Polynyas are common occurrences all around the Arctic and Antarctic. Coastal polynyas are generally highly productive, which can lead to substantial CO2 drawdown. Consequently, they are important sink regions for atmospheric CO2. Depending on the surface area, the timing, duration and other factors, large differences exist as to the importance of polynyas in a biogeochemical sense. In the Arctic, the North Water Polynya seems to be the most important one, while in the Antarctic the most important is the Ross Sea Polynya. Polynyas in the Arctic have been better investigated and therefore the important polynyas are described with some confidence as to accuracy and completeness. For the Antarctic, this only holds for the Ross Sea Polynya. For many other Antarctic polynyas, only incomplete information is available. This is true even for the large, well known Weddell Polynya of the 1970s, which represents one of the few open-ocean polynyas. Here its biogeochemical role is semi-quantitatively assessed by combining the physical data from the 1970s with the known distributions of biogeochemical properties from recent years. It is deduced that the Weddell Polynya was a significant one-time sink for anthropogenic CO2 and CFCs, with ensuing deep-sea sequestration. Notably, some coastal polynyas are instrumental in transferring anthropogenic CO2 from the ice-free shelves to the abyssal oceans.