NOAA satellite images (November through June 1984 to 1989) show sea ice arches accompanied by unique polynya patterns immediately north of the Nares Strait. Typically the arches formed by late November, but the polynya patterns did not stabilize until January, the month when sea ice transport through the Strait usually ceases. The polynyas created to the lee of the arches appear to be of an unusual ''hybrid'' mix, switching from a combined latent and sensible heat type in fall to a ''pure'' sensible heat type in winter. Early in the polynya formation, sea ice is removed through the temporarily open Nares Strait, while the ice arch to the north blocks ice from drifting into the polynya. Once the Strait freezes solid, newly formed ice cannot be transported downstream. The polynya then begins to freeze but ice growth is still moderated apparently due to upward vertical mixing of warmer, more saline water generated by tidal currents flowing over the shallow seabed northwest of Robeson Channel.