Compound drivers of Antarctic sea ice loss and Southern Ocean destratification
A 2013–2023 data-assimilative ocean model identifies three sequential mechanisms behind Antarctic sea ice hitting its post-1970s minimum in 2023—not a single forcing event.
What Matters
- Antarctic sea ice trended slightly positive 1979–2015, then collapsed to record lows by 2023 wintertime and summertime.
- Phase 1 (pre-mid-2015): intensifying westerlies increased equatorward freshwater export, stabilizing the surface and growing ice.
- Phase 2 (2015–2016): same westerlies then upwelled warm, saline Circumpolar Deep Water (CDW) past the pycnocline, triggering ice loss—the two-timescale hypothesis in action.
- Phase 3 (post-2018): reduced sea ice cut freshwater export, sustaining upper-ocean salinification and weak stratification, locking in a low-ice state.
- East Antarctic loss was subsurface-driven via enhanced upward CDW flux; West Antarctic loss also required longwave radiative flux anomalies—mechanistically distinct regions.
- Upper-ocean DO depletion and DIC enrichment in SOSE confirm CDW intrusion into the top 100 m, not just surface warming.
- Anthropogenic forcing sustaining upwelling-favorable westerlies may permanently shift the Southern Ocean into a low sea ice regime.