SYNCHRONOUS, GLOBAL, LATE PLEISTOCENE ICE SHEET AND ALPINE GLACIAL FLUCTUATIONS

Multiple, post-LGM moraines in both the Northern and Southern Hemisphere imply that abrupt, short-lived, glacial fluctuations were the result of global, synchronous, climatic oscillations. The sensitivity of these global climatic changes is shown by the simultaneous readvance and retreat of Younger Dryas (YD) and Intra-Allerød Cold Period (IACP) alpine and ice sheet glaciers in the Pacific NW, Rocky Mts., eastern Canada, Swiss Alps, Scandinavia, and New Zealand. In all of these areas, moraines from two phases of the YD has been recognized, suggesting that synchronous, global, climatic events were sensitively recorded in the glacial record. The Cordilleran Ice Sheet built two well-dated, YD moraines in the northern Puget Lowland 10,980-10,250 14C yrs B.P. and ~10,250-10,000 14C yrs B.P. Double YD moraines in the Titcomb Basin and at Temple Lake in the Wind River Range have been 10Be dated at 11 ka. Twin YD and perhaps IACP moraines also occur in the North Cascade Range of Washington. Double YD moraines occur at Julier Pass in the Swiss Alps where the mean 10Be age of the outer YD moraine is 11.75 ka and the inner moraine 10.47 ka. The classic, well-dated YD moraines of the Scandinavian Ice Sheet are also double. In New Zealand, double YD moraines at Arthur’s Pass have been10Be-dated at 11.8 ka and 11.4 ka, and at Birch Hill at 12.1 ka and 11.0 ka, indicating that the climatic-sensitive double YD occurs in both hemispheres with no time lag. The double nature of the YD readvances of both ice sheets and alpine glaciers in widely separated regions on several continents in both hemispheres indicates a common, global, climatic cause. What that cause is remains uncertain.