THE PHYTOPLANKTON 



Northern Region 



The northern region included forty stations between 

 Carnegie stations 109 and 149, which were in the east- 

 ern and western Pacific and along a great circle course 

 between Yokohama and San Francisco. The most north- 

 ern station was number 124 at latitude 52° 19' north. In 

 this region one hundred and twelve samples were taken: 

 thirty-nine at the surface, forty at 50 m, and thirty- 

 three at 100 m. 



This was by far the richest region visited. Only 

 thirteen samples of the one hundred and twelve contained 

 no diatoms or dinoflagellates, sixty had less than 50 

 cells, nine counts were between 50 and 100, and thirty 

 had more than 100 cells--of the last fourteen had more 

 than 1000. The richest sample obtained on the entire 

 cruise was taken at 50 m at station 115. It contained 

 16,954 diatom cells and 26 dinoflagellate cells per liter. 



All but one of these very rich samples were con- 

 fined to the cruise between Yokohama and San Francis- 



co, at stations 115 to 125. The other rich station (131) 

 was about 300 miles southwest of San Francisco. 



The dates for the collections in this region were as 

 follows: from station 109 to Japan, May; Japan to the 

 United States, June and July; southwest of the United 

 States, September and October, 1929. 



The stations in this region lay near the center of 

 the North Pacific vortex and in the currents surround- 

 ing it. In general, the richer samples occurred in the 

 regions of more rapid currents and nearer land, fur- 

 ther removed from the center of the vortex. Samples 

 with more than 100 cells per liter occurred intheKuro- 

 shio or Japan Current (.beginning with station 115), in its 

 continuation- -the North Pacific Drift--in the California 

 Current, and in the water flowing westward from this 

 current. Stations located in the central part of the North 

 Pacific, in the northern edge of the North Equatorial 

 Current, and south of Japan contained less than 100 cells 

 and most of them less than 50 cells per liter. 



DISCUSSION 



Comparison of the Regions 



A summary of the physical, chemical, and phyto- 

 plankton data for the three regions is presented in ta- 

 bles 1 and 2. The highest mean temperatures for the 

 three levels occurred in the tropical region and the low- 

 est in the norther region (except at the surface). The 

 range of temperature was much greater in the northern 

 region with some values far below any in the other re- 

 gions. The tropical region had the next greatest range. 



The mean salinities were highest in the tropical re- 

 gion and lowest in the northern region. The range was 

 greatest in the north and would have been lowest in the 

 tropics except for the low salinity of the surface water 

 in the Gulf of Panama. 



The hydrogen-ion concentration was greatest in the 

 south and lowest in the north. The range was greatest 

 in the north and least in the south. 



The highest mean phosphates occurred in the north, 

 where also the greatest range occurred. The lowest 

 means were in the south where the range was also low- 

 est. 



Table 1. Summary of the diatom and dinoflagellate 



counts (in cells per liter) in the northern, tropical, 



and southern regions of the Pacific, showing the 



number of samples occurring in selected groups 



Highest mean oxygen saturations occurred in the 

 northern region, the lowest in the tropical region. The 

 greatest ranges occurred in the tropics and the lowest 

 ranges in the south. The oxygen data are meager here, 

 however. 



Silicate data are available for only the tropical and 

 northern regions. The means were lower at northern 

 stations except at the surface. The ranges were great- 

 er in the north except at the 100-m level. 



The Carnegie plankton series is not well distributed 

 throughout the seasons. Since the ship's itinerary was 

 planned to take it into the summer in each hemisphere, 

 it usually was passing through the tropics in the spring 

 and fall, seasons characterized in higher latitudes by 

 diatom maxima. No collections were made outside the 

 tropics in the spring, but samples were obtained in Sep- 

 tember 1929 in higher latitudes between San Francisco 

 and Honolulu. Indication of an outburst of diatoms was 

 found at station 131. 



In regard to the density of population of diatoms and 

 dinoflagellates, all three sections, on the whole, were 

 regions of very scant plant life (see table 1). The only 

 exception to the otherwise consistently poor areas was 

 the region along the Kuroshio Current between stations 

 115 and 123, unless the area off the coast of Peru be 

 considered also, at least as a potentially rich area (see 

 figure 1). 



In regard to the vertical distribution of the plankton 

 there is no indication that the phytoplankton is more 

 abundant at the 50- and 100-m levels than at the surface. 

 Of the one hundred and fourteen stations occupied, only 

 twenty-eight showed richer samples at a level below the 

 surface. Half of these were in the tropics. 



Dinoflagellates 



It is well known that dinoflagellates, although more 

 diversified in form in the tropics, are more numerous 

 in individuals in the higher latitudes. In the Carnegie 

 samples the dinoflagellates never attained very large 

 numbers. In the south only one sample contained more 

 than 100 cells per liter. In the north only two samples 



