Monte Carlo inverse modelling of the Law Dome (Antarctica) temperature profile

Abstract

ABSTRACT. The temperature profile in the 1200 m deep Dome Summit South (DSS) borehole near the summit of Law Dome, Antarctica, was measured in 1996, 3 years after the termination of the deep drilling.The temperature profile contains information on past surface temperature over the last 4 ka. This temperature history is determined by the use of a Monte Carlo inverse method in which no constraints are placed on the unknown temperature history and no solution is assumed to be unique. The temperature history is obtained from a selection of equally well-fitting solutions by a statistical treatment.The results show that solutions covering the last 4 ka have a well-developed central value, a most likely temperature history. The temperature record has two well-developed minima at AD1250 and 1850. From 1850 to the present, temperatures have gradually increased by 0.7 K. The reconstructed temperatures are compared with the stable oxygen isotope ( IV y) from the DSS ice core. TEMPERATURE PROFILE FROM LAW DOMEIn 1993 the glaciology group of the Australian Antarctic Division completed the drilling of a 1200 m deep ice core to bedrock 4.68 km south-southwest of the highest point on the Law Dome ice cap (66³46 H S,112³48 H E;1370 m a.s.l.) (Morgan and others, 1997). In 1996 a temperature profile was inferred from measurements every 10^20 m in the deep borehole, with a measuring accuracy of 0.02 K (Van Ommen and others, 1999). Temperature measurements in the top 50 m are from the cased part of the deep borehole, above the liquid level, and they are disturbed and influenced by the temperature and pressure conditions in the building constructed over the borehole. They do not represent the undisturbed firn and ice temperatures.In 1997, temperatures were measured in a 270 m deep dry borehole drilled 80 m south of the deep borehole (Van Ommen and others, 1999). These temperatures have an accuracy of 0.05 K, but are believed to be a better representation of the undisturbed firn and ice temperatures than those from shallow depths in the deep borehole. The two temperature profiles were combined in such a way that the shallow borehole profile was used down to 50 m, the depth zone between 50 and 270 m was used to align the two profiles, and the temperatures from the deep borehole were used below 50 m. The combined temperature profile (Fig. 1a, solid curve) is used to reconstruct the past temperature history. A study of the noise in the data (Fig. 1b) clearly shows the increased errors in the measurements from the shallow borehole. Below 750 m depth, convection cells in the borehole liquid are seen to appear. Temperature excursions in the profile due to these cells increase as the temperature gradient increases (Gundestrup, 1989; Gundestrup and others, 1994; Gundestrup and Clow, 1997).The convection cells are smoothed out before the reconstruction of the past temperatures is attempted, as they do not represent ice temperatures.A temperature profile assuming steady-state conditions and the present-day ice-sheet configuration (accumula...

Holocene volcanic history as recorded in the sulfate stratigraphy of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core

“…This warm/cold step could be like a Medieval Climate Optimum–like to Little Ice Age–like transition. Medieval Warming is well defined in the Northern Hemisphere by several proxies [e.g., O'Brien et al , 1995; Wilson et al , 2000], while no clear evidence has been reported for Austral regions [ Dahl‐Jensen et al , 1999]. In a recent paper, Goosse et al [2004, and references therein] report evidence from δD and δ 18 O measurements on Antarctic ice cores in support of a Medieval Warming–like period in the Southern Hemisphere, delayed by about 150 years with respect to Northern Hemisphere Medieval Warming.…”

Antarctic temperatures over the past two centuries from ice cores

“…From our reconstruction, we estimate that Antarctic temperatures over the 1961–1999 calibration period were about 0.2°C higher than in the period 1861–1899. Other evidence for long‐term warming includes ice borehole temperature inversions at Siple Dome [ Engelhardt , 2004] in West Antarctica and Law Dome [ Dahl‐Jensen et al , 1999] in East Antarctica. At Law Dome, the minimum (∼1850) to maximum (1990) temperature difference was quantified as 0.7°C, which agrees with the difference of 0.6°C that is evident in a smoothed version of our reconstruction between the low in the 1800s to the maximum around 1990 (Figure 3c).…”

Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) Divide

“…[18] 3. The amplitude of the climate changes is on the order of s x = 0.5 C, following the work of Dahl-Jensen et al [1999] at Law Dome, where they found using a Monte Carlo scheme that the standard deviation of the reconstructed past temperature was around 0.3 C.…”