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39
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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40
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.
40
40
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.
40
40
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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41
41
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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42
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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43
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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44
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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45
✣✤✥ ✦✧★✩✪✩ ★✫✬ 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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47
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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48
✯✰✱✲✳✴ ✵✶✷ ✸✹✺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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49
❂❃❄❅❆❇ ❈❉❊ ❋●❍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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50
50
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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51
❝❞❡❢❣❤ ✐❥✐ ❦ ❣❧♠❞♥♦ ♣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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52
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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53
53
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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54
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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55
55
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
55
55
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
55
55
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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56
➡➢➤➥➦➧ ➨➩➫ ➭➯➧ ➲➢➳➵➦➢bution of Trace elements concentration in
the ODP Site Sediment core
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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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58
ÚÛÜÝÞß àáâã- b PAAS normalized REE diagram of ODP Sediments
CoreLeg 121
58
58
Figure 4.7a- b PAAS normalized REE diagram of ODP Sediments
CoreLeg 121
58
58
Figure 4.7a- b PAAS normalized REE diagram of ODP Sediments
CoreLeg 121
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59
äåæçèé êëì í-e. PAAS normalized REE diagram of ODP Sediments
CoreLeg 121 PAAS normalized REE diagram of ODPSediments
59
59
Figure 4.7 c-e. PAAS normalized REE diagram of ODP Sediments
CoreLeg 121 PAAS normalized REE diagram of ODPSediments
59
59
Figure 4.7 c-e. PAAS normalized REE diagram of ODP Sediments
CoreLeg 121 PAAS normalized REE diagram of ODPSediments
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60
îïgure 4.8 Age VS Eu* and REE of the marine sediments
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61
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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62
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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63
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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64
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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65
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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71
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
-
73
❮❰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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