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.