CONTRIBUTI ONS FROM THE CUSHMAN FOUNDATION F O R FORAl\lIH IFERAL "'RESEARCH 47 CONTRIBUTIONS FROM THE CUSHMAN' FSmmATION FOR FORAMINIFERAL RESEARCH VOLUM E XXI, PART 2, APRIL, 1970 382. COMPARISON OF GLOBIGERINA PACHYDERMA (EHRENBERG ) IN ARCTIC AND ANTARCTIC AREAS JAMES P. KENNETT Florida State University, Tallahassee, Florida 32306 ABSTRACT Arctic samples examined were obtained by Populations of Glubigerin a Il8chnle rmu, in Al'ctic boltom dredge and bottom trawls from ice islands (Arlis sediments exh ibit distinct m orphological diffe rences from those in Antarc tic bottom sedim e nts, Arctic populations 11; Fletcher's Ice Island-T-3) from 1962-1965 in the are less heavily e nc rus t ed, m ore lobulate, have a highe l' central Arctic Ocean and the northern Beaufort Sea al'chad a perture, and have a dominance of 4 "h -chamber ed (Table 1). Antarctic samples have been examined form s (umbilical v iew), compared with a dominance of from numerous cores collected during operations of 4-chamber ed forms in Antarctic populations . Both are dominated by s inis tra lly coiling form s a nd they h ave s im­ National Science Research Vessel Ellanill in the ila r sIze c haracteristics. Becau se of a s hortage of m orpho­ Antarctic area (Kennett, 1968). For both Arctic logical data on G. J)achYlle rma in s ubArctic a nd northern and Antarctic areas, many thousands of specimens hemisph e r e s u btropical a r eas, It is not possible to deter­ of G. pachyderm a have been examined in order to mine whether these morphological differences result from phenotypiC val'lation or s Ubsoecia tion. make the comparisons. Arctic samples were sup­ C haracteristic ranges of variation of G .•}achY ll erma plied by Dr. J. Mohr and Mr. S. Geiger as part of from l>oth areas are illustrated by scanninG'-e leclmn the Arctic Drift Station Biology Program. The microgr aphs, scanning electron micrographs (Plates 8 and 9) INTRODUCTION were taken by R. Parker, using a Cambridge stereo­ G /obigerilla pachyderma is the only species of scan, mark II-A, in the Biology Department, planktonic foraminifera found in both Arctic and Florida State University. This research was sup­ Antarctic water masses, so it is of special interest in ported by Nonr 228(19) and NR 307-270 (Arctic studies of faunal-floral bipolarity. Despite this, Biology, University of Southern California) and popuiations of this species in the two polar areas N.S.F . GA-4002 (Antarctic foraminifera, Florida have not been compared in detail until now. State University) . Shchedrina (1964), in a discussion of bipolarity of foraminifera, stated that G. pachyderm a is the only species that can be called identical in both areas. MORPHOLOGICAL DIFFERENCES During examination of both Arctic and Antarctic BETWEEN ARCTIC AND ANTARCTIC foraminiferal faunas, I noticed, on the contrary, that distinct differences do occur in G. pachyderma POPULATIONS from the two areas. The purpose of this paper is The fo ll owing comparisons are tabulated between to describe these differences and to discuss briefly G. pachyderma populations in the Antarctic area their possible significance. (A), and populations in Arctic areas (B). A. CHARACTERISTICS OF G. l"ACHYDER?ilA I N ANT ARCTIC B. CHARACTERISTICS OF AREAS (KENNETT. 1968) G. l'A C HYDER~rA IN ARCTIC AREAS I. Dominated by forms with 4 cham- I. Dominated by forms with 4 112 -5 bers (umbilical view). Four-cham- chambers (umbilical view). 4112-5 bered forms constitute 54 - 80% of chambered forms constitute 56-36% G. pachyderma samples, with an of G. pachyderm a samples with an average of 66 % . average of 59 % . 2. Test highly thickened, heavily pit- 2. Test less thickened, less heavily pit- ted, compact, and only slightly ted, less compact and rather lobulate. lobulate. 3. Aperture usually relatively low, 3. Aperture usuall y higher arched, narrow arch; lip thickened. more open; lip less thickened. 4. Sinistrally coiled forms dominate 4. Sinistrally coiled forms dominate (greater than 97 % ). (greater than 95%). 5. Large size. Median diameter in- 5. Large size. Median diameter 180- creases southwards from about 160" 187". near the Antarctic convergence to 200" near the Antarctic continent. 48 KENNETT-ARCTIC AND ANTARCTIC GLOUIGERINA PACHYDF': RMA Arctic populations of G. pachyderm a (Plate 8), Environmentally-controlled changes in coiling are readily distinguished from Antarctic popula­ direction in G. pachyderma are well known tions (Plate 9) because they are less heavily en­ (Bandy, 1960; Ericson, 1959). Other gradational crusted, more lobulate, generally have a more morphological changes possibly under environ­ highly arched, more open aperture, and are dom­ mental control have been described for forms from inated by forms with 4 Yz to 5 chambers (umbilical the South Pacific (Kennett, 1968) . It is conceivable view), while those in Antarctic populations are that distinct Arctic and Antarctic forms have arisen dominated by 4-chambered