Paper No. 5
Presentation Time: 9:00 AM
LAND/SEA CORRELATIONS: SEPARATING CLIMATE EVENTS AT THE 5E/D AND 5A/4 TRANSITIONS IN CHUKOTKA AND ACROSS THE WESTERN ARCTIC
The fragmented coastal record of the Bering Strait registers clear evidence for the rapid initiation of valley glaciation at or near the end of interglacial periods. In shallow Kotzebue Sound near the middle of the Bering Strait, glaciomarine sediments directly overlying Stage 11 (or 9) interglacial prodeltaic deposits record the rapid expansion of glaciers in the western Brooks Range while global sea level was still high (Pushkar et al., 1999: Huston et al., 1990). Kaufman et al (1996, 2001) document the expansion of valley glaciers beyond LGM limits in the Ahklun Mountains of SW Alaska at the end of the last interglacial. Similar valley glacier expansion is seen at the substage 5e/5d transition and the substage 5a/4 transition in parts of coastal Chukotka (Brigham-Grette et al, 2001)). On Chukotka Peninsula, new ESR ages of ~126 ka and ~ 73 ka coupled with new D/L aspartic acid amino acid ratios allow us to separate climatic events within Stage 5 for the first time. The Flaxman member (Gubik FM) originally dated to MIS stage 5a and confirmed with new D/L aspartic ratios on the Alaskan North Slope, records the collapse of ice sheets that likely accumulated since 5d over parts of the western Canadian Arctic. At ~88ka ice sheets expanded out of the Kara/Barents Sea into the Ural Mountains damming proglacial lakes in the Eurasian arctic (Mangerud et al., 2001). We speculate that flooding of the Bering Strait in substage 5a, coupled with an insolation high, may have contributed to the collapse of these Canadian and Eurasian ice sheets. The collapse of these ice sheets may have then allowed the penetration of moisture across the continent permitting the expansion of valley glaciers in the Bering Straits region and elsewhere in the high latitudes well beyond LGM limits. Increasing continentality, sea ice cover and the expansion of the Scandinavian/Eurasian ice sheet (ala Siegert et al., 2001) then limited available moisture supply across most of Beringia.