Trends and Patterns in Sea Ice Age Distributions Within the Arctic Basin and Their Implications for Changes in Ice Thickness and Albedo

Sea ice age, calculated using Lagrangian tracking of regions of ice cover depicted using satellite data, provides new insights into the changing arctic ice pack. The ice age product keeps track of how many summer melt seasons that particular ice "parcels" have survived. Examining the spatial distributions of ice of different ages tells us that the Arctic Ocean has shifted from a predominantly multiyear, perennial ice pack to a seasonal one and that age characteristics of the remaining multiyear ice pack have changed. The change has been dramatic, emphasizing not only the loss of multiyear ice, but that the remaining multiyear ice is much younger and likely much thinner than was the case in the 1980s and early 1990s. For the period from 1979 through 2007, we find that the oldest ice types (ice that had survived at least 6 melt seasons) nearly disappeared from the Arctic Basin for areas with at least 40% ice cover. The remaining multiyear ice pack had become younger, with 58% of the multiyear cover consisting of second- and third-year ice compared to 35% during the mid 1980s. Updating the ice age analyses through April 2009 shows that the loss in the older ice types has continued since 2007 within the Arctic Basin and in fact has accelerated.

While the change in age distribution is in itself a significant indicator of a large-scale transition of the ice cover to a new regime, the physical characteristics of ice of different ages are also relevant. Two of these characteristics—ice thickness and albedo—are discussed. By deriving relationships between ice age and thickness, we examine two processes—ice mass loss due to loss of older ice and ice mass loss due to thinning, which provide key insights into how the Arctic Ocean is changing, and what the potential might be for recovery to pre-2000 conditions.

A second aspect of changes in age distribution is potential change in the albedo of the ice cover. We find that overall, first-year ice has a lower albedo than multiyear ice, and younger multiyear ice has a lower albedo than older ice. Some differences also exist in the timing of change in albedo, with first-year ice albedo decreasing faster than for multiyear ice. These differences translate into 28% more absorbed solar radiation by first-year ice during spring through autumn. This suggests a positive feedback that fosters ice melt and helps maintain a predominant first-year ice cover at the expense of older ice.