Our study examined how sea ice in the Beaufort Sea has changed over the past 13 000 years to better understand today's rapid losses. By analyzing chemical tracers preserved in seafloor sediments, we found that the Early Holocene was largely ice-free, with warmer waters and lower salinity. Seasonal ice began forming about 7000 years ago and expanded as the climate cooled. These long-term patterns show that continued warming could return the region to mostly ice-free conditions.