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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS017 Oral Presentation 2372
Characterising the influence of latent heat effects on GST history
Prof. Christoph Clauser
Applied Geophysics RWTH Aachen University IASPEI
Darius Mottaghy
In moderate and high latitudes, the signature in borehole temperatures due to past surface temperature
variations can be significantly influenced by latent heat liberated or consumed by freezing or thawing
pore water, respectively. The magnitude of the effect depends on several parameters, most important
porosity, but also the present-day and past ground surface temperature (GST), and basal heat flow.
Depending on the depth of available borehole temperatures, we studied the impact on short term GST
history inversions, as well as long term histories as far back as to the last glaciation. The influence of
different parameters is investigated by generating a number of synthetic temperature logs and inverting
them for ground surface temperature histories by a regularised Tikhonov inversion scheme. To this end
we used a simple step forcing function. These simulations are performed both with and without latent
heat effects. Regarding long-term GST history reconstructions and in view of possible corrections
applied to inversions which neglect the latent heat effect, we find the difference between present-day
and glaciation temperatures useful to quantify this effect. To illustrate possible corrections, we plot the
dependence of this temperature difference (as a function of the latent heat effect) versus porosity,
basal heat flow, present-day and past GST. Depending on parameter combination and present-day
surface temperature, the neglect of freezing and thawing processes results in an overestimation of the
postglacial warming of up to 4 K. We also studied the impact of the latent heat effect on GST history
inversions on shorter time scales. Using a simplified, synthetic model for the temperature variations
within the last 1000 years, we find that amplitude and duration of the cool period of the Little Ice Age
and the recent warming are not large enough to cause a significant influence of the latent heat effect.
However, neglect of this effect results in a clearly deteriorated timing.
Keywords: paleoclimate, borehole temperature, inversion