Influence of Orbital Forcing of North American Hydroclimate on Paleolake Depth During the Early Eocene Greenhouse
Abstract
Geological records from greenhouse climate intervals can provide key insights into future climate system behavior in a warming world through an improved understanding of past warm climate dynamics. The Early Eocene Climatic Optimum (EECO; 53-50 Ma) is Earth's most recent greenhouse climate period and is associated with the warmest sustained temperatures of the Cenozoic. Although the EECO is one of the most highly-studied greenhouse climate intervals, the behavior of the hydrologic cycle on the continents during this warm period remains one of the least understood elements of its paleoclimate.
Here we present an expanded high-resolution leaf wax δD record from the lacustrine Wilkins Peak Member (WPM) of the Green River Formation in Wyoming, one of the best-dated terrestrial records of the early Eocene. We use this orbitally-resolved δDwax record to investigate hydroclimate variability in western North America during the EECO and to evaluate linkages between these variations in the hydrosphere and changes in lake depth in this ancient lacustrine system. Our results show decameter-scale δDwax variations of up to 60‰ at a temporal scale consistent with the ~100 ky short eccentricity cycle. Additionally, we find that these eccentricity-scale variations in δDwax have a consistent association with the two primary sedimentary depositional modes of the WPM, alluvial and lacustrine deposition. Alluvial deposition-indicative of low water levels in the lake basin- is broadly associated with increasing δDwax, while lacustrine deposition-indicative of higher water levels in the lake basin-is broadly associated with decreasing δDwax. To decipher the drivers of changes in precipitation and precipitation isotopes, we performed climate-isotope simulations using the water isotope-enabled Community Earth System Model (iCESM) across a range of orbital parameters. Model simulations show that high eccentricity is associated with an enhanced seasonal cycle in precipitation and isotopes, suggesting that the large amplitude of δDwax observed in the Green River Formation likely reflects orbitally-driven shifts in the seasonality of precipitation. This astronomical forcing of the EECO hydrosphere also influenced water depth in the paleolake depositing the WPM, leading to cyclical changes in depositional mode.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMPP35B..06W