Hydrographic characterization of southeast Arabian Sea during the wane of southwest monsoon and spring intermonsoon |
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Authors: | K G Vimal Kumar P K Dinesh Kumar B R Smitha H Habeeb Rahman Jacob Josia K R Muraleedharan V N Sanjeevan C T Achuthankutty |
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Institution: | (1) Regional Centre, National Institute of Oceanography, P.O. Box 1913, Kochi, 682018, Kerala, India;(2) Centre for Marine Living Resources and Ecology, Ministry of Earth Sciences, Kochi, 682037, Kerala, India |
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Abstract: | Seasonal variation of the hydrography along the southeast Arabian Sea is described using data collected onboard FORV Sagar
Sampada in September–October 2003 (later phase of Southwest monsoon, SWM) and March–April 2004 (Spring inter monsoon, SIM).
During the later phase of the SWM, upwelling was in the withdrawal phase and the frontal structure was clearer in the northern
sections (13 and 15°N lat) indicating strong upwelling in the area. The driving force of upwelling is identified as the combination
of alongshore wind stress and remote forcing with a latitudinal variability. Although a more prominent upwelling was found
in the north, a maximum surface Chlorophyll-a was found in the south (10°N). During the SIM, the area was characterized by oligotrophic water with relatively high Sea
Surface Temperature (>29°C) and low salinity (33.8 to 35.4). During March, the surface hydrography was found to be controlled
mainly by the intrusion of low-saline waters from the south, while during September by the high saline water from the north.
The presence of various water masses Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), Red Sea Water (RSW)]
and their seasonal variations in the region is discussed and their decreasing influence towards the south is noted during
both periods of observation. During the SWM, the dynamic topography showed the equator-ward flow of the West India Coastal
Current (WICC) at the surface and a pole-ward coastal under current at sub-thermocline depth. During the SIM, surface circulation
revealed the WICC flowing pole-ward north of 13°N, but equator-ward flow in the south, with a clockwise circulation around
the Lakshadweep High. |
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Keywords: | Upwelling Arabian Sea high salinity water Pole-ward undercurrent Arabian Sea Hydrography |
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