Temporal and Regional Variation of Sea Ice Draft And Coverage in the Weddell Sea Obtained from Upward Looking Sonars

Abstract

Abstract: Up to two years long time series of ice draft and coverage were obtained between 1990 and 1994with moored Upward Looking Sonars (ULSs) at six locations in the Weddell Sea. The six mooring locations,between the tip of the Antarctic Peninsula and Kapp Norvegia, cover the flow into and out of the southernWeddell Sea. The measurements are analyzed for the temporal and regional variations, and used to estimatethe relative contribution of thermodynamic growth and deformation to the ice draft distribution in the WeddellSea.Whereas the ice draft in the gyre centre undergoes a distinct annual cycle, temporal changes occur ratherirregularly in the boundary regions, especially in the east. The mean ice draft varies between 0.8 m in the centralWeddell Gyre, 2.2 m in the eastern inflow and 2.8 m in the western outflow. In opposition to this, the mode of theice draft is highest (0.7 m) in the gyre centre and lowest (0.2 m) in the boundary regions. In the western outflow asecond maximum at 1.1 m results from advection of deformed ice. During circulation with the Weddell Gyremainly ice with a draft of less than 1 m is transformed into thicker ice; the major transformation occurs from draftsof 0.2 m to drafts of 1.2 m. It is concluded that deformation (rafting and ridging) contributes a minimum of 30 % tothe total amount of ice formed in the inner Weddell Sea and a minimum of 50 % in the boundary regions.