HORIZONTAL DISTRIBUTION OF CERATIUM 



the North Equatorial Current with a tongue of 34 per 

 mllle water reaching 140° west longitude. 



fii the South Pacific there is a zone of maximum sa- 

 linity centered at 20° south latitude and about 125° west 

 longitude with values over 36 per mille. Salinities de- 

 crease westward to 35 per mille at Samoa. Southeast- 

 ward from the zone of maximum the surface salinities 

 decrease to 34 per mille. 



Phosphate 



Since the nutrient salt content of sea water is known 

 to be important in the total production of the phytoplank- 

 ton, it Is necessary to examine the variation in nutrients 

 as a possible important factor In the distribution of in- 

 dividual species. Phosphorus and nitrogen are the most 

 important plant foods in this respect. Only phosphate 

 data are available for a discussion of the oceans as a 

 whole but, since the variations in quantities of phosphate 

 and nitrate run parallel, a description of phosphate dis- 

 tribution will suffice to give a general picture of the dis- 

 tribution of phytoplankton foods in the areas investigated 

 by the Carnegie . The discussion that follows deals with 

 values which are the means of observed values for the 

 surface and for 50 meters, from Carnegie data. 



The warm North Atlantic waters are practically de- 

 void of phosphate to 40° north latitude. Two stations just 

 south of this latitude (stations 1 and 2) showed values 

 above 10 mg P04/m3. North of 40° north latitude the 

 mean values for the upper 50 meters were practically 

 everywhere between 25 and 75 mg P04/m3. 



Most of the great area of the North Pacific between 

 latitudes 10° and 38° north is practically devoid of phos- 

 phate, with values less than 10 mg. Along the subpolar 

 convergence northeast of Japan the phosphate content 

 rapidly increases northward to over 100 mg. In the 

 North Pacific West Wind Drift the values are well above 

 100 mg to longitude 150° west where they gradually be- 

 gin to drop off southward. This southward gradient is in 

 the California Current. Close off California the values 

 are between 25 and 75 mg. Farther out there is a rapid 

 decrease to the very low values of the "Sargasso Sea of 

 the Pacific." The North Equatorial Current lies in this 

 area of extremely low phosphate content. 



Nowhere to the south of this current in the Pacific 

 is there an area devoid of phosphate. The area of lowest 

 phosphate content in the South Pacific is in the Easter 

 Island Eddy. At only two stations here, however, did the 

 values fall below 10 mg. The subantarctic waters of the 

 South Pacific West Wind Drift are rich in nutrient salts. 

 The effects of this are shown by phosphate values above 

 50 mg at Carnegie stations 60 and 61 at about 40° south 

 latitude. Values over 100 mg were found along the Pe- 

 ruvian coast, probably the combined effect of the Hum- 

 boldt Current and local upwelling. In the general region 

 between Peru and the Galapagos and in the Panamic re- 

 gion the values are above 50 mg. In the South Equatorial 

 Current and its offshoots to the south the mean phosphate 

 values for the upper 50 meters are mostly between 25 

 and 50 mg as far west as Samoa. South and west of here 

 there is a tendency for the values to fall off. 



HORIZONTAL DISTRIBUTION OF CERATIUM 



Ceratium Life Zones in the Areas 

 Traversed by the Carnegie 



The area traversed by the Carnegie can be divided 

 into five regions on the basis of the Ceratium floras 

 (chart 54). Two of these regions are in the North Atlan- 

 tic, three are in the Pacific. They are also character- 

 ized by particular hydrographlc conditions. 



Region 1. Cold North Atlantic (stations 3 to 13). -- 

 This region Includes the loop of eleven stations lying 

 north of 40° north and extending to Iceland. The entire 

 area is composed of eutrophic water with surface tem- 

 peratures below 16° C and the phosphate content of the 

 upper 50 meters above 20 mg P04/m3. The Ceratium 

 flora in this region is characterized by subpolar species 

 as well as by tolerant tropical species which probably 

 have been carried northward by the West Wind Drift and 

 its tributaries. It is also characterized by a paucity of 

 species (see p. 6), although the total population is rela- 

 tively high. The number of species at each station was; 

 ten at two stations, less than this at the rest, and as low 

 as one and two at some.^ The total number of species 

 found In the region was only fourteen. 



The following species were found at five or more of 

 the eleven stations in the region. They are either sub- 

 polar or cosmopolitan species. 



C. arcticum 

 v. arcticum at six stations 

 V. longipes at seven stations 

 v. ventricosum at five stations 



C. furca 



C. fusus 



C. horridum v. horridum 



C. lineatum 



C. macroceros subsp. macroceros 



C. tripos subsp. atlanticum 



The following species were found at only one to 

 three stations in the region. They are all tolerant tropi- 

 cal or cosmopolitan species. 



C. arietinum subsp. bucephalum 



C. azoricum 



C. declinatum 



C. extensum 



C. hexacanthxun 



C. horridum var. molle 



C. macroceros subsp. gallicum 



C. massiliense 



C. ranipes 



Thus, the dominant flora of region I is subpolar in 

 character and a subdominant element is made up of tol- 

 erant tropical species. No strictly tropical forms were 

 found here. The least tolerant forms were C. declina - 

 tum . C. macroceros subsp. gallicum . and C. ranipes . 



'^ to order to make the records comparable, only 

 oceanc-jraphlc stations are considered in the discussion 

 of nimibers of species at stations. The records of the 

 Interposed surface plankton stations have not been used. 



