Description on variability of shelf-edge hydrography and current structure of the South Eastern Arabian Sea during summe
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Description on variability of shelf-edge hydrography and current structure of the South Eastern Arabian Sea during summer and winter monsoons K. G. Vimal Kumar & K. Rasheed & B. R. Smitha & S. Vishnu Narayanan Nampoothiri & M. Sudhakar
Received: 7 February 2020 / Accepted: 24 September 2020 # Springer Nature Switzerland AG 2020
Abstract The paper describes the hydrography and vertical current structure along the shelf edge of South East Arabian Sea (SEAS) during summer and winter monsoons based on current profiles from moving Acoustic Doppler Current Profiler (ADCP). During summer monsoon, SEAS was characterized by upwelling with low saline water at the surface along the southern sector (8° N to 11° N). During winter, thermal structure was vertically homogeneous in the upper 80 m, and intrusion of low saline Bay of Bengal waters were found up to 14° N. In the southern sector, turbidity was more than the northern sector during winter and summer seasons. ADCP-derived current profiles during summer along 200-m isobath show dominant northward flow in the south, and southeasterly in the north as part of the West India Coastal Current (WICC). A comparison between ADCP current profiles and Ekman currents during summer indicates dominance of remote forcing (coastal Kelvin waves) over the local wind forcing in the 8–9° N sector whereas a combined influence of both remote forcing and wind in the 9–15° N sector. During winter, the direction of surface current reversed and was poleward generally except at the K. G. Vimal Kumar : K. Rasheed : B. R. Smitha : S. V. N. Nampoothiri (*) : M. Sudhakar Centre for Marine Living Resources and Ecology (CMLRE), Ministry of Earth Sciences, Kochi 682508, India e-mail: [email protected] K. G. Vimal Kumar Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi 682506, India
southern sector (7–8° N) where the flow was southwestward. Sector-wise comparison of ADCP and Ekman current showed less influence of wind on current fields throughout the sector except at south; wind has a major role in the current generation, whereas along the 8–15° N sector, the remote forcing dominates over the wind. Keywords Shelf edge . Ekman current . ADCP . Circulation . South Eastern Arabian Sea
Introduction South Eastern Arabian Sea (SEAS), in the western part of the North Indian Ocean, is under the influence of reversing monsoons. The seasonal reversing monsoon winds, i.e., southwesterly during summer monsoon (June–September) and northeasterly during winter monsoon (November–February), with interim quiescent periods fall inter-monsoon (October) and spring intermonsoon (March–May), defined the four seasons of the region. The SEAS ecosystem processes are governed by these seasonal atmospheric forcing; summer is characterized with moderate coastal upwelling, and winter is influenced by the intrusion of less saline Bay of Bengal (BoB) water due to the pressure gradient flow resulting from remote forcing (McCreary et al. 1993; Shankar et al. 2002). Shetye and Shenoi (1988) explained the surface circulati
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