*54 



HYDROGRAPHY. 



From this will be seen that the boundary surface, at the stations 47, 48, 49, and 65, is lying at 

 a greater depth than 400 fathoms (753 M.), at the stations 67, 68, 78, and 80, at a less depth than 

 600 fathoms (1130 M.). It has been mentioned before that the temperature-curves for these stations 

 south of Iceland, continue their course nearly horizontally, until they attain a certain depth, and the 

 farther the stations are situated to the eastward, the greater this depth will be. It is therefore likely to be 

 supposed that the boundary surface is to be found at the depth where the temperature begins to decrease 

 rapidly, so that the whole of the large stratum of water with an approximately constant temperature, 

 has got this constant temperature on account of the vertical circulation that takes place during the 

 winter time. If the whole of the layer really be formed in this manner, we find at the same time a 

 natural explanation of its great thickness to the westward by the fact of water constantly mak- 

 ing its way from west to east in the surface-layer. To account for it by the supposition of 

 the cold during the winter time having the effect of cooling larger bodies of water at the eastern 

 than at the western stations is an impossibility. 



Station 78 has at the bottom a temperature of absorption of 6°7; at 600 fathoms (1130 M.) it 

 is 4°6. At this station the salinity is also higher at the bottom than in the said depth, and it appears 

 that the values for salinity, and the temperature of absorption at the bottom, are exactly the same 

 as at a small depth — less than 400 fathoms (753 M.). From this the inference might be drawn, that 

 part of the surface-layer with the constant temperature had made its way down to the bottom through 

 the colder stratum of water. According to my opinion, it is more likely to be supposed that the 

 water bottle has fetched up water from a smaller depth and not from the bottom. 



THE AMOUNT OF OXYGEN ABSORBED IN SEA-WATER. 



In the table of the gas-analyses, the quantity of oxygen is noted with the designations stated 

 on p. 85. The values used for the quantity N . 1 when the water is saturated with atmospheric air, 

 has been taken from Dittmar's determinations, but it is only the values for the positive temperatures 

 that can be found in Dittmar's table, so I was obliged to deduce the values for the negative ones by 

 extrapolation. The values computed for °° 2 through the observations made by me, are noted under 

 f in the next column. Under f—e is found the difference between the last and the first-named 

 quantity. According to this,^/-— e may, as it were, be regarded as an expression for the 

 supersaturation of the water with oxygen. That f— c is positive, signifies therefore 

 that there has been a generation of oxygen in the water after the absorption took 

 place, while just the reverse is the case when/— « is negative, namely that there has 

 been a consumption of oxygen. 



It will be seen that there has been a constant consumption of oxygen in the depth, 

 while, on the other hand, it has been observed frequently that there was a supersaturation with oxygen 

 in and near the surface. This state of matters was already observed during the Challenger-Expedition 

 and the Norwegian North Atlantic-Expedition. Thus Dittmar writes (1. c, page 188): «What puzzled 

 me very much at first, was the not unfrequent occurrence in our table of negative oxygen deficits. 



