But the probability is that the curves are due to the formation of eddies in the currents.  In an eddy the light and warm water will be depressed to greater depths if the eddy goes contrary to the hands of a clock and is situated in the southern hemisphere.  We appear to have such an eddy around Station 19, for example.  Around Station 2 an eddy appears to be going the other way; that is, the same way as the hands of a clock.  On the chart of currents we have indicated some of these eddies from the observations of the distribution of salinity and temperature made by the Fram Expedition.

While this, then, is the probable explanation of the irregularities shown by the lines of the sections, it is not impossible that they may be due to other conditions, such as, for instance, the submarine waves alluded to above.  Another possibility is that they may be a consequence of variations in the rapidity of the current, produced, for instance, by wind.  The periodical variations caused by the tides will hardly be an adequate explanation of what happens here, although during Murray and Hjort’s Atlantic Expedition in the Michael Sars (in 1910), and recently during Nansen’s voyage to the Arctic Ocean in the Veslemoy (in 1912), the existence of tidal currents in the open ocean was proved.  It may be hoped that the further examination of the Fram material will make these matters clearer.  But however this may be, it is interesting to establish the fact that in so great and deep an ocean as the South Atlantic very considerable variations of this kind may occur between points which lie near together and in the same current.

As we have already mentioned in passing, the observations show that the same temperatures and salinities as are found at the surface are continued downward almost unchanged to a depth of between 75 and 150 metres; on an average it is about 100 metres.  This is a typical winter condition, and is due to the vertical circulation already mentioned, which is caused by the surface water being cooled in winter, thus becoming heavier than the water below, so that it must sink and give place to lighter water which rises.  In this way the upper zones of water become mixed, and acquire almost equal temperatures and salinities.  It thus appears that the vertical currents reached a depth of about 100 metres in July, 1911, in the central part of the South Atlantic.  This cooling of the water is a gain to the air, and what happens is that not only the surface gives off warmth to the air, but also the sub-surface waters, to as great a depth as is reached by the vertical circulation.  This makes it a question of enormous values.

This state of things is clearly apparent in the sections, where the isotherms and isohalins run vertically for some way below the surface.  It is also clearly seen when we draw the curves of distribution of salinity and temperature at the different stations, as we have done in the two diagrams for Stations 32 and 60 (Fig. 9).  The temperatures had fallen several degrees at the surface at the time the Fram’s investigations were made.  And if we are to judge from the general appearance of the station curves, and from the form they usually assume in summer in these regions, we shall arrive at the conclusion that the whole volume of water from the surface down to a depth of 100 metres must be cooled on an average about 2deg.  C.