Archive image from page 117 of Discovery reports (1934) Discovery reports discoveryreports09inst Year: 1934 io6 DISCOVERY REPORTS travels south-eastwards across the line of the isotherms he will meet with important changes, especially while crossing a belt running approximately from the South Shetland Islands to South Georgia. This zone of rapid qualitative change will be mentioned again in a later section. The point to be emphasized at the moment is that the chart indicates a connection between the distribution of species and the surface temperature of the water within the Antarctic Zone. T
Archive image from page 117 of Discovery reports (1934) Discovery reports discoveryreports09inst Year: 1934 io6 DISCOVERY REPORTS travels south-eastwards across the line of the isotherms he will meet with important changes, especially while crossing a belt running approximately from the South Shetland Islands to South Georgia. This zone of rapid qualitative change will be mentioned again in a later section. The point to be emphasized at the moment is that the chart indicates a connection between the distribution of species and the surface temperature of the water within the Antarctic Zone. This temperature ranges from nearly - 2° C. to about + 50 C, and a quantitative comparison of the different species in respect of their Fig. 22. Approximate positions of the mean summer isotherms. occurrence in water of different temperatures will provide a clearer distinction between the warm- and cold-water species than is given in the notes on general distribution. It must be supposed that plankton organisms which have an optimum temperature cannot make active movements to avoid changes in temperature caused by the seasons, the weather, the approach and departure of ice, etc. We should therefore expect more reliable results from the mean temperature of the locality than from the actual tempera- ture of the water in which a species is taken. It would be desirable if possible to compare the distribution of a species with the temperature of the water at the mean depth at which it lives. But at a great many of the stations at which the N ioo B was used the
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