2o8 DISCOVERY REPORTS 



the deeper layers remained high, a fresh south-easterly breeze having followed on a 

 period of northerly and variable winds. Throughout the ensuing week northerly winds 

 were experienced and at the next station the salinity was greatly increased in spite of a 

 slight easterly breeze on the day of the station itself. This station was worked in the 

 morning, and it would seem that there had not been sufficient time for the easterly wind 

 to affect the existing northerly conditions. 



Forty-eight hours of heavy rain, with light variable winds and a very heavy northerly 

 swell, preceded and accompanied St. MS 102, and the salinity was found to be reduced 

 at all depths. South-easterly weather maintained this condition until March 12 (St. 

 MS 104) with a very slight rise in the lower layers. 



At the last two stations the mean salinity value for the upper layers rose, for in spite 

 of heavy rain, snow and ice causing low surface values, that of the lower layers was 

 considerably increased. Strong northerly winds prevailed at the time, and it is to them 

 that this rise in salinity was doubtless due. 



Summing up then, it seems to be generally true that with a pronounced northerly 

 wind the salinity of the upper layers in the middle of East Cumberland Bay is raised, 

 while with southerly and easterly winds it is lowered. The changes when the winds are 

 light are slower, and conditions at stations taken at such a time may be modified by the 

 winds prevailing during the preceding days, by heavy precipitation, and by the presence 

 of glacier ice (cf. surface values of St. MS 105). During the first half of the season 

 studied, the quality and quantity of the phytoplankton showed a close relation to the 

 water movements so set up. Later it became uniformly scanty as other adverse factors 

 came into play. 



PRECIPITATION 



The effect of precipitation in lowering salinity, mainly by increased land drainage, 

 has already been described in considering the effect of wind. Unless the wind be light, 

 the effect of increased precipitation is not at once apparent out at the station position. 



The most important elTect of heavy precipitation is to cut down the light available 

 for phytoplankton growth by increasing the amount of fine inorganic particles carried 

 into the bay by land drainage. From Fig. 81 it will be seen that the general level of 

 precipitation was higher during the second half of the season than the first. It is to the 

 increased opacity of the water, due both to precipitation and to thawing from the glaciers 

 and snow-slopes, that the abrupt decline in diatom catches from January 22 onwards is 

 ascribed. It is interesting to note that the five richest diatom hauls of the season were 

 obtained at stations following the only weeks in which the precipitation was below 

 10 mm., as is well shown by Table II. 



In time heavy precipitation leads naturally to dilution at the surface, and to the forma- 

 tion of a discontinuity layer at a depth varying with the extent of the dilution and 

 limited by the mixing efTect of the wind. Should the wind be light or offshore therefore, 

 a layer of turbid water of low salinity will tend to form in the upper 10 m. or so, 

 effectively cutting off the light from any diatoms remaining in the colder water of more 



