Indian Journal of Marine SciencesVol. 1, June 1972,pp. 1-7

Planktonic Foraminifera in Sediment Samples from theEastern Arabian Sea

K. KAMESWARA RAO

National Institute of Oceanography, ~anaji

ManuscriPt received 24 January 1972

Twenty-two. species af planktanic Faraminifera have been identified fram the battam sedi­ments af the Arabian Sea aff Bambay and their percentage accurrence has been studied.Species campasitian has shawn that the sediments af the cantinental slape regian aff Bambayare represented by a larger number af 'species than the shelf sediments. The farms which arecamman in the eastern part af the Arabian Sea are: Glabigerina bullaides, Glabigerinoidesruber, G. sacculiJer, Globigerinita glutinata, Globigerinella aequilateralis, Orbulina unillersa,Pulleniatina obliquilaculata, Globarotalia menardii and G. tumida. Cancentratian af the plank­tanic Faraminifera decreases fram the affshare regians to. regians tawards the caast. In theslape sediments the per cent af CaCOs is prapartianal to. the number af planktanic Foramini­fera. The presence af high latitude cald water species alang with the warm water species inthe Arabian Sea aff Bambay suggests the mixing af Antarctic water with ather types af waterfaund alang the west caast af India. Similarity af the planktanic Faraminifera of the easternArabian Sea with that af Red Sea has been shawn an the basis af species campasitian anddaminance af certain species in bath the seas. On the basis af this abservatian, it is cancludedthat Red Sea water has spread into. the affshare regian of Bombay.

PLANKTONIC Foraminifera in the ArabianSea were first studied by Chapmanl whoreported 17 species from the Laccadive

region. Stubbings2 recorded 18 species flom theArabian Sea during John Murray Expedition. Inthe north-eastern part of the Arabia,n Sea whichincludes Gulf of Cambay, Kameswara Rao3,4 fourid9 species. Recently Be' and McIntyre5 reportedthe presence of an 'extinct' subspecies, Globoro­talia men£lrdii flexuosa (Koch), from the samplescollected for the present investigation. From theforegoing account it is obviGUS that there is nothorough quantitative documentation of variousspecies of planktonic Foraminifera present in thewest coast of India, although their presence in dif­ferent regions of the Arabian Sea has been noted.

In this paper the quantitative distribution ofvarious planktonic foraminiferal species presentin the bottom sediments of the Arabian Sea offBombay is reported. Such a study has a bearingon oceanographic conditions of the sea and alsoit will be useful for the (omparison of the faunawith other regions.

During a cruise sponsored by the Institute onboard INS 'Darshak' in January J 969 into theArabian Sea off Bombay, several bottom sedimentsamples were collected using Lafond-Dietz snapper.Altogether 7 snapper samples were obtained andthe sampling stations are shown in Fig. 1. Thepurpose of the collectioW' of these samples is todetermine species composition of planktonic Fora­minifera and their quantitative distribution in thebottom sediments of the Arabian Sea off Bom­bay. The study area extends between longitudes69°30·4'E and n022·0'E and latitude,> between18°33·5'N and 19°15·0'N. The water depths at thesites in the area range between 62 and 1820 m.

The continental shelf off Bombay coast haf amaximum width of about 161 km. The inner shelf

is flat whereas the outer shelf is highly irregularall the way to its edge (140 m) being formed ofpinnacles and knolls with intervening depressions.The continental slope of the west coast of Indiais gradual.

Materials and Methods

Eight stations were covered during the saidcruise. At the station 47 (lat. 19°15·0'N andlong. 69°45·0'E), a pipe dredge was used andit came up with coral rocks and oolite limestones.The snapper did not get any sample at this localityand therefore for planktonic foraminiferal analysisonly 7 samples Were taken. The method of sepa­rating the Foraminifera from the ~amples is sameas earlier4. Percentages of various planktonicspecies present in the samples have been calculat­ed (Table 2). Station locations, sampling times andbottom character are given in Table 1 and data onwater deptbs, salinity, temperature, calcium carbonateand total number of Foraminifera are presentedin Figs. 2 to 6. Calcium carbonate content of thesediment samples was determined using the method

ARABIAN I SEA

19· I _46

."

