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ÚÛÜÝÞßà á

àßâãäÞâ

åæç èéê ëèìè èíë îïðñíñòìðèìóéðèôïõ

The time frame of the studied core is based on planktonicforaminiferal faunal datum based on Vincent (1977) and Gupta (1999). Theages of the samples were interpolated between these datums and calibrated tothe Berggen et al (1995) time scale. The youngest datum at the Site 758 wasbased on the occurrence of Pseudoemiliana lacunosa (nannoplankton) whichwass dated to 0.47Ma at 6.75 mbsf as per Leg 121 Initial Reports.Considering the rate of sedimentation to be uniform throughout the timeperiod (length of the core) the sampling interval of every 2 cm is ~1400 yearsper sample (Dr. A.K. Gupta, IIT, Kharagpur personal communication). Basedon this assumption the sediment core was dated upto 120 ka. Howeverchanges in ancient oceanic current patterns have been strongly influenced byplate tectonics, particularly by the opening or closing of gateways betweendifferent oceans. Such modifications of oceanic circulation have importantconsequences on climate (Gourlan et al 2008, 2010). Gourlan et al (2008,2010) studied the Nd seawater isotopic composition of Indian and PacificOcean cores using Nd isotopes, which are good paleo-oceanographic tracers.We focused on the past 25 Ma which are marked by the closure of theIndonesian gateway as well as the Mediterranean connection. We show that astrong westerly oceanic surface current, which we refer to the Miocene IndianOcean Equatorial Jet (MIOJet), linked the eastern and western Indian Oceanfrom 14 Ma to 3 Ma and infer that this major change in oceanic circulation

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probably induced important variations of global climate (Gourlan et al 2010).Nd isotopes are useful tracers for paleoceanography due to the short Ndresidence time in seawater and the large differences between the isotopicsignatures of various geological reservoirs. Therefore, Nd variations reflectthe geological history of individual oceanic basins.

Using a differential dissolution technique, which extracts Nd isotopesof seawater trapped in MnO2 coatings and carbonates in marine sediment,Gourlan et al (2010) measured almost two hundred samples from ODP Sites758 and 757 in the Northern Bay of Bengal covering the last 4 Ma. For thefirst time, we have shown a covariation between Nd and 18O over at leastthe last 800 ka. We also show that from 4 Ma to 2.6 Ma, Nd is almostconstant and starts to fluctuate at 2.6 Ma when northern glaciations increased.From 2.6 Ma to 1 Ma the fluctuation period is close to 40 ka while from 1 Mato present it is dominantly 100 ka. They attributed these findings to mixingbetween Himalayan river water (that ultimately originates as Indian summermonsoon rain) and normal Bay of Bengal seawater. Previous studies onseawater, using Nd, 18O analyzed on planktonic foraminifera andsedimentary data, can be integrated into this model. A simple quantitativebinary, mixing model suggests that the summer monsoon rain was moreintense during interglacial than glacial periods. During last glacial episode,the monsoon trajectory was deviated to the east (Gourlan et al 2010). At alarge scale, the Indian monsoon is fully controlled by the variations inNorthern Hemisphere climate but with a complex response function to thisforcing. Gourlan et al (2010) established the large potential of Nd isotope datato evaluate the hydrological river regime during the Quaternary and itsrelationship with climate fluctuations, particularly when the sediment archiveis sampled close to sediment sources.

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probably induced important variations of global climate (Gourlan et al 2010).Nd isotopes are useful tracers for paleoceanography due to the short Ndresidence time in seawater and the large differences between the isotopicsignatures of various geological reservoirs. Therefore, Nd variations reflectthe geological history of individual oceanic basins.

Using a differential dissolution technique, which extracts Nd isotopesof seawater trapped in MnO2 coatings and carbonates in marine sediment,Gourlan et al (2010) measured almost two hundred samples from ODP Sites758 and 757 in the Northern Bay of Bengal covering the last 4 Ma. For thefirst time, we have shown a covariation between Nd and 18O over at leastthe last 800 ka. We also show that from 4 Ma to 2.6 Ma, Nd is almostconstant and starts to fluctuate at 2.6 Ma when northern glaciations increased.From 2.6 Ma to 1 Ma the fluctuation period is close to 40 ka while from 1 Mato present it is dominantly 100 ka. They attributed these findings to mixingbetween Himalayan river water (that ultimately originates as Indian summermonsoon rain) and normal Bay of Bengal seawater. Previous studies onseawater, using Nd, 18O analyzed on planktonic foraminifera andsedimentary data, can be integrated into this model. A simple quantitativebinary, mixing model suggests that the summer monsoon rain was moreintense during interglacial than glacial periods. During last glacial episode,the monsoon trajectory was deviated to the east (Gourlan et al 2010). At alarge scale, the Indian monsoon is fully controlled by the variations inNorthern Hemisphere climate but with a complex response function to thisforcing. Gourlan et al (2010) established the large potential of Nd isotope datato evaluate the hydrological river regime during the Quaternary and itsrelationship with climate fluctuations, particularly when the sediment archiveis sampled close to sediment sources.

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probably induced important variations of global climate (Gourlan et al 2010).Nd isotopes are useful tracers for paleoceanography due to the short Ndresidence time in seawater and the large differences between the isotopicsignatures of various geological reservoirs. Therefore, Nd variations reflectthe geological history of individual oceanic basins.

Using a differential dissolution technique, which extracts Nd isotopesof seawater trapped in MnO2 coatings and carbonates in marine sediment,Gourlan et al (2010) measured almost two hundred samples from ODP Sites758 and 757 in the Northern Bay of Bengal covering the last 4 Ma. For thefirst time, we have shown a covariation between Nd and 18O over at leastthe last 800 ka. We also show that from 4 Ma to 2.6 Ma, Nd is almostconstant and starts to fluctuate at 2.6 Ma when northern glaciations increased.From 2.6 Ma to 1 Ma the fluctuation period is close to 40 ka while from 1 Mato present it is dominantly 100 ka. They attributed these findings to mixingbetween Himalayan river water (that ultimately originates as Indian summermonsoon rain) and normal Bay of Bengal seawater. Previous studies onseawater, using Nd, 18O analyzed on planktonic foraminifera andsedimentary data, can be integrated into this model. A simple quantitativebinary, mixing model suggests that the summer monsoon rain was moreintense during interglacial than glacial periods. During last glacial episode,the monsoon trajectory was deviated to the east (Gourlan et al 2010). At alarge scale, the Indian monsoon is fully controlled by the variations inNorthern Hemisphere climate but with a complex response function to thisforcing. Gourlan et al (2010) established the large potential of Nd isotope datato evaluate the hydrological river regime during the Quaternary and itsrelationship with climate fluctuations, particularly when the sediment archiveis sampled close to sediment sources.

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ö÷ø ùúúûüýùþüÿ� ÿ✁ ✂ü�✄☎ùû ✂ù✆�✄þüý ✝þ✞✟ü✄✝ ù�✟úùû✄ÿýûü✂ùþ✄ ☎✄ýÿ�✝þ☎✞ýþüÿ�

Mineral magnetism derives its origin from the pioneering workspublished by Thompson and Oldfield (1986). Mineral magnetism helps ininvestigating the inherent magnetic mineralogy while palaeomagnetic studiesexplore the plausible intensity and direction of the earth s magnetic field asrecorded by the natural remanent magnetization and sediment samples themagnetic minerals (O Reilly 1983).

Rock-magnetic techniques are being applied to marine sediments todecipher the amount, the grain size and the mineralogy of the magneticfraction within the sediments. Magnetic properties of the minerals are notonly a function of the supply of the clastic material, but they also representdigenetic processes occurring after the deposition. They reflect physicalchanges in the depositional environment that are strictly related topalaeoclimatic changes as well as human environmental impact (Oldfield andRobinson 1985; Robinson 1986; Bloemendal et al 1992). Magneticmineralogy reflects the course of climate change by recording evidence of thechanges in sedimentation. Mineral magnetic measurements, whetherconcentration dependent or not, can reflect palaeoclimatic conditions as aresult of the effect that the changing climate has on the environmentalprocesses which control the concentration and type of magnetic mineralsdeposited in sea sediments. For palaeomonsoon studies using environmentalmagnetism, it is extremely important to understand the spatial variability ofmineral magnetic properties of sediments in modern depositionalenvironments (Basavaiah and Khadkikar 2004). Palaeomonsoon changes inthe present study were studied using isotopic and foraminiferal proxies fromthe Sea/Oceans using marine sediment cores.

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Magnetism arises from the uncompensated spin movement of theouter most electrons orbiting around a nucleus, giving rise to properties likedia-, para-, and ferro- magnetism. Diamagnetic minerals such as quartz,feldspar, calcite, water etc. are weakly magnetic and the magnetic propertyresults when an applied magnetic field interacts with the orbital motion ofelectrons which gives rise to very weak negative magnetization and isindependent of temperature. However, the magnetization is lost as soon as themagnetic field is removed. On the other hand, para magnetic behaviour ariseswhen magnetic dipoles align themselves parallel with the direction of appliedmagnetic field to cause weak positive magnetization, which is dependent ontemperature. Natural minerals like olivine, biotite, garnet, pyroxene andcarbonates of iron and manganese are paramagnetic.

Ferrimagnetism and antiferromagnetism are the basic variants offerromagnetism. Ferrimagnetism have anti-parallel magnetic movements ofdifferent magnitudes such that the sum of the moments pointing in onedirection exceeds that in the opposite direction. Anti-ferromagnets too haveanti-parallel magnetic movements, but of similar magnitude such that theyexhibit zero bulk spontaneous magnetization in contrast to the alignmentpattern of antiferromagnets.

The sediment sections cored along the crest of the Ninetyeast Ridgesduring Ocean Drilling Program (ODP) Leg 121 are composed primarily ofpelagic carbonates. The samples collected from this section differ in grain-size distributions, biogenic siliceous intervals, and terrigenous sediments.

In the present study the ODP sediment core samples were subjectedto measurements of magnetic susceptibility ( ), Anhysteretic RemanentMagnetization (ARM) (peak field = 100 mT, bias field = 0.05mT) togetherwith Saturation Isothermal Remanent Magnetization (SIRM) at 1.5 T. Theirinterparametric ratios like S-ratio (simplified here as (IRM/SIRM) and

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ARM/SIRM have been computed. , ARM and SIRM are concentrationdependent. To eliminate this dependence, ratios between individual magneticparameters of S-ratio and ARM/SIRM were used to assess the magneticassemblage grain size in sediments.

✠✡☛✡☞ ✌✍✎✏✑ ✒✓✔✍✕✎✖ ✗omp✘✙✓✚✓✘✔

Microscopic observations reveal that magnetic heavy mineralfractions are dominated by heamatite, magnetite and ilmenite. Magnetites areof three main types. One type has rounded-off corners, is dark black in colour,with high relief and shows no or slight variation in reflectivity. The poorlyreflected parts of the grains are due to minor alteration. The second type isfresh, sub-angular and dark greyish black in colour. The third type is darkgrey in colour with the margins serrated. Ilmenite is also of the same size andshape, and exhibits alteration along the periphery. Heavy minerals wereidentified and qualitatively studied.

✠✡☛✡☛ ✒✓✔✍✕✎✖ ✛✎✜✔✍✚✓✢ data

The S-ratio provides a measure of relatively higher proportions ofcoercivity magnetic minerals (heamatite) to lower coercivity magneticminerals (Magnetite). Relatively high values of magnetic susceptibility andS-ratio indicate a close relationship between the erosion processes andincreasing coarser detritus.

From the mineral magnetic data, it is noted that the down corevariation of KARM/K and SIRM/KARM ratios decrease with increasinggrain size and are sensitive to magnetic mineralogy (Thompson and Oldfield1986).

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ARM/IRM values can be used to determine the occurrence offerrimagnetism or ferromagnetism. Down core variations of magneticproperties for this single core are presented in (Figure 3.7). The IRMacquisition of the sediments is almost saturated below 0.3 T (Figure 3.9)indicating that the magnetic properties are dominated by ferrimagneticminerals (magnetite-type).

Down core variations of X, ARM and SIRM (Figure 3.8) exhibit auniform trend between 0-98 cm with minor variations between 0-10 cm. Thelower part of the core corresponds to a lithological variation indicating aterrigenous provenance of sediments. In this sediment core multiple phasesexist i.e. between 150-130cm 130-110 110-60, 60-25 cm with a distinctoccurrence of ash between (40-35 cm) and 25-0 cm. Coarse ferromagneticminerals occurring at the depth 125-150 cm indicate an arid and dry climate.Sediments at the depth 98 cm 124 cm represent a distinctive subzonedistinguishable for its high SIRM, SIRM/K values.

The main feature is represented by an interval (124-98 cm depth;zone II and III), marked by a sharp decline in all the indicators of magneticconcentration (X, ARM) (Figure 3.7, 3.8), an increase of grain size (lowvalues of KARM/K, SIRM/K, Xfd) and low values of S-ratios (Figure 3.7and3.8). These characteristics are typical of rapid sediment deposition in reducingoxic conditions. Sulphate reduction due to bacterial degradation of organicmatter leads to a progressive dissolution of the ferrimagnetic minerals and tothe formation of iron sulphide (Karlin and Levi 1983; Canfield and Berner1987; Karlin 1990; Alvisi and Vigliotti 1996).

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✣✤✥ ✦✧★✩✪✩ ★✫✬ ZONES OF DEPOSITION

The occurrence of magnetite and titanomagnetite, contributes to thesuccess of determining S-ratio that can be used as a proxy forpaleoenvironmental/palaeomonsoon study. In this present study based on theS ratio reveal four zones namely: Zone- I (150-130 cm), Zone- II (130-110cm), Zone-III (110-60 cm) and Zone- IV (60-25 cm with volcanic ash layersbetween 40-35 cm), Zone V (25-10 cm) and Zone VI (10-0 cm).

Zone VI: (10-0cm) exhibits high ARM, SRM values andsusceptibility values indicate oxic conditions with coarser detrituscontribution at the depth 6-8 cm.

Zone V: 25-10 cm indicates anoxic conditions with finer sedimentsand comparitively high S ratio values. This may be also due to higher surfaceproductivity and intense monsoonal condition.

Zone IV: In this Zone (depth 60-25 cm), the S ratio varies from 0.940.98. The variation is probably due to the high content of titanomagnetite.Subsequent layers with magnetite minerals have been formed probably due tothe low temperature oxygenated oxic conditions of the tianomagnetites, andalso contributions from volcanic activity between 40-35 cm (24-28 Ka whenthe global sea level was low the conditions were arid). The sediment corerevealed the presence of volcanic ash (occurring between 40-35 cm depths)and variation in sediment texture.

Zone-III: In this Zone (110-60 cm), the down core S ratio fluctuatesbetween 0.94-0.96 with the occurrence of unaltered fresh, Titanomagnetitebetween 40-55 cm, probably indicating monsoonal anoxic conditions between28-38 Ka.

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Zone-II (130-110 cm): In this zone the down core variation startsfrom 130-110 cm depth with S ratio falling between 0.94- 0.99. This zonecontains coarse magnetite and Titanomagnetite grains. This indicates a dry,arid, climate with oxic conditions between 70-82 Ka encompassing theYounger Toba tuff event around 75 Ka (Westgate et al 1998).

Zone-I (150-130 cm): In this zone the down core variation form the120-150 cm which had the fluctuation of 0.96-0.94.This zone consists of finegrain size magnetite grains and also bears the signature of amelioratedclimate, anoxic conditions around 82-103 Ka.

S-Ratio together with ARM/SIRM results also points towards thesalinity variations. Mineral magnetic studies reveal six zones, with highunaltered fresh Titanomagnetite concentration between 40-35 cm 130-110 cmpointing towards contribution of a different provenance and coarser grains(Figures 4.1, 4.2, 4.3). This inference is corroborated with the microscopicobservation of volcanic ash occurring between 40-35 cm. However there is nosharp peak observed in the AIRM and S ratio values.

The magnetic susceptibility ( ) and ARM/ SIRM display highervalues in the same depth levels, though shows an alternating high and lowphases. For example, the low variations in the reverse field S-ratio can bedirectly related to the presence of haematite (Basavaiah and Khadkikar 2004).

S-ratio can be directly related to low discharge conditions (weakermonsoons). High S-ratio values reflect intense oxidation conditions at 120-100 cm depth in the sediments and increased less haline water influx duringarid and dry periods. It is further argued that during the dry periods, theformation of single domain (Titano) magnetite grains is promoted probablydue to the break down of multi-domain grains in the sediment. Thishypothesis is further supported by high ARM/SIRM values (Figure 3.8)

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during increased discharge periods bringing in coarser grains. Such conditionspresumably give rise to fluctuations in salinity conditions, atleast locally. It isalso observed that the S-ratio, Mn and Fe content largely mirror-image thefluctuations with respect to depth and planktic foraminifera forms such as✭✮ ruber has also responded to these fluctuations resulting in variations in itsrelative abundance (Figure 4.4).

The KARM/ K ratios, S ratios and susceptibility data indicate that thesediments have undergone diagenetic loss of titanomagnetite and magnetite.From this it can be inferred that the interval periods represent periods whenthe sedimentary deposition is inimical to the preservation of magneticminerals, increased organic matter flux, increased productivity or increasedpreservation of organic matter in the sediments. The interval periods wereapproximately 6, 48 and 60 ka. In this sediment core the oxidation oftitanomagnetite to magnetite is a low temperature oxidation phenomenon withalteration of silicates especially pyroxenes and olivine. A close study of thedata at the 120-110 cm (70-82 ka), 40-55 cm (38-28 Ka) and 8-4cm (2-6 Ka)reveal the occurrence of unaltered Titanomagnetite and magnetite grainsindicating terrigeneous flux due to dry and arid conditions. Occurrence ofvolcanic ash material 40-35 cm (28-24 Ka) indicates a near by sourceprobably reactivation of the Ninetyeast ridge or sub oceanic volcanic eventnear the Ninetyeast ridge. Toba event of 73 Ka very subdued and is not veryclearly discerned in the marine core studied as the susceptibility data does notshow a peak for the occurrence of ash. As there is siginificant in the influx ofterrigenous material as seen in the sediment core the rate of sedimentationwould also vary rather than remain constant through out.Gourlan et al (2008,2010) have dated this ODP 758 core using Nd/Sm isotope where they clearlyshow the varying rate of sedimentation.

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✯✰✱✲✳✴ ✵✶✷ ✸✹✺n ✻✹✳✴ ✼✽✹✾✿ ✹❀ m❁gnetic properties for ODP leg 121core 758. Susceptibility 10-8 m3kg-1, ARM, SIRM 10-5A m2 kg -1 versus depth (cm)

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❂❃❄❅❆❇ ❈❉❊ ❋●❍n ■●❆❇ ❏❑●▲▼ ●◆ m❖gnetic properties for ODP leg 121cores 758. fd%, ARM/SIRM, SIRM 10-5 A m2 kg -1 versusdepth (cm)

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P◗❘❙❚❯ ❱❲❳ ❨❩❬n ❭❩❚❯ ❪❫❩❴❵ ❩❛ m❜gnetic properties of the ODP leg121 cores 758 Soft IRM,10-5 A m2kg -1, Hard IRM,10-5 A m2 kg -1, S-ratio -300mT versus depth (cm).

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❝❞❡❢❣❤ ✐❥✐ ❦ ❣❧♠❞♥♦ ♣q ❧qd Fe content largely mirror-image the fluctuations with respect to depth and plankticforaminifera forms such as G. ruber has also responded to these fluctuations resulting in variations in itsrelative abundance

- 5.00 10.00Fe ppm0 50 100Mn ppm

0.92 0.94 0.96 0.98 1.00 1.02Sratio-300m T

05

101520253035404550556065707580859095

100105110115120125130135140145150

0.00 5.00 10.00 15.00

Depth/Age

G. Ruber %

Zone VZone VI

Zone I

Zone II

Zone III

Zone IV

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rsr t✉✈✇①✉②③④⑤⑥⑦ ✈⑧ ⑤①✉ ④✉⑨③②✉⑩⑤ ✇✈⑥✉

Species in seawater are important parameters in controlling thetransport, and bio-availability of many trace metals and trace organiccontaminants in marine environments (Bruland et al 1991; Honeyman andSantschi 1992; Campbell et al 1997; Santschi et al 1999). Recent studies haveshown that colloidal material isolated from seawater is mostly organic innature (Benner et al 1992; Guo and Santschi 1997). Many review papers onmarine sediment composition have subsequently been published (Li et al2000).

Of all the major elements Al and Fe, the latter of which is wellknown to be essential for the growth and metabolism of all marine organisms(de Baar et al 1995; Turner and Hunter 2001; Morel and Price 2003).Lithogenous constituents of marine sediments are the minerals derived fromweathering of rock on land or on the seafloor, or from the volcanic eruptions(Goldberg et al 1963; Windom 1976). The biogenous component is made upof the tests of planktic and benthic organisms, as well as biogenic apatite(Berger 1976). The hydrogenous fraction of marine sediment encompassesphases formed by inorganic precipitation from seawater. Elderfield (1976)and Piper and Heath (1989) provide a comprehensive reviews of hydrogenousmaterial in marine sediments. Aluminum is an ideal tracer for the indicationof dust input into the surface ocean seawater (Wedepohl 1995).

The chemical composition of sediments at the ODP Site 758 isexpected to be sensitive to variations in the provenance of terrigenous detritusand transport paths, both of which could be affected by changes in theterrestrial climate. Thus, sediments at this location can be expected to containhigh-resolution records of changes in the intensity of the oxygen minimumzone, the intensity of surface circulation (Richter 1997), ecological responsesto climate shifts, and variability in detritus input through time.

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❶❷❶❷❸ ❹❺❻❼❽❾❿ ➀❼➁➁➂❺➃ ➀❼➄or ❹➅❾➆➂➇➃ ➈❺❼❿➂ ➀➂➁❼➉ ❼❽➆ ➊➋➋ ➌❼➁❼

The organic matter (1.4 % at a depth of 120-122 cm and high 6.1% atthe depth of 80-82 cm) content varied with depth within the sediment core.Calcium carbonate percentage varied between 45.6% to 50.9% exhibiting nosignificant change within this sediment core.

Geochemical studies reveal variations in the SiO2, Al2O3, tracemetals concentrations with depth and age (Figure 4.5, 4.6). The graph SiO2and Al2O3 versus depth shows negative correlation with SiO2 and Al2O3 andhigh content of SiO2 at the depth 40-35 cm 115-108 cm can be related to theterrigeneous fluxes. High SiO2 could also be biogeneic silica but thisinference demands verification using detailed microscopic identification. If itis terrigenious then the sediments are hemipelagites, if it is biogenic, thenthey are pelagites. Occurrence of diatoms and radiolaria would not besurprising as the sediment core has been collected from the near the equatorialupwelling zone. Relatively high content of Al2O3 is due to intense weatheringof feldspars, pyroxenes and olivine. Less clay content, organic matter, Al2O3and CaCO3 percentages validate high SiO2 content (Fig. 4.5).

Trace element data reveal the occurrence in order ofNi>Co>Cu>Cr>Pb that remain constant throughout the depth whereas theconcentration of Zn and Mn are higher in surface sediments and decreasegradually with depth. Cu content is high at 50 cm depth; Mn and Cr are highbetween 12-10 cm and 125-100 cm (Figure 4.6). However, Ni concentrationis high amongst the trace metals analysed and this is probably due tosecondary alteration. The oxidized sediments have high Fe content and lowMgO and CaO concentrations. Fe and Mg show moderate inter-elementcorrelation suggesting that the effect of alteration on their distribution mayhave been intense. However down core variation of MgO content and itsabundance at various depths may have been affected by secondary alteration.

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In Ocean ridge environment, sea water also alters minerals. Tracemetals with low Fe%, Mn, Cr, CO, Pb, Ni and Zn (ppm) and high Cu (ppm)between 40-35 cm points towards a different sediment source at this depth.High Cu and low Co (ppm) content is due to the occurrence of volcanic ash.There is a moderate correlation between Al2O3, Zr and occurrence of positiveEu anomaly in the REE shows that there has been removal of plagioclaseduring weathering. Alteration of pyroxenes, feldspars and clays are alsoresponsible for the Eu anomaly. In the present study REE data werenormalised using PAAS data and were presented in Table (3.6, 3.7 and 3.8)and Figure (4.7a-e). The data reveals a flat LREE and HREE pattern but apositive anomaly of Eu in all the samples analysed.

Active ridge/ margin sediments often show strong similarities of REEcomposition to volcanic arc rocks. The volcanic arc rocks with low REEabundance and La/Yb ratio values (0.86 to 0.69 and Eu/Eu* (0.6 to 1.0)(Table 3.8) corroborates to a different sediment source. Positive Eu anomalysuggests intense weathering of terrigeneous fluxes, and diagenetic changes.PAAS normalised REE pattern and low ratios of La/Yb, Zr/Y, and Zr/Nb withLa/Zr (>2.0) values suggest that the detritus sediments were probably derivedfrom largely felsic source rocks.

Correlation matrix of the major oxides and the trace metals of thesediments analysed reveals that: ➍➎ SiO2 shows positive correlation withAl2O3, CaCO3, OM, FE, Ni. b. Al2O3 shows positive correlation with CaCO3,Fe, Mn, and Zn. c. CaCO3 reveals positive correlation with OM, Fe, Pb, Mn,and Zn. d. OM indicates a good correlation with Mn. e. Fe shows positiveassociation with Ni, Pb, Mn, and Zn. f. Ni and Pb reveal a goodcorrespondence with Zn. All the positive correlations point towardsweathering of oceanic basalts followed by diagenesis and biogenic source inanoxic conditions.

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➏➐➑➒➓➔ →➣↔➣ ↕➙➛n ➜➙ n ➝➔➓➜➔➞➟➠ gh organic matter content is due to thesedimentation in an open ocean environment and thesediments are pelagic nature. The variation in calciumcarbon content is due to dissolution of microfossils andterrigenious input.

110-100 ka

28-24 ka

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Figure 4.5. Down core variation of SiO2, Al2O3, OM and CaCO3percentages. The high organic matter content is due to thesedimentation in an open ocean environment and thesediments are pelagic nature. The variation in calciumcarbon content is due to dissolution of microfossils andterrigenious input.

110-100 ka

28-24 ka

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Figure 4.5. Down core variation of SiO2, Al2O3, OM and CaCO3percentages. The high organic matter content is due to thesedimentation in an open ocean environment and thesediments are pelagic nature. The variation in calciumcarbon content is due to dissolution of microfossils andterrigenious input.

110-100 ka

28-24 ka

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➡➢➤➥➦➧ ➨➩➫ ➭➯➧ ➲➢➳➵➦➢bution of Trace elements concentration in the ODP Site Sediment core

57

➸➺➻➼➽ ➾➚➪ ➸➶➽ ➹➘➴➴➽➼➺➷➬➘➮ ➱➺➷➴➬✃ ➘❐ ➷➶➽ ❒➺❮➘➴ ➘✃➬❰➽Ï ➺➮❰ ➷➶➽ ➷➴➺Ð➽ m➽➷➺➼Ï

Ñ➬ÒÓ Ô➼ÓÒÕ ➹➺➹ÒÕ Òm Ö➽ ×➬ Ø➻ ➹➘ ➹Ù ➱➮ ➹➴ ZnSiO2 1Al2O3 0.60 1

CaCO3 0.79 0.81 1Om 0.71 0.55 0.67 1Fe 0.61 0.77 0.85 0.49 1Ni 0.33 0.41 0.43 0.07 0.62 1Pb 0.58 0.48 0.72 0.39 0.64 0.44 1Co 0.45 0.49 0.59 0.47 0.45 0.28 0.56 1Cu 0.01 0.24 0.30 0.10 0.03 -0.02 0.32 0.44 1Mn 0.65 0.69 0.80 0.65 0.72 0.24 0.38 0.20 0.02 1Cr 0.29 0.24 0.52 0.28 0.32 0.31 0.53 0.37 0.40 0.27 1Zn 0.34 0.61 0.67 0.25 0.88 0.71 0.55 0.43 0.12 0.50 0.36 1

a) SiO2 shows positive correlation with Al2O3, CaCO3, OM, FE, Ni, Pb. b) Al2O3 shows positive correlation with CaCO3, Fe,Mn, and Zn. c) CaCO3 reveals positive correlation with OM, Fe, Pb, Mn, and Zn. d. Om indicates a good correlation with Mn.e) Fe shows positive correlation with Ni, Pb, Mn, and Zn. f. Ni and Pb reveal a good correlation with Zn. All the positivecorrelations point towards a biogenic source, weathering of oceanic basalts followed by diagenesis.

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ÚÛÜÝÞß àáâã- b PAAS normalized REE diagram of ODP Sediments CoreLeg 121

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Figure 4.7a- b PAAS normalized REE diagram of ODP Sediments CoreLeg 121

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Figure 4.7a- b PAAS normalized REE diagram of ODP Sediments CoreLeg 121

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äåæçèé êëì í-e. PAAS normalized REE diagram of ODP Sediments CoreLeg 121 PAAS normalized REE diagram of ODPSediments

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Figure 4.7 c-e. PAAS normalized REE diagram of ODP Sediments CoreLeg 121 PAAS normalized REE diagram of ODPSediments

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Figure 4.7 c-e. PAAS normalized REE diagram of ODP Sediments CoreLeg 121 PAAS normalized REE diagram of ODPSediments

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îïgure 4.8 Age VS Eu* and REE of the marine sediments

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ðñò óôõö÷øùú ûüýõþùöùûÿýõ

Surface water circulation in the Eastern Indian Ocean (ODP Leg 121site 758) is controlled by the South Equatorial Current (SEC) which is drivenby the Indian monsoon system. The SEC is intensified by the Southeast Trade(ST) winds during the southwest (SW) or summer monsoon (Tchernia 1980).The study site is severely affected by the export of low-salinity (fresh) surfacewater from the Pacific into the Indian Ocean. This also contributes to the SECthus forming a low-salinity front at 5oN in the Indian Ocean (Gordon et al1997). The study area has been under the influence of low-salinity surfacewaters from the west Pacific through the Indonesian Trough flow (ITF) atleast since the last 4-3 million years (Cane and Molnar 2001), and is a part ofthe Global Conveyor (Broecker 1995, Martinez et al 1999). Therefore,Ninetyeast ridge Quaternary sediments holds signature for understandingpaleoproductivity, provenance of marine sediments and terrigeneous flux andclimate change.

Plankton in the tropical Atlantic, intercept the majority of�✁✂✄☎✆✝✞☎✟oides ruber and pre-gametogenic �lobigerinoides sacculifer at 20^40 m, indicating their shallow mixed-layer habitat (Ravelo and Fairbanks1992). Furthermore, Deuser (1986 1987) suggested that, based on seasonalvariation in shallow-water temperatures and N18O of deep sediment trap-collected �✠ ruber in the Sargasso Sea, �✠ ruber calices in the upper 25 m ofthe water column. These experiments illustrate that the depth habitat for thesurface-dwelling planktic foraminifer Globigerinoides is very close to that ofnannoplankters within the upper photic layer. However, the surface waters aresubjected to seasonal fluctuations associated with development of seasonalthermo cline and vertical mixing, and thus surface-water properties (e.g.,nutrient contents and temperatures) vary annually. Therefore, despite thesame depth of calcification, the two surface-dwelling plankton taxa

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lithophorids and Globigerinoides may exhibit different chemical signalsreflecting a particular season of growth

Oxygen isotope-based estimates of paleo-SST are generally derivedfrom measurement of a single surface-dwelling planktic foraminiferal species.Seasonal variations in the abundance of individual species have beenrecognized Bé (1960 a, b), Tolderlund and Bé (1971), Sautter and Thunell,(1991), implying that the species of interest may have recorded isotopicvalues that reflect the hydrographic conditions (i.e., intensity of upwelling,development of seasonal thermo cline) of a particular season in which theshell precipitated (Deuser et al 1987; Williams et al 1981; Deuser 1987;Deuser and Ross 1989).

The planktic foraminifera showed that significant changes in therelative abundance of ✡☛☞✌✍✎✏rina bulloides correspond to the periods ofenhanced productivity caused by the summer Monsoon upwelling activity(Curry et al 1992). Earlier studies on the planktonic foraminifera in thenorthern Indian Ocean documented that the ✡☛☞✌✍✎✏✑✍✒☞ides bulloides andNeogloboquadrina dutertrei are reliable indicators of upwelling and seasurface salinity. The immediate response of G. bulloides to variation inprimary productivity makes it a useful indicator of past changes inproductivity (Clemens et al 1991; Steens et al 1991; Anderson and Prell 1993;Brock et al 1992; Vergnaud Grazzini et al 1995; Naidu and Malmgren 1996 a,b and c).

Cullen (1981) has used the relative abundance of N. dutertrei tocharacterise the salinity gradients in the Bay of Bengal during the Holoceneand Last Glacial Maxima (LGM). The surface water salinity, summermonsoon strength and productivity are coupled together in the Bay of Bengal.Therefore, by studying the relative abundance of N. dutertrei in the sedimentcores, it is possible to trace the monsoon and productivity variation strengths

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from the Bay of Bengal sediment records. The changes in biologicalproductivity, surface water salinity and river water discharge areinterdependent along the east coast of India. The planktonic foraminiferspecies, N. dutertrei is well attuned to low salinity water. Therefore, thefrequency variations and mass accumulation rates of N. dutertrei can be usedas a proxy of pale salinity and paleoproductivity in the Bay of Bengal (Naiduet al 1999)

The planktic foraminifer O. universa d'Orbigny is a common andwidely studied species in all the oceans. Be' et al (1973) and Hechtet al (1976) studied the variation in the diameter of the spherical test (externalshell) of this species in surface sediment samples from the Indian ocean andfound that a direct correlation can be demonstrated between mean testdiameter of O. universa and surface water temperature.

Haenel (1987) re-analysed the data of Bé et al (1973) statistically,and showed that the mean diameter of this species is: (i) directly proportionalto temperature (r = - 0.90) and (ii) inversely proportional to salinity. Since thisspecies has a short lifespan of 9 to 15days (Caron et al 1987), and settlingtime for planktic tests to the bottom (in laboratory conditions) isapproximately 400 m/day (Takahashi and Bé 1984), the diameter of tests ofthis species preserved in these sediments may be expected to reflect theregional sea surface temperature prevailing at that time. One such study forthis area has already been made by Nigam (1990).

Seasonal variations in planktonic foraminifera1 assemblages werefirst observed by Bé (1960) in the Sargasso Sea off Bermuda. The presentstudy not only corroborates Bé s findings but also indicates the geographicrange of their applicability. Sarkar et al (1990) provided evidence for thetransport of low salinity water from the Bay of Bengal.

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The abundance of chemical elements has been used in definingsediment sources, elucidating mechanisms of formation of the sediments,estimating abundance of different components, fluxes of various elements,and in understanding depositional environments (Goldberg and Arrhenius1958; Krishnaswami 1976; Graybeal and Heath 1984; Thomson et al 1984;Toyoda and Masuda 1990).

The Eastern Indian Ocean is an important region to understand theIndo-Pacific connection as well as climate changes over short and long timescales (Conolly 1967; Bé and Duplessy 1976; Prell et al 1980; Gupta andSrinivasan 1990 1992; Wells and Wells 1994; McKorkle et al 1994; Okadaand Wells 1997; Gupta 1999; Hermoyian and Owen 2001). Deep Oceanenvironments have undergone significant changes during the Pleistocene-Holocene period and this has left imprints on the distribution patterns of theforaminifera (Schnitker 1979 1986; Kurihara and Kennett 1986; Thomas1986; Woodruff and Savin 1989; Gupta and Srinivasan 1992 1996; Miller etal 1992; Thomas et al 1992; Rai and Srinivasan 1996; Gupta 1997). Severalauthors (Schnitker 1984 1986; Boersma 1985; Thomas 1986 and Kurihara andKennett 1988) have observed significant changes in the composition of thebenthic fauna in the Plio Pleistocene sequences in several DSP and ODPholes.

The present study is aimed at understanding surface waterpaleoceanographic changes at ODP (Ocean Drilling Project) site 758 over thelast ~100 ka using planktonic foraminifer faunal assemblage data.

In the present study 12 most abundant species such as ✓✔bulina✕✖✗✘✙✔✚✛✜ ✢✣✤✥✛✔otalia tumida, Pulleniatina obliquiloculata, Globigerina spp,Sphaeroidinella dehiscens, Neogloboquadrina dutertrei, Candeina nitida,Globoquadrina hexagona, Globigerinoides conglobatus, Globigerinoidesruber, Globigerinoides sacculifer, Globorotalia scitula occurred. Of these the

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four most dominant species are ✦✧★✩✪✫erinoides rub✬✭✮ ✦✯ sacc✰✧✪✱✬✭✮ ✦✯conglobatus and ✲✭bulina univers✳✴ ✲✭✩✰✧ina universa and ✦✧★✩✪✫erinoidesruber show an increasing trend towards the surface of the sediment core.(Figure 4.10).

✵✶✷ ✸✹✺✻✼✽ ✹✾✹✿❀❁❂❁

R-mode factor analysis of 12 species of planktonic foraminifera fromthe ODP site 758 had yielded four factors, which accounts 76% of the totalvariance (Table 4.2, and Figure 4.11).

Factor 1: Accounts for 30.3% of the total variance. Dominant speciesof this factor were ✦✧★✩✪✫✬✭✪❃oides congl★✩✳❄✰✯✮ ✦✧★✩✪✫erinoides ruber ✮✦✧★✩✪✫✬✭✪❃oides saccu✧✪✱✬✭✮ ✦✧★borotalia scit✰✧✳✮ ✲✭✩ulina universa havingstrong positive loading, preferring to live infaunal mode of life and reflectwarm climate with high organic carbon flux and relatively calmsedimentation. Cluster I coincides well with the distribution of higher loadingof factor 1.

Factor 2: Accounts for 16.5% variance of the total matrix. Thecharacteristic species were Neogloboquadrina dutertrei and Sphaeroidinelladehiscens that have strong positive loading on this factor whereas Candeinanitida exhibits a negative loading. The characteristic species ofSphaeroidinella dehiscens shows dominance and indicates relatively highnutrient and high oxygen conditions. The high positive loading of this factorclosely coincides with cluster III.

Factor 3: Accounts for 15.80 % variance of the total matrix. Thespecies Candeina nitida, Globigerina spp, have strong positive loading on thisfactor, whereas Orbulina universa and Pulleniatina obliquiloculata shows

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negative loading on this factor. The distribution of samples in cluster IIclosely coincides with the distribution of higher loading values of factor 3.

