GeolCarp_Vol66_No1_69

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, FEBRUARY 2015, 66, 1, 69—80 doi: 10.1515/geoca-2015-0011

Distribution of coccolithophores as a potential proxy in

paleoceanography: The case of the Oman Sea monsoonal

pattern

ELHAM MOJTAHEDIN

, FATEMEH HADAVI

and RAZYEH LAK

Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, IR Iran;

e.mojtahedin@yahoo.com

Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, IR Iran; lak@ries.ir

(Manuscript received April 22, 2014; accepted in revised form December 10, 2014)

Abstract: High abundances of coccoliths have been observed in surface sediment samples from near the coasts of the
Oman Sea in February 2011. At the end of the NE monsoon, the locally observed high Gephyrocapsa oceanica produc-
tion is hypothesized to respond to local injections of nutrient-rich deep water into the surface water due to sea-surface
cooling leading to convection. The most abundant coccolithophore species are G. oceanica followed by Emiliania
huxleyi, Helicosphaera carteri, Calcidiscus leptoporus. Some species, such as Gephyrocapsa muellerae, Gephyrocapsa
ericsonii, Umbilicosphaera sibogae, Umbellosphaera tenuis and Florisphaera profunda, are rare. The G. oceanica
suggested a prevalence of upwelling conditions or high supply of nutrients in the Oman Sea (especially West Jask) at the
end of the NE monsoon. E. huxleyi showed low relative abundances at the end of the NE monsoon. Due to the location
of the Oman Sea in low latitudes with high temperatures, we have observed low abundances of G. muellerae in the study
area. Additionally, we have identified low abundances of G. ericsonii at the end of the NE monsoon. Helicosphaera
carteri showed a clear negative response with decreasing amounts (relative abundances) at the end of the NE monsoon.
C. leptoporus, U. sibogae and U. tenuis have very low relative abundances in the NE monsoon and declined extremely
at the end of the NE monsoon. F. profunda, which is known to inhabit the lower photic zone ( < 100 m depht) was rarely
observed in the samples.

Key words: Coccolithophores, northeast monsoon, nannoplankton distribution, paleoceanography, Oman Sea.

Introduction

Coccolithophores, being very sensitive to changing environ-
mental  conditions,  play  a  vital  role  in  reconstructing  the
paleoceanography of Quaternary sediments. Recently, cocco-
lithophores have gained increased attention as they make an
important contribution to oceanic primary production (West-
broek et al. 1993). However, a better understanding of cocco-
lithophore  ecology  is  necessary  in  order  to  use  them
successfully as a biotic proxy of past climate change and to
assess the quality and accuracy of the information preserved
in the sedimentary record (Ziveri & Thunell 2000). The hy-
drography  of  the  Oman  Sea  is  controlled  by  the  Indian
Ocean monsoon. This inter- hemispheric phenomenon repre-
sents one of the Earth’s most dynamic interactions between
atmosphere,  oceans  and  continents,  and  influences  climate
seasonally  from  eastern  Africa  through  to  southeast  Asia.
Environmental  gradients  change  distinctly  between  the
SW-monsoon  in  summer  and  the  NE-monsoon  in  winter
(Fig. 1a). Plankton productivity is directly dependent on the
seasonally changing wind system leading to strong seasonality
in export production with peaks during the SW- and NE-mon-
soons  (Nair  et  al.  1989;  Haake  et  al.  1993;  Ramaswamy  &
Nair 1994). Upwelling is one of the phenomena that occur in
the West Oman Sea near West Jask.

A new insight into the reconstruction of the oceanographic

variations in the Oman Sea related to the monsoon system is
presented in this paper. A first step attempts to relate cocco-

lithophore assemblages with oceanographic conditions in the
upper water column. Thereby, we hope to obtain information
on the oceanographic response to the recent monsoonal sys-
tem useful for the paleo-climatic and paleo-oceanographic
interpretation of fossil coccolithophores in the Oman Sea
sediments during the Holocene.

