Seasonal sea ice characterized the glacial Arctic-Atlantic gateway over the past 750,000 years

The past occurrence of an extreme ~1-kilometer–thick Arctic Ocean–Nordic Seas ice shelf has been inferred from submarine landscape features and geochemical records, although fundamental aspects of its characteristics, impacts, and timing remain highly debated. Here, we challenge this pan-Arctic glaciation hypothesis by investigating two sites from the Arctic-Atlantic gateway (AAG) and the Nordic Seas. Suborbital to millennial-scale surface water bioproductivity changes provide no evidence for a continuous ice shelf in the AAG and the Nordic Seas over the past ~750,000 years. Instead, proxy data and model simulations reveal the persistent presence of seasonal sea ice cover and open water phytoplankton blooms during both glacial and interglacial times. If the AAG and Nordic Seas were ever covered by an ice shelf during these times, then it must have been a partial, or at best, a very short-lived glacial phenomenon.