,- Centre for Polar Observation and Modelling, Department of Meteorology, University of Reading, Reading, United Kingdom
As the summer Arctic sea ice extent has retreated, the marginal ice zone (MIZ) is becoming a larger fraction of the ice cover. The MIZ is defined as the region of the ice cover that is influenced by waves and for convenience here is defined as the region of the ice cover between sea ice concentrations (SIC) of 15 % to 80 %.
We use model simulations to analyse individual processes of ice volume gain and loss in the ice pack (SIC > 80 %) versus those in the MIZ. We use an atmosphere-forced, physics-rich, sea-ice-mixed layer model based on CICE, that includes a joint prognostic floe size and ice thickness distribution (FSTD) model including brittle fracture and form drag. Our model produces realistic simulations as compared with satellite observations of sea ice extent and PIOMAS (the Pan-Arctic Ice Ocean Modeling and Assimilation System) estimates of thickness.
We compare the ice cover and mass balance processes between the 1980s, 2010s and 2040s. The MIZ fraction of the July sea ice cover, when the MIZ is at its maximum extent, increases by a factor of 2 to 3, from 14 % (20 %) in the 1980s to 46 % (50 %) in the 2010s in NCEP (HadGEM2-ES) atmosphere-forced simulations. In a HadGEM2-ES forced projection, the July sea ice cover is almost entirely MIZ (93 %) in the 2040s.
Basal melting accounts for the largest proportion of melt in regions of pack ice and MIZ for all time periods. During the historical period, top melt is the next largest melt term in pack ice, but in the MIZ, top melt and lateral melt are comparable. This is due to a relative increase of lateral melting and a relative reduction of top melting by a factor of 2 in the MIZ compared to the pack ice. The volume fluxes due to dynamic processes decrease due to the reduction in ice volume in both the MIZ and pack ice.
For areas of sea ice that transition to being MIZ in summer, we find an earlier melt season: in the region that was pack ice in the 1980s and became MIZ in the 2010s, the peak in the total melt volume flux occurs 20(12) d earlier. This continues in the projection where melting in the region that becomes MIZ in the 2040s shifts 14 d earlier compared to the 2010s.
How to cite: Feltham, D., Bateson, A., Frew, R., and Schroeder, D.: Melting, freezing and dynamics of Arctic sea ice: pack ice versus marginal ice zone , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12450, https://doi.org/10.5194/egusphere-egu26-12450, 2026.
