Arctic Sea Ice decreasing in Volume

Here's a paper people have been anticipating: the decrease in Arctic sea ice volume, and not just the 2-dimensional extent.

Kwok, R., G. F. Cunningham, M. Wensnahan, I. Rigor, H. J. Zwally, and D. Yi (2009), Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008, J. Geophys. Res., 114, C07005, doi:10.1029/2009JC005312.

There's a lot of methodology and crosschecks to wade through in the paper, but basically they find that is getting thinner due to warmer temperatures. -- and, of course, volume is a better indicator than mere extent. They find the older ice has thinned by about 0.6 m over the last five years (the ice is about 2-3 m thick, depending on the time of year).

Along with a more than 42% decrease in multiyear (MY) ice coverage since 2005, there was a remarkable thinning of ~0.6 m in MY ice thickness over 4 years. In contrast, the average thickness of the seasonal ice in midwinter (~2 m), which covered more than two-thirds of the Arctic Ocean in 2007, exhibited a negligible trend. Average winter sea ice volume over the period, weighted by a loss of ~3000 km^3 between 2007 and 2008, was ~14,000 km^3. The total MY ice volume in the winter has experienced a net loss of 6300 km^3 (>40%) in the 4 years since 2005, while the first-year ice cover gained volume owing to increased overall area coverage. The overall decline in volume and thickness are explained almost entirely by changes in the MY ice cover. Combined with a large decline in MY ice coverage over this short record, there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the Arctic Ocean ice cover. Seasonal ice, having surpassed that of MY ice in winter area coverage and volume, became the dominant ice type. It seems that the near-zero replenishment of the MY ice cover after the summers of 2005 and 2007, an imbalance in the cycle of replenishment and ice export, has played a significant role in the loss of Arctic sea ice volume over the ICESat record.

From an AGU press release:

"Even in years when the overall extent of sea ice remains stable or grows slightly, the thickness and volume of the ice cover is continuing to decline, making the ice more vulnerable to continued shrinkage," says Ron Kwok, senior research scientist at NASA's Jet Propulsion laboratory in Pasadena, Calif., and leader of the study.

It will be interesting to see how this gets spun (around).