forms (Table 1). In­ as phenotypic variations reflecting environmental deed, Arctic populations have more in common differences in the two oceans. If this is the case, it with subAntarctic populations than with Antarctic is difficult to explain why the Arctic form of G. populations (Kennett, 1968). It is important to pachyderma is more like the subAntarctic form, note that the Arctic forms described in this paper since Arctic water masses are more like those of are mature, relatively thickly encrusted forms, and the Antarctic than the subAntarctic. should not be confused with thin-shelled, immature Unfortunately, since little is known about G. forms characteristi c of relatively shallow Arctic pachyderma in other northern hemisphere areas, it waters (Be, 1960). All of the Arctic samples used is not possible to determine at this time whether the in this study were from depths greater than 1300 m., distinct Arctic and Antarctic forms represent sub­ which is substantially deeper than the critical depth speciation or are merely an expression of pheno­ (200 m.) below which more typical G. pachyderma typic variation. populations, characterized by crystalline thickening of the test wall (Be, 1960), are found. REFERENCES DISCUSSION BANDY, O. L., 1960, The geologic significance of The morphological differences between Arctic coiling ratios in the foraminifera Globigerilla and Antarctic populations of G. pachyderm a can pachydernia (Ehrenberg): JOllr. Pal., vol. 34, be accounted for in two possible ways: no. 4, pp. 671-681, text-figs. 1-7. I. Subspeciation resulting from geographic isolation of the two forms. BE, A. W. H., 1960, Some observations on Arctic planktonic foraminifera: COlllr. Cllshmall 2. Phenotypic variati on reflecting differences FOlllld. FO"'III. Research, vol. II, pI. 2, pp. in the environment of Arctic and Antarctic 64-68. water masses. In present-day seas, G. pachyderm a is essentially ERICSON, D. B., 1959, Coiling direction of Globig­ restricted to water masses as far north as 25 ' S in erinG pachyderm a as a climatic index: Science the southern hemisphere and as far south as 25 ' N vol. 130, no. 3369, pp. 219-220, text-fig. 1. in the northern hemisphere (Parker, 1962). It is KENNETT, J. P., 1968, Latitudinal variation in Glo­ possible that the present-day equatorial water bigerilla pachyderma (Ehrenberg) in surface masses form a barrier to the migration of G. pachy­ sediments of the southwest Pacific Ocean: derma between the northern and southern hemi­ Micropaleolltology, vol. 14, no. 3, pp. 305- spheres. On the other hand, significant oceanic 318, pI. 1. cooling associated with the Pleistocene glacial PARK ER, F. L., 1962, Planktonic foraminiferal spe­ stages possibly enabled the latitudinal range of G. cies in Pacific sediments: Micropaleolltology, pachyderma to be extended close to the equator in vol. 8, no. 2, pp. 219-254, pis. 1-10. some areas, enabling the reasonably free inter­ change of northern and southern hemisphere popu­ SHCHEDRINA, Z. G., 1964, The foraminiferen fauna lations, thereby preventing subspeciation. of the eastern sector of the Antarctic: ill Soviet Alltarctic Expeditioll, Ill/ormatio/! Bull., v. I, An alternative explanation is that subspeciation pp. 125-127, Elsevier Publ. Co. has occurred independently within northern hemi­ sphere populations, and that the Arctic form has SHARP, W. E., and POW-FOONG FAN, 1963, A sort­ evolved as the result of subspeciation in the relative ing index: JOllr. Geol., vol. 71, no. I, pp. isolation of the Arctic Ocean. 76-84. EXPLANATION OF PLATE 8 Morphological variation in mature specimens of Globigerilla pachydermu (Ehrenberg) from Arctic surface sediments. Sample 298a. All figures X 120............... ......... ................ ................................ ................................................. 48 CONTRIB. CUSHMAN FOUND. FORAM. RESEARCH, VOL. 21 PLATE 8 Kennett: Arctic and Antarctic Globigerina pachyde·rma. CONTRIB. CUSHMAN FOUND. FORAM. RESEARCH, VOL. 21 PLATE 9 Kennett: Arctic and Antarctic Globigel'ina pachyderma. CONTRI BUTIONS FROM THE CUSHMAN F OUNDATION FOR FORAMIN1FERAL RESEARCH 49 TABLE 1 } 'C• 0 'C• Ii: ~ } ~ :l •" ~•" 3 :>~ ~> • :;; ."0 E ~ 0- E ~" ..l• ".'" .<:••- '? ~ ~ •E '" .3 • !oE 0> 'C .; 0" ~ :: 'C•" Z I I -0 ~:> E ;a• 0 0 .§ "E o~ E 0 • in .. .<:~"~ .<:E c • £ ~- E .<: • .~- ~" " ~ ~E " ~ -s;::c ~ (fj • ~ E .. 0 0 0= ' E x ;a 8 0 •0 " • • ~ Ul• ..l ..l C• ", 8 ~ E ;a • " '" "' 2 '" "" 98 87"12'N 64' 06'W 1340 100 97 38 62 432 180 65 298a 84' 22'N 169' 48'E 3175 100 96 43 57 504 180 70 22 76' ll'N 141 ' 56'W 3700 100 95 37 63 360 185 68 73c 74' 28'N 141 ' 58'W 3650 100 97 44 56 450 187 67 Data for Globigerina paclr yderma from Arctic samples. Each parameter determined from counts of more than 200 specimens. The sorting index is explained by Sharp and Pow-Foong Fan (1963 ). An increase in percentage of sorting indicates greater numbers of specimens within a narrower size range.