2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
Paper No. 164-2
Presentation Time: 2:05 PM-2:25 PM

Stable Isotope Proxies for Polar Paleoprecipitation in Ancient Greenhouse Worlds

LUDVIGSON, Greg A., Kansas Geological Survey, The University of Kansas, 1930 Constant Ave, Lawrence, KS 66047-3726, gludvigson@kgs.ku.edu, GONZÁLEZ, Luis A., Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Room 120, Lawrence, KS 66045-7594, and PAGANI, Mark, Department of Geology & Geophysics, Yale Univ, P.O. Box 208109, New Haven, CT 06520

Polar regions are sensitive to changing global heat budgets, and global warming is strongly expressed near the poles. There are uncertainties about responses of hydrologic cycle to episodes of global warming, and about roles of the hydrologic cycle in amplifying polar warming. Stable isotope proxies from authigenic minerals and fossil materials from ancient terrestrial ecosystems of the mid-Cretaceous and Early Eocene have been used to interpret records of the δ18O and δD of precipitation during ancient greenhouse worlds. From one example, a transect of mid-Cretaceous pedogenic carbonate δ18O in the Americas spans from the Colombian paleoequator to the North Slope Alaskan paleo-Arctic. This Cretaceous latitudinal mineral δ18O gradient is isotopically lighter and declines northward more steeply than that of the modern; 18O mass-balance models of these data argue for higher Cretaceous precipitation rates in temperate-polar latitudes than today. They also argue for increased latent heat fluxes (3.6x -- 10.6x at 50º N) to the poles; a mechanism for amplified polar warming. Models of Cretaceous paleoclimates by GCMs with water isotope modules do not simulate the steeper empirical Cretaceous mineral 18O gradient or mass balance-modelled higher precipitation rates; orographic influences of the Brooks Range on Alaskan δ18O data have been cited as a possible confounding effect masking true δ18O values of polar paleoprecipitation. From another example, long-chain n-alkanes (n-C27/29) recovered from Early Eocene sediments recording the PETM event (IODP Expedition 302) in the Arctic Ocean have characterized the δD of Arctic paleoprecipitation. The δD values of n-C27/29 alkanes are dramatically higher in the PETM interval than in bounding strata, arguing for decreased rainout during poleward moisture transport, but in higher moisture and latent heat delivery to the North Pole during this event. Discrepant results call for coordination of multiple proxies, and we are pursuing this objective for the Cretaceous North Slope example.

2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
General Information for this Meeting
Session No. 164
Ancient Polar Ecosystems and Environments: Proxies for Understanding Climate Change and Global Warming
George R. Brown Convention Center: 330A
1:30 PM-4:45 PM, Sunday, 5 October 2008

Geological Society of America Abstracts with Programs, Vol. 40, No. 6, p. 192

© Copyright 2008 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.