Identification of Thermohaline Structure of a Tropical Estuary and its Sensitivity to Meteorological Disturbance through Temperature, Salinity, and Surface Meteorological Measurements

Abstract

Thermohaline structure of Kochi backwaters (KB) in India and its sensitivity to meteorological disturbances has been identified through measurements of temperature, salinity, and surface meteorological parameters. Silicon p-n junction semiconductor sensors have been used for measurements of subsurface temperature. Linearity and accuracy based on laboratory calibration of the sensors are found to be better than 0.4% and -0.8% respectively beyond 20degC. Induction type conductivity cell was used for salinity measurement. Linearity and accuracy of salinity measurements are found to be better than plusmn3% and plusmn5% respectively beyond 20 psu. In-situ measurements show that the thermohaline structure of KB exhibits fortnightly spring-neap variability in which thermal and haline variability bear an inverse relationship, with cooling and enhanced salinity during spring tide and vice versa during neap tide. The diurnal variability in temperature is controlled by day/night cyclicity rather than tidal, whereas this feature is absