Hydrographical features of the continental shelf waters off Cochin during the years 1958 and 1959

Abstract

The hydrographical features and the seasonal variations in the physical and chemical conditions of the shelf waters off Cochin form an interesting subject of study. In this region, as well as in other areas along this coast, the influence of the southwest monsoon is very profound while that of the north-east monsoon is at best indirect. The changes in the conditions of these waters from time to time more or less reflect the changing pattern in the climatic conditions. The main circulation in the Arabian Sea results in the establishment of a surface current along this coast which reverses itself in the course of the year. This stream is southerly (i.e., towards south) when the circulation in the open part of the Arabian Sea is clockwise and northerly when the circulation is counter-clockwise. Associated with these drifts are the upwelling and sinking along this coast. The existence of these phenomena has been pointed out earlier by Sastry and Myrland (1960). In a preliminary analysis of the wind data during the period when upwelling is in evidence Jayaraman (1959) has pointed out that the prevailing winds are somewhat favourable for upwelling to take place, while Banse (1959) has regarded the prevailing current system and not the wind to be the main cause of the upwelling. It is not, however, the purpose of the present paper to discuss in detail the possible causes for upwelling or sinking along this coast, but it is intended to indicate that these various phenomena and the associated water movements could provide an explanation for the hydrographical features and their seasonal variations in the shelf waters along this coast. The interest is all the greater because Banse has shown that the demersal fisheries along this coast are fully dependent upon the prevailing hydrographic conditions.