HYDROGRAPHY. jcr 



It is difficult to see, how sea water can contain more oxygen per litre than is demanded by the 

 law of gas-absorption. I tried to account for the apparent anomaly in a variety of ways, and at last 

 was led to suspect that it may be the result of observational errors. » Tomoe writes (The Norwegian 

 North-Atlantic-Expedition 1876 — 78 Chemistry pag. 19): «Now, assuming the results of these experiments 

 to furnish a normal standard, the relative large proportion of oxygen as compared with the total 

 amount of air present in the surface-water of the northern tracts of the sea investigated, will be found 

 to arise from supersaturation with oxygen, and not, as might be supposed, from imperfect saturation 

 with nitrogen, seeing that the proportion of oxygen exceeded that computed from these experiments 

 by as much as, or even more than, 0-5 cc; for a difference so considerable does not admit of being 

 ascribed to errors of observation. On the basis of these facts, the proportion of oxygen in surface- 

 water is shown to depend not only on pressure and temperature, but, probably, also on the effect of 

 one or more causes as yet unknown.* 



Seeing that my analyses of the surface-water gave similar inexplicable results as those pointed 

 out by Tor tide, that is to say, supersaturation with oxygen, and as there was good reason to suppose 

 that the variation of the percentage of oxygen was due to the plankton contained in the water, I 

 asked Mr. Ostcnfeld, M. A., and botanist of the expedition, to undertake researches of plankton at the 

 same places where I made the gas-analyses. In compliance with this request, Mr. Ostcnfeld made 

 this kind of preliminary investigations on board, and the list of «the species and quantity of the 

 plankton* which is inserted in the table of the gas-analyses, I had the pleasure of receiving from 

 Mr. Ostenfeld. At many places the quantity of the plankton was determined by measuring the volume 

 of the same to as great an exactness as possible, but in consequence of a final investigation of the 

 plankton not having been carried out as yet, no attempt will be made here to set up any universal 

 theory regarding the relation of the different organisms to the oxygen dissolved in the water. 



It appears from the table that a specially marked vegetable plankton has 

 caused a supersaturation with oxygen, and to such an extent that where the quantity of 

 vegetable plankton has been specially great, we shall always be pretty sure of meeting with a corre- 

 sponding great supersaturation with oxygen, which is manifesting itself here by a great positive value 

 for/-— r. Reference is made to the stations 46, 71, 80, 98, 120. 



We cannot, on the other hand, because there has been a great supersaturation, expect to find 

 a great quantity of vegetable plankton. That nothing has been noted under station 48 regarding the 

 quantity of plankton, is probably a sign of its not having been extraordinarily great Under station 100 

 is certainly noted for a supersaturation f—e = ri that the plankton has been of an entirely vegetable 

 nature, but the quantity has been almost inappreciable. Under station 125 withy* 1 — e = 1-4 is noted 

 that the plankton was of an entirely animal nature, and only of a very small quantity; the same 

 applies to station 133, where/ 1 — e is equal to r8. 



That a great quantity of vegetable Plankton has the effect of producing a supersaturation with 

 oxygen, is of course not to be wondered at, as the plants that contain chlorophyll or kindred pigments 

 may assimilate carbonic acid when exposed to the light, and in consequence of this disengage the 

 oxygen causing the supersaturation. As will be seen afterwards and proved by experiments, the 

 respiratory process of the plants is in this case a matter of quite a subordinate importance. 



