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Ample geological and geophysical evidence shows that the Norwegian Channel Ice Stream has been one of the major Pleistocene ice streams along the eastern North Atlantic seaboard. The ice stream followed the 800 km long and up to 700 m deep Norwegian Channel in the epicontinental North Sea, and drained a large portion of the southern Fennoscandian ice sheet during ice sheet maxima (King et al. 1996, Sejrup et al. 2003). Arguably its most prominent legacy is the North Sea Fan, a deposit of more than 32 000 km3 of glacigenic debris flows found on the continental slope. The fan stretches 500 km from water depths of 450 m at the shelf break, to its feather edge at 3600 m in the Norwegian Sea. The glacigenic debris flows were sourced directly from the ice stream, most probably by subglacial till deformation. This relation enables us to use the occurrence of debris flow packages as a proxy for ice streaming in the Norwegian Channel. Several distinct debris flow packages have been related to each major glacial stage, suggesting that each glaciation saw separate ice streaming episodes in the Channel.
The uppermost debris flow package deposited during the last part of the Weichselian glaciation is particularly well-resolved on high-resolution seismic data, and combined with radiocarbon chronology it has provided unique insight in the longevity and sediment transport efficacy of the ice stream (Nygrd et al. 2007). These data shows that the ice stream transported approximately 800 km3 of sediment to the shelf break in a thousand years, from ∼20.0 to ∼19.0 cal. ka BP. This gives an annual flux of 8000 m3 pr. metre width of the ice stream front, which is an order of magnitude higher than most previous estimates for other palaeo-ice streams. The total sediment output of 1.1 Gt of sediment per year is comparable to the present yield from the world's largest rivers. Furthermore, the well-constrained and short interval between 20 and 19 ka BP of Norwegian Channel Ice Stream activity provides direct evidence of a rapid on/off switching of the ice stream and thus a highly punctuated ice delivery to the North Atlantic. This opens the possibility that the ice stream was able to switch at centennial to millennial time scales and may thus have participated in rapid and high-amplitude climatic shifts during glacials, such as the prominent Dansgaard-Oeschger cycles recorded in Greenland ice cores.
References:
King, E.L., Sejrup, H.P., Haflidason, H., Elverhøi, A. and Aarseth, I., 1996. Quaternary seismic stratigraphy of the North Sea Fan: Glacially fed gravity flow aprons, hemipelagic sediments, and large submarine slides. Marine Geology, 130: 293-315.
Nygrd, A. et al., 2007. Extreme sediment and ice discharge from marine based ice streams; New evidence from the North Sea. Geology, 35(5): 395-398.
Sejrup, H.P. et al., 2003. Configuration, history and impact of the Norwegian Channel Ice Stream. Boreas, 32(1): 18-36.
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