Changes in sea ice properties in the transition region from pack ice zone to marginal ice zone in the Arctic Ocean

The transition from pack ice zone (PIZ) to marginal ice zone (MIZ) is a critical driver of Arctic climate change, significantly intensifying heat exchange within the atmosphere–sea ice–ocean system. This exchange is closely coupled with variations in the physical state and dynamics of sea ice. However, the evolution of sea ice properties during this transition remains insufficiently quantified. To address this problem, this study compares variations in key sea ice characteristics across three regions: perennial PIZ, PIZ transitioning to MIZ, and MIZ transitioning to open water. Results indicate that the transition from PIZ to MIZ coincides with accelerated ice loss, with the most pronounced declines in concentration (–1.3%·a^–1) and thickness (–0.04 m·a^–1) in September, and in area (–4.2×10⁴ km²·a^–1) in October. This transition is accompanied by a dramatic loss of multi-year ice, peaking at –1.8%·a^–1 in August. Furthermore, this transition corresponds to higher ice drift speeds and enhanced responses of sea ice motion to wind forcing, particularly in October (0.12 km·d^–1·a^–1 and 0.02 a^–1) when the transition extent reaches its maximum. An earlier melt onset on ice surface occurs in some parts of the transition region from PIZ to MIZ in May (–0.4 d·a^–1, P<0.05), and a delayed continuous freeze onset is observed in this transition region in October (1.0 d·a^–1, P<0.05). This transition region exhibits amplified sea ice changes relative to the pan-Arctic Ocean.