Helga do Rosario Gomes and Joaquim I. GoésBigelow Laboratory for Ocean Sciences, ME, USA
ALGAL BLOOMS IN THE ARABIAN SEA – ARE THEY CHANGING?
Prasad ThoppilNaval Research Laboratory, Stennis Space Centre, MS, USA
S.G. Prabhu Matondkar and Sushma G. Parab National Institute of Oceanography, Dona Paula, Goa
Adnan R. N. Al-AzriSultan Qaboos University, Oman
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
Cruise SASU-45 (2nd-5th May 2003) Late
Spring
SK-186 (3rd-19th Jan 2003) Northeast monsoon
FORV 212 (27th Feb-5th Mar 2003) Spring
Intermonsoon
FORV 222 (22nd Feb - 8th Mar 2004)
Spring Intermonsoon
SK 214 (4th -17th Dec 2004) Northeast monsoon
Fahal and OFF, Gulf of Oman (24th of Jan
2006)
Comparison between ship and satellite data
0
0.5
1
1.5
2
2.5
3
3.5
4/1/20
035/1
/2003
6/1/20
038/1
/2003
9/1/20
0310/
1/200
312/
1/200
313/
1/03
14/1/0
316/
1/03
17/1/0
318/
1/03
28/02/
032/3
/2003
3/3/20
035/3
/2003
22/2/2
004
23/2/2
004
26/2/2
004
28/2/2
004
1/3/20
043/3
/2004
5/3/20
047/3
/2004
Sampling Dates
Chl
orop
hyll a
(mg
m-3 )
In SituSeaWiFSMODISOCM
PHYTOPLANKTON BLOOM OF 2003
57%
29%
14%
41%
3%
56%
SPRING INTERMONSOON 2003
NORTHEAST MONSOON 2003
PHYTOPLANKTON TAXA ASSOCIATED WITH THE BLOOM OF 2003
80%
20%
44%56%
Dinoflagellates
Diatoms
Noctiluca miralis
Trichodesmium
Dinoflagellates
Diatoms
>1%
100%
Trichodesmium
LATE SPRING INTER MONSOON MAY 2003
Trichodesmium erythraeum
PHYTOPLANKTON BLOOM OF 2004
19%
78%
3%
86%
14%
SPRING INTERMONSOON 2004
PHYTOPLANKTON TAXA ASSOCIATED WITH THE BLOOM OF 2004
Noctiluca miliaris
Diatoms
Trichodesmium
PHYTOPLANKTON BLOOM OF 2005
PHYTOPLANKTON TAXA ASSOCIATED WITH THE BLOOM OF 2005
92%
8%
54%41%
5%
Diatoms
DiatomsDinoflagellates
NORTHEAST MONSOON 2005
2%
69%
29%
NOCTILUCA MILIARIS BLOOM IN THE GULF OF OMAN, 24TH JAN 2006
Pedinomonasnoctilucae
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.
Gulf of Oman
0.6
1
1.4
1.8
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Area averaged chlorophyll for the Gulf of Oman
Temperature (oC)
0
20
40
60
80
100
120
140
160
180
200
20 25 30
St 2
ST 13
Salinity (psu)33 35 37
Density (kg m-3)20 22 24 26
Dep
th
TYPICAL HYDROGRAPHY CONDITIONS AT TWO STATIONS SAMPLED ON CRUISE FORV 222 (22nd Feb-8th Mar 2004)
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
Bay of Bengal
OMAN INDIA
LakshadweepSea
AndamanSea
Arabian Sea
Trichodesmium
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)
Noctiluca
WMC
EICC
CONCLUSIONS
Winter blooms of diatom-dinoflagellate assemblages are short lived and are replaced by widespread blooms of Noctiluca miliaris
The seed population for the Noctiluca miliaris emerges in the Gulf of Oman in association with colder, denser and nutrient rich waters
The 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
Trichodesmium associated with warmer, less saline and highly stratified waters appears in spring along the southern west coast of India
These low salinity waters originate in the Bay of Bengal and theAndaman Sea
ACKNOWLEDGEMENTSThis 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.