Thoughts On the Study of Shore Lead Convection
James Morison
Polar Science Center, Applied Physics Laboratory
University of Washington
Seattle, Washington, U.S.A.
Abstract
Common features of the coastal regions of frozen seas are openings in the ice near shore. Because these regions are held open for extended periods, they can produce a great deal of new ice and saline convection. They ventilate the shelf waters and can drive shelf basin exchange. Data from the 1974 AIDJEX Lead Experiment show evidence of penetrative convection under a nearly stationary lead. They also reveal the presence of a saline bottom boundary layer believed to be due to convection from large shore lead. New methods of observing shelf convection with autonomous vehicles and other instruments offer the opportunity to study and parameterize the effect of nearshore convection sources.
1. Observations of Convection from a Nearshore Lead
An important feature of polar seas in winter is the widespread presence of openings in the ice near the shore. These may be a shore leads parallel to the coast formed at the separation of shorefast ice and moving pack ice. They may be coastal polynyas held open by wind driven advection of new ice away from the coast. Because these regions are held open for extended periods, they can produce a great deal of new ice and sailne convection. Such convection certainly produces vertical fluxes of mass, salt and heat and therefore is important in ventilating shelf waters. The density increase which results may create dense waters which flow across the shelf to deeper water, thereby causing exchange with the deep ocean.
Figure 1 shows data gathered in 1974 during the AIDJEX Lead EXperiment (ALEX). It illustrates what may occur under nearly stationary leads in shallow water. ALEX was conducted as part of the Arctic Ice Dynamics Joint Experiment (AIDJEX) and involved near-surface atmospheric and oceanographic measurements at sites off Barrow,
