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Seasonal and interannual variability of chlorophyll-a in the Gulf of Oman compared to the open Arabian Sea regions
SERGEY PIONTKOVSKI*, ADNAN AL-AZRI and KHALID AL-HASHMI
Department of Marine Science and Fisheries, College of Agricultural and Marine Sciences, Sultan Qaboos University, CAMS, P.O. 34, Al-Khod 123, Sultanate of Oman

Abstract
Field sampling, remote sensing and modelling were employed to understand the seasonal and interannual changes of chlorophyll-a concentrations in the Gulf of Oman in comparison to open sea regions. In these regions, maximal chlorophyll concentrations were reported during the summer monsoon (with peaks in June and August), while in the Gulf of Oman, the chlorophyll maximum was observed during the winter monsoon (February–March). From 1997 through to 2008, the interannual variability in chlorophyll-a concentrations in the Gulf of Oman has not exhibited pronounced trends and neither have the other two (oceanic) regions in the western Arabian Sea. However, an increase of the annual variation in chlorophyll concentrations over the years was noticed. The diatom biomass decreased two-fold from 1997 to 2007. Nitrate concentration and mixed-layer depth also declined. In comparison to the seasonal blooms driven in the Gulf of Oman by the dinoflagel- late Noctiluca scintillans, the year 2008 was markedly different. The summer bloom was shifted to September; it was gradually extended in time and formed by the other species. An applicability of the concept of ecosystem regime shift is discussed.

Mesoscale Eddies of Arabian Sea: Physical-biological Interactions

S.A. Piontkovski1 , N.P. Nezlin2
1Sultan Qaboos University, CAMS, P.O. 34, Al-Khod 123, Sultanate of Oman
2Southern California Coastal Water Research Project, 3535 Harbor Blvd., Costa Mesa, CA 92626, USA

Abstract
Satellite derived (SeaWIFS, TOPEX/Poseidon) products for chlorophyll-a concentration, sea surface heights, and calculated kinetic energy of eddies were employed, to analyze physical-biological coupling from 1997 to 2008. It was shown that, when cyclonic eddies dominated throughout the year, the chlorophyll-a concentration was positively related to the kinetic energy of eddies.
For the other years, when the total annual balance of negative to positive sea surface heights was dominated by anticyclonic eddies, the correlation was negative. The evaluated switch contributes a useful detail to the understanding of the mechanism mediating variability of the chlorophyll-a in regions with vigorous eddy fields.

Keywords
Mesoscale eddies; Arabian Sea; Chlorophyll-a; Remote sensing

Seasonal Changes of Chlorophyll a and Environmental Characteristics in the Sea of Oman
Al-Hashmi, Khalid A. Claereboudt*, Michel R. Al-Azri, Adnan, R. Piontovski, Sergey. A.
Sultan Qaboos University, Department Marine Science and Fisheries College Agricultural and Marine Sciences, Box 34
Al-Khod 123 Sultanate of Oman

Abstract
Monthly estimates of chlorophyll a, temperature, salinity, and nutrients were collected through sampling at two stations from January 2001 to January 2002, in and near Bandar Al-Khyran, the largest semi-enclosed bay on the southern coast of the Sea of Oman. Although the sampling location was at the limit of the tropical range, the seasonal changes of the coastal phytoplankton were more related to temperate dynamics, showing seasonal fluctuation of more than 10o C.
Sharp temperature drops observed in August and July were likely due to rises of the thermocline under the influence of coastal upwelling events or to deep water injections along the north coast of Oman generated by changes in the coastal wind patterns. Overall, small phytoplanktonic cells [0.7-5 μm] dominated the phytoplankton community of the mixed layer with an average of 69.7 % and 73.5 % of the extracted chlorophyll a at the station "Inside" and "Outside" the bay, respectively.

Keywords: Arabian Sea, picoplankton, chlorophyll a, coastal upwelling, phytoplankton blooms.

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