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Science Frontiers ONLINE No. 80: Mar-Apr 1992 |
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Dead Water
Two recent issues of Weather discuss some of the unusual geophysical phenomena encountered by F. Nansen in his epic attempt to reach the North Pole at the end of the last century. Nansen first endeavored to go as far north as he could in his specially constructed vessel, the Fram. It was on the Fram that he struggled with "dead water." J.M. Walker, drawing from Nansen's marvelous written account Farthest North, describes the phenomenon:
"Towards the end of August 1893, when Fram was off the Taymyr Peninsula, near the Nordenskiold Archipelago, 'dead water' was encountered. In the words of Nansen, this is 'a peculiar phenomenon', which 'occurs where a surface layer of fresh water rests upon the salt water of the sea, and this fresh water is carried along with the ship, gliding on the heavier sea beneath as if on a fixed foundation'. It 'manifests itself', he observed, 'in the form of larger or smaller ripples or waves stretching across the wake, the one behind the other, arising sometimes as far foward as almost midships'. When caught in dead water, Nansen reported, Fram appeared to be held back, as if by some mysterious force, and she did not always answer the helm. In calm weather, with a light cargo, Fram was capable of 6 to 7 knots. When in dead water she was unable to make 1.5 knots. 'We made loops in our course', Nansen wrote, 'turned sometimes right around, tried all sorts of antics to get clear of it, but to very little purpose.'"
Nansen asked the noted physicist and meteorologist V. Bjerknes to look into the frustrating phenomenon. Bjerknes found that the energy of the ship's propeller was, in essence, being siphoned off to create internal waves along the interface between the light fresh water and dense ocean water underneath rather than propelling the ship forward.
(Walker, J.M.; "Farthest North, Dead Water and the Ekman Spiral," Weather, 46:158, 1991.)
Reference. Dead water and "slippery seas" are cataloged in GHC5 in: Earthquakes, Tides. This book is described here.