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. Changes in the MIZ
extent has implications for the level of atmospheric and ocean heat and gas
exchange in the area of partially ice-covered ocean and for the
extent of habitat for organisms that rely on the MIZ, from primary producers
like sea ice algae to seals and birds. 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 over the last 40 years from observations.
Our results indicate that the constancy of the MIZ extent is the result of
an observed increase in width of the MIZ being compensated for by a decrease in
the perimeter of the MIZ as it moves further north. 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 four
satellite-derived sea ice concentration datasets used. We find a large and
significant increase (>50 %) in the August and September MIZ
fraction (MIZ extent divided by sea ice extent) for the Bootstrap and
OSI-450 observational datasets, which can be attributed to the reduction in
total sea ice extent. Given the results of this study, we suggest that
references to “rapid changes” in the MIZ should remain cautious and provide
a specific and clear definition of both the MIZ itself and also the property
of the MIZ that is changing.
A Thermodynamic Model of the Formation, Growth, and Decay of First-Year Sea Ice