Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere

摘要

The relative timing of late Quaternary glacial advances in mid-latitude(40-55° S) mountain belts of the Southern Hemisphere (SH) has become acritical focus in the debate on global climate teleconnections. On the basisof glacial data from New Zealand (NZ) and southern South America it has beenargued that interhemispheric synchrony or asynchrony of Quaternary glacialevents is due to Northern Hemisphere (NH) forcing of SH climate througheither the ocean or atmosphere systems. Here we present a glacial snow-massbalance model that demonstrates that large scale glaciation in the temperateand hyperhumid Southern Alps of New Zealand can be generated with moderatecooling. This is because the rapid conversion of precipitation from rainfallto snowfall drives massive ice accumulation at small thermal changes (1-4°C).Our model is consistent with recent paleo-environmental reconstructionsshowing that glacial advances in New Zealand during the Last Glacial Maximum(LGM) and the Last Glacial Interglacial Transition (LGIT) occurred undervery moderate cooling. We suggest that such moderate cooling could begenerated by changes in synoptic climatology, specifically through enhancedregional flow of moist westerly air masses. Our results imply that NHclimate forcing may not have been the exclusive driver of Quaternaryglaciations in New Zealand and that synoptic style climate variations are abetter explanation for at least some late Quaternary glacial events, inparticular during the LGIT (e.g. Younger Dryas and/or Antarctic ColdReversal).