Fig. 1 - Station locations in the Arabian Sea off Bombaywhere sediment samples were collected

1

INDIAN J. MAR. SC1., VOL. 1, JUNE 1972 ,I

is of importance a~ it will give an idea on theproblem of eustatic changes in sea level along theWtst coast of India.

Planktonic foraminiferal species - Twenty-t\\Ospecies of planktonic Foraminifera belonging to9 genera and 2 families, viz. Globigerinidae andGloborotaliidae, are identified. The fauna isdominated by warm water species and with theexception of Globigerina bulloides, all ot.her coldwater species reported in this paper are uncommon.The collection of planktonic Foraminifera in theArabian Sea off Bombay is typical of Indo-Pacificregion and the list of species is as follows:

Hastigerina pelagica (d'Orbigny), Fig. 7Orbulina universa d'Orbigny, Fig. 8Globigerinoides conglobatus (Brady), Fig. 9Globigerinoides ruoer d'Orbigny, Fig. 11Glooigerinoides sacculifer (Brady), Fig. 10Globigerina rubescens Hofkel', Fig. 12Globigerina quinqueloba Natland, Fig. 13Globigerina pachyderma (Ehrenberg), Fig. 14­

Globigerina falconensis Blow, Fig. 15GlolJigerina bulloides d'Orbigny, Fig. 16Glubigerina calida Parker, Fig. 17Globigerinella aequilateralis (Brady), Fig. 18Globigerinella adamsi (Banner and Blow), Fig. 20Globigerinita glutinata (Egger), Fig. 19Globoquadrina dutertrei (d'Orbigny), Fig. 21Globoquadrina conglomerata (Schwager), Fig. 22PuZleniatina obliquitoculata (Parker and Jones),

Fig. 23Globorotalia truncatulinoides (d'Orbigny), Fig. 24Globorotalia hirsuta (d'Orbigny), Fig. 25Globorotalia menardii (d'Orbigny), Fig. 26Globorotalia tumida (Brady), Fig. 27Globorotalia menardii jlexuosa (Koch), Fig. 28

The total population of planktonic Foramini­fera shows greater variation in abundance atvarying depths in the continental shelf region ofthe Bombay coast and the sediments in the sloperegion are quite rich in planktonic Foraminifera.The area of greatest planktonic foraminiferalabundance (34750 specimensfg dry sediment) is thesite No. 44. High concentrations of planktonicForaminifera have been observed in the slope regionoff Bombay. In the shelf region concentration ofplanktonic Foraminifera varies from 750 to 9150specimens{g dry sediment.

Planktonic foraminiferal species found in allthe samples are: Hastigerina pelagica, Orbulinauniversa, Globigerinol:des conglobams, G. ruber, G.sacculifer, Globigerina falconensis, G. bulloides, Globi­gerinella aequilateralis, Globigerinita glutinata, Globo­quadrina dutertrei, PulZeniatina obliquiloculata, Globo­rotalia menardii and G. tumida ..

Three of the 22 species recorded are found at4 sites only, they being Globigerina quinqueloba,G. calida and G. pachyderma.

Planktonic foraminiferal species found at 2 sitesare: Globigerinella adamsi and Globorotalia hirsuta.

Planktonic forms observed at one station onlyare: Globorotalia truncatulinoides and Globorotalia

menardii jlexuosa.The general relationship between planktonic for­

aminiferal number (number of planktonic foramini­feral specimens present in one gram of dry sediment)and depth indicated that the number increases

46

FIG.6

FIG.5

f1G.4

FIG.3

45STATION NUMBER

2 43

Ecological data and distributional trend of plank­tonic foraminiferal fauna

f..:2: 1000

l;: wCla: 1500w i

o

TV!.OOO« '"~ __~ 27D. '" •••::E",a:w::>::> 26•...• 1-C11--"':=-25

500

TABLE'1 - DATA ON BOTTOM SEDIMENTS FROM THEARABIAN SEA OFF BOMBAY

..~. 35z~::; 34«~---33'ioWU 70U"a:U

~ 50-----30~ffi 30000•..Z

!~20f::E

::>

yZZ~ 10'"z~D.