Factor 4: Factor 4 accounts for 12.48% of the total matrix. Thespecies ❅❆❇❈orotalia tumida, Pulleniatina obliquiloculata show positiveloading where as Candeina nitida, Globigerinoides sacculifer, Globorotaliascitula and Sphaeroidinella dehiscens show low to high negative loading onthis factor. The sample distribution coincides with cluster III.

❉❊❋ ●❍■❏❑▲▼ ◆❖◆❍P❏◗❏

Q mode cluster analysis reveals six associations defined by threedominant clusters. The characteristic species in this cluster are represented as:

●❘❙❚❯❱❲ ◗❳ Globigerinoides conglobatus, Globigerinoides ruber, andGlobigerinoides sacculifer

●❘❙❚❯❱❲ ◗◗❳ Globorotalia scitula, Orbulina universa, Globorotaliatumida and Globigerina spp

●❘❙❚❯❱❲ ◗◗◗❳ Neogloboquadrina dutertrei, Sphaeroidinella dehiscens,Candeina nitida and Pulleniatina obliquiloculata

The multivariate analysis attempted in this thesis, document animportant change in the distribution pattern of the Pleistocene-Holoceneplanktonic foraminifera at site 758 reflecting fluctuations due to the warmenvironment of deposition. A plot of planktonic assemblages versus depth andage (Figure 4.6) within the sequence at site ODP 758 reveals an overallprogression (with minor fluctuations) in time from high to low food, or fromlow to high oxygen content and preservation of shells through thePleistocene-Holocene. Several physicochemical and sedimentological factorshave been suggested to explain the distribution patterns of deep-sea

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planktonic foraminifera and these include water mass properties such astemperature, salinity, dissolved oxygen content and carbonate saturation(Phleger 1960; Lagoe 1976; Lohmann 1978; Murray 1979; Corliss 1979;Schnitker 1980 1993; Douglas and Woodruff 1981; Bremer and Lohmann1982 and Burke et al 1993). A comparison with planktonic foraminifer faunalvariability in the Indian Ocean sediments shows that the down core speciesvariability can be related to the changes in the mixed layer and the amount oftime the thermocline is in the photic zone. The variations can also be relatedto nutrient productivity and sea surface temperature. A Relative decrease inthe abundance of the population can be related to cool climate.

Planktonic faunal record of the core samples from the site 758shows significant variations over the last 100 ka (Figure 4.6) In this studymost of the species in cluster one and three are related to warm water origin.The patterns of variability for important species can be correlated with theMarine Isotope stage 3 and 2 (MIS 3 and 2) i.e. 28 ka to 60 Ka and 11ka to~27 ka and also a mild increase of CaCO3% during these stages.

An abundance of ❨❩❬❭❪❫❴❵❪❛❬❪❜❴s sacculifer (a surface dwelling,warm water, mixed layer tropical planktonic foraminifer), and ❝❵❭❞❩❪❛❡universa (an intermediate depth warm water subtropical foraminifera) with❨❩❬❭❪❫❴❵❪❛oides ruber indicate a warm, thick mixed layer in the easternIndian Ocean during 68 Ka, 42 Ka and 6 Ka. Relative abundance of ❝❵❭❞❩❪❛❡universa with ❨❩❬❭❪❫erinoides ruber in the core top samples at the northernend of Ninetyeast Ridge in the Indian Ocean correlates well with winterupwelling and productivity. A comparison of foraminifer faunal variationwith carbonate also points towards faunal variability that is decoupled fromchanges in preservation. A decrease in the population of ❝❵❭❞❩❪❛❡ universaand abundance of ❨❩❬bigerinoides sacculifer❢ ❨❩❬❭❪❫❴rinoides ruber togetherwith variation in the organic matter, organic carbon in the shell carbonate

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along the depth of the cores indicate a fluctuation in surface productivity ofnannos, cool climate during the Terminal Pleistocene.

Grain size data from ODP leg 121, North Indian Ocean indicatesthat the intensity of ocean circulation decreased bet 6-2.5 Ma and increasedthree times since 2.5 Ma (on the order of Berggren et al 1985 time scale) andthe sediment properties are organic carbon content, grain size, and pore wateroxygen concentration (Miller and Lohmann 1982; Corliss and Emerson 1990;Jorissen et al 1992; Gooday 1993; Smart et al 1994; Miao and Thunell 1993).However, the role of individual factor varies from place to place. Forinstance, Miller and Lohmann (1982) suggested that organic carbon,independent of oxygen levels, plays a major role in controlling distribution ofplanktonic foraminifera on the northeast United State Continental slope. Onthe other hand, Miao and Thunell (1993) found that sedimentary organiccarbon content and oxygen penetration depth are the two important factorscontrolling planktonic foraminiferal distribution in the South China and SuluSeas. Most of the recent studies acknowledge that organic matter plays animportant role in controlling population composition of planktonicforaminifera (Thomas et al 1992; Gooday 1993; Smart et al 1994; Gupta andThomas 1999). But, both oxygen content and food supply are inverselycoupled in the modern ocean and it is difficult to separate the two signals. Anincreased flux of organic matter to the sea floor consumes a significantamount of oxygen at the sediment-water interface, which can lead to oxygen-deficient conditions. On the other hand, with increasing water depth thedecline in organic carbon flux to the sea floor results in less oxygenconsumption and deeper oxygen penetration depth (Miao and Thunell 1993).Deep-sea ventilation also plays a role in controlling oxygenation (Gupta andThomas 1999).

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Several processes linked to the SW monsoon and Southeast Tradewinds control surface productivity. Open Ocean upwelling is due to themaximum vigor of the SEC and Rossby waves westward propagation(McCreary et al 1993) and westward transport of nutrients from theIndonesian region. These also play an important role in controlling surfaceproductivity at site 758. The southeasterly upwelling favourable along shorewinds induces upwelling along the Indonesian Archipelago during thesouthwest monsoon. The negative wind circulation between the Northeastmonsoon in the Southern Hemisphere and the southwest monsoon in theNorthern Hemisphere generates divergence south of the equator, shallowingmixed layer and causes Open Ocean upwelling (McCreary et al 1993). Allthese processes have led to the high surface productivity and higher rates ofbiogenic sediment accumulation (Cushing 1973, Tchernia 1980) duringMarine Isotope stage III and II (MIS 3 and 2) i.e. 28 Ka to 60 Ka and 11 Ka to~27 Ka.

