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A Millennial Thermal History of Lower Murray Lake, Canada
Reference
Besonen, M.R., Patridge, W., Bradley, R.S., Francus, P., Stoner, J.S. and Abbott, M.B. 2008. A record of climate over the last millennium based on varved lake sediments from the Canadian High Arctic. The Holocene 18: 169-180.

What was done
The authors derived thousand-year histories of varve thickness and sedimentation accumulation rate for Canada's Lower Murray Lake (8120'N, 6930'W), which is typically covered for about eleven months of each year by ice that reaches a thickness of 1.5 to 2 meters at the end of each winter. With respect to these parameters, they say -- citing seven other studies -- that "field-work on other High Arctic lakes clearly indicates that sediment transport and varve thickness are related to temperatures during the short summer season that prevails in this region, and we have no reason to think that this is not the case for Lower Murray Lake.

What was learned
In the words of Besonen et al., the story told by both the varve thickness and sediment accumulation rate histories of Lower Murray Lake is that "the twelfth and thirteenth centuries were relatively warm," and in this regard we note their data indicate that Lower Murray Lake and its environs were often much warmer during this time period (AD 1080-1320) than they were at any point in the 20th century, which has also been shown to be the case for Donard Lake (66.25N, 62W) by Moore et al. (2001).

What it means
Evidence from High Arctic lakes continues to demonstrate that this region -- which climate models suggest should be super-sensitive to greenhouse-gas-induced warming -- is still not as warm as it was many centuries ago during portions of the Medieval Warm Period, when there was much less CO2 and methane in the air than there is today, which further suggests that the planet's more modest current warmth need not be the result of historical increases in these two trace gases of the atmosphere.

Reference
Moore, J.J., Hughen, K.A., Miller, G.H. and Overpeck, J.T. 2001. Little Ice Age recorded in summer temperature reconstruction from varved sediments of Donard Lake, Baffin Island, Canada. Journal of Paleolimnology 25: 503-517.

Reviewed 21 May 2008