Figs. 2-6

of Hutc~inson and Maclennan as described byBarnes6•

Results

The b ttom sediment samples can he classifiedinto 5 c tegories, viz. silty clay, silty sand, sand,sandy si and silt. The sediments from the shoreto a de h of 62 m are silty clay; from depths of62 to 96 the deposits are either silty sand or sandand fro the outer shelf towards the sea the de­posits a found to be sandy silt or silt. Seawardfrom 62 m to a depth of 96 m a calcareom: zoneis found It i~ possible that the calcareous mate­rial mus have been derived largely from the flag­mentati of coral rocks as well as from oolitelimeston s. Evidence for this observation couldbe made on the basis of rock fragments and coralsthat Wer dredged from sites 42 and 47. The find­ing of t e oolites and coral rocks at these otatiom

Station ateLatitudeLongitudeBottomNo.

969) character

40

71118°34'5'Nn022'0'ESilty clay41

71118°35·7'N71°33'5'ESilty sand42

81118°36'0'N70039'4'ESand43

8/118°33·5'N70021'6'ESandy silt44

81118°35'0'N70003'O'ESilt45

81118°49'O'N69°47'5'Edo46

81119°03'O'N69°30'4'Edo

2

KAMESW ARA RAO: PLANKTONIC FORAMINIFERA FROM E. ARABIAN SEA

O.3mm O.8mm O.Smm

7 8 90

130

11011b

O·3mm

O·1mm

13b

10b

03Smm

O·2mm

12b120

100

140O.15mm

14b

O·2mm

15b 150

Figs. 7-15 - Planktonic foraminiferal species [(7) Hastigerina pelagica, (8) Orbulina universa, (9) Globigerinoides con­globatus, (10) Globigerinoides sacculifer, (11) Globigerinoides ruber, (12) Globigerina rubescens, (13) Globigerina quinqueloba,

(14) Globigerina pachyderma, and (15) Globigerina falconensis. a, dorsal view; and t, ventral view]

3

INDIAN J. MAR. SCI., VOL. 1, JUNE 1972

O.2mm

16b0.35 mrn

230

21b

19b

0·2mm

0.35mm

17b

O.3mm

23b

190

170

18b

O.35mm

22b

Figs. 16-23 -t Planktonic foraminiferal species [(16) Globigerina bulloides, (17) Globigerina calida, (18) Globigerinellaaequilateralis, I (19) Globigerinita glutinata, (20) Globigerinella adamsi, (21) Globoquadrina dutertrei, (22) Globoquadrina con­glomej'ata, and (23) Pulleniatina obliquiloculata. a, dorsal view; and b, ventral view]

4

KAMESW ARA RAO: PLANKTONIC FORAMINIFERA FROM E. ARABIAN SEA

240O.2mm.--J24b 250

L-0·2mm

25b

260Q.5mm

26b 270

O.4mm

27bJ

2801·0mm

28b

Figs. 24-28 - Planktonic foraminiferal species [(24) Globorotalia truncatulinoides, (25) Globorotalia hirsHta, (26) Globo­rotalia menardii, (27) Globorotalia tumida, and (28) Globorotalia menardii flexuosa. a, dorsal view; and b, ventral view]

5

INDIAN J. MAR. SCI., VOL. 1, JUNE 1972

TABLE 2 - PERCENTAGE OCCURRENCES OF PLANKTONIC FORAMINIFERAL SPECIES

Plttnktonic Station number;pecies

-----_.~---40

414243444546

Depth, m:

628796204182016601460

Hastigerin

pelagica 1·21-42·61·21-60·20·4Orbulina

iversa 9,69·87·25·22·62·03·2Globigerin 'des conglobatus

3-23,03,41·01·01·01'2Globigerin des ruber

30,832·033·036·238·228·841·0

Globigerin 'des sacculifer

4-63-01·01'211·23,65,0Globigerin

rubescens 0'60'60·40,60,40·2

Globigerinquinqueloba --1·01·00·20'4

Globigerinpachyderma 0·20·41·22·0

Globigerinfalconensis 2·83,04'82·22·03-45·2

Globigerinbulloides 15·815·216·020'16,812'68,8

Globigerincalida -0,4-0·21·2-1·0

Globigerine la aequilateralis4,84,43·65,05·21·83,0

Globigerine la adamsi

---1·00·2--Globigerini a glutinata

14,815·416·216,610'818·212·8Globoquadr na dutertrei

5·24,81-41-63,85,84,6Globoquadr na conglomerata

1·6-0·8-1·00'40·2Pulleniati

obliquiloculata 0,81-43·22·66·010·06·2Globorotali

truncatulinoides ---0'2

Globorotalihirsuta --1·80·4

Globorotalimenardii 2·60,80'40,43·22'81·0

Globorotalitumida 1·23,81'60'43-48,86,4

Globorotalimenardii flexuosa ----1'2

<

{~-

j

It

I

with dep and di5tance from the shore (Fig. 6). Theslope se 'ments are represented by larger numberof specie.

Studie on this group have shown that in theslope se 'ments the percentage of CaCOa increaseswith the abundance of planktonic Foraminifera.

Discuss' n

Quant' ative analysis of planktonic Foraminiferafrom the sediments bas shown that the silty sandand san dep05it,; contain only a few forms whereasthe sand silt and silt deposits are fairly rich invariety nd numerical abundance. The sedimentsof the c ntinental slope region are represented bya larger number of specimens of planktonic For­aminifer than th05e of the shelf. It can be infeaedthat low concentrations of planktonic Foraminiferain the sl elf region is due to low productivity ofthis gro p in the shelf waters.

The s diments in the shelf region off Bombayare fairl rich in CaCOa and the content of CaCOavaries f m 38 to 66%. Seaward from 62 m toa depth f 96 m, a calcareous sand zone exi5ts andin this a ea CaCOa varies from 52 to 66% and thecalcareo s material is largely derived from thecoral ro s and oolite limestones. From the edgeof the ntinental shelf and continuing into theslope, C COa content in the dep05its varies from30 to 4 X>. The content of CaCOa in the pelagicsedimen is actually the balance of the two pro­cesses, iz. produotivity of calcareous organismsand the action of water on the deposited calcareousremains7 It has been found that in this region thesource 0 calcareous material is dominantly fromfloating calcareous organisms, namely planktonicForamin era, and in the deposits of this area CaCOacontent nCleases with the number of planktonicForamin ela (Fig. 5). This confirms the observationof Corre S8 that the amount of CaCOa in the siltis propo ional to the number of foraminiferal tests.

6

The planktonic foraminiferal species from theeastern part of the Arabian Sea can be classifiedinto two categories: warm and cold water species.Some dominant warm water species in the ArabianSEa off Bombay are: Hastigerina pelagica, Globigeri­noides ruber, G. sacculifer, Globigerinetla aequila­teralis, Orbulina universa :md Gioborotalia tumida.All the cold water species which ale rare with theexception of Globigerina bulloides are Globigerinapachyderma and G. quinqueloba. The occmrenceof cold water species with warm water species inthe bottom sediments of tllf Arabi2n Sea off Bom­bay is an indication of the mixing of the Antarcticwater with other types of water, viz. the Indianequatorial water, the Red Sea water and the Indi?ncentral water found along the west coast of India.It is also known that the upwelling of the coldbottom "\-vaters of the Antarctic comes to thesurface in the Arabian Sea when confronted with theCarlsberg Ridge9.

In connection with the mixing of the two typesof faunal elements, it is worth mentioning aboutan interesting species, namely GlobOiotalia mcnardiiflexuosa (Koch). Ericson et al.lO observed speci­men,; of GI. m. flexuosa at certain Quaternarylevels of Atlanitc deep-sea cores and it was con­sidered by these authors on the basis of this ob­servatron that this subspecies became extinct afterhaving lived about 90000 to 125000 yeals ago ina circumtropical belt in the Atlantic, Indian andPacific Oceans during the warm Interstadial ofthe Wisconsin and the Sargamon Interglacial.Furthermore, this subspecies has not been recordedso far in the recent deposits of the Atlanticand Pacific Oceans. Based on this available infor­mation that this subspecies is an extinct one,Bhattll reported by the presence of forms resem­bling Gl. m. flexuosa along with other sp~cies ofplanktonic Foraminifera flOm a sample flOm theouter shelf region off the Visakhapatnam coast,

(

KAMESW ARA RAO: PLANKTONIC FORAMINIFERA FROM E. ARABIAN SEA

that the mixing of the two faunal categorie!' is• relict' in nature but this conclusion is not truein view of the fact that Be' and McIntyre5 coulddiscover living specimens of the same species inthe northern Indian Ocean which includes Bay ofBengal and Arabian Sea. From this report wecan conclude that it is still living dnce its incep­tion. Report of Be' and McIntyre5 about the pre­sence of Gl. m. flexuosa from the sediment samplesof the present investigation is further an evidenceof its presence in the Arabian Sea besides Bay ofBEngal and other adjacent seas of northern IndianOcean.

