On the Development and Cause of the Weddell Polynya in a Sea Ice Simulation

Occurrence of the Weddell polynya, a large open-water area in the midst of the wintertime pack ice of the southern ocean, is examined through a sequence of numerical simulations of the sea ice cover. Using mean climatological input data, the numerical model realistically simulates the emergence of the polynya through the encircling of an open water region by ice. In addition, with only the wind fields altered, the model successfully simulates winter seasons totally lacking a Weddell polynya. Since the vertical ocean heat flux inserted into the model is spatially-invariant, these results call into question—without actually refuting—those explanations of the polynya based exclusively on oceanographic factors. On the other hand, the failure of the modeled polynya to survive the winter season without significant weakening, as the observed polynya did in each of the years 1974–76, suggests that the oceanography and/or the ocean/atmosphere feedbacks are essential to the polynya maintenance, even if not to the polynya formation.