat landscape with only a few high- Moisture stripped from the westerlies by these ice lands (the modern islands of the northern Bering Sea sheets left little but strong dry winds to sweep the region). Eastern Beringia is defined as the unglaciated landscapes of Beringia. Consequently, despite being regions of Alaska and the Yukon Territory. The east- cold enough to accumulate glacial ice, the desiccating ern boundary of Beringia has been considered to be environment of the land bridge restricted glaciation the lower Mackenzie River in the Canadian to isolated mountain ranges and kept glacial ice out Northwest Territories (Hopkins, 1982). This places of the lowlands of Alaska, the Yukon Territory, and the eastern edge of Beringia along the margin of the eastern Siberia, plus the land bridge itself. The largest Laurentide ice sheet at its maximum extent. of the Alpine glacier complexes was, in fact, the The vast regions of Beringia contained enormous westernmost extension of the Cordilleran Ice Sheet topographic diversity, spanning over more than 20 that once occupied western North America. This ice of latitude and 80 of longitude (Fig. 1). One of the sheet covered the Alaska Range, and extended south principal differences between western and eastern and west to the Alaskan Peninsula and the continen- Beringia is that the former region is topographically tal shelf regions of Prince William Sound and the more complex and rugged than the latter (Brigham- Gulf of Alaska (Mann and Hamilton, 1995). The Grette et al., 2004). The northward-draining river Beringian lowlands remained ice-free throughout basins of the Lena, Indigirka, and Kolyma are broken the Pleistocene. by steep mountain ranges, as well as broad uplands. Beringia is most conveniently partitioned for dis- The geography of eastern Beringia is marked by three cussion into three geographic sectors: western sets of mostly east-west trending mountain ranges. Beringia, central Beringia, and eastern Beringia. From south to north these comprise (1) the Pacific GLACIATIONS/Late Pleistocene Events in Beringia 1059 coastal ranges that continue southwest along the modern levels as well. However, not all researchers Alaska Peninsula, (2) the Alaska Range, about agree on these temperature reconstructions. For 100 km inland from the Gulf of Alaska, and (3) the instance, periglacial features that developed during Brooks Range, separating the interior lowlands from the LGM, indicate that mean annual temperatures the North Slope region. The interior