Our knowledge of planktonic Foraminifera pre­sent in the Red Sea is mainly from the contJibu­tions of Said12, Herman13 and Berggren andBoersma14• Said12 recorded 5 plankton~c forms.Herman13 reported 16 species from the samples ofthe Red Sea. Further studies on ~his g10Up fromthe Red Sea by Berggren and Boersma14 have shownthat some species like Orbulina universa, Gloli­gerinella acquilateralis, Globigerinoidcs ruber andG. sacculifer are dominant. In the off~hore regionof Bombay, the above-mentioned species are quiteabundant. Globigerinoides ruber which is knownto tolerate high salinity conditions in the Red Seais very dominant in the offshore region of Bombay.Out of the 16 species reported by Hermanl3, 14of them are encountered in the samples of the dudyarea. From the results of the present investiga­tion and those of earlier studies by Chapman1 andStubbings2 it is ::ieen that thEre is some identityof the pla.nktonic foraminiferal fauna of the RedSea with that of Arabian Sea. This similarity ofplanktonic foraminiferal fauna in both the seassuggests that the Red Sea watEr has spread intothe offshore region of Bombay. This finding isof importance as it i", the only available biologicalevidence so far for the mixing of Red Sea waterwith that of Arabian Sea. Physical evidence forthis phenomenon is that of Rochford15 who hasshown the presence of Red Sea water along the

west coast of India on the basis of T-S charac­teristics.

AcknowledgementThe author expresses his deep gratitude to Dr

N. K. Panikkar, Director, for advice and sugges­tions during the C(,Ulse of the investigations andto Dr Allan W. H. Be' of Lamont GeologicalObservatofY, Pali~ades, New YOlk, USA, for discus­sions on certain protlems during the study.Thanks are due to CaptaiL F. L. Fraser and otherofficer s and crew of INS 'Darshak' for theircooperation in collecting samples. The authoris also thankful to Dr T. S. S. Rao, Regional Centreof National Institute of Oceanography, Cochin,for his encouragement and to his colleagne ShriC. V. Gangadhara Reddy, for help in the determina­tion of the chemIcal composition of sediments.

References1. CHAPMAN,F., Proc. Zool. Soc., (1895), 1.2. STUBBINGS, H. G., Scient. Rep. John Murray Exped.,

1933-34; 3(1939), 31.3. KAMESWARARAO, K., J. Bombay nat. Hist. Soc., 66

(1969), 584; 67 (1970), 137; 68 (1971), 9.4. KAMESWARARAO, K., Proc. Indian Acad. Sci., 73 (1971),

155.5. BE', A. W. H. & McINTYRE, A., Deep Sea Res., 17 (1970),

595.6. BARNES, H., Apparatus and methods of oceanograPhy

(George Allen & Unwin Ltd, London), 1959, 341.7. MURATA,K. J. & ERD, R. C., J. sedim. Petrol., 34 (1964),

633.8. CORRENS,C. W., Naturwissenschaften, 26 (1937), 196.9. SEWELL, R. B. S., Mem. Asiat. Soc., Beng., 9 (1929),207.

10. ERICSON,D. W., EWING, M. & WOLLIN, G., Deep Sea Res.,3 (1956), 104.

11. BHATT, D. K., Contr. Cushman Fdn foramin. Res., 20(1969), 30.

12. SAiD, R., Contr. Cushman Fdn foramin. Res., 1 (1950), 9.13. HERMAN, Y., Etude des sediments quaternaires de laMer

Rouge, Doctoral thesis, University of Paris, 1965.14. BERGGREN, W. A. & BOERSMA, A., cited in Hot brines

and recent heavy metal deposits in the Red Sea, edited byE. T. Degens & D. A. Ross (Springer-Verlag Inc.,New York), 1969, 282.

15. ROCHFORD,D. J., Aust. J. mar·freshwat. Res., 15 (1964), 1.

7