A Quantitative Paleoclimatic History of the Southern Great Basin Since the Middle Miocene
Abstract
The southern Great Basin presents an example of dramatic climatic evolution since the middle Miocene. There is strong evidence that during the middle Miocene the Great Basin constituted a well-watered mid-elevation plateau covered by lush forests. Today the upland portions contain a cold, xeric shrub steppe and the lowlands sparse hyperarid desert shrubs. In this study, I have attempted to characterize and quantify the climate changes that have driven this environmental transition, based on synthesis of previous studies. In performing this reconstruction, I have relied most heavily on quantitative analysis of temperature and precipitation based on the biogeographic distribution of the closest relatives of plant species found in the ancient floras. I have supplemented this with paleotemperature reconstructions from alkenone unsaturation measurements of marine sediments from cores off the west coast of the United States and paleoprecipitation estimates from hypsodontic measurements on the teeth of fossil mammals in the Great Basin. Further constraints are provided by paleoenvironment analysis from the sedimentology of basin-fill deposits, the stable isotope composition of lacustrine and soil carbonates, water-balance analysis of the extent of paleo-lakes, interpretation of micropaleontological data, and Great Basin speleothem records. Taken together, these indicate that the climate of the latest middle Miocene was about 8 ºC warmer than present. Throughout the late Miocene the temperature declined to modern averages by about 6 Ma. After ~4 Ma, the amplitude of temperature fluctuations caused by global glacial/interglacial cycles increased, but the average temperature decreased, so the glacial minimum temperatures were about 6 ºC colder than present and interglacials were close to present temperature for the past 0.5 Ma. Mean annual precipitation varied in a similar fashion, from about four times modern in the middle Miocene to three times in the early Pliocene, and twice modern for Pleistocene glacial stages. Modern conditions are the driest in the entire record. This long reconstruction shows that prior to the late Pliocene, warmer climate states were associated with wetter conditions, but subsequent to that this correlation reversed and the wetter states were associated with the coldest climates.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP0240001P
- Keywords:
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- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 1655 Water cycles;
- GLOBAL CHANGE;
- 4914 Continental climate records;
- PALEOCEANOGRAPHY