International Journal of Geosciences, 2010, 1, 79-86
doi:10.4236/ijg.2010.12011 Published Online August 2010 (http://www.SciRP.org/journal/ijg)
Deep-Sea Benthic Foraminiferal Distribution in South
West Indian Ocean: Implications to Paleoecology
Nadimikeri Jayaraju1, Balam Chinnapolla Sundara Raja Reddy2, Kambham Reddeppa Reddy2,
Addula Nallappa Reddy3
1Department of Geology & Geoinformatics, Yogi Vemana University, Kadapa, India
2Department of Geology, Sri Venkateswara University, Tirupati, India
3ONGC Regional Geoscience laboratory, Chennai, India
Received May 14, 2010; revised June 13, 2010; accepted July 11, 2010
Abstract
Five grab samples from the southwestern part of the Indian ocean were collected by ORV Sagar Kanya dur-
ing the third expedition to the southern Indian ocean in June 2009. The sediment samples have been analyzed
and recorded 36 benthic foraminiferal species belonging to 21 genera and 3 suborders. All the species were
taxonomically identified, SEM photographed and illustrated. Deep sea-benthic foraminiferal species at dif-
ferent locations of South of West India Ocean (3150-4125 m water depth) is examined in terms of number of
species (n) and diversity (d). The observed depth ranges of benthic foraminifera have been documented to
recognize their bathymetric distribution. The valves of these parameters reached their maximum at 3190 m
water depth. Productivity continued in the Indo-Pacific Ocean (the biogenic boom) and the Oxygen mini-
mum zone (OMZ) intensified over large parts of Indian Ocean continually. The diversity values show more
abrupt trend as depth increases. Species like Epistominella exigua and Pullenia bulloides occur at both 3150
m & 3465 m depths indicating depth persistence. Further, Oridorsalis umbonatus and Melonis sphaeroides
occur at both 3150 m & 3465 m depths. Species like Gyroidina sp an indicate of low oxygen environment
and Uvigerina hispida-costata indicative of high organic carbon are found to occur at 3150 m & 3740 m re-
spectively. Factor analysis and Pearson correlation matrix was performed on foraminiferal census data of 10
highest ranked species which are present in at least one sample. 3 factors were obtained accounting for
72.81% of the total variance. Thus the study suggests that fluctuations in species diversity at the locations of
the present study were related to changes in productivity during the geological past. Further, the faunal data
do indicate the early Holocene Indian Ocean was influenced by increased ventilation perhaps by North At-
lantic deep water and or circumpolar deep waters.
Keywords: Paleoecology, Benthicforaminifera, Holocene, Indian Ocean
1. Introduction
Considerable amount of work has been done to under-
stand Paleoecology, Paleoclimatic and Paleoocenogra-
phic evolution of the Indian Ocean during Pleistocene
and Holocene using faunal data [1,2]. Benthic foraminif-
era have substantial scope in paleoecological studies be-
cause of their wide distribution in all marine environ-
ments and the high fossilization potential of their tests.
During the last three decades, several hypotheses have
been proposed to explain the distribution patterns and
ecologic preferences of this group. For instance, benthic
foraminifera have been used extensively to reconstruct
the past variability in deep water properties in different
ocean basins explained the relationship of various taxa
with different levels of deep-sea oxygenation, whereas
other studies have related benthic assemblages to the
intensity of deep sea currents and ventilation [3]. The
fact that benthic foraminifera occupy both epifaunal and
infaunal microhabitats led some workers to suggest that
sediment and pore water properties may be more impor-
tant than bottom water conditions in controlling benthic
foraminiferal distribution [4,5]. Other studies indicate
that benthic foraminiferal assemblages are strongly cor-

N. JAYARAJU ET AL.
80
related with productivity of the overlying surface waters
and the flux of organic matter to the seafloor. Faunal
proxy data suggests major changes in the Cenozoic
Earths climate forms relatively warm and equable cli-
mate in the Paleocene to cold conditions with nearly
frizzing temperatures at the poles in the Pliocene [6].
Other changes during this time include those in ocean
circulation and productivity and opening and closing of
different seaways, including the closure of Tethyan Sea-
ways, including the closure of the Panamanian sea way
in the Pliocene [7]. The changes in Antarctic climate
during the middle Miocene brought significant changes
in ocean surface productivity and oxygenation of deep
waters as well [8], which had an impact on the oceans
faunal regime. Productivity has increased significantly in
all oceans since the late middle Miocene (~ 13 Ma). The
increased glaciations on Antarctica may have intensified
wind regimes, loading to widespread open-ocean as well
as coastal upwelling over large parts of the Indian, Pa-
cific and Atlantic oceans during the middle Miocene [8].
These productivity events are believed to have triggered
the “biogenic bloom” and expansion of the oxygen mini-
mum zone in large parts of the intermediate water of the
Indian and Pacific Oceans in the late middle Miocene,
about 15 Ma [9]. With these climatic and oceanic changes,
deep-sea faunal diversity changed considerably [10].
Availability of nutrients, heterogeneity of the habitat
and predation are factors controlling diversity patterns in
the deep-sea fauna [10]. It’s also observed, low values of
species diversity during intervals of environmental insta-
bility in the South Indian Ocean in the middle – late
Miocene. The high productivity and subsequent micro-
bial decay of organic matter, as well as biotic respiration
and other oceanographic factors, lead to extremely low
oxygen concentrations in the water column, forming a
pronounced oxygen minimum zone (OMZ). Underlying
sediments thus contain a geological record of changes in
the SW monsoon and OMZ variability [11]. Benthic fo-
raminifera dominate modern ocean floor meiobenthic
communities, and in many deep-sea areas, constitute a
substantial proportion of the eukaryotic biomass [6]. Due
to their high fossilization potential they area very useful
in paleooceanograpgic studies. The factors controlling
their distribution and abundance are complex and con-
troversial [12], but it appears that two usually inversely
related parameters, the flux of organic particulate matter
to the sea floor and oxygen concentrations of bottom wa-
ter and pore waters, are major controlling variables [5].
Other factors which have been suggested (and some of
which are not independent of these two) include the type
of food supply, bathymetry, sediment type, chemistry of
bottom waters current flow intensity and hydrostatic
pressure [13]. The supply of organic matter from the
euphotic zone to the ocean floor exerts a strong influence
on the abundance and biomass of deep-sea benthic fo-
raminifera [12] as on other deep-sea organisms.
The composition of benthic foraminiferal assemblages
is closely related to the amount and quality of organic
matter. Assemblages dominated by the in faunal species
Bolivina, Bulimina, Melonis and Uvigerina commonly
occur in areas with high, continuous fluxes of organic
matter to the sea floor, often associated with reduced
bottom water oxygen concentrations. It has been shown,
however, that Uvigerina spp are correlated to organic
flux and not to low oxygen conditions. To understand the
distribution and diversity of benthic foraminifera at dif-
ferent bathymetric levels, the present study was carried
out. Benthic foraminiferal species used in the faunal
study include, Uvigerina hispida-costata which was
dominant during times of high productivity and /or low
oxygen and Oridorsalis umbonatus and Quinqueloculina
parkeri characteristic of well oxygenated, oligotrophic
conditions. Changes in organic flux to the sea floor due
to variations in surface productivity modulate deep-sea
faunal composition [3]. The amount of organic flux to
the sea floor not only depends on surface production but
also on the nature of deep-sea column. Well oxygenated
deep-sea circulation may cause remineralization of or-
ganic carbon resulting in little organic material reaching
the sea floor [14]. To understand if the changes in the
surface and deep-water column of the tropical condition
ocean driven by the Indian ocean climate (monsoon) and
deep-sea circulation, an attempt has been made to ana-
lyze deep-sea benthic foraminifera from varying depths
from (3150 m, 3465 m and 4125 m) (Figure 1). The in-
vestigations of benthic foraminifera from south west In-
dian Ocean provided data on the species distribution and
species-specific relations for different depths and areas.
These data were later used to distinguish faunistive
provinces with the implication to paleoecology. The
study presented is aimed at the description of the bio-
geography and ecology of foraminifera communities
based on the data about the dominant species in the
tropical Indian Ocean and their occurrences in other ar-
eas of the world Ocean.
2. Materials and Methods
The study sites are located at different depths of 3150 m
(N 10º E 65º ); 3465 m (N 5º E 65º); 3790m (N 0º E 65º )
and 4125 m (N 5º E 65º) in the South West Indian Ocean.
The samples were collected from ORV Sagar Kanya
during the third expedition to the southern Indian Ocean
by National Center for Antarctica and Ocean Research,
(NCAOR) Goa, India, in June, 2009. Sediment samples
were transferred into plastic bags and frozen until analy-
sis was carried out. The sediment samples were first
washed over a sieve which is an average opening of
0.625 mm. This process helps to wash the sample free of
sea water, fixatives, and the fine silt and clay size parti-

N. JAYARAJU ET AL.
81
cles. Then a sample was air dried and a suitable sample
weighing about 100 grams was obtained by coning and
quartering. Samples were spilt using a micro splitter and
all benthic foraminifera were picked and identified [15].
Quantitatively, foraminifera could not be separated easily
with washing carbon tetra chloride only, so a mixture of
Bromoform (specific gravity 2.8) and Acetone (specific
gravity 2.4) were used to obtain about 15% crop from the
sediment [16]. The residue was examined under a stereo
binocular microscope for any left out fauna. Such tests
were handpicked by a very fine pointed long haired
welted Windsor Newton sable hair brush (“0”). The
fauna thus obtained was sorted, counted and identified
under a stereo binocular microscope using medium to
high magnifications (6.3 × 2.5; 6.3 × 4.0). The sampling
procedures especially sieving and drying reduce the
number of the most fragile arenaceous foraminifera (Ta-
ble 2). Statistical analysis was done by multivariate
analysis, correlation analysis was applied to compare and
correlate the data generated based on bathymetry [17].
Details of the hydrography, primary productivity and
upper ocean mixed layer dynamics are given earlier [18].
To day, the depth of site 4125 m (S 10º E 65º) is close
to the calcite Lysocline which, in this part of the Indian
Ocean, has been considered to lie between 4000-4200 m
and approaches calcite composition depth (CCD). This
area was selected because it is a relatively flat area, far
from continental shelf to the east and the mid-ocean
ridge to the west and so is unlikely to be influenced by
strong down slopes or adjective process. Recent sedi-
ments in the study area are calcareous oozes with rich
biogenic carbonate with CaCO3. In this study, the abso-
lute abundance and species diversity of fauna in the
sediment fraction of > 63 µm in weight % of total sedi-
ment. In addition, the state of preservation of foraminif-
eral tests was noted in the samples. Benthic foraminiferal
species Uvigerina hispida-costata, Oridorsalis umbona-
tus and Quinqueloculina spp to understand changes in
deep-sea organic carbon and oxygen content. Approxi-
mately 100-300 specimens of benthic foraminifera were
picked from a suitable sample and their diversity and
distribution were calculated (Table 1).
3. General Setting
Sampling stations are, at present located in subtropical
waters. In the present-day locations, is bathed by low-
oxygen and relatively productive deep waters of the
northern Indian origin deep-sea benthic foraminife ra-
provides useful information on the influence of various
deep-water masses in the region. The physico-chemical
properties of the surface waters in the western Indian
Ocean are strongly influenced by African through flow
water because of substantial export of freshwater and
heat from the Pacific into the Indian Ocean through the
Indian seas. At present, the area is influenced by the
summer monsoon winds producing major divergence and
an open-ocean upwelling. In the present-day ocean, the
in situ primary production in the surface waters is be-
tween 200 and 300 mg during the summer monsoon,
which is reduced during the winter monsoon.
Table 1. Benthic foraminiferal species number with depth (m).
Depth (m)
S.No.Species
3150 3465 3790 4125
1 Marginopora vertibralis 164
2 Sorites marginalis 131
3 Borelis schlumbergeri 152
4 Heterostegina depressa 140
5 Elphidium crispum 131
6 Ammonia tepida 129
7 Quinqueloculina parkeri 153
8 Spirillina decorata 146
9 Textularia sagittula 133
10 Eponides repandus 136
11 Calcarina calcar 166
12 Gyroidina sp. 156
13 Pyrgo murrhina 145
14 Bulimina alazanensis 135
15 Pullenia subcarinata 148
16 Discopulvinulina
bertheloti 164
17 Epistominella exigua 281 292
18 Pullenia bulloides 136 156
19 Gyroidina neosoldani 145
20 Astrononion umbilica-
tulum 142
21 Planulina wuellerstorfi 132
22 Oolina apiculata 163
23 Oolina desophora 155
24 Laticarinina pauperata 145
25 Fissurina sp. 165
26 Fissurina alveolata 148
27 Nummoloculina sp. 156
28 Pullenia quinqueloba 148
29 Lagena stelligera 158
30 Oridorsalis umbonatus 286 278
31 Melonis sphaeroides 279 214
32 Chilostomella
ovoidea 153
33 Uvigerina hispida 289
34 Uvigerina his-
pido-costata 163
35 Eggerella bradyi 180
36 Karreriella bradyi 163

N. JAYARAJU ET AL.
82
4. Ecological Preference of Foraminiferal
Proxies Used
The study of benthic foraminifera is very useful in inter-
preting the changes in deep-sea environment. They are
the longest biomass present at the lower (> 1000 m) and
abyssal depths in the modern oceans and are the dominant
carbonate tests to be preserved in the deep sea sediments.
Many benthic species have separate stratographic ranges
and their evolutionary and migratory patterns provide
significant biostratigraphic and paleo-ecological informa-
tion about the deep-sea environments [19].
Uvigerina hispido-costata preferentially occupies the
uppermost surface centimeter of organic rich sediments
feeding on sediment aggregates, algal remains, and bac-
teria having highest abundance in the lower part of the
OMZ below upwelling areas reflecting a preference for
suboxic or dysoxic conditions in the pore bottom water
[20]. This species has highest population at water depths
between ~300 and 800 m with insitu temperature 10-
15ºC and low oxygen. This species has been used as an
indicator species for deepening/shoaling of the OMZ
base in the northern Arabian Sea [21]. The large abun-
dance of U. perigrina in the lower part of the OMZ or
below indicate adaptation of this species to degraded
organic matter [21]. Oridorralis umbonatus is a cosmo-
politan taxon or lower bathyal and abyssal faunas in the
Indian [22]. The Atlantic [23] and Antarctic oceans [24]
and is often found associated with Antarctic bottom wa-
ter (AABW) [22]. This species has been reported to in-
dicate a well oxygenated and low organic carbon envi-
ronment [25]. This species was probably of southern
origin with a strongly pulsed food supply and carbonate
preservation in an overall oligitrophic environment in the
eastern Indian [26]. O. umbonatus reflects low organic
carbon and higher carbonate saturation levels of bottom
waters in the Sulu Sea [27]. Quinqueloculina is a cos-
mopolitan miliolid group found between 800-5000 m
water depths in the Indian Ocean [28]. The persistence
occurrence of milioliods in the Arabian sea indicates an
overall better oxygenation of benthic environment and
thus this group can be regarded as a sensitive oxygen
marker and its population a toll for reconstructing past
climatic changes in bottom water oxygenation [29]. High-
er abundance of miliolid group in sediments deposited
during glacial intervals under higher-salinity conditions in
the northern Red Sea. Miliolids in general, are rare or
absent oxygen deferent environments [13]. Bulimina al-
zaninsis is an intermediate to deep in faunal (> 2 cm) spe-
cies in the Sulu sea and is dominant at bathyal depths
(1500-2000 m) just below the Arabian sea OMZ [30].
5. Discussion
In the Indian Ocean, changes in benthic foraminiferal po-
pulations have occurred at orbital time scales and have
been related to changes in the Indian monsoons [31].
More recently, [2] used environmental preferences of
various benthic foraminiferal assemblages and related
them to change in seasonality in the Indian Ocean mon-
soon during the Plio-Pleistocene. In the present study, we
attempt to understand paleoceanographic changes in the
southeastern Indian Ocean using multivariate analysis of
deep-sea benthic foraminiferal census data from south
western sampling stations (Figure 1). The interpretations
are based on recent environmental preferences of various
benthic foraminiferal taxa observed in the Indian as well
as abroad.
Deep-sea benthic foraminifera have been used to un-
derstand changes in deep water condition driven by cli-
mate forcing during the Pliocene and Pleistocene [29].
Several studies have been shown the relationship be-
tween benthic faunal composition, productivity of the
overlying waters and organic flux to the sea floor [12].
Others suggested oxygen and food supply are the main
factors controlling the spatial and in-sediment distribu-
tion of benthic foraminifera [29]. This group explains
seasonal fluctuations in primary production [5]. Thus
benthic foraminifera are considered useful for estimating
paleoecology and they are also more resistant to dige-
netic change compared to planktic foraminifera. How-
ever, in oligotrophic areas deep-sea oxygenation plays an
important role in controlling benthic foraminifera over
different time scales. It is believed that changes in oxy-
genation are linked partially to productivity and partially
to changes in deep-water ventilation [3]. Wind driven
coastal and open-ocean surface productivity influences
organic carbon flux and oxygenation of deep waters con-
trolling benthic populations in the Arabian Sea. In the
Northern part of the Indian Ocean, the wind regimes fol-
low seasonal changes in circulation producing wide
spread upwelling controlling surface productivity. Be-
cause of the sampling locations in oligotrophic areas
Figure 1. Map showing sampling locations in the tropical
Indian Ocean.

N. JAYARAJU ET AL.
83
with high dissolved oxygen content during the studies
period, the changes in benthic foraminiferal population
might have been linked to the supply of organic food.
6. Results
The absolute abundances (number of specimens per gram
bulk sediment) of benthic foraminifera fluctuate largely.
A total of 36 species of benthic foraminifera were recog-
nized comprising predominantly of small calcareous
species. In the samples (3150 m, 3465 m, 3790 m and
4125 m water depth) used in the benthic foraminiferal
distribution, the abundant species occur in sample 3150 m
are Gyroidina sp, Pyrgo murrhina, Bulimina alazanensis
Pullenia subcarinata, Discopulvinulina bertheloti, Epis-
tominella exigua and Pullenie bulloides; at sample 3465
m depth are Epistominella exigua, Pullenia bulloides,
Gyroidina neosoldani and Astrononion umbilicatalum; at
sample 3790 m depth are Planulina wullerstorfi, Oolina
apiculata, Oolina desophora, Laticarinina pauperata,
Fissurina alveolata, Nummoloculina sp, Pullenia quin-
queloba, Lagena stelligera, Oridorsalis umbonatus,
Melonis sphaeroides and Chilostomella ovoidea at sam-
ple 4125 m water depths are Uvigerina hispido-costata,
Eggerella bradyi and Karreriella bradyi.
7. Factor Analysis
The foraminiferal data census of 10 species was sub-
jected to the factor analysis. The analysis yield three
factors namely Factor 1 (37.11%), Factor 2 (25.87%) and
Factor 3 (10.83%) accounting for 72.81% (Table 3).
Factor 1
Factor 1 represented by Uvigerina hispida (0.827),
Eggerella bradyi (0.827), Epistominella exigua (−0.796)
and Pullenia bulloides (0.766). Uvigerina hispida relates
continuous, high organic flux, low seasonality. Eggerella
bradyi reflects cool, carbonate corrosive organic flux,
variable and high oxygenation [8].
Factor 2
Factor 2 is dominated by Gyroidina neosoldani (−
0.984), Astrononion umbilicatulum (−0.984); Oridorsalis
umbonatus (0.713) and Melonis sphaeroides (0.700).
This factor indicates intermediate organic flux, interme-
diate to high seasonality, high-moderate organic flux,
intermediate high seasonality, refractory organic matter.
However, Oridorsalis umbonatus tend to reflect rela-
tively warm intermediate organic flux, intermediate sea-
sonality, and moderate oxygenation [8].
Factor 3
Factor 3 comprises of Calcarina calcar (−0.465), Ori-
dorsalis umbonatus (0.364) and are Epistominella exigua
(−0.306). Three species indicate cool strongly pulsed, low
to intermediate organic flux, high seasonality. In addition,
relatively warm intermediate organic flux, intermediate
seasonality, moderate oxygenation is also reflected.
A cross plot of Factors 1 & 2 and Factors 1& 3 gives
district information of faunal assemblages a set clustered
similar factor. Pearson correlation matrix of dominated
species (Table 2) shows the distinct positive and nega-
tive correlation with a specific species. Calcarina calcar
and Gyroidina sp shows high positive relation with
Melonis sphaeroides (0.717), Oridorsalis umbonatus
(0.594), Epistominella exigua (0.555). Epistominella
exigua and Pullenia bulloides correlated positively with
Pullenia bulloides (0.998), Gyroidina neosoldani (0.599)
and Astrononion umbilicatulum (0.599). Where as Gy-
roidina neosoldani, Astrononion umbilicatulum, Oridor-
salis umbonatus, Melonis sphaeroides shows negative
correlation with other species (Table 2). The vertical
distribution of living benthic foraminifera within the
sediment is controlled largely by a combination of oxy-
gen content and organic carbon levels [4,13]. In eutro-
phic regions, oxygen decreases close to the sediment
surface and becomes a limiting factor, favouring low-
Table 2. Pearson correlation matrix of 10 dominant species.
Variables Calcarina
calcar
Gyroid-
ina sp.
Epistominella
exigua
Pullenia
bulloides
Gyroidina
neosoldani
Astrononion
umbilicatulum
Oridorsalis
umbonatus
Melonis
sphaeroides
Uvigerina
hispida
Eggerella
bradyi
Calcarina calcar 1
Gyroidina sp. 1.000 1
Epistominella
exigua 0.555 0.5551
Pullenia bulloides 0.496 0.4960.998 1
Gyroidina neo-
soldani −0.333 −0.333 0.599 0.653 1
Astrononion
umbilicatulum −0.333 −0.333 0.599 0.653 1.000 1
Oridorsalis um-
bonatus 0.594 0.594−0.005 −0.055 −0.577 −0.577 1
Melonis sphaer-
oides 0.717 0.7170.108 0.053 −0.568 −0.568 0.987 1
Uvigerina hispida −0.333 −0.333 −0.577 −0.575 −0.333 −0.333 −0.577 −0.568 1
Eggerella bradyi −0.333 −0.333 −0.577 −0.575 −0.333 −0.333 −0.577 −0.568 1.000 1

N. JAYARAJU ET AL.
84
Table 3.Factor loading scores for 10 dominant species.
Species F1 F2 F3
Calcarina calcar −0.786 0.408 −0.465
Gyroidina sp. −0.786 0.408 −0.465
Epistominella exigua −0.796 −0.522 −0.306
Pullenia bulloides −0.766 −0.579 −0.281
Gyroidina neosoldani −0.146 −0.984 0.100
Astrononion umbilicatulum −0.146 −0.984 0.100
Oridorsalis umbonatus −0.600 0.713 0.364
Melonis sphaeroides −0.679 0.700 0.220
Uvigerina hispida 0.827 0.161 −0.539
Eggerella bradyi 0.827 0.161 −0.539
oxygen species. In oligotrophic areas, most of the or-
ganic matter is remineralized near the sediment surface
and the sediment is well oxygenated to a significant
depth. Such environments are foodlimited and favour
epifaunal species, which are intolerant of low oxygen
concentrations. [5] suggested that the dynamics of fo-
raminiferal populations can be explained by the interplay
between food and oxygen availability. For example, in
eutrophic environments population fluctuations will be
driven mainly by changes in both food and oxygen avai-
lability whereas in food-limited (oligotrophic) systems
the populations will be driven solely by changes in the
food supply [14]. It has been found that some species of
benthic foraminifera are opportunistic and prefer to feed
on seasonal fluxes of organic matter in overall oligotro-
phic central oceanic areas or seasonally upwelling areas
on continental margins [32]. The non-opportunists thrive
during sustained supply of organic particles [6,32]. Be-
sides, certain species have a preference to decayed or-
ganic matter that reaches the seafloor [4,21].
The vertical distribution of benthic foraminifera in In-
dian Ocean is given in Table 2. A total of 36 species of
benthic foraminifera were recognized comprising pre-
dominantly of small calcareous species from western
Indian Ocean and 11 larger benthic species from Mauri-
tius. The table shows that species like Epistominella ex-
igua and Pullenia bulloides occur at both 3150 m and
3465 m depths indicating depth persistence. Epistomi-
nella exigua is an epibenthic, cosmopolitan, abyssal spe-
cies, which feeds opportunistically on phytodetritus de-
posited seasonally on the sea floor [11]. It is suggested
that this species is most abundant at highly seasonal food
fluxes that occur more than once a year (e.g., spring and
fall blooms; [14]). Futhermore, Oridorsalis umbonatus
and Melonis sphaeroides occur at both 3150 and 3740 m
depths indicating shelf fauna. species like Gyroidina spp
an indicative of low oxygen environment and Uvigerina
hispido-costata indicate high organic carbon are found to
occur at 3150 m and 4125 m respectively. Changes in
open-ocean surface productivity, linked to the wind re-
gimes and major surface currents, influence the organic
carbon fluxes and oxygenation of deep waters and thus
benthic populations. Samplings Sites has moved from a
temperate to subtropical position through the Miocene
and is suitable to understand the effect of this northward
movement on deep-sea fauna. The benthic foraminiferal
vertical distributional pattern indicates important shifts in
the character and amount of organic carbon flux and in
oxygenation of deep waters at stations. This study sug-
gests that benthic ecosystem variability in the deep In-
dian Ocean is not only driven by variations in monsoonal
upwelling and related organic matter flux but also by
changes in deeper water ventilation; increased summer
monsoon circulation may not always result in an oxygen
poor deep ocean with increased to total organic carbon
(TOC) accumulation.
8. Conclusions
1) Benthic foraminiferal faunal distribution and species
is erratic and appears to be influenced by availability of
nutrients and oxygen content during seasonal upwelling
(Table 4).
2) Changes in the abundance and diversity of benthic
foraminiferal fauna are likely caused by variations in
seasonal upwelling on the ocean floor at the sampling
site.
3) The foraminiferal data show that it’s relatively well
oxygenated OMZ where the influence of intense mon-
soon-related production was migrated.
4) The high variability in the tropical deep-sea envi-
ronments occurred at a time when the earth’s climate was
exploring large scale turnovers due to the increased in-
tensity of glacial-interglacial cycles (Table 4).
9. Acknowledgements
We thank students for providing the samples used in this
Table 4. Benthic foraminiferal species and bio faces.
Factors Environment
Factor I
Uvigerina hispida (0.827)
Eggerella bradyi (0.827)
Epistominella exigua (−0.796)
Calcarina calcar (−0.786)
Continuous High organic flux
Low seasonality, Cool
Carbonate, Corrosive organic
flux variable, high oxygenation.
Factor II
Gyroidina neosoldani
(−0.984)
Astrononion umbilicatalum
(−0.984)
Oridorsalis umbonatus (0.713)
Melonis spharoides (0.700)
Intermediate organic flux,
Intermediate to high seasonality
High-moderate organic flux
intermediate seasonality
Factor III
Calcarina calcar (−0.465)
Oridorsalis umbonatus (0.364)
Epistominella exigua (−0.306)
Cool, Strong by pulsed organic
flux, high oxygenation, high
seasonality, Relative warm,
intermediate seasonality, Mod-
erate oxygenation
*Values in parenthesis indicate factor scores for species.

N. JAYARAJU ET AL.
85
study, collected from Indian Ocean expedition organized
by National Center for Antarctica and Ocean Research
(NCAOR), in Sagar Kanya, 2009. The very useful com-
ments of the anonymous reviewers significantly im-
proved the manuscript and are grateful acknowledged.
SEM microphotographs are taken at Oil Natural Gas
Corporation, Regional Labs, Chennai, India. Thanks are
due to Prof A. R. Reddy, Vice-Chancellor, Yogi Vemana
University, Kadapa for encouragement.
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