Tuesday, April 10, 2012

New paper shows surface temperature of Arctic icecap was warmer during most of past 11,000 years

A paper published today in the Journal of Geophysical Research shows that a large ice cap in the Canadian Arctic had surface temperatures higher than the present for the vast majority of the past 11,000 years [see graph below]. The paper also shows that the meltwater fraction in 2010 was slightly less than the vast majority of a 7000 year period from roughly 10,000 to 3000 years ago.

Fig. 10 from the paper shows in top graph an oxygen isotope proxy for surface temperature over the past 11,000 years. The added red line shows the present surface temperature is colder than the vast majority of the past 11,000 years. The second graph shows the percentage meltwater fraction (MF) of snow on the icecap surface was slightly less than 100% in 2010, and at a full 100% during the vast majority of the 7000 year period from about 10,000 to 3,000 years ago [The Holocene Thermal Maximum labelled HTM above]. The bottom graph is a blowup of the past 300 years, showing how the meltwater % has increased since the low levels of the Little Ice Age (LIA).

Key Points
  • Summer melt rates on Penny Ice Cap have increased greatly in the past decades
  • The firn temperature of the ice cap is rising
  • The present thermal state of the ice cap resembles that last seen 3000 years ago
Christian Zdanowicz
Geological Survey of Canada, Natural Resources Canada, Ottawa, Ontario, Canada
Anna Smetny-Sowa
Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
David Fisher
Geological Survey of Canada, Natural Resources Canada, Ottawa, Ontario, Canada
Nicole Schaffer
Department of Geography, University of Ottawa, Ottawa, Ontario, Canada
Luke Copland
Department of Geography, University of Ottawa, Ottawa, Ontario, Canada
Joe Eley
6 Sullivan St., Saskatoon, Saskatchewan, Canada
Florent Dupont
Centre d'Applications et de Recherches en Télédétection, Université de Sherbrooke, Quebec, Canada
Laboratoire de Glaciologie et Géophysique de l'Environnement, UMR 5183, UJF-CNRS, Grenoble F-38041, France
At latitude 67°N, Penny Ice Cap on Baffin Island is the southernmost large ice cap in the Canadian Arctic, yet its past and recent evolution is poorly documented. Here we present a synthesis of climatological observations, mass balance measurements and proxy climate data from cores drilled on the ice cap over the past six decades (1953 to 2011). We find that starting in the 1980s, Penny Ice Cap entered a phase of enhanced melt rates related to rising summer and winter air temperatures across the eastern Arctic. Presently, 70 to 100% (volume) of the annual accumulation at the ice cap summit is in the form of refrozen meltwater. Recent surface melt rates are found to be comparable to those last experienced more than 3000 years ago. Enhanced surface melt, water percolation and refreezing have led to a downward transfer of latent heat that raised the subsurface firn temperature by 10°C (at 10 m depth) since the mid-1990s. This process may accelerate further mass loss of the ice cap by pre-conditioning the firn for the ensuing melt season. Recent warming in the Baffin region has been larger in winter but more regular in summer, and observations on Penny Ice Cap suggest that it was relatively uniform over the 2000-m altitude range of the ice cap. Our findings are consistent with trends in glacier mass loss in the Canadian High Arctic and regional sea-ice cover reduction, reinforcing the view that the Arctic appears to be reverting back to a thermal state not seen in millennia.
The Minoan Warming Period occurred ~ 3000 years ago

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