The Multiyear Sea Ice area budget of the Arctic Ocean: export, melt, replenishment and a recent plateau

The loss of multiyear sea ice (MYI) is one of the clearest climate-driven changes taking place in the Arctic Ocean. MYI is inherently thicker than seasonal sea ice and has a higher albedo, hence MYI is more robust and resilient to summer melt. Historically, MYI was present throughout much of the Arctic Ocean, with an estimated area of 5.5 x 106 km2 in the 1960s. However, MYI area began to decline in the 1970s and accelerated during the 2000s, eventually falling to a record minimum of 1.6 x 106 km2 in 2017. MYI loss reflects an imbalance in the three factors that dictate the MYI area budget of the Arctic Ocean, 1) export, 2) melt and 3) replenishment. The first two terms collectively represent MYI loss, while the latter term is the sole "source" of MYI and represents the area of seasonal ice that survives through the melt season. When replenishment offsets export and melt the MYI budget is in equilibrium, however the long-term loss of MYI implies that the MYI budget has been in a deficit. Using 36 years (1984 - 2021) of remotely sensed fields of ice age, motion and concentration we calculate the annual values of these three terms and formulate a MYI budget for the Arctic Ocean. Our results show that the MYI budget has been in a deficit through much of the observational record, though there has been a transition to younger MYI types that is the result of a dramatic loss (90%) of the oldest MYI types (5+ years old) and a positive long-term trend in MYI replenishment. The greatest loss of MYI occurred around the 2007 sea ice minimum when melt and export peaked and replenishment was limited. However, since 2007 MYI export through Fram Strait has declined which, coupled with an increase in MYI replenishment, has reduced the rate of MYI loss and led to replenishment wholly offsetting MYI loss during 5 of the last 13 years. This relative stabilization of the MYI budget has supported a recent plateau in the MYI pack that remains in a narrow band along the northern coast of Greenland and the Canadian Arctic Archipelago, or an area now commonly referred to as The Last Ice Area. However, continued loss of the oldest ice types coupled with thinning of the MYI pack may make this plateau only temporary as we continue to witness a persistent transition of the Arctic Ocean towards seasonal sea ice domain.