PHYTOPLANKTON OF EAST CUMBERLAND BAY 209 



normal salinity below, though the upper layer may show a slight development of neritic 

 forms. These conditions were well shown by Sts. MS 99 and 100 (Figs. 81 and 83). 



SUNSHINE 



In general it may be said that the amount of sunshine varied inversely with the pre- 

 cipitation, as might be expected. Thus the general level of the sunshine curve was 

 highest during the first half of the season when diatoms were most plentiful (Fig. 81). 



This figure also brings out the interesting fact that the two highest peaks in the sun- 

 shine curve are associated with the first two diatom maxima, in November and 

 December, when the typical neritic form, Fragilaria sp., was an important constituent 

 of the phytoplankton. It is true that there was a lag in the second instance, the sunshine 

 during the week preceding St. MS 88 being the highest recorded during the season 

 though diatoms were practically absent at that time and did not turn up in force until 

 the week following, the sunshine during the interval being again very high. This was 

 probably due to the unfavourable wind conditions during the week preceding St. MS 88, 

 which undoubtedly led to rapid movements in the upper layers. Apart from this the 

 agreement is so close as to leave no doubt that it has a real significance. 



It is noteworthy that this association of diatom abundance with sunshine occurred 

 comparatively early in the season, before thawing was complete. In fact it was the 

 second sunny period that finally began to clear the lower slopes of snow, a process 

 normally completed at least three weeks earlier. After St. MS 90 (December 24) no 

 more heavy catches of Fragilaria sp. were obtained, and indeed the only other catch of 

 note was due to the invasion of Coscinodisciis stellaris with high salinity water from out- 

 side in January. 



It would seem that this falling off was due in part to the amount of inorganic material 

 brought down by the belated thaw. In normal seasons a spring increase would be 

 expected with the first periods of reasonably sunny weather in October, before thawing 

 on a large scale began ; but this increase would only attain significant proportions during 

 relatively calm periods. 



PENETRATION OF LIGHT 



During the first half of the season the polished metal top of the Nansen-Pettersen 

 bottle was as a rule visible at a depth of 5 m., and transparency was logged " moderate " 

 and "water opaque" as the limit became only 4 m. From St. MS 97 onwards it was 

 barely visible at 2-3 m. and transparency was logged "water very opaque". 



It was unfortunate that the importance of this effect of inorganic particles in sus- 

 pension was not recognized sooner, or efforts would have been made to obtain more 

 exact data on light penetration. It was felt that with diatoms so scarce that the centrifuge 

 method could not be worked, this point could safely be left to analogy with results 

 obtained offshore, which showed that the optimum light zone lay between the surface 

 and 10 m. Actually, when the " sediment" factor is taken into consideration, it becomes 



nVTIT ^7 



