No abstract

AVHRR imagery has been used to document the sites of 22 polynyas in the Bering and Chukchi seas. Two principal classes of polynyas have been identified that tend to be negatively correlated: 1) persistent polynyas, which are present much of the time and form off southand west-facing coasts, and 2) north coast polynyas, which are only occasionally open and form off north-facing coasts. Median extent values characterizing 17 of these polynyas for six years have been compiled for the winter and spring months, and the results of attempts to correlate these values with synoptic meteorological measurements are reported. These attempts were not very successful, suggesting that more sophisticated approaches to the problem are required. Other factors, such as currents, may play a principal role in determining actual polynya extent.

Multi‐temporal satellite images, field observations and field measurements were used to investigate the mechanisms by which sea ice melts offshore from the Mackenzie River Delta. Satellite data recorded between April and August 1986 were corrected to a map projection and calibrated such that albedo and temperature values could be compared. Three stages in the melting of sea ice were identified: flooding (overflows), insolation and melting by warm river water. The albedo values of overflows were as much as 1/7 that of ice values while the albedo of ice decreased by 1/3 over the summer. Approximately two weeks after the overflows develop, sea surface temperatures rise as the river‐discharge peaks and becomes the dominant source of energy. By this process, ice removal in the delta regime is initiated two months earlier than adjacent coasts with minimal runoff. However, the net result is only a two‐week acceleration of ice removal in the delta region.

It has been observed that arctic coastal regions which receive river discharge show significant ice regression in advance of other coastal areas without this source of sensible heat. This phenomena has been particularly apparent on satellite imagery. The work reported here attempts (1) to quantify and assess the influence of springtime river discharge on the removal of nearshore ice and (2) to demonstrate the utility of satellite imagery as a source of data to “drive” a model assessing the influence of springtime river discharge on the removal of nearshore ice. Central to this work is a sequence of advanced very high resolution radiometer images of the Mackenzie Delta region, Northwest Territories, Canada. These images constitute a database establishing the temporal sequence of observable breakup events from which a thermodynamic model for the ice decay can be parameterized. The emphases of this model are the influence of the riverine sensible heat on the melting of sea ice and the ability of satellite imagery to monitor this process. For simplicity, climatological values rather than meteorological values for atmospheric and solar influences have been used. The results suggest that the river discharge supplies a significant amount of sensible heat to the base of the nearshore ice, accounting for nearly half of the energy required to melt the ice cover. As a result, the coastal ice is removed 7–14 days in advance of areas without significant river discharge.

Weingartner, T. 1994: The influence of river discharge on the thawing of sea ice, Mackenzie River Delta: albedo and temperature analyses. Polar Research 13, 83-94.Multi-temporal satellite images, field observations and field measurements were used to investigate the mechanisms by which sea ice melts offshore from the Mackenzie River Delta. Satellite data recorded between April and August 1986 were corrected to a map projection and calibrated such that albedo and temperature values could be compared. Three stages in the melting of sea ice were identified: flooding (overflows), insolation and melting by warm river water. The albedo values of overflows were as much as 1/7 that of ice values while the albedo of ice decreased by 1/3 over the summer. Approximately two weeks after the overflows develop, sea surface temperatures rise as the river-discharge peaks and becomes the dominant source of energy. By this process, ice removal in the delta regime is initiated two months earlier than adjacent coasts with minimal runoff. However, the net result is only a two-week acceleration of ice removal in the delta region.