Long-term stability of the North Water Polynya and emerging productivity hotspots driven by sea-ice arch dynamics in Nares Strait

Abstract Nares Strait, at the southern edge of the Last Ice Area, is a key ecological gateway where seasonal sea-ice arches modulate ice export, stratification and light availability, shaping the timing and intensity of phytoplankton blooms. Using two decades (2003–2023) of satellite sea-ice observations combined with depth-resolved estimates of phytoplankton primary production, we identify two recurrent productivity hotspots with contrasting temporal dynamics. Primary production in the North Water Polynya ( Pikialasorsuaq / Sarvarjuaq ) remains remarkably stable over the satellite record, despite pronounced interannual variability in sea-ice conditions. In contrast, a northern hotspot in Kennedy Channel is highly variable and develops only under specific sea-ice arch configurations, with its spatial footprint constrained by underlying local bathymetry. We also observe increasing production in the northern strait, consistent with earlier ice retreat and longer open-water seasons. Together, these results identify sea-ice arches as key physical regulators of ecosystem functioning at the gateway to the Last Ice Area and provide new insights into the stability of the North Water Polynya and its role for regional ecosystems and local communities under ongoing climate-driven environmental changes.