STUDIES m FORAMmiFERA 



A pelagic community in tropical seas may have 20 

 species of Foraminifera, whereas one in polar water 

 will have only a few. However, species found in polar 

 faunas may be exceedingly rich in number. The 

 abundance of diatoms in polar seas is an ample supply 

 of food in summer months. In fact, in actual numbers 

 of organisms per liter of water it has been shown that 

 cold water contains about three and a half times as 

 abundant a fauna as the water warmer than 20° C. 

 But this abimdance is limited to the summer months, 

 and there is a relative scarcity of hfe in winter, when 

 the absence of simhght causes the plant life to remain 

 dormant; so that the total annual production may not 

 be greater than that of tropical seas. 



There is a great similarity in the faunas of the Arctic 

 and Antarctic seas. This may partially be due to a 

 connected distribution through the deeper and there- 

 fore colder waters between. For example, of 14 Ant- 

 arctic Foraminifera, 12 also occur in the Arctic, they 

 are partly generally distributed forms, but partly are 

 found normally at great depths and only in the polar 

 regions do they ascend to within 30-70 meters of the 

 surface. (Faur6-Fremiet, 1913, p. 268.) 



There are other cases where the identity of the polar 

 forms has been referred to the convergent evolution of 

 species. The thick shelled Globigerina pachyderma is 

 found in both polar seas and was considered by Heron- 

 AUen and Earland (1922, p. 190) to be a local sub- 

 species of 6. dutertrei, a species, found in the interme- 

 diate areas, which develops into pachyderma under the 

 influence of low temperature. 



Wiseman and Ovey (1950, p. 65) consider living 

 planktonic species of Foraminifera to be useful as tem- 

 peratm-e indicators. They listed the species typical of 

 the various zones as follows: Arctic and Antarctic 

 species: Globigerina dutertrei d'Orbigny and Globigerina 

 pachyderma (Ehrenberg). Temperate species: Globiger- 

 ina hulloides d'Orbigny, G. inflata d'Orbigny, Globoro- 

 talia crassula Cushman and Stewart, G. canariensis 

 (d'Orbigny), G. truncatulinoides (d'Orbigny), and G. 

 hirsuta (d'Orbigny). Warm and tropical forms: Orbu- 

 lina universa d'Orbigny, Globigerina dubia Egger, Glo- 

 bigerinella aequilateralis (Brady), Globigerinoides rubra 

 (d'Orbigny), G. sacculifera (Brady), G. conglobata 

 (Brady), Globorotalia menardii (d'Orbigny), G. tumida 

 (Brady), G. scitula (Brady), Sphaeroidinella dehiscens 

 (Parker and Jones), and Pulleniatina obliquiloculata 

 (Parker and Jones) . 



Phleger, Parker, and Pierson (1953, p. 17) give the 

 distribution of species in the Atlantic as follows: Spe- 

 cies characteristically abundant in low latitudes (less 

 than lat. 20° N.) are Globorotalia menardii (d'Orbigny), 

 G. tumida (Brady) and Pulleniatina obliquiloculata 

 (Parker and Jones). They also occur in lesser num- 

 bers in middle latitudes. Abundant in low latitudes, 

 but in lesser abundance in all other localities as well 

 are Globigerina eggeri Rhumbler and Globigerinoides 

 sacculijera (Brady). Only in high and middle lati- 

 tudes is Globigerina pachyderma (Ehrenberg). Abun- 



dant in middle latitudes and rarer in low latitudes are 

 Globigerina bulloides d'Orbigny, G. inflata d'Orbigny, 

 Globorotalia hirsuta (d'Orbigny), G. scitula (Brady), 

 and G. truncatulinoides (d'Orbigny). Uniformly dis- 

 tributed in uniform abundance over the entire ai"ea 

 were Globigerinella aequilateralis (Brady), Globigerinita 

 glutinata (Egger), Globigerinoides conglobata (Brady), G. 

 rubra (d'Orbigny), and Orbulina universa d'Orbigny. 



However, Phleger (1954, p. 8) did not believe that 

 surface temperature was the most important ecological 

 factor in this distribution. He considered that the dif- 

 ferent faunas were due to different "ecologic water 

 masses," with some mixing of faunas at the boundaries 

 of these water masses. The Gulf Stream was cited as 

 an example of a water mass transporting low-latitude 

 species such as Globorotalia menardii (d'Orbigny) into 

 middle latitudes, i. e., the southern Gulf of Maine. 

 These "water masses" had been earUer discussed by 

 Sverdrup, Johnson, and Fleming (1942) and by Thomsen 

 (1935). 



Oceanic currents may of course carry the plankton 

 through varying temperatiu-e zones. For example, the 

 closed cm-rents of the South Atlantic carry water from 

 the equator to the 48th parallel of south latitude. The 

 plankton in such a current requires several months and 

 even years to return to its origin, about one and one- 

 fourth years in the North Atlantic current, and two 

 and a fourth years in the South Atlantic. Among 

 short-lived plankton, many generations are included 

 in this period. A different condition results in the non- 

 circulating currents, which may carry warm water into 

 a cold region, as does the Gulf Stream, or cold water 

 into warm, like the Labrador current. Here the plank- 

 ton may be carried from a favorable environment to 

 an unfavorable one in which they may suffer or die. 

 Murray (1897, p. 23) showed that the deposits of 

 pelagic Foraminifera on the sea bottom were greatest 

 where currents of different temperature met. Possibly 

 the water-masses cited by Phleger are themselves an 

 influence because of differing temperatures. 



Studies of planktonic Foraminifera in deep sea cores 

 have been made by many workers in recent years. 

 Faunas from sediments below the surface have been 

 recognized as containing species typical of modern 

 faunas of higher latitudes than that of the core being 

 studied. These are generally considered to represent 

 temporai'ily colder water during the various Pleistocene 

 stages. These studies have been made by Cushman 

 and Henbest (1940); Stubbings (1939); Phleger (1939, 

 1942, 1947, 1948), and Ericson, Ewing, and Heezen 

 (1952) in various areas of the Atlantic, Pacific, Carib- 

 bean, Gulf of Mexico, Ai-abian Sea, and Tyrrhenian 

 Sea. However, as noted by Phleger (1954, p. 16) this 

 alternation of faunas in a core may not be entirely due 

 to widespread climatic changes influencing surface 

 water temperatiu-e variations. SmaUer changes in 

 boundaries of water-masses could cause similar fluctua- 

 tions. Phleger stated: "The position of the Gulf 

 Stream varies considerably, and . . . there are eddies, 



