Sea-ice arches structure Arctic primary production hotspots at the Last Ice Area gateway

Nares Strait, located at the southern edge of the Last Ice Area, is a significant ecological zone where seasonal sea-ice arches influence regional ice dynamics, air–sea exchange and ecosystem productivity. By modulating ice export, stratification, and light penetration, these arches determine the timing, location, and intensity of phytoplankton blooms. Based on two decades (2003–2023) of satellite sea-ice observations and depth-resolved primary production estimates, we found a pronounced increase in production, particularly in northern regions where earlier ice retreat and longer open-water seasons promoted phytoplankton growth. Two recurrent productivity hotspots were identified. The first is a variable northern hotspot in Kennedy Channel, which only emerged under specific ice-arch configurations and bathymetric conditions, highlighting the structural role of arches in regulating bloom dynamics. In contrast, the second hotspot, located in the North Water Polynya ( Pikialasorsuaq ), sustained consistently high production across all sea ice conditions. This stability, in contrast to previously reported declines, highlights the North Water Polynya as an ecologically and culturally significant marine area. Our findings identify sea-ice arches as ecosystem constitutive features within the Last Ice Area and emphasize the critical role of the North Water Polynya for biodiversity conservation and subsistence of Indigenous under continued Arctic warming.