Ocean circulation within the North Water polynya of Baffin Bay

Abstract

The North Water Polynya is a recurrent polynya at the northern end of Baffin Bay. As part of the International North Water Project, recording current meters were moored within this polynya during 1997–98 to study the physical reasons for its existence. The data demonstrate that the North Water Polynya is dominated by a strong southward flow of cold water and ice from the Arctic Ocean. Although the West Greenland Current directs a modest flow of warmer water towards the polynya from the south‐east, this flow loses much of its heat south of the polynya through re‐circulation into and isopycnal mixing with the Arctic outflow. If an ice jam stops the inflow of ice from the north, the continued drift of ice southward ‘below’ the blockage is sufficient to create a large polynya without oceanic heating. However, upwelling near the Greenland coast can bring relatively warm water to the base of the turbulent surface layer where it is entrained via convection driven by brine growing from ice. The resulting flux of sensible heat supplies about one‐third of the heat loss at the surface and slows ice growth. Because the sensible heat flux is dependent upon freezing, it decreases as ice growth slows in spring and cannot, itself, generate ice‐free waters early in the year.