Timing of glaciation during the last glacial cycle: Evaluating the concept of a global 'Last Glacial Maximum' (LGM)

摘要

It has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle, often well before the global Last Glacial Maximum (LGM; c. 23-19. ka), which is formally defined by peaks in global sea-level and marine oxygen isotope records. However, there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global LGM but also some regions of the large continental glaciers. The Barents-Kara Ice Sheet in northern Eurasia together with a majority of ice masses throughout Asia and Australasia reached their maximum early in the last glacial cycle, a few thousand years before the global LGM period. The East Antarctic Ice Sheet also reached its maximum extent several millennia before the global LGM. In numerous mountainous regions at high-, mid- and low-latitudes across the world, glaciers reached their maximum extent before Marine Isotope Stage (MIS) 2, in MIS 5, 4 and 3. This is in contrast to most sectors of the Laurentide Ice Sheet, the Cordilleran Ice Sheet, the SE sector of the Fennoscandinavian Ice Sheet and the Alpine Ice Sheet in central Europe, which appear to have reached their maximum close to the global LGM in MIS 2. The diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle, means that the term and acronym Last Glacial Maximum (LGM) has limited chronostratigraphical meaning when correlating glacial deposits and landforms.