ALGAL BLOOMS IN THE ARABIAN SEA – ARE THEY
CHANGING?
Helga do Rosario Gomes and Joaquim I. Goés
Bigelow Laboratory for Ocean Sciences, ME, USA
S.G. Prabhu Matondkar and Sushma G. Parab
National Institute of Oceanography, Dona Paula, Goa
Adnan R. N. Al-Azri
Sultan Qaboos University, Oman
Prasad Thoppil
Naval Research Laboratory, Stennis Space Centre, MS, USA
WIND FIELDS OVER THE ARABIAN SEA DURING THE
MONSOONS
Sea surface winds reverse
direction seasonally
Development and
intensity regulated by
thermal gradient between
land and sea
Winds responsible for
convective mixing during
winter monsoon and
coastal upwelling during
summer monsoon
SALIENT FEATURES OF THE NORTHEAST WINTER
MONSOON
Winter convective mixing results in nutrient enhancement
Phytoplankton blooms
Predominance of diatoms
CRUISE TRACKS AND BLOOM SAMPLING
SK-186 (3rd-19th Jan 2003)
Northeast monsoon
FORV 222 (22nd Feb
- 8th Mar 2004)
Spring Intermonsoon
FORV 212 (27th Feb-5th
Mar 2003) Spring
Intermonsoon
SK 214 (4th -17th Dec
2004) Northeast monsoon
Cruise SASU-45 (2nd5th May 2003) Late
Spring
Fahal and OFF, Gulf of
Oman (24th of Jan
2006)
3
2.5
28
/0
2/
0
2/ 3
3/
20
0
3/ 3
3/
20
0
5/ 3
3/
20
22 03
/2
/2
0
23 04
/2
/2
0
26 04
/2
/2
0
28 04
/2
/2
00
4
1/
3/
20
0
3/ 4
3/
20
0
5/ 4
3/
20
0
7/ 4
3/
20
04
4/
1/
20
0
5/ 3
1/
20
0
6/ 3
1/
20
0
8/ 3
1/
20
0
9/ 3
1/
20
10 03
/1
/2
0
12 03
/1
/2
00
3
13
/1
/0
3
14
/1
/0
3
16
/1
/0
3
17
/1
/0
3
18
/1
/0
3
-3
Chlorophyll
a (mg m)
3.5
In Situ
SeaWiFS
MODIS
OCM
2
1.5
1
0.5
0
Sampling Dates
Comparison between ship and satellite data
PHYTOPLANKTON BLOOM OF 2003
PHYTOPLANKTON TAXA ASSOCIATED WITH THE
BLOOM OF 2003
NORTHEAST MONSOON
2003
SPRING INTERMONSOON
2003
Diatoms
Dinoflagellates
Noctiluca miralis
44%
56%
41%
56%
3%
Diatoms
20%
29%
Trichodesmium
57%
Dinoflagellates
14%
80%
LATE SPRING INTER MONSOON
MAY 2003
>1%
100%
Trichodesmium
Trichodesmium erythraeum
PHYTOPLANKTON BLOOM OF 2004
PHYTOPLANKTON TAXA ASSOCIATED WITH THE
BLOOM OF 2004
SPRING INTERMONSOON 2004
Diatoms
19%
3%
78%
Noctiluca miliaris
14%
Trichodesmium
86%
PHYTOPLANKTON BLOOM OF 2005
PHYTOPLANKTON TAXA ASSOCIATED WITH THE
BLOOM OF 2005
NORTHEAST MONSOON
2005
8%
Diatoms
92%
5%
41%
54%
Dinoflagellates
Diatoms
NOCTILUCA MILIARIS BLOOM IN THE GULF OF
OMAN, 24TH JAN 2006
2%
29%
69%
Pedinomonas
noctilucae
Sea surface geostrophy superimposed on chlorophyll
field of 24th Jan 2006
Weekly SeaWiFS and MODIS/Aqua
Level-3 merged Chl a images from
9th Jan -4th Mar 2006 (a-d) and Sea
Surface Height anomalies with
superimposed geostrophic velocity
vectors from TOPEX/POSEIDON
and ERS-2 for the same period
Eddy kinetic energy for the region off the coast of Oman
for the period from 2001 to 2006.
1.8
Gulf of Oman
1.4
1
0.6
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
Area averaged chlorophyll for the Gulf of Oman
2007
TYPICAL HYDROGRAPHY CONDITIONS AT TWO STATIONS
SAMPLED ON CRUISE FORV 222 (22nd Feb-8th Mar 2004)
Salinity (psu)
o
Temperature ( C)
20
25
0
30
33
35
37
-3
Density (kg m )
20
22
24
26
20
40
Depth
60
80
100
120
140
160
St 2
180
ST 13
200
St 2: Trichodesmium dominated station in the south at 10.7oN lat, 74.8oE long
St 13: N. miliaris dominated station in the north at 22.4oN lat. and 66.9oE long
Noctiluca
INDIA
OMAN
Arabian Sea
Trichodesmium
Bay of
Bengal
Lakshadweep
Sea
EICC
Andaman
Sea
WMC
Potential route of dispersal of N. miralis bloom from the Gulf of
Oman into the northern Arabian Sea (hatched line) and of
Trichodesmium sp. from the Bay of Bengal and the Andaman Sea
(solid black lines)
CONCLUSIONS
ƒWinter blooms of diatom-dinoflagellate assemblages are short lived
and are replaced by widespread blooms of Noctiluca miliaris
ƒThe seed population for the Noctiluca miliaris emerges in the Gulf
of Oman in association with colder, denser and nutrient rich waters
ƒThe emergence of the bloom is tied to the cold eddy at the mouth of
the Gulf of Oman while its dispersal is effected by the warm eddy
ƒTrichodesmium associated with warmer, less saline and highly
stratified waters appears in spring along the southern west coast of
India
ƒThese low salinity waters originate in the Bay of Bengal and the
Andaman Sea
ACKNOWLEDGEMENTS
This work is supported by grants NNG04GH50G and
NNG04GM64G from NASA to JIG and HRG and from
SAC, Ahmedabad to SGPM.
We are grateful to Dr. Satish Shetye, Director, NIO,
Goa and Dr. Sayed Ahmed, Head, Dept. of Marine
Sciences, Sultan Qaboos University for facilitating
and supporting this work.
Ocean color data for this work came from NASA
Goddard Space Flight Center and Altimetry data from
the Colorado Center for Astrodynamics Research.
A very special thanks to Dr. Raleigh Hood for the
opportunity to attend this workshop.