HR: 1340h
AN: PP43A-0619    [Abstracts]
TI: Quantitative reconstruction of paleoclimate - Air and ground temperature tracking from Emigrant Pass Observatory
AU: * Chapman, D S
EM: dchapman@mines.utah.edu
AF: Department of Geology and Geophysics, University of Utah, 135 South 1460 East WBB 719, Murray, UT 84112 United States
AU: Bartlett, M G
EM: bartlett@mines.utah.edu
AF: Department of Geology and Geophysics, University of Utah, 135 South 1460 East WBB 719, Murray, UT 84112 United States
AU: Harris, R N
EM: rnharris@mines.utah.edu
AF: Department of Geology and Geophysics, University of Utah, 135 South 1460 East WBB 719, Murray, UT 84112 United States
AB: Borehole temperature-depth profiles contain information about surface ground temperatures histories and provide a useful complement to proxy indicators of climate change. An inherent assumption in borehole temperature reconstructions is that air and ground temperatures are coupled through heat diffusion track each other at annual and longer periods. The Emigrant Pass Observatory (EPO), located in the Grouse Creek Mountains of northwestern Utah, is designed to test ground-air temperature tracking. Analyses of 10 years of observations at EPO demonstrate the following: 1) Ground temperatures track air temperatures at annual and longer periods exceptionally well at the site. Divergence between the observed temperatures at 1 m in the subsurface and air temperatures modeled as a boundary layer forcing is less than 0.04 K per annum. 2) Seasonal variations in incident solar radiation are ~200 Wm$^{-2}$ leading to an average annual difference between ground and air temperatures, $\Delta$T$_{g-a}$, of 2.55 K ($\pm$0.01) from 1993-2003. The temperature difference varies from -5 K to +10 K when averaged over a diurnal cycle, and from 2.50 K to 2.60 K over an annual cycle. However, inter-annual variations in insulation are less than 1 Wm$^{-2}$; consequently, solar radiation is not observed to affect the inter-annual tracking at the site. 3) Model studies snow-ground thermal interactions at EPO demonstrate that seasonal snow cover can either warm or cool the ground relative to the annual mean air temperature and that the winter snow effect is an order of magnitude smaller than the summer radiation effect at the site. 4) Temperature observations at various depths within the granite and soils at the site allow us to make estimates of in-situ thermal diffusivity and its changes with time. The "apparent" thermal diffusivity of the upper meter of granite at EPO ranges from 0.88-0.98 x 10$^{-6}$ m$^{2}$s$^{-1}$ while the soil varies from 0.57-0.68 x 10$^{-6}$ m$^{2}$s$^{-1}$. The accumulation of data at EPO leads to a quantitative understanding of paleoclimate signals in rock temperatures without the need for an empirical calibration.
DE: 3322 Land/atmosphere interactions
DE: 1694 Instruments and techniques
DE: 1620 Climate dynamics (3309)
DE: 1645 Solid Earth
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting