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| Titel |
Quantifying the effects of the maximum borehole depth on ground surface temperature histories inferred from borehole temperature profiles |
| VerfasserIn |
Hugo Beltrami, Jason Smerdon, Gurpreet Matharoo, Nick Nickerson |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048817
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| Zusammenfassung |
| It is illustrated how the minimum depth of a temperature-depth profile impacts the estimation
of the climate signal in a borehole temperature profile, and subsequently the derived ground
surface temperature (GST) reconstruction. In particular, the effects and uncertainties that
arise from the analyses of borehole temperature logs of different depths are quantitatively
illustrated. Because the vast majority of measured borehole temperature profiles are acquired
from boreholes of opportunity, the maximum measurement depth in data used for
paleoclimatic studies varies considerably (beginning at depths as shallow as 100-150 m and
extending to depths of more than 1 km). The depth of the borehole is important
because the downwelling climatic signal must be separated from the quasi-steady state
thermal regime established by the Earth’s interior. This component of the signal is
estimated as a linear increase in temperature with depth from the lower section
of a borehole temperature profile, which is assumed to be unperturbed by recent
climatic changes. The validity of this assumption is dependent on both the subsurface
thermophysical properties and the character of the downwelling climatic signal.
Such uncertainties can significantly impact the determination of the quasi-steady
state thermal regime, and consequently the magnitude of the temperature anomaly
interpreted as a climatic signal. Results demonstrate that widely different GST
histories can be derived from temperature profiles truncated at different depths,
even when the profiles are generated from the identical surface and subsurface
conditions. Borehole temperature measurements approaching 500-600 m depths
are shown to provide the most robust GST reconstructions spanning 500 to 1000
ypb, while shallower holes indicate a muted warming in the synthetic examples
investigated. It is further shown that the bias introduced by a temperature profile of depths
shallower than 500-600 m remains even if the time span of the reconstruction target is
shortened. |
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