Air-Sea Interaction, Coastal Circulation and Primary Production in the Eastern Arabian Sea: A Review

Tohoku University, Miyagi, Japan
Journal of Oceanography (Impact Factor: 1.27). 04/2004; 60(2):205-218. DOI: 10.1023/B:JOCE.0000038327.33559.34


Air-sea interaction, coastal circulation and primary production exhibit an annual cycle in the eastern Arabian Sea (AS). During
June to September, strong southwesterly winds (4∼9 m s−1) promote sea surface cooling through surface heat loss and vertical mixing in the central AS and force the West India Coastal
Current equatorward. Positive wind stress curl induced by the Findlater jet facilitates Ekman pumping in the northern AS,
and equatorward-directed alongshore wind stress induces upwelling which lowers sea surface temperature by about 2.5°C (compared
to the offshore value) along the southwestern shelf of India and enhances phytoplankton concentration by more than 70% as
compared to that in the central AS. During winter monsoon, from November to March, dry and weak northeasterly winds (2–6 m
s−1) from the Indo-China continent enhance convective cooling of the upper ocean and deepen the mixed layer by more than 80 m,
thereby increasing the vertical flux of nutrients in the photic layer which promotes wintertime phytoplankton blooms in the
northern AS. The primary production rate integrated for photic layer and surface chlorophyll-a estimated from the Coastal
Zone Color Scanner, both averaged for the entire western India shelf, increases from winter to summer monsoon from 24 to 70
g C m−2month and from 9 to 24 mg m−2, respectively. Remotely-forced coastal Kelvin waves from the Bay of Bengal propagate into the coastal AS, which modulate
circulation pattern along the western India shelf; these Kelvin waves in turn radiate Rossby waves which reverse the circulation
in the Lakshadweep Sea semiannually. This review leads us to the conclusion that seasonal monsoon forcing and remotely forced
waves modulate the circulation and primary production in the eastern AS.

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    • "Upwelling commences at the southern tip of India and propagates northward along the coast as the monsoon advances (Madhupratap et al. 2001; Luis and Kawamura 2004; Rao et al. 2008 and Jayaram et al. 2010). However, there is ample scope to understand the relation between changes in wind pattern and the upwelling related productivity of this region which at present is unclear and this issue is attempted in the present work. "
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    ABSTRACT: The role of wind stress in modulating upwelling and subsequent changes in mixed layer depth and chlorophyll concentration in southeastern Arabian Sea are studied for the period encompassing 2000 – 2008. During southwest monsoon season favoring upwelling in this region, it is observed that decrease in wind stress is always followed by an increase in chlorophyll concentration with approximately two weeks delay, accompanied by the shoaling of mixed layer depth, whereas the opposite is observed during high wind stress periods. This is attributed to the mixing and entrainment of nutrients into the euphotic zone which enable increase in surface chlorophyll and thereby boosting the primary productivity of the region. Wavelet analysis is used to deduce the temporal variability of winds, chlorophyll and mixed layer for the region. A time lag of 2 weeks is observed between the decrease in wind stress followed by a high in the surface chlorophyll concentration, often well captured by satellite. Another interesting observation is the bimodal variability of chlorophyll-a concentration during summer monsoon is observed in this region which was hitherto unnoticed. This spatial and temporal relation between wind, chlorophyll and mixed layer depth can provide valuable insight towards future studies on upwelling induced productivity for this region
    06/2012; 3(2):97-108. DOI:10.1260/1759-3131.3.2.97
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    • "Surface cooling and convection resulting from reduced solar radiation and increased evaporation make the northern region productive in winter (Prasanna Kumar et al., 2000). Luis and Kawamura (2004) reported that the primary production rate integrated for photic layer and surface Chl-a estimated from the CZCS, both averaged for the entire western India shelf, increases from winter to summer monsoon from 24 to 70 g C m -2 month and from 9 to 24 mg m -2 , respectively. "
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    ABSTRACT: This monograph is the outcome of an attempt by the authors to present a synthesis of the studies on physical processes in the Tropical Indian Ocean (TIO) in relation to air-sea interaction, monsoon/climate variability and biological productivity through a review of the published work so far and analysis of the latest available data sets. Various oceanic features and processes in the upper 1000 m of the TIO are described and discussed. An Oceanographic Atlas prepared for this purpose is appended to the monograph. The monograph consists of six chapters. Chapter 1 entitled ‘Introduction’, gives the significant/special features of TIO, the names of various expeditions/experiments carried out in this region and the scope of the different aspects covered in the monograph. Chapter 2 deals with the features of surface parameters/fields. Chapter 3 describes the hydrographic features in the upper 1000 m. Chapter 4 gives a comprehensive account of upwelling processes in the TIO. Chapter 5 deals with internal waves. Summary of the results and a few suggestions for improving our understanding of the physical processes are included in Chapter 6 entitled ‘Concluding Remarks’.
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