❣❤✐❥igerinoides sacculifer is abundant in tropical and subtropicalwaters and prefers to live in the uppermost 25 m water column (Bé andHutson 1977; Hemleben et al 1989; Oberhansli et al 1992). Ravelo et al(1990) and Kroon et al (1991) considered it a warm water low salinity, mixedlayer, oligotrophic species. In the Indian Ocean, its highest percentages occurin tropical waters north of 10oS where temperature is relatively high (>25oC)and salinity is low (Bé and Hutson 1977). Oberhansli et al (1992) observedincreased percentages of ❣❤✐❥❦❧♠♥❦♦✐❦♣♠s sacculifer with increasing oxygencontent and slightly lowered salinity in the South Atlantic. While q♥❥r❤❦♦auniversa prefers to live in 25-100 m water depth (Hemleben et al 1989)having the highest abundance in the Indian Ocean in areas of modernupwelling and convergence in relatively cool waters (Bé et al 1973). Acomparative study of q♥❥r❤❦♦s universst ❣❤✐❥❦❧♠♥❦♦oides sacculifer and❣❤✐❥❦❧♠♥❦♦oides ruber indicates that the upper water column in the eastern

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Indian Ocean was warm during the MIS 3 and 2 periods of the LatePleistocene times. High occurrence of ✉✈✇①②gerinoides sacculifer (a surfacedwelling (~50 m), warm water, planktonic foraminifer), and ③④①⑤✈②⑥⑦universa (an intermediate depth (50m to100m) warm water subtropicalforaminifera) with ✉✈obigerinoides ruber during 68 Ka, 42 Ka and 6 Kaindicate warm water conditions in the eastern Indian Ocean.

Samples were analysed for planktonic assemblage, organic matter,organic carbon and calcium carbonate content to understand thepalaeoenvironmental change since the Late Middle Pleistocene period.

The four most abundant species (✉✈✇①②⑧⑨④②⑥oides rub⑨④⑩✉✈✇①②⑧⑨④②⑥oides sacc⑤✈②❶⑨④⑩ ✉✈✇bigerinoides conglobates and ③④①⑤✈②⑥⑦universa ) from the ODP site 758 (Leg 121) reveal fluctuations since the last100 Ka probably due to major changes in surface water properties liketemperature, salinity, dissolved oxygen content and carbonate saturation inthe Indian Ocean. Frequent changes have resulted from changes in surfaceproductivity associated with monsoon variability.

The dominant occurrence of ✉✈✇①②⑧⑨④②⑥✇②❷⑨s sacculifer (a surfacedwelling (~50 m), warm water, planktonic foraminifer), and ③④①⑤✈②⑥⑦universa (an intermediate depth (50 m to 100 m) warm water subtropicalforaminifera) with ✉✈obigerinoides ruber during 68 Ka, 42 Ka and 6 Kaindicate warm water conditions in the eastern Indian Ocean.

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❸❹❺❻❼ ❽❾❿ ➀➁➂❹➂❼➃ ➄➁mp➁➅❼➅➂ m❹➂➆➇➈ ❹➅➃ ➉❹➄➂➁r ❹➅❹❻➊➋❼➋ ➁➉ ➂➌❼➍❻❹➅➎➂➁➅➇➄

Component➏ ❿ ➐ ❽

Candeina nitida .179 7.974E-02 ❾➑❿➒ 3.381E-02Globigerinoides conglobatus, ❾➓➓➔ .345 .165 .241Globoquadrina hexagona .473 .366 .397 .294Globigerinoides ruber ❾→➔➒ .107 .169 .177Globigerinoides sacculifer ❾→→➒ .116 .223 7.980E-02Globorotalia scitula, .➓➑❿ .264 .240 3.749E-02Globigerina spp, .283 .368 .➔➔➒ .218Globorotalia tumida .419 .316 .458 ❾➣➏➏Neogloboquadrina dutertrei, .243 .➔→➒ .111 .262Orbulina universa ❾➣➐➑ .499 1.676E-02 .303Pulleniatina obliquiloculata .140 .118 9.978E-02 ❾➑➏➑Sphaeroidinella dehiscens .149 .→❿➏ .247 -2.12E-02

Extraction Method: Principal Component Analysis.Rotation Method: Varimax with Kaiser Normalization.Rotation converged in 6 iterations.

❽❾→ ↔↕➙❸➛➀ ↕➜↕➝➞➟➠➟ ➛↔ ❸➡➠ ➢➝↕➜➤❸➛➜➥➙

↔➛➀↕➦➥➜➥↔➠➀ ➟➙➛➀➠➟ ↔➛➀ ↔↕➙❸➛➀ ➏-4

Factor 1: Globigerinoides conglobatus, Globigerinoides ruber,Globigerinoides sacculifer, Globorotalia scitula, andOrbulina universa

Factor 2: Neogloboquadrina dutertrei, Sphaeroidinella dehiscens,Orbulina universa

Factor 3: Candeina nitida, Globigerina spp,Factor 4: Globorotalia tumida, Pulleniatina obliquiloculata

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➧➨➩➫➭➫➯➲➨➯➭➳ ➵➳➸➺➻➩➫ ➼➽➭➳➾➺➨➺

➚➩➽➪➫➶➹➫➭m ➸➺➨ng Average Linkage (Between Groups)Rescaled Distance Cluster Combine

C A S E 0 5 10 15 20 25Label Num. +---------+---------+---------+---------+---------+➘➴➷➬➮➱➷ 4 -+-----+➘➴✃❐❒❒UL 5 -+ +---+G.CONGLO 2 -------+ +-------------+G.SCICUL 6 -----------+ +---+G.HEXAGO 3 -------------------------+ +---------+G.SPP 7 -----------------+-------+ I IG.TUMIDA 8 -----------------+ +---+ +---+ORBULINA 10 -------------------------+ I +-+N.DUTERT 9 ---------------------------------------+ I +---+S.DEHISC 12 -------------------------------------------+ I IC.NITIDA 1 ---------------------------------------------+ IP.OBLIQU 11 -------------------------------------------------+

* * * * * * ** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Figure 4.9 Dendrogram of the planktonic foraminifer assemblage

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❮❰ÏÐÑÒ ÓÔÕÖ ×ØÙÚÛÜÝÚ❰Þ ßÝÑÙmàá âãá äÒÑÞÒÚÜÙÏÒà åà ÙÏÒÔ æÝÜÒ ÜçÙÜ ÜçÒÑÒ ❰à Ù à❰ÏÚ❰ß❰ÞÙÚÜ ❰ÚÞÑÒÙàÒ Ýß Orbulina universaGs sacculifer ÙÚè és ruber ÙÑÝÐÚd 68 Ka, 44 Ka and ~6 Ka.There is a positive trend during the MidHolecence period with the data relating to êëìíîïðñòó and other planktic species and this probably due toincrease in high palaeo productivity upwelling and intensity of monsoon. ôëõðíardii was not used as apotential proxy as this species in the sub samples was highly fragement and few species in full form.

Zone I 110 ka

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