Changes of the Arctic marginal ice zone

Abstract. Many studies have shown a decrease in Arctic sea ice extent. It does not logically follow, however, that the extent of the marginal ice zone (MIZ), here defined as the area of the ocean with ice concentrations from 15 to 80 %, is also changing. Here, we present, for the first time, an analysis of satellite observations of pan-Arctic averaged MIZ extent. We find no trend in the MIZ extent during the last 40 years from observations. We present simulations from a coupled sea ice-ocean mixed layer model using a prognostic floe size distribution which we find is consistent with, but poorly constrained by, existing satellite observations of pan-Arctic MIZ extent. We provide seasonal upper and lower bounds on MIZ extent based on the 4 satellite-derived sea ice concentration datasets used. An extrapolation of the observations shows the MIZ extent as remaining relatively constant in the coming decades, at least until the Arctic is completely covered by seasonal ice. We find a small increase in the summer MIZ fraction (MIZ extent divided by sea ice extent), which can be attributed to the reduction in total sea ice extent. The MIZ location is trending northwards, consistent with other studies. Given the results of this study, we suggest that future studies need to remain cautious and provide a specific and clear definition when stating the MIZ is ‘rapidly changing’.