1,350,000 Year History of Siberian Permafrost Based on U-Pb Chronology of Speleothems

Abstract:

Permafrost history of the last ~1.35 millions of years (Ma) was reconstructed using chronology of speleothems from a Siberian cave. Rain and snowmelt waters can penetrate into caves only when soil and subsoil temperatures are above 0°C and permafrost above the cave is discontinuous or absent. Speleothems in regions currently affected by permafrost therefore provide a tracer of past permafrost thawing events.

Ledyanaya Lenskaya Cave is located at 60°22’N-116°57’E, on the southern boundary of modern continuous permafrost, with no present-day water seepage and a mean annual temperature of -5°C ‒ -6°C. U-Th dating of speleothems from this cave in a previous study [1] showed that the youngest speleothem growth period occurred at 427±23 thousand years ago (ka), during early Marine Isotope Stage (MIS) 11. In this study we dated several horizons of older speleothems from this cave using the U-Pb method [2]. Two high precision ages indicate growth at 1074.2 +6.6/-5.2 ka and 947.8 +3.3/-3.4 ka, while new preliminary data provide strong evidence of an older growth period around 1.35-1.30 Ma. Other preliminary data mostly overlap the high precision ages, but also hint at limited growth at ~860 ka, with one data point suggesting younger, but minor growth at ~560 ka. The timing of these permafrost thawing events apparently correlates with interglacial episodes of exceptionally high Pacific Warm Pool sea surface temperature (~30°C) [3]. During these warm episodes the average global temperature was 1.1-1.5°C higher than pre-industrial temperatures. These findings put the threshold of thawing of continuous permafrost at its southern boundary at slightly more than 1.0°C above preindustrial level.

References:

1. Vaks, A., et al., Science, 2013. 340 (6129): p. 183-186.

2. Mason, A.J., G.M. Henderson, and A. Vaks, Geostandards and Geoanalytical Research, 2013. 37(3): p. 261-275.

3. Hansen, J., et al., Proceedings of the National Academy of Sciences, 2006. 103(39): p. 14288-14293.