HR: 16:45h
AN: PP24A-04    [Abstracts]
TI: Oceanographic Influences on the Style and Timing of Glacial-Interglacial Change in Western Beringia
AU: * Brigham-Grette, J
EM: juliebg@geo.umass.edu
AF: University of Mass, Dept Geosciences UMASS, Amherst, MA 01003 United States
AU: Glushkova, O Y
EM: glushkova@neisri.magadan.ru
AF: NEISRI, 16 Portovaya, Magadan, 685000 Russian Federation
AU: Anderson, P
EM: pata@u.washington.edu
AF: Quaternary Research Center, QRC, University of Washinton, Seattle, WA 98195 United States
AU: Lozhkin, A
EM: lozhkin@neisri.magadan.ru
AF: NEISRI, 16 Portovaya, Magadan, 685000 Russian Federation
AU: Gualtieri, L
EM: gualtieri@cascadia.ctc.edu
AF: Cascadia Community College, 18345Campus Way, Bothell, WA 98011 United States
AB: Late Cenozoic glacial/interglacial change imposed on the Bering Strait region radical changes in paleogeography unique to the Northern Hemisphere. A forested middle Pliocene Arctic gave way to the first major glaciation of the northern hemisphere. Glacial and marine deposits found interbedded along the coasts of Alaska and Chukotka record a number of critical transitions in the evolution of Northern Hemisphere climate. Glacial periods across much of Beringia during the early and middle Pleistocene were at least an order of magnitude more extensive than during the Last Glacial Maximum (LGM) for reasons that remain unclear but must be related to fundamental changes in moisture flux. Valley glaciers (not ice sheets) dominated the landscape of central and western Beringia throughout the Quaternary, though some valley glaciers reached the sea. Eurasian ice sheets to the west and perhaps extensive sea ice over parts of the deep Bering Sea prevented vapor flux to Beringia creating pervasive aridity, limiting the size of ice sheets and the distribution of deep snow cover especially during the LGM. Interglacial periods repeatedly flooded the Bering Strait, rapidly changing the configuration of the coastlines, altering regional continentality, and reinvigorating the exchange of water masses between the North Pacific, Arctic Ocean and North Atlantic. During the last interglacial (MIS 5e) the winter sea ice limit was as much as 800 km further north than now, and summer sea ice may be been periodically absent. Treeline was hundreds of kilometers further north, notably eliminating tundra across Chukotka to the Arctic Ocean. The fragmented coastal record of the Bering Strait registers clear evidence for the rapid initiation of valley glaciation and the deposition of glaciomarine sediments at or near the end of warm interglacial periods including Stage 11 (or 9), but especially the substage 5e/5d transition and the substage 5a/4 transition in parts of coastal Chukotka. The Flaxman deposits (Gubik FM) dated to MIS stage 5a on the Alaskan North Slope, record both flooding of the Bering Strait and collapse of an ice sheet that likely accumulated since 5d over some part of the western Canadian Arctic. Flooding of the Bering Strait in MIS 5a, coupled with an insolation high, may have contributed to the collapse of Canadian and Eurasian ice sheets allowing the penetration of moisture across the continent and the expansion of valley glaciers in the Bering Straits region well beyond LGM limits. Increasing continentality, sea ice cover and the expansion of the Scandinavian/Eurasian ice sheet (Siegert et al., 2001) then limited available moisture supply across most of Beringia. During MIS stage 3 climate remained relatively harsh across much of Alaska, but parts of western Beringia experienced the temporary return of interglacial vegetation to near modern conditions coincident with insolation highs. LGM glaciation across most of Beringia was restricted to local mountain ranges and dominated by valley and cirque glaciers. A mosaic of dry habitats characterized by herb and forb-tundra dominated ice -free valleys and lowlands with some evidence for mesic conditions across parts of central Beringia. A rapid rise of sea level at the end of the LGM likely caused swift migration of the shoreline as summers warmed into the early Holocene and re-established modern vegetation.
UR: http://www.geo.umass.edu/faculty/jbg
DE: 5462 Polar regions
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 3309 Climatology (1620)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting