WHERE THE WHALES FEED

Taranaki Daily News, 14 August 1930, Page 18

WHERE THE WHALES FEED

STUDY OF POLAR WATERS VARIATIONS IN TEMPERATURE. / MAWSON EXPEDITION’S RESEARCH (By A. Howard, Hydrologist to the B.AN.Z. Antarctic Research Expedition.) (All rights- reserved.) The physico-chemical nature of the water both in the surface layer and throughout: its depth has been studied in detail throughout the recent cruise of the B.A.N.Z. Antarctic Research Expedition. The temperature . and salt content, or salinity, as it is termed, are the two properties which are ot the Greatest importance. When water moses in horizontal streams there is lithe mingling between adjacent layers, with the result that the salinity remains practically unchanged and is thus an indication of its origin. . The temperature is subject to much Greater variation but nevertheless giveo a very valuable guide to the source of the current. Thus in the sectors of.the Antarctic seas covered during the cruise it was found' that when a series of water samples was taken at various depths from the surface to the bottom the temperature first diminished slightly and then suddenly increased when the depth reached ' 2OO to 300 metres, and finally slowly decreased. again, reaching a temperature a little below 0 degrees C at the bottom.’ This type of temperature distribution has been reported from various parts of the Antarctic and indicates an inflow of warm water from the north and an outflow of cold polar water in the surface Jayeis and along the bottom. The cold surface layer flows northwards to. about’latitude 45 degrees S, where it meets ’and mingles with warm intermediate layers found further : south. . The presence of a south-flu wiug^w arli; stream in the region of latitude. o 5 degrees 8 was further demonstrated when on the return voyage from Kerguelen to Australia a sudden decrease of surface temperature was. noticed as soon as we reached the lee-formed by the south-west coast of Australia. In modern, oceanography it is possible to calculate quantitatively the circulatory movement. By mathematical. analysis of the vertical distribution of temperature and salinity at neighbour ing positions oil the lines developed by V.° Bjerknes, Sandstrom and others the velocity and direction of the- cul l cuts can be obtained not only at the surface but in the deep water? At* present the application of these methods to the results obtained during our cruise in the pack-ice zone has not been completed, but the preliminary results show that tie. conditions in the region, covered are similar tS those obtained by the Gauss Expedition in neighbouring regions off Gaussberg. This work requires a large amount of valuable, specially constructed apparatus. The designing of instruments which will take a sample and measure the temperature’ when several miles below the surface and subjected to a pressure of several tons -per square . inch is a problem which has been solved only after years of experimenting. ‘ For working in shallow water to a depth of metres the water-b,ottle designed by Nansen and Petterssen is used. This instrument consists essentially, of an accurate thermometer in a well-insulat-ed metal chamber, which is closed by water-tight ends’ when a messenger is sent down the wire on which it is suspended. With this Nansen-Petterssen water-bottle a sample of the sea-water is brought to the surface of the temperature of the water obtained with an accuracy, of 1/100 .degrees C. , . With this simple and- efficient ins trument it would be possible to tell the temperature at any depth' were’it not for the fact that when a sample of water is brought up from a. great depth, it expands owing to the ' diminishing pressure, and the .temperature, in consequence, falls. To overcome this the reversing water bottle was devised. This type of bottle is so designed that when a messenger is sent down the wire the apparatus is caused to turn upside down. In doing so the waterbottle closes, and traps a sample of .the water’and at the same time breaks pff the mercury thread at a.constriction in the, thermometer, so that any change of temperature as the sample is drawn to the surface does not affect the reading. The thermometers used for this, deep sea work have to be .made except tionally strong and of special design, to withstand the great pressure, which would crush an' ordinary thermometer to powder. The determination of the water move-, ments in the depths of the ocean is not merely of academic interest,- but has an important economic value. The migrations of fish are affected by the distribution of .the minute marine' animals, classed under the general term plankton, on which they feed, and which arc borne along on the,. ocean currents.* Moreover,, the plankton feed on com-.. pounds of nitrogen, phosphorous and silicon dissolved in the , water and circulating with it. Hence the determination of the sub-surface currents give's us an indication of the possible posi-. tions and. movements of .the feeding grounds of the larger fish. With' this end in view the determination of temperature and salinity are -supplemented by a micro-analysis of the water for phosphorous, silicon and nitrogen. These are present in water • as the result of tne decomposition of-dead organic'matter. Phosphorous ’ and silicon are given off directly as . phosphate and silicate, and as such are immediately available for reassimilation. But in the case of nitrogen a series of stages is undergone, the protein matter giving first aminoacids and then ammonia, which is then oxidised first to nitrites and then to nitrates. The greater part of the nitrogen consumed by the plankton is assimilated in the form of nitrate but under certain conditions it is possible that the intermediate compounds may become a source of food. ■ - ’ The results obtained show that in the t region between Queen- Mary Land and . Enderby Land the Antarctic Ocean from the continent to approximately latitude .45 degrees S is characterised by a high surface content of these nutrient salts. This abundance is due to the fact that when the plankton in the waters of lower latitudes die they slowly sink and decompose, reforming the salts which •they originally consumed. Thus a high content of nutrient salt is t formed in the depths, and when this water flows south and reaches the continental -shelf vigorous mixing takes place and a uniform distribution is set up. This mixed, water then flows north and then dips

below the surface, aud the surface plankton content falls off. In accordance with this theory the phosphate and nitrate are . present m uniform, concentration from surface tQ bottom, but this does not hold for nitrite and silicate. With silicate tin surface content is higher than for lower decreases, presumably because the silicious skeletons are sufficiently heavy to. sink in spite of the vertical movement" of the water, and so on resolution a

high silicate content is formed in the depths. But. the case of the nitrites is quite different. In the surface layers there is a high nitrite content, but when the depth reaches about 80 metres the nitrite suddenly disappears completely. A possible explanation of this is that an active transformation of ammonium salts to nitrites and then to nitrates may be taking place under the influence of an external stimulus such as the action of sunlight. As yet little is known concerning the fluctuations which occur in physical and

chemical properties of the water at any fixed position in the Antarctic, and it is to be hoped that in future it will be possible to attack this question more thoroughly, for the information obtained would be of the utmost value to the whaling industry by making it possible to attempt the prediction of the movement of the feeding areas and the sizeof the season’s catch in the same way as similar information ‘is now uti Used ' for - estimating’ the mackerel catch in the;Bal tie.' - '■