HR: 1340h
AN: U13B-1144    [Abstracts]
TI: A Late Quaternary Climate Reconstruction Based On Combined Heat Flow And Borehole Temperature Data
AU: * Huang, S
EM: shaopeng@umich.edu
AF: Department of Geological Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109-1005, United States
AU: Pollack, H N
EM: hpollack@umich.edu
AF: Department of Geological Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109-1005, United States
AB: Reconstructions of ground surface temperature history (GSTH) from geothermal data have contributed to an understanding of the contemporary global warming in the context of long-term climate variability. Among the reconstructions based on geothermal data are a twenty-millennium GSTH published in Geophysical Research Letters (1997, 31: 267-280) and a five-century GSTH published in Nature (2000, 403: 756-758) by the Huang- Pollack-Shen (HPS) team. But there have been questions regarding the different amplitudes and temporal coverage of these two reconstructions. Here we explain their differences and present a reconstruction based on the combination of the climate information carried independently by the data sources of these two previous studies. The HPS(2000) study is based on a global database of borehole temperatures compiled for the explicit purpose of climate reconstruction. Signals of past temperature changes at the ground surface are recorded in the rocks as transient perturbations to the steady-state subsurface temperature field. However, there are several constraints on the amount of climate information one can retrieve from a borehole temperature profile. In particular, the temporal length of a reconstruction is basically limited by the depth of the borehole temperature profile and the noise level of the borehole data. Given that most of the temperature profiles are shallower than 400 m, the HPS(2000) focused on reconstructions representing the past five centuries. The HPS(1997) reconstruction is not a "standard" borehole reconstruction in which a temperature versus depth profile is inverted to yield a GSTH. This reconstruction is based on a heat flow versus depth profile assembled from over 6,000 data entries residing in the heat flow database compiled for the original purpose of mapping the heat loss from the interior of Earth. Compared to the data used in HPS(2000), the data set of HPS(1997), while more abundant, is much noisier. We converted the heat flow versus depth profile into a 2000 m temperature versus depth profile prior to inversion. Data shallower than 100 m were excluded from the analysis due to the concern over high noise level. The inversion of this converted profile yielded a highly smoothed late Quaternary climate history. To integrate the climate information preserved in the borehole temperature database and the heat flow database, we use the century-long trends from HPS(2000) supplemented by the SAT instrumental record to generate a globally representative temperature-depth profile from the surface down to 300 m depth at 10 m depth intervals. We then extend this synthetic temperature-depth profile down to 2000 m with the converted heat flow data of the HPS(1997) study. The inversion of this composite temperature data set shows an average late Pleistocene temperature some 4K below the reference level (1961-1990 mean), and a long mid-Holocene warm episode averaging about 1K above the reference level. The temperature in the Medieval Warm Interval some 600-1,000 years ago was at or slightly above the reference level. The Little Ice Age is apparent around 200-500 years ago, averaging almost 1K below the reference level.
UR: http://www.geo.lsa.umich.edu/~ shaopeng/
DE: 1600 GLOBAL CHANGE
DE: 1620 Climate dynamics (0429, 3309)
DE: 1645 Solid Earth (1225)
DE: 5418 Heat flow
SC: Union [U]
MN: 2007 Fall Meeting