ABSENCE OF DIATOMS 9 



for a reason that is given in the paragraph dealing with the Blue Mud resembling Red Clay. It is not 

 a question of depth, for the ditference is inconsiderable, about 2400-2700 fathoms for the Blue Mud 

 and 2100-2500 fathoms for the Diatom Ooze ; nor can it be accounted for by the surface currents ; in 

 the southern part of the Weddell Sea these are westerly, and in the northern part, about the boundary 

 of the Blue Muds and Diatom Ooze, easterly. One is thrown back on the explanation tentatively put 

 forward by Dr Philippi who found the same condition on the German Antarctic Expedition, viz. a 

 northerly undercurrent which carries off the diatoms northward. Some indication of a strong under- 

 current was got on the 'Scotia' while trawling; although this was south of 70° S lat., it may be a 

 widespread condition, and possibly the study of the temperatures and salinities at different depths 

 will throw further light on this question. 



Again, referring to the diatom ooze found by the ' Scotia ' along the meridian of 

 10° W, Pirie writes: 



The band (of diatom ooze, A.E.) is here much wider (than the band between the Falklands and 

 South Orkneys, A.E.) extending from about 48°-59^ S. The transition from the Blue Mud on the 

 southern edge is probably pretty sharp — in the Blue Mud from 61" 21' S, 13° 2' W (St. 432A, A.E.) 

 there are no diatoms; in the ooze from 56° 58' S, 10° 3' W (St. 438, A.E.) they form 55 per cent of 

 the whole deposit, in 51° 7' S, 9° 31' W (St. 447, A.E.) 2103 fathoms, the percentage rises to 70. 



The theory of the removal of the diatoms by a northerly undercurrent, postulated by 

 Philippi and accepted by Pirie, meets with the approval of Mr G. E. R. Deacon of the 

 Discovery staff, to whom I am indebted for much useful information. He writes as 

 follows : 



The coldest stratum of the bottom water in the whole of the Southern Hemisphere, and in a great 

 part of the Northern Hemisphere, has its origin chiefly in a cold current which sinks from the 

 Continental Shelf in the south-west corner of the Weddell Sea. The distribution of temperature, 

 salinity and oxygen in the bottom waters shows very clearly that the current from this source spreads 

 eastwards round the whole of the Antarctic Continent, sending off northward current branches in 

 the Atlantic, Indian and Pacific Oceans. 



Since the bottom current from the Weddell Sea spreads over such a vast area, it is reasonable to 

 suppose that, in the Weddell Sea itself, it will flow much more rapidly than it does elsewhere, and 

 the freedom of the bottom deposits from diatom ooze and light muds may be due to a greater 

 scouring of the bottom here than in any other region. Bruce speaks somewhere of a trawl being 

 carried off the bottom, although more than the customary length of warp had been paid out. 



There are several entries in the Scotia's Station Log which confirm Mr Deacon's 

 statement of the force of the undercurrent. Gear was lost at several stations : at St. 416 

 it was "doubtful if trawl reached bottom"; at St. 418 "trawl did not touch bottom"; 

 at St. 422, 2660 fathoms in 68° 32' S, 12° 49' W, Bruce remarks " Ross Deep obliterated ; 

 Ross obtained 4000 fathoms, no bottom, in 68° 34' S, 12° 49' W". 



The chief difficuky in accepting this theory of the removal of diatoms by a northward 

 current appears to me to lie in the fact that a current which removed the diatoms should 

 also remove the clay and finer mineral particles, and deposit them to the northward. The 

 diatoms might dissolve during their long journey, but the mineral particles should 

 survive. But such detritus and clay does not form any large proportion of the diatom 

 ooze belt in the north, where the inorganic material is described by Pirie as "mostly 

 volcanic. . .the probability is that these particles have been carried from the South 



