A 400-year ground surface temperature history inferred from three temperature depth profiles in Northern Quebec
The inversion of three temperature profiles measured in permafrost near the Raglan mine in Northern Quebec, Canada, was carried out to infer the ground surface temperature history (GSTH). The site is located in the Katinniq Plateau, a barren rock desert, at the northern tip of the Ungava Peninsula. The 400-500 m exploration boreholes were logged in September 2005 and 2006, more than three years after drilling was completed. Repeat measurements were made in one the boreholes to verify that the boreholes had returned to thermal equilibrium after the drilling perturbation. Thermal conductivity measurements were made on core samples. Radiogenic heat production is small and can be neglected. Marked deviations from steady state affect the temperature profiles in the uppermost 200 m with inverted gradients above 80 m. These deviations are assumed to be caused by recent (< 300 years) variations in ground surface temperature. Three methods were used to infer the GSTH: 1) forward modeling where an assumed GSTH model developed from proxy data is used to calculate the temperature anomalies at depth which are then compared with the measured ones, 2) a standard inversion using an algorithm based on singular value decomposition, and 3) a Monte Carlo inversion. The GSTH models show a marked warming (approx. 1.4K) between the mid-1700s and the early 1900s associated with the end of the Little Ice Age followed by a cooling episode (approx. 0.4K) which lasted 40-50 years. The models suggest also a recent ground surface temperature warming of about 1.5 K over the past 15 years. The ground surface at Raglan has experienced a 1.7 K warming over the past century and a 2.7 K warming since the Little Ice Age minimum (late 1700s).
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1616 Climate variability (1635;
- 1621 Cryospheric change (0776)