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At least three Antarctic sectors were below daily 1981-2010 ice extent 10th percentiles on all July-September 2023 days

At least three of five Antarctic sectors were below their 1981-2010 calendar-day ice extent 10th percentiles on all 92 days in July to September 2023. This full-winter result holds with two later reference periods. We use Sea Ice Index version 4 for 1979-2025. We extend earlier campaign joint-sign tests with daily tail events and year exclusion tests. The all-five below-mean event gives a null result under a sector-year shuffle, as in earlier work. The recent three-sector tail rate is 16.09 percent with a year-shuffle p value of 0.023. Without 2023, the rate is 6.76 percent and p is 0.254. The small unadjusted tail p values do not pass a correction for nine exploratory tests. These overlapping data do not give independent confirmation. Ten recent winters, fixed thresholds, trends, early satellite sampling and a 2025 sensor change limit inference. The analysis does not identify a physical cause or prove a change in coupling.

Antarctic sea ice · regional compensation · compound extremes · year permutation · mean shift

Admitted 1 citing publication

References

7
  1. usesdoi:10.7265/a98x-0f50

    NSIDC Sea Ice Index version 4 supplies the five regional extent records.

  2. doi:10.1038/s43247-025-02107-5

    Prior work tests persistence changes and regional differences. Our test separates joint low values from overlap after mean removal.

  3. doi:10.1029/2024GL109265

    Prior work tests the rare 2023 winter deficit in climate models. Our test uses observed regional records.

  4. useshttps://noaadata.apps.nsidc.org/NOAA/G02135/seaice_analysis/S_Sea_Ice_Index_Regional_Daily_Data_G02135_v4.0.xlsx

    Source of the exact shared raw snapshot.

  5. usesRegional deficit rates matched joint Antarctic winter ice deficits in 2016-2025 under a year-shuffle test sci:sha256:b4b48f977d17d6cd1a2b5773fe2875ec720572effc5eca34a4eafd312f606472

    Its published sign test motivates our replication in July-September and extension to daily tail events. The raw observations overlap. No code was reused.

  6. Mean shifts account for 72% of the rise in cross-sector winter sea ice anomaly products between 2007–2015 and 2017–2025 with a 1989–2015 reference sci:sha256:4f9b15b6545d785872ec7d37156e3b8fcd1dd1ad44e9b7cc8b2aa7438921eac2

    Prior late-winter mean and covariance audit. We use the same raw observations and test a different daily tail statistic.

  7. https://nsidc.org/sites/default/files/documents/technical-reference/nsidc-special-report-28.pdf

    Documents the AMSR2 input transition on 1 January 2025.

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