High Resolution Time-Series of California Climate Over the Last 12,000 Years: Testing the Influence of the North Atlantic and North Pacific

点击翻译按钮获取中文摘要

Instrumental records of climate in California extend back approximately 100 years and are too short in length to capture the full range of natural variability of temperature and precipitation in the state. The project will provide records of climatic variability that extend back over 12,000 years. The project will analyze fossil midge fly larva (Chironomids), crustaceans (Cladocera), unicellular aquatic algae (diatoms), terrestrial plant microfossils, and geochemical evidence from lake sediments from the eastern Sierra Nevada to reconstruct records of temperature and effective moisture that extend back over 12,000 years. Chronologies will be linked to the records by the radiocarbon dating of organic matter in the lake sediments. Previous work has developed mathematical models that provide numerical estimates of past temperature and effective moisture from fossil chironomid and diatom assemblages. Previous preliminary work has also led to the recovery of several lake sediment records that extend back past 11,000 years in age and show clear evidence of both high and low frequency changes in temperature and effective moisture during the transition from glacial to modern climatic conditions between 12,000 and 9000 years ago. This project will complete analysis of these core sections. The project will then use the existing lake sediment cores and new cores collected from climatically sensitive settings to reconstruct changes in temperature and effective moisture over the past 9000 years. The project will construct records with better than 50 year temporal resolution for both high and mid-elevation sites. In addition to the significant multi-centennial to millennial variations seen in the glacial to non-glacial transition, the project will use previously published data for the past 2000 years to uncover evidence of multi-decadal to multi-centennial droughts during the past 9000 years. The temporal patterns of variations in California temperature and effective moisture will be compared to temporal patterns of variability evident in cores from the North Pacific Ocean, North Atlantic Ocean and Greenland Ice Cap, in order to help deduce the larger scale causes of long-term variability in California climate. Long-term climate records are essential to anticipating the full range of variability in the severity and duration of long-term drought periods, wet periods and warm and cold periods that can occur in California. The records will help determine if there is long-term periodicity in phenomena such as multi-decadal droughts that will make such events more predictable. These records of past climate will also help in assessing the role of changes in the Atlantic and Pacific oceans in driving climatic variations in California. Finally, the long-term climatic records provided by this project will furnish baseline data on natural variability of climate in California that will allow for the detection of truly unusual variations that might be attributable to greenhouse warming. The records will be of importance for water resource management, forestry and conservation management, and climatic change detection and management.