Physical characteristics of waters and water masses off the West Coast of India during late spring

Abstract

The paper presents an approximately synoptic distribution of temperature, salinity and sigma-t and the associated hydrographic features of the shelf and slope waters off the west coast of India for late spring, based on data collected between Bombay and Alleppey during 22 March to 1 April 1965. Significant space variations have been noticed in all the parameters. The salient features are: (1) Surface temperature shows a gradual increase from north to south (temperature variation about 3.5°C) while salinity and sigma-t show a decrease (salinity variation about 1.4% and variation in sigma-t about 2.0). (2) A tongue of high salinity water (with salinity greater than 36.0%) extends from the offshore region towards the shelf. The depth of the core varies mostly between 70 and 80 m over the shelf region. (3) The thermocline tilts upward towards the coast and is found uo to the mid-shelf in most of the areas. There is a genetral increase of temperature of the top of the thermocline and a decrease in its depth from north to south. (4) Vertical sections of temperature , salinity and sigma-t indicate the tilting up towards the coast, of isolines of these parameters in the shelf and slope regions, revealing the existence of upwelling. This feature is more pronounces off Karwar and Mangalore but the upwelled waters do not seem to reach the surface in any of the areas. (5) The density of waters decreases from north to south in hte surface waters but the reverse is the case at 100 m depth. This indicates commencement of upwelling in the south earlier than in the north. (6) The presence of Persian Gulf waters (between 200 and 385 m depth) and the spread of Red Sea waters (between 436 and 643m depth) is noticed in the offshore regions.