Previous studies

There is no report on coccolith distribution in the sediments

of the Oman Sea, but some papers were produced on micropa-
leontology  from  the  foraminifera  point  of  view,  including
Moghaddasi et al. 2009a,b. The first report on the coccolitho-
phores  of  the  Persian  Gulf  was  written  by  Martini  (1971).
Kassler  (1971)  observed  the  calcareous  nannofossils  in  the
Holocene soft and fine grain marls of the Persian Gulf as pre-
dominant microfossils which exist mainly in the surface sedi-
ments as well as in the area with huge amounts of carbonate.
A list of 10 species of calcareous nannoplankton was reported
by Al-Saadi et al. (1978). The first study of phytoplankton of
the Iranian part of Persian Gulf was carried out by Hulburt et
al. (1981). According to Andruleit et al. (2000), G. oceanica,
F.  profunda  and  E.  huxleyi  are  abundant  in  the  NE  Arabian
Sea  samples  and  their  productivity  increases  during  the  SW
and NE monsoon. Andruleit et al. (2003) studied the samples
from the North of the Arabian Sea. Andruleit et al. (2005) re-
ported  the  origin  and  the  oscillation  of  Coccolithophores  in

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the  North  of  the  Arabian  Sea.  The  oscillation  of  Coccolitho-
phores varies in the sediments which are deposited per season.
The relationships between seasonal deposition, the abundance
of index species and their calcification were investigated. Ha-
davi  (2011)  has  sampled  the  Persian  Gulf  from  various  lati-
tudes  in  order  to  investigate  the  variety  of  Coccolithophores
and  the  paleoecological  studies.  Pouresmaeil  et  al.  (2012)
studied Holocene surface sediments of the Persian Gulf.

Environmental settings

The Oman Sea is located between 22 and 26°N and 56 and

62°E.  It  opens  onto  the  Northwestern  Indian  Ocean  and
Arabian  Sea.  The  general  orientation  of  the  Oman  Sea  is
northwest-southeast.  In  terms  of  geomorphology,  this  semi-
enclosed basin is “a bathymetric triangle” featuring a range of
depths of up to 3000 m in its oceanic part, but with the shal-
low  Murray  Ridge  extending  across  the  mouth  of  the  Oman
Sea. It is situated in the subtropical zone and has the total area

of 94,000 km

. The basin narrows down and gets shallower

towards the Strait of Hormuz – the westernmost boundary of
the Oman Sea, where depths of 70—110 m separate it from the
inner part of the Oman Sea, with an average depth of ~ 35 m.
The region is arid leading to substantial evaporation, greatly
exceeding precipitation and river discharge.

White & Louden (1982) showed that the crust beneath the

Oman Sea is oceanic in nature, with about 6 km of oceanic
igneous crust underlying 7 km of normally compacted sedi-
ments; from a refraction line on the Makran continental crust
they found that the oceanic crust dips northward to an angle
of 1.5°  to  2°  with  a  steadily  thickening  wedge  of  overlying
sediment. This is in agreement with simple two dimensional
gravity models across the margin (White 1979). These sedi-
ments mainly consist of a lower section with turbidite about
4 km  thick  called  the  hymalayas  (Paleocene—Miocene)  and
an  upper  section  with  a  thickness  of  about  3 km  known  as
the  Makran  Sand  (Pliocene—Pleistocene).  Sediments  known
as  the  Makran  Sand,  are  covered  by  a  thin  coating  of  Ho-
locene sediments on them.

Fig. 1. a – General wind and surface water circulation in the Oman Sea and Arabian Sea, b – Sea surface Temperature in the Oman Sea in
February 2011, c – Chlorophyll concentration (mg/m

) in Oman Sea in February 2011.

