HR: 17:15h
AN: PP34A-06    [Abstracts]
TI: Understanding the Causes of Mid-Cretaceous Warming: Implications of Terrestrial Carbonate Isotope Data on Latent Heat Transport and Methane Fluxes During the Albian
AU: * Gonzalez, L A
EM: lgonzlez@ku.edu
AF: Department of Geology, University of Kansas, Lawrence, KS 66045-1763 United States
AU: Ufnar, D F
EM: David.Ufnar@usm.edu
AF: Department of Geology, University of Southern Mississippi, Hattiesburg, MS 39046 United States
AU: Ludvigson, G A
EM: gludvigson@igsb.uiowa.edu
AF: Department of Geoscience, University of Iowa, Iowa City, IA 52242 United States
AU: Brenner, R L
EM: robert-brenner@uiowa.edu
AF: Department of Geoscience, University of Iowa, Iowa City, IA 52242 United States
AU: Witzke, B J
EM: bwitzke@igsb.uiowa.edu
AF: Department of Geoscience, University of Iowa, Iowa City, IA 52242 United States
AB: The distribution of pedogenic spherulitic siderite (sphaerosiderites) and calcareous paleosols provide evidence of changes in the Albian hydrologic cycle. These pedogenic deposits attest to intensified precipitation in the tropics and mid to high latitudes and enhanced aridity in the dry subtropical belts. The isotopic compositions of the pedogenic minerals provide constraints for an isotope mass balance model of paleolatitudinal changes in the \delta$^{18}$O of Albian paleoprecipitation, and suggest that Albian precipitation rates were 156-220 % greater in the mid-latitudes [2600-3300 mm/yr], and 99 % greater at high latitudes [550 mm/yr]. These higher precipitation rates were sustained by a 76-96 % increase in evaporation fluxes, principally focused in the tropics and subtropics. Comparison of modeled Albian and modern P-E curves suggest amplification of the Albian moisture deficit between 7.5 and $30\deg$N latitude (up to 65% greater), and amplified Albian moisture surplus in the mid to high latitudes (up to 45% greater). The tropical moisture deficit is calculated to represent an average heat loss of approximately 74 W/m$^{2}$ at $10\deg$N paleolatitude (present 16.5 W/m$^{2}$), an average heat gain of approximately 83 W/m$^{2}$ at $45\deg$N (present 23 W/m$^{2}$); and an average heat gain of 19 W/m$^{2}$ at $75\deg$N (present 4 W/m$^{2}$). These quantitative estimates of increased poleward heat transfer by H$_{2}$O vapor during the mid-Cretaceous greenhouse warming help to explain the reduced equator-to-pole temperature gradients.ÿ Sphaerosiderites are widely distributed, and often formed under methanogenic conditions. Their \detla$^{13}$C values clearly indicate that methane fluxes from Albian wetland soils of the tropics and the mid-to-high latitudes were significantly higher than present day fluxes. Coupled with episodic clathrate releases, pedogenic methane production may provide an alternative to CO$_{2}$ as the sole driver on warm conditions of the Albian greenhouse world.
DE: 9609 Mesozoic
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 0325 Evolution of the atmosphere
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting