The influence of river discharge on the thawing of sea ice, Mackenzie River Delta: albedo and temperature analyses

Abstract

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.

Is there a “new normal” climate in the Beaufort Sea?

“…Given that freely moving sea ice amplifies the effect of wind stress on the underlying water layer (Pite et al 1995), it is certain that river water was carried along under the ice. Buoy data indicate that the ice pack was moving westward at a mean rate of 15.1 cm s 55 km 3 of fresh water impounded under coastal fast ice (Macdonald & Carmack 1991;Dean et al 1994;Dunton et al 2006), half of the total summer discharge (129 km 3 of 246 km 3 in 2011) had already entered the Beaufort Sea by mid-July. Although sea-ice melt obviously contributes fresh water to the surface layer, there was enough Mackenzie River water discharged under the ice cover of the Beaufort Sea early in the season to create a plume of the dimensions described here of an average thickness of 6Á8 m and salinity of 20 psu.…”

The Changing Climate of the Arctic

“…The regions of fast ice, already subject to changes in spring river discharge that modify the melting rate of offshore ice, are also being affected by the changes in atmospheric and oceanic forcing throughout the Northern Hemisphere (Dean et al, 1994;O'Brien et al, 2006). In general, there is a tendency for earlier onset of melt and the later onset of freeze-up of fast-ice areas (Johannessen et al, 2004).…”

“…Landfast ice begins to decay in the Amundsen Gulf in mid June and disappears along the Tuktoyaktuk Peninsula in early July. However, the decay of landfast ice is also influenced by the Mackenzie River discharge: the thawing rivers flood surrounding sea ice and deposit sediments, which increase albedo and transport heat from the terrestrial to the marine environment (Dean et al, 1994;O'Brien et al, 2006).…”

Phytoplankton productivity on the Canadian Shelf of the Beaufort Sea

“…The transition to summer begins in late April and early May with the break-up of river ice in the headwaters of the Mackenzie River and the subsequent flooding of the delta and coastal area. According to Dean et al (1994), heat from the Mackenzie River, which overflows and underflows the landfast ice in the nearshore, accelerates ice removal in the nearshore delta region. Break-up of the middle and outer shelf typically spreads from existing open water in the flaw polynya, where incoming solar radiation is more rapidly absorbed by the water.…”