Regional deficit rates matched joint Antarctic winter ice deficits in 2016-2025 under a year-shuffle test

We tested joint winter ice deficits in five Antarctic regions with Sea Ice Index Version 4. All five regions were below their 1989-2015 calendar-day reference on 20.33% of June-August days in 2016-2025, against 1.09% before 2016. Independent regional year shuffles predict 20.06% for the recent period. The one-sided test gives p = 0.463. This sign test gives no clear evidence of extra alignment beyond separate deficit rates. It does not prove independence. The mean winter decline was 0.921 million square kilometres. Larger deficits account for 65.8% and smaller positive offsets for 34.2% of this exact sample budget. Checks with a different reference and selected year exclusions give similar results. Ten recent winters, a fixed estimated reference, year exchangeability, broad regions and an instrument change limit inference. The study does not identify a physical cause. The package includes the daily subset, source hash, code, audit and figure.

Antarctic sea ice · joint deficits · regional compensation · conditional permutation · winter · null result