A MULTIDISCIPLINARY TEST OF THE ACCURACY AND APPLICATION OF BOREHOLE PALEOCLIMATOLOGY

Data from the disciplines of geothermics, remote sensing, microclimatology, climatology, paleoclimatology, and solar radiation have been assembled to test the accuracy and applicability of borehole paleoclimatology. We addressed the following three questions: (1) What is the coherence between the ground surface temperature (GST), surface air temperature (SAT), soil temperatures and solar radiation? (2) Have microclimate changes at borehole sites and climate stations affected temperature trends? (3) If good coherence is obtained, can the coherence between thermal energy stored in the ground and radiative forcing during the time between T-z measurements be extended several centuries into the past? To address the first two questions, we obtained repeat T-z measurements in 20 boreholes that have been logged two or more times in the past two decades and compared the results to meteorological data. The results show that, in most cases, the boreholes faithfully record the same temperature changes as the meteorological stations. At three sites which showed differences between the borehole and meteorological data, we identified microclimate changes at either the borehole or meteorological station. In a second experiment, we made a detailed analysis of long-term air-soil temperature coupling using data from the Automated Weather Data Network (AWDN) station at Fargo, ND linked with a shallow borehole. Our results support the hypothesis that conduction is the dominant heat transfer process between the surface microclimate and the soil regime, and that the relationship between air and ground temperatures are consistent over long time periods. To address the third question we analyzed a twenty-three-year record of soil temperature, air temperature and downward shortwave solar radiation at 87 AWDN stations extending from southern Kansas to the US/Canada border. The results indicate the following: (1) Mean Annual Air Temperatures have increased systematically with increasing latitude. (2) Monthly temperature averages show winters becoming warmer, with early springs becoming cooler. (3) Mean Annual Soil Temperatures have risen and show an increase with increasing latitude. (4) Downward shortwave solar radiation decreased in most places with the greatest deficits in the southern regions.