The Stepwise Reduction of Multiyear Sea Ice Area in the Arctic Ocean Since 1980

The loss of multiyear sea ice (MYI) in the Arctic Ocean is a significant change that affects all facets of the Arctic environment. Using a Lagrangian ice age product, we examine MYI loss and quantify the annual MYI area budget from 1980 to 2021 as the balance of export, melt, and replenishment. Overall, MYI area declined at 72,500 km2/yr; however, a majority of the loss occurred during two stepwise reductions that interrupt an otherwise balanced budget and resulted in the northward contraction of the MYI pack. First, in 1989, a change in atmospheric forcing led to a +56% anomaly in MYI export through Fram Strait. The second occurred from 2006 to 2008 with anomalously high melt (+25%) and export (+23%) coupled with low replenishment (-8%). In terms of trends, melt has increased since 1989, particularly in the Beaufort Sea, export has decreased since 2008 due to reduced MYI coverage north of Fram Strait, and replenishment has increased over the full time series due to a negative feedback that promotes seasonal ice survival at higher latitudes exposed by MYI loss. However, retention of older MYI has significantly declined, transitioning the MYI pack toward younger MYI that is less resilient than previously anticipated and could soon elicit another stepwise reduction. We speculate that future MYI loss will be driven by increased melt and reduced replenishment, both of which are enhanced with continued warming and will one day render the Arctic Ocean free of MYI, a change that will coincide with a seasonally ice-free Arctic Ocean. Sea ice that has survived through at least one melt season is referred to as multiyear sea ice. It is inherently thicker, has a higher albedo and is overall more resilient to melt than seasonal sea ice. Historically, multiyear ice covered a vast majority of the Arctic Ocean, however its areal extent has declined and transitioned the Arctic ice pack to a younger state that is more susceptible to melt. To this point, the loss of multiyear ice is known, but it remains unclear whether it was a change in multiyear ice loss through export or melt or the source of multiyear through replenishment that has driven this change. By quantifying these three terms for each of the past 42 years, we find that multiyear ice loss primarily occurred through two stepwise reductions, with the budget otherwise generally being in balance. The first loss occurred in 1989 due to anomalously high export, while the second loss occurred between 2006 and 2008 through a confluence of anomalously high export and melt and low replenishment. Trends of reduced export, increased melt and increased replenishment, and overall negative multiyear ice balance, suggest the eventual disappearance of multiyear ice from the Arctic Ocean. Multiyear sea ice (MYI) loss from the Arctic Ocean has primarily occurred through two stepwise reductions: 1989 and 2006-20081989 was the result of high MYI export, while 2006-2008 was the result of high MYI export and melt, and limited MYI replenishmentThough presently stable, reduced retention to older MYI has created a younger thinner MYI pack that may be conditioned for another reduction