Easterbrook 9628624 This proposal is for mapping and dating late Pleistocene moraines that represent abrupt climatic reversals in the North Cascades of Washington that are equivalent in age to the Younger Dryas, using both 14C and 10Be methods. Among the objective of this proposal are: (1) to identify, map, and date these late Pleistocene moraines, (2) determine if a significant lag time occurred between these climatic changes on the west coast, controlled by cyclonic weather systems of the Pacific Ocean, and climatic reversals in the North Atlantic Ocean on opposite sides of North America, and (3) to establish possible correlations with similar events in the Rocky Mts. Among the moraines that will be mapped and dated are (1) nine apparent YD (?) moraines of alpine glaciers in the North Cascades of Washington that readvanced 20-50km downvalley from their sources following disappearance of the Cordilleran Ice Sheet from the maximum moraine and recessional moraines of the Okanogan lobe of the Cordilleran Ice Sheet on the east side of the Cascade Range. Because the YD event was first recorded and dated in Europe and Greenland, it has been attributed to changing conditions in the North Atlantic. Despite evidence for a late-glacial readvance of the Cordilleran Ice Sheet in northwestern Washington at about the time of the YD, the apparent absence of evidence for the YD in eastern and central North America led to a generally-held belief that such an event did not affect North America. If the YD cooling of the North Atlantic simultaneously affected the west coast of North America, reflecting climatic changes in the North Atlantic. Until recently, no YD alpine glacial advances had been recognized in the Cascade Range, but, new evidence for an extensive system of alpine valley glaciers younger than the Cordilleran Ice Sheet and of much greater extent than the YD glacial readvance in the Rocky Mts. has recently been discovered in the Nooksack drainage of the North Cascades, just south of the mora ines of the Sumas readvance of the Cordilleran Ice Sheet. One of the greatest problems in assessing the validity of events in the North Atlantic as causing the climatic reversals of the YD is that moraines of this age rarely have organic material suitable for 14C dating, so their ages remain speculative. However, not only is organic material available for dating of YD moraines in the North Cascades, but large erratic boulders on moraines are also available for 10Be dating. A multi-pronged approach is proposed for this project: (1) Identifying and dating moraines that represent climatic reversals during late Pleistocene deglaciation: The accuracy of 14C and 10Be will allow the distinguishing of late-glacial pulses and demonstration of whether or not a consistent pattern is present in western North America. At present, "suspected" YD moraines are known in the Pacific Northwest, but they are not well dated--a problem that can be resolved by 14C and 10Be dating. Recognition of a persistent post-late-glacial-maximum pulse in widely separated localities will be a big step forward in our understanding of global climatic changes. (2) Demonstrating the synchroniety (or lack of it) of late glacial moraines in northwestern North America and the Rocky Mts. To establish correlations with the YD moraines in the Rocky Mts. and elsewhere, comparison of atoms per gram of 10Be from boulders on moraines, rather than calculated ages, will be used to minimize accuracy problems related to 10Be production rates. In addition, 26Al will be measured, newly developed corrections factors for geomagnetic flux variations will be used, and calculated 10Be ages will be compared with 14C ages from organic material. The results of this investigation will then be used to establish correlations with dated moraines in the mid-continent Rocky Mts. and events in the North Atlantic. If synchroneity of ages can be demonstrated, they will have significant implications of the validity of events in the North Atlantic as the cause of abrupt climatic changes.
