Canadian Arctic Permafrost Observatories: Detecting contemporary climate change through inversion of subsurface temperature time series

We describe long-term permafrost temperature and climate change observatories established in the northeastern Canadian High Arctic (77 degrees-82.5 degrees N). Two sites have deep temperature logs (165 and 800 m), and thermistor cables and automatic loggers have been installed in the upper similar to 65 m. The third site has multiple temperature logs at three 61-m boreholes with thermistor cables frozen into the permafrost. A fourth deep site (750 m) is included for regional completeness. Geothermal spectrum inversion is used to determine ground surface temperature histories. The Little Ice Age is resolved from the mid-1700s to mid-1800s with surface temperatures similar to 1 K below the long-term mean; a subsequent recovery yields late 20th century surface temperatures similar to 3 K higher. These results correlate with similar reconstructions reported for Greenland ice cap holes GRIP and Dye-3 to the southeast. The Canadian and Greenland surface temperatures show a weak, inverse correlation with the North Atlantic Oscillation, suggesting recent climate change as a common causal source. Simultaneous inversions of multiple logs over 22 years at the 61-m holes resolve two to three major cycles in ground surface temperature variation over the latter half of the 20th century. Here permafrost ground temperatures increase 0.3 degrees-0.5 degrees C/decade, compared to 0.6 degrees C/decade for air temperatures; annual total snow increases 22 cm/decade and may insulate permafrost from the larger transient trends in air temperatures. Finally, atmospheric temperature inversions prevalent in Arctic winters may contribute to anomalously high ground surface temperatures observed at two locations.