In the aftermath of the First World War Germany was made to deliver most of its warships to the allies. The gunboat Meteor, lying at a yard in Gdansk (Danzig), was excused under the argument that she was to be turned into a survey vessel. German naval ships were also debarred from calling at foreign ports, a prohibition circumvented by sending the Meteor out on a scientific cruise. This became the famous German Atlantic Expedition 1925-27.
Eighty years ago, in August 1926, German research and survey vessel Meteor (Figure 1) then underway on its two-year expedition, took soundings off the Namibian coast. The ship was equipped with two acoustic sounding machines for shallow water and two for the deep-sea. The first was called â€˜Freilotâ€™ and had an exactly 2m/sec little free-falling weight of torpedo shape with a cartridge at the tip which exploded when it hit the bottom. The time that elapsed between it touching the sea surface and detonation at the bottom gave fairly precise depth information. The second was a â€˜Behmlotâ€™, constructed by the physicist Karl Behm in Kiel, which measured the time it took a sound signal from a detonation just below the surface to be received by a hydrophon at the hull of the ship after reflection from the sea bottom. While the measurements of these two methods were started by hand, the deep-sea soundings were done automatically by an electromagnetic transmitter. The instruments were developed by the â€˜Signalgesellschaftâ€™ in Kiel and the â€˜Atlaswerkeâ€™ in Bremen, in co-operation with the Submarine-Signal-Corporation in Boston. The latter was called the â€˜Fathometerâ€™.
Each sounding was a single measurement, since development of continuous recording was still underway. During the expedition soundings were taken at a total of 33,000 positions: by then the most extensive work ever obtained (Ritchie 1980). During the thirteen east-west-oriented crossings of the tropical and southern Atlantic (Figure 2) all main features of the seafloor were exposed.
But it was not only the seafloor that was scanned at much higher resolution than before; the whole water column was examined. At over three hundred stations, physical, chemical and biological parameters were measured from the surface to the bottom by lowering reversing water-bottles in up to four separate casts (Figure 3). A deep-sea station therefore took many hours, challenging the capability of the watch officer to keep the ship at the same position, in addition to the hydrographic wire vertical and free of the shipâ€™s side (Figure 4).
The 1925-27 expedition covered two thirds of the entire Atlantic, the northern area being successively worked up over the following ten years. It is remarkable that the area west of 60Â°W was omitted, leaving it to the zone of influence of the United States, since the Woods Hole Oceanographic Institution established at Cape Cod in 1930 had begun surveying this part from R/V Atlantis.
The scientific results of the Meteor Expedition were published in over forty volumes, contributing new insights into physical, chemical and biological oceanography, as well into meteorology and geology. The most outstanding results were obtained by the oceanographers. They calculated the vertical density fields along each profile and by comparing them with neighbouring profiles were able to determine three-dimensional circulation. The results have been checked by current measurements at deep-sea anchor stations and laid the basis of our understanding of general turnover in the oceans: what is now known as the â€˜Conveyer Beltâ€™.
The achievements of the Meteor Expedition were certainly due to the abilities of the persons involved: A. Merz, who designed the programme, G. WÃ¼st and H. Wattenberg, who processed the 9,389 single measurements over 24 months onboard, and A. Defant, who invented dynamical approaches. Each had been or later became directors of marine research institutions in Germany. Merz became head of the Institute of Marine Science in Berlin; he died during the early stage of the expedition and was followed by Defant. Wattenberg became director of the Institute of Marine Science in Kiel and was killed in 1944 by a bomb attack on the institute. WÃ¼st. Captain F. Spiess became president of the German Hydrographic Office.
Oceanography the Past, eds. M. Sears & D. Merriman, Springer-Verlag New York, Heidelberg, Berlin 1980 (contributions by G. S. Ritchie: 148-156; W.J. Emery: 690-702).
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