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Being situated between the shallow high salinity waters of

the  Persian  Gulf  and  the  deeper  Arabian  Sea,  the  Oman  Sea
possesses a unique hydrological regime. The modern summer
monsoon is primarily driven by differential (land-ocean) sen-
sible  heating  and  tropospheric  latent  heating  (Clemens  et  al.
1991). These combined mechanisms result in a distinct atmo-
spheric circulation system with seasonally changing wind di-
rections. In winter, during the Northeast Monsoon, the current
transporting the Arabian Sea water mass from the oceanic re-
gions into the Oman Sea is headed towards its inner part along
the northern (Iranian) coast. In summer, during the Southwest
Monsoon, the sea is influenced by the outflow of high saline
Oman Sea water mass. The current exits from the Oman Sea
in the Strait of Hormuz at a depth of  ~ 100 m, cascade down to
the bottom and propagate along the Omani coast towards the
open Arabian Sea. A well pronounced density front separates
high saline deep water in the Oman Sea from fresher surface
waters  in  it  (Piontkovski  et  al.  2012).  The  most  prominent

feature of the Oman Sea is the seasonal upwelling along the
Iranian coast, with a peak in February—March, although the
onset of the Northeast monsoonal winds could occur in De-
cember. During the Northeast Monsoon, the Oman Coastal
Current reverses to a southeastward flow. The climate in the
Oman Sea is markedly different from the climate in the Ara-
bian Gulf. While the Oman Sea is affected mainly by extra-
tropical weather systems from the northwest, the Oman Sea is
situated on the northern edge of the tropical weather systems
in the Arabian Sea and Indian Ocean.

The sea surface temperature (http://seawifs.gsfc.nasa.gov/

SEAWIFS.html)  distribution  exhibits  medium  to  relatively
high temperature  of  the  study  area  (Fig. 2b).  This  configura-
tion clearly depicts the influence of the NE monsoon. During
the NE-monsoon, low water temperatures in the northeast are
caused  by  cool  and  dry  winds.  Chlorophyll  concentrations
(http://seawifs.gsfc. nasa.gov/SEAWIFS.html) have their ma-
xima during the NE-monsoon in the entire Oman Sea (Fig. 2c).

Fig. 2. Bathymetry of the study area with location of the samples (Gabrik area).

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Materials and methods

Surface sediment samples for the present study were col-

lected  in  the  Oman  Sea  in  February  2011  at  the  end  of  the
NE-monsoon.  The  samples  were  collected  with  grabs  by  a
research cruise. The materials were carefully taken from the
average  of  3—5  centimeters  from  beneath  the  Oman  Sea.  In
this  time  of  the  year  sea  surface  temperatures  are  still  on  a
relatively high level with up to 23 °C (Fig. 1,b). A total of 72
surface sediment samples were collected at the end of the NE
monsoon (February 2011) in the Oman Sea to define cocco-
lith abundance from the Gabrik (Fig. 2) and West Jask areas
(Fig. 3) from 0—250 m water depth. In order to study general
changes  in  the  floral  composition  light  microscope  study
was undertaken using simple smear slides (Bown & Young
1998). A smear slide is a thin layer of unconsolidated sedi-
ment embedded on a glass slide for microfossil microscopic
examination. This is a powerful method for ascertaining the

presence of microfossils. With experience, smear slides pro-
vide  surprisingly  accurate  percentage  data  useful  for  recog-
nizing  trends  in  cored  sequences  and  surface  sediment
samples. The slide was labelled temporarily with a felt mark-
ing pen. The hot plate was placed in a fume hood and it was
set at about 150 °C (or about 300 F). The exact setting must
be  determined  by  experiment.  A  small  amount  of  sample
was placed in the center of the slide. A drop of distilled wa-
ter  was  added  and  the  sample  was  spread  into  a  thin  layer
with a glass rod. The slide was placed on the hot plate to dry.
Then, several minutes were allowed (exact time depends on
the temperature and amount of xylene used as a thinner), be-
fore a glass cover slip was placed over the sample. The cover
slip was pressed down with a pair of tweezers. The slide was
removed  from  the  hot  plate  and  cooled.  The  slide  was  then
permanently labelled with a glass scriber (carbide tip).

The samples were examined with an OLYMPUS BH-2 mi-

croscope using polarizing light at a magnification of X1000.

Fig. 3. Bathymetry of the study area with location of the samples (West Jask area).

