Recirculating pumps are rarely a good idea during the winter months in your pond. Water in your pond will form very distinct temperature layers during the winter, especially if your pond starts to ice over. Mixing these warmer and cooler waters can cause harm to your fish, who are seeking warmth in the bottom parts of the pond. Pumps are also easily damaged by freezing water which expands as it turns into ice. This can permanently ruin a pump, so it's better to remove the pump from the water altogether to avoid this.
To keep your water moving without disrupting the layers of water temperature can be done by using aerators, bubblers, or agitators. These are less likely to be damaged in cooler temperatures, and will still oxygenate the water without subjecting your fish to suddenly cold water.
