Coastal polynyas are areas in an ice-covered ocean where the ice cover is exported, mostly by off-shore winds. The resulting reduction of sea ice enables an enhanced ocean-atmosphere heat transfer. Once the water temperatures are at the freezing point, further heat loss induces sea ice production. The heat exchange and ice production in coastal polynyas in the southwestern Weddell Sea is addressed using the Finite-Element Sea-ice Ocean Model, a primitive-equation, hydrostatic ocean circulation model coupled with a dynamic-thermodynamic sea-ice model, which allows to quantify the amount of heat associated with cooling of the water column. Three important polynya regions are identified: at Brunt Ice Shelf, at Ronne Ice Shelf and along the southern part of the Antarctic Peninsula. Multiyear winter means (May–September 1990–2009) give an upward heat flux to the atmosphere of 311 W/m^2 in the Brunt polynyas, 511 W/m^2 in Ronne Polynya and 364 W/m^2 in the Antarctic Peninsula polynyas, whereof 57 W/m^2, 49 W/m^2 and 48 W/m^2, respectively, are supplied as oceanic heat flux from deeper layers. The mean winter sea ice production is 7.2 cm/d in the Brunt polynyas corresponding to an ice volume of 1.3x10^10 m^3/winter, 13.2 cm/d at Ronne polynya (4.4x10^10 m^3/winter), and 9.2 cm/d in the Antarctic Peninsula polynyas (2.1x10^10 m^3/winter). The heat flux to the atmosphere inside polynyas is 7 to 9 times higher than the heat flux in the adjacent area; polynya ice production per unit area exceeds adjacent values by a factor of 9 to 14.