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Fig. 4. 1—3 – Gephyrocapsa oceanica Kamptner, 1943; 4, 5 – Coccosphere of G.oceanica Kamptner, 1943; 6—9 – Emiliania huxleyi
(Lohman, 1902) Hay & Mohler in Hay et al., 1967; 10—12 – Umbilicosphaera sibogae (Weber-van Bosse, 1901) Gaarder, 1968;
13, 14 – Helicosphaera carteri (Wallich, 1877) Kamptner, 1954; 15, 16 – Calcidiscus leptoporus (Murray & Blackman, 1898) Leoblich
& Tappan, 1978; 17, 18 – Umbellosphaera tenuis (Kamptner, 1937) Paasche in Markali & Paasche, 1955; 19, 20 – Florisphaera profunda
Okada & Honjo, 1973.

At least 300 specimens per sample were identified following
the taxonomic descriptions of Kleijne (1993), Jordan &
Kleijne (1994) and Young et al. (2003).

The count was performed with the light microscope and

only the check of species taxonomy was done with the SEM.
The results are expressed as percentages. Samples were in-
vestigated using a Scanning Electron Microscope (SEM).
The samples for the SEM examination were prepared using
the filtration technique of Andruleit (1996). The freeze-dried

sediment was weighed on a high precision balance, wet sep-
arated with a rotary splitter (FRITSCH Laborette 27) and fil-
tered  through  polycarbonate  filters  (pore  size  0.25 µm)  by
means  of  a  vacuum  pump.  A  wedge-shaped  piece  was  cut
out of the dry filter, mounted on an aluminium stub and sput-
ter  coated  with  gold.  High-resolution  images  were  taken
from  the  tip  to  the  margin  of  the  filter  wedge  on  a  SEM
(LEO 1450VP) and subsequently examined on a qualitative
and quantitative basis (Fig. 4).

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Results and discussion

The knowledge obtained from sinking coccolithophore as-

semblages as collected from surface sediments is a basic pre-
requisite for interpreting and validating the paleoceanographic
and paleoecological significance of the fossil remains in the
Oman Sea sediments.

We have drawn the following conclusions from our data:
(1) This study has enabled us to identify 41 species of coc-

coliths. This study is a part of an ongoing investigation aim-
ing at the reconstruction of paleoenvironmental conditions in
the Oman Sea as revealed by coccolithophores;

(2) From a total of 41 identified taxa Gephyrocapsa ocea-

nica is the most important species of the assemblages. All
coccoliths and coccospheres are well to moderately well pre-
served;

(3) Several species showed spatial trends according to the

NE monsoon development which may be used to improve
paleoclimatic reconstructions:

Relative species abundances and oceanographic

conditions

Relative abundances of some coccolith species show spe-

cific spatial trends according to the monsoonal development
and are used to discuss the pattern distribution of species. The

(a) The relative proportions of E. huxleyi are low in

relative abundance compared to G. oceanica. E. hux-
leyi shows low relative abundances at the end of the
NE monsoon in these areas suggesting that it is not a
typical upwelling species;

(b) The Oman Sea is located at a low latitude and

has high temperatures. Low abundances of G. muel-
lerae were observed in the study area. The relative
abundance of G. ericsonii declines during the NE
monsoon;

abundances in the NE monsoon and declines with
the NE monsoon;

(d) Calcidiscus

leptoporus,

Umbilicosphaera

sibogae and Umbellosphaera tenuis responded neg-
atively  with  decreasing  amounts  (relative  abun-
dances)  at  the  end  of  the  NE  monsoon  in  these
areas. These species are regarded as oceanic species
but  also  seem  not  to  be  able  to  positively  react  to
conditions.

High relative abundance of coccolithophores prevails dur-

ing  the  NE  monsoonal  phase.  This  seems  to  be  related  to
high coccolithophore productivity possibly triggered by high
nutrient  availability.  The  positive  response  of  coccolitho-
phores  to  improved  nutrient  availability  within  upwelling
areas  was  mentioned  by  Kleijne  et  al.  (1989).  In  the  Oman
Sea  surface  water  productivity  is  very  high  during  the  NE
monsoon. With the beginning of the NE monsoon, nutrients
are injected into the upper layer due to surface water coo-
ling and wind-induced deeper mixing by the relatively cold
winter  monsoonal  winds  (Madhupratap  et  al.  1996).  This
process is indicated by a decline in temperature. Coccolitho-
phore production appears to respond to these environmental
changes.  This  results  in  a  strong  increase  in  the  relative
abundance  of  some  coccolith  species  as  well  as  foram-
inifers (Moghaddasi et al. 2009a,b). Apparently, the input of
nutrients  rather  than  the  decline  in  temperature  during  the
winter monsoon is the controlling factor for coccolithophore
distribution.

Fig. 5. Distribution pattern of Gephyrocapsa oceanica, Emiliania
huxleyi and Helicosphaera carteri in the Oman Sea (Gabrik and
West Jask areas).

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Lat

Stati

36.69

1.66

4.66

41.33

3.66

25.69

57.45

WJ-3

46.37

3.66

0.33

5.66

31.33

1.66

4.33

1.66

25.66

57.45

WJ-4

47.7

3.33

4.33

27.66

4.33

0.33

5.66

0.66

25.62

57.45

WJ-5

42.36

0.66

4.66

2.66

3.33

1.33

25.57

57.45

WJ-6

41.36

2.66

1.66

4.33

2.33

25.62

57.4

WJ-9

45.36

2.66

31.33

6.33

0.66

25.72

57.4

WJ-12

41.7

1.33

5.66

41.66

3.66

3.33

5.66

25.74

57.35

WJ-15

34.7

0.66

0.33

4.33

1.66

25.72

57.35

WJ-16

32.36

1.33

51.33

1.66

4.66

0.66

25.69

57.35

WJ-17

37.35

37.66

1.33

0.33

1.33

25.57

57.35

WJ-19

31.03

3.66

0.33

41.66

4.66

6.33

2.33

25.66

57.3

WJ-20

36.7

4.66

0.33

4.66

2.33

39.33

0.33

5.66

25.72

57.3

WJ-22

41.71

1.66

0.66

2.66

4.33

0.66

1.66

4.66

25.75

57.3

WJ-23

40.37

2.33

5.66

34.66

2.33

3.33

0.66

6.66

25.66

57.25

WJ-25

51.02

2.66

1.33

32.33

0.66

25.71

57.25

WJ-26

30.7

2.66

3.66

5.33

47.33

1.33

0.33

5.66

25.75

57.25

WJ-27

36.69

3.66

2.66

1.33

4.33

25.8

57.25

WJ-28

41.37

1.66

4.33

40.66

4.33

1.66

0.33

5.66

25.84

57.27

WJ-32

45.03

0.33

5.33

1.66

0.33

4.66

0.66

25.84

57.25

WJ-33

41.36

2.66

41.66

2.66

1.66

25.89

57.25

WJ-34

31.36

1.33

4.33

45.66

4.66

1.66

25.97

57.2

WJ-41

33.7

1.66

2.33

50.33

3.66

0.66

3.33

0.33

25.93

57.2

WJ-39

43.36

4.33

3.66

41.66

1.33

3.66

25.89

57.2

WJ-40

37.04

2.33

0.66

4.66

42.66

1.66

2.33

0.66

25.84

57.2

WJ-41

32.36

1.66

6.33

1.33

2.66

5.66

25.8

57.2

WJ-42

47.03

5.66

2.66

0.66

1.33

25.75

57.2

WJ-43

42.36

2.33

2.66

36.66

3.33

2.33

7.33

25.71

57.2

WJ-44

33.03

1.66

46.33

1.66

3.66

1.66

25.66

57.2

WJ-45

42.41

1.66

0.66

3.66

41.33

2.66

1.33

4.66

0.66

25.66

57.19

WJ-46

36.36

1.33

2.33

0.66

0.33

6.33

0.33

25.71

57.98

WJ-47

41.69

1.66

1.33

2.33

0.33

4.66

25.75

57.15

WJ-48

27.03

4.66

3.66

47.66

4.33

3.66

25.8

57.15

WJ-49

39.7

3.66

2.66

1.66

1.33

4.33

0.66

25.84

57.15

WJ-50

41.71

1.66

0.33

1.66

41.66

3.66

5.66

25.93

57.15

WJ-52

46.69

0.33

3.66

1.66

6.33

0.33

25.97

57.15

WJ-53

39.36

2.33

37.33

4.66

2.33

7.33

1.33

25.97

57.1

WJ-54

35.68

3.66

4.66

25.93

57.1

WJ-55

54.36

1.33

2.66

0.33

2.66

25.89

57.1

WJ-56

39.03

2.66

4.66

0.33

5.33

0.33

25.84

57.1

WJ-57

51.03

0.33

2.33

3.66

3.33

3.66

0.66

25.75

57.1

WJ-59

36.7

1.66

1.33

6.33

41.66

1.33

4.33

1.66

25.66

57.1

WJ-61

45.68

3.33

3.66

34.33

25.71

WJ-63

46.71

0.66

1.66

4.66

31.33

2.66

0.66

5.66

25.75

WJ-64

41.02

2.33

0.66

40.33

2.33

3.33

25.8

WJ-65

54.36

1.66

2.33

1.66

29.66

1.33

25.84

WJ-66

43.37

2.66

1.66

4.66

3.66

0.33

2.33

0.33

25.89

WJ-67

55.36

3.66

0.33

3.33

1.33

0.66

1.33

25.93

WJ-68

42.02

4.33

0.33

3.66

2.66

25.97

WJ-69

Table 1: Location of the investigated surface sediment samples and data of species (% relative abundance) in the Gabrik area.

relative  abundance  of  the  different  species  identified  in  the
studied areas is as follow (the percentage of abundance from
Gabrik  and  West  Jask,  respectively):  G.  oceanica  (47.9 %
and  38.92 %),  E.  huxleyi  (4.71 %  and  4.77 %),  H.  carteri
(3.03 %  and  3.27 %),  C.  leptoporus  (0.34 %  and  0.79 %),
G.  muellerae  (0.43 %  and  2.69 %),  G.  ericsonii  (0.93 %  and
2.62 %), F. profunda (0.14 % and 0.17 %), U. sibogae (0.22 %

and 2.51 %) and U. tenuis (0.16 % and 0.19 %). A spatial
trend can be recognized in the calculated relative abundance
of coccolith species. Data are shown in Tables 1 and 2 in alpha-
betical order, with only the important species presented here:

According to Bollmann (1997) at least one morphological

group of the genus Gephyrocapsa is preferentially found in
sediments from upwelling areas. Despite the very short sam-

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pling periods, the important monsoonal phase, the NE mon-
soon during winter, was covered by Gephyrocapsa oceanica,
which  is  clearly  the  most  important  species  throughout  the
investigated  period  showing  a  relative  abundance  of  up  to
50 %  of  the  total  coccolith  assemblage.  This  species  is
known to preferentially thrive in high-nutrient environments,
such  as  upwelling  areas  or  continental  shelves  (Mitchell-
Innes & Winter 1987; Houghton & Guptha 1991; Giraudeau
1992;  Young  1994).  It  was  suggested  by  Broerse  et  al.
(2000) that this species indicates maximum upwelling condi-
tions and that it positively responds to the input of nutrients
(Andruleit  et  al.  2000).  Although  nutrient  data  are  lacking,
maximum abundances in the near shore samples support the
impression of it being a r-selected species. The trophic pref-
erence  of  this  species  is  confirmed  by  our  study,  generally,
during the NE monsoon, nutrient contents increase (Madhu-
pratap et al. 1996). G. oceanica exhibits the widest range in
abundance of all species, ranging from 27.66 % to 76.33 %.
Its distribution pattern is opposite that of Emiliania huxleyi,
with  the  highest  values  in  the  Gabrik  and  lowest  values  in
the West Jask (Fig. 5).

In contrast, E. huxleyi is low in relative abundance com-

pared to G. oceanica (Tables 1—2). The species E. huxleyi
is the most ubiquitous coccolithophore species on the Earth
(McIntyre & Be 1967; Winter & Siesser 1994), and able to
form strong blooms with coccosphere densities of up to

aer

ibo

los

a t

eli

cos

eri

lor

aer

a h

s l

ept

por

ati

Sta

25.03

1.66

1.33

0.66

1.66

25.37

58.43

Gb-5

17.71

0.66

1.66

62.33

0.66

2.33

1.33

9.66

0.66

25.43

58.36

Gb-8

48.03

1.33

0.33

39.33

1.66

0.33

4.66

1.33

25.59

58.4

Gb-13

60.69

0.66

0.33

0.66

0.33

2.33

25.57

58.3

Gb-16

55.68

2.33

30.33

0.66

25.54

58.3

Gb-17

34.35

4.33

50.33

0.33

4.66

25.5

58.3

Gb-18

12.7

0.33

2.66

0.33

76.33

0.33

6.66

0.33

25.43

58.29

Gb-19

18.03

1.33

0.66

2.66

0.66

25.41

58.22

Gb-21

48.37

2.33

0.66

2.66

3.66

0.66

0.33

25.43

58.22

Gb-22

42.03

2.66

0.33

1.66

45.66

0.66

25.5

58.25

Gb-23

53.35

3.66

1.66

3.33

25.5

58.2

Gb-28

21.34

1.33

0.33

25.5

58.15

Gb-30

39.35

3.33

0.33

7.33

0.66

25.43

58.15

Gb-31

31.02

50.66

1.33

9.33

1.66

25.41

58.15

Gb-32

16.01

1.33

5.33

0.33

25.43

58.08

Gb-33

49.69

4.33

40.66

0.66

4.66

25.5

58.1

Gb-34

26.36

2.66

0.66

2.66

25.54

58.1

Gb-35

36.69

55.66

0.66

3.66

0.33

25.55

58.1

Gb-36

32.36

0.66

0.33

0.66

61.66

3.33

25.58

58.05

Gb-37

42.69

0.33

2.66

43.66

4.66

25.54

58.05

Gb-41

27.36

2.33

0.33

65.66

0.33

1.33

2.66

25.5

Gb-39

47.01

41.66

0.33

25.54

Gb-40

45.02

3.66

1.66

47.33

0.33

25.58

Gb-41

53.01

0.33

4.33

37.33

25.62

Gb-42

Table 2: Location of the investigated surface sediment samples and data of species (% relative abundance) in the West Jask area.

> 106  cells  per  litre  in  the  North  Atlantic  (Holligan  et  al.
1983, 1993). Its distribution in the surface waters was found
to  be  largely  independent  of  water  temperature  and  ther-
mocline depth (Samtleben et al. 1995). In our study, E. hux-
leyi  showed  low  relative  abundances  at  the  end  of  the  NE
monsoon.  Therefore,  E.  huxleyi,  being  a  cosmopolitan  spe-
cies, may not be regarded as an indicator of convection pro-
cesses, but be more typical for stable regimes with relatively
high nutrient availability. In addition, in our study tempera-
tures may be already above the optimum level for E. huxleyi.
This species is rare in West Jask, and its relative abundances
decrease  from  Gabrik  to  West  Jask  (Fig. 5).  A  rather  nega-
tive connection to the monsoonal phases can be seen in the
relative abundance pattern of Helicosphaera carteri and Cal-
cidiscus  leptoporus.  H.  carteri  showed  a  clear  negative  re-
sponse with decreasing amounts (relative abundances) at the
end of the NE monsoon (Fig. 5). The  relative  abundance  of
H. carteri decreases from West Jask to Gabrik (from 3.27 %
to  3.03 %)  which  shows  a  spatial  trend.  C.  leptoporus  also
decreases from West Jask to Gabrik (from 0.79 % to 0.34 %)
also showing a spatial trend.

Due to the fact that coccolithophore species like Gephyro-

capsa muellerae prefer cold and high-nutrients conditions
(Bollmann 1997; Flores et al. 1997; Knappertsbusch et al.
1997), while the condition in the Oman Sea is high tempera-
ture. This species is very rare or missing in Gabrik (Fig. 6).

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Fig. 6. Distribution pattern of Calcidiscus leptoporus, Gephyrocapsa
muellerae and Gephyrocapsa ericsonii in the Oman Sea (Gabrik
and West Jask areas).

Gephyrocapsa ericsonii thrives in high nutrient environ-
ments (Takahashi & Okada, 2000) between 13 and 22 °C
(Okada & McIntyre 1979). We observed low abundances of
G. ericsonii at the end of the NE monsoon. This species ap-
pears with the lowest abundance in Gabrik (Fig. 6).

Florisphaera profunda is well known as a deep dwelling

species living in the lower photic zone (Winter & Siesser
1994). It was suggested that this species can be used to mon-
itor variations in the depth of the nutricline (Molfino &
McIntyre 1990). The species dominates coccolithophore as-

Fig. 7. Distribution pattern of Umbilicosphaera sibogae, Umbello-
sphaera tenuis and Florisphaera profunda in the Oman Sea (Gabrik
and West Jask areas).

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semblages in the lower photic zone ( > 100 m) (Cortes et al.
2001; Haidar & Thierstein 2001). F. profunda had very low
abundance  in  the  studied  samples  (from  0.14 %  to  0.96 %,
in Gabrik and West Jask) (Fig. 7). F. profunda is known as
a  key  species  to  trace  nutricline  depth  etc.  The  rare  occur-
rence  in  the  samples  can  be  explained  by  the  fact  that  the
sampling area was not deep enough for this species to thrive.
According  to  Young  (1994),  Umbilicosphaera  sibogae  be-
longs  to  the  “placolith-bearing  coccolithophores”  which
often  superficially  appear  to  exhibit  an  erratic  biogeogra-
phical  distribution  worldwide,  but  all  typical  environments
exhibit  similar  ecological  conditions  in  that  they  are  all
eutrophic.  U.  sibogae  and  Umbellosphaera  tenuis  are  ex-
tremely  low  in  relative  abundance  at  the  end  of  the  NE
monsoon. U. sibogae exhibits a rather similar distribution to
G. ericsonii and G. muellerae, with the highest values only
in West Jask (Fig. 7). Here, in some cases, U. sibogae reaches
5 % of the assemblages, but it is very low in number or even
missing in Gabrik. U. tenuis ranges in abundance from only
0  to  1 %  (Fig. 7).  Generally  this  species  shows  low  abun-
dances in all parts of the study area.

Sporadically occurring fossil coccoliths older than the

Quaternary  (e.g.  Discoaster  brouweri,  D.  deflandrei,    D.
kugleri  or  Sphenolithus  abies,  S.  heteromorphus,    S.  cipero-
ensis,  S.  radians,  S.  moriformis,  Reticulofenestra  minuta,
R.  pseudoumbilica,  R.  umbilica,  Cyclicargolithus  abisectus,
C. floridanus, Pseudoemiliania lacunosa, Coccolithus pelagi-
cus,  Watznaueria  biporta,  W.  barnesiae),  were  grouped  to-
gether as ‘Reworked’. The reworked species may be related
to the rivers or floor sediments. According to Fig. 8, the val-
ues  of  reworked  species  increase  in  abundance  from  West
Jask to Gabrik.

Acknowledgments: We are grateful to many unnamed indi-
viduals who have helped with sample preparation, discus-
sions, comments, and data. The author wishes to thank the
University of Bremen, Germany, for taking images with the
Scanning Electron Microscope. The sampling for the stations
was provided by the Geological Survey of Iran.

Fig. 8. Distribution pattern of reworked species in the Oman Sea.

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Appendix (Taxonomic list)

Identification of coccolithophore taxa followed Jordan & Kleijne (1994) (all species references are given here), Kleijne
(1993) and Young et al. (2003). Most of the taxa were identified to species level. Fossil species older than Quaternary were
grouped together as ‘Reworked’.

The taxonomic list includes all taxa cited in the manuscript:

Calcidiscus leptoporus (Murray & Blackman, 1898) Loeblich
& Tappan, 1978
Emiliania huxleyi (Lohmann) Hay & Mohler, 1967
Florisphaera profunda Okada & Honjo, 1973
Gephyrocapsa ericsonii McIntyre & Bé, 1967
Gephyrocapsa muellerae Bréhéret, 1978

Gephyrocapsa oceanica Kamptner, 1943
Helicosphaera carteri (Wallich) Kamptner, 1954
Umbellosphaera tenuis (Kamptner, 1937) Paasche in Markali
& Paasche, 1955
Umbilicosphaera sibogae

(Weber-van Bosse, 1901) Gaarder,

1970