The Danish Ingolf Expedition took place in the summer months of 1895 and 1896, with C. F. Wandel as captain, a man with long experience in hydrographical work in the Arctic. The other scientific participants were the zoologists H. Jungersen, W. Lundbeck and H. J. Hansen during the 1895 cruise; C. Wesenberg-Lund replaced Hansen during the 1896 cruise. C. H. Ostenfeld was the botanist and M. Knudsen the hydrographer. The Ingolf (see Figure 1) was a naval cruiser. In both years the voyages were hindered by ice that had moved much further south than normal, even closing most of the Denmark Strait. In 1895, the best results were obtained south of Iceland and in the Davis Strait; in 1896 south and east of Iceland and as far north as Jan Mayen Island. A total of 144 stations were completed, all with soundings, trawlings and (for the first time) continuous hydrographical work associated with the deep-sea trawling (bottom measurements of temperature, salinity, chlorine contents and specific gravity). Eighty of the stations were deeper than 1,000 m. There were more than 800 hydrographical measurements, with about 3,300 registrations recordings added on the basis of the measurements. 138 gas analyses were performed on board with samples from the surface and the sea bottom.
The main result of the expedition was the final demonstration of probably the most important threshold boundaries in the world: the Wyville Thompson Ridge from East Greenland to Scotland with maximum depths of 600 m, separating the fauna in the Norwegian and Polar Sea to the north, always with negative below-zero temperatures except close to the Norwegian coast, from the fundamentally different general Atlantic deep-sea fauna to the south of the ridge with positive temperatures.
The results are published in the Ingolf Report, with fifteen volumes containing forty-three papers by nineteen Danish authors and fourteen papers by six foreign authors. The sieving technique was excellent—due to an apparatus designed by H. J. Hansen that kept the animals under water until preservation and using the finest silk for sieving. In this way, the expedition collected more smaller animals than had been acquired by previous deep-sea expeditions. Hansen's studies of the peracarid crustaceans and parasitic copepods and Lundbeck's report on the sponges were particularly noteworthy. The 130 photographs taken on board and on land by the ship's doctor William Thulstrup represent a cultural/historical treasure.
On the conditions which determine the presence or absence of animal life on the deep sea bottom
