A Study of Tidal Influences in the North Water Polynya using Short Time Span Satellite Imagery

Abstract

The North Water Polynya (NOW) is an area of ocean between Greenland and Ellesmere Island that does not freeze completely during the winter months. The mechanism that maintains the polynya during the Arctic winter and early spring is not precisely known, but the presence of open water is a critical factor in allowing oceanic heat to escape into the atmosphere. The northerly location of the NOW permitted the collection of an Advanced Very High Resolution Radiometer (AVHRR) image every 101 minutes for seven consecutive orbits. The unique, short time span imagery allowed thermal features of the NOW to be mapped over a tidal cycle. The combination of AVHRR imagery, Acoustic Doppler Current Profiler data, and the Composite Arctic Sea Surface Temperature Algorithm show the dynamic nature of the NOW over a tidal cycle. Both the amount and configuration of open water can change dramatically over a 12-hour period in response to tidal fluctuations. The evidence suggests that the amount of open water in the NOW during March and April is related to the velocity of the current, which in turn is influenced by the tidal cycle. The open water caused by the tide-induced movement of ice then allows oceanic heat to escape into the environment. During March and April, the considerable temperature difference between the ocean and the atmosphere at their interface results in a high incidence of ice fog near leads and open water in the NOW. The amount of ice fog observed on the satellite imagery fluctuates with the tidal cycle, suggesting that open water within the NOW is influenced by the tide in the short term.