Decline in thickness and volume of Arctic Ocean sea ice: 2004-2008

We present our best estimate of the thickness and volume of the Arctic Ocean ice cover from ten ICESat campaigns that span a 5-year period between 2004 and 2008. Along with a more than 48% decrease in multiyear (MY) ice coverage since 2005, there is a thinning of ~0.7 m of the average MY ice thickness in four years. In contrast, the average thickness of the seasonal ice in mid-winter (~2 m), that covered more than two-thirds of the Arctic Ocean in 2007, has remained relatively unchanged over the same period. Even though the seasonal ice cover was formed quite late after the record minimum in summer ice extent in 2007, the thinner snow depth during that growth season suggests that higher ice production was due in part to reduced accumulation of that large fraction of snowfall that typically occurs in October and November (resulting in lower insulation). We will discuss the total volume loss and its variability during the period. It seems that the near zero replenishment of the MY ice cover, an imbalance in the cycle of replenishment and ice export, after the summers of 2005 and 2007 has played a significant role in the loss of Arctic sea ice volume over the ICESat record.