Overview
- A University of Washington–led team reported in Science that extraterrestrial helium‑3 to thorium‑230 ratios in Arctic sediments reveal long-term sea-ice cover.
- The proxy shows year-round central Arctic ice during the last ice age, a major retreat beginning about 15,000 years ago, and mostly seasonal ice in the early Holocene.
- Sea-ice shifts tracked air-temperature changes more closely than ocean heat inflows, challenging assumptions about dominant drivers.
- Variations in ice cover were tightly coupled to stronger surface nutrient consumption by plankton, though the exact mechanisms remain uncertain.
- The extended record provides context for the modern decline of more than 42% since 1979 and for model projections of ice-free Arctic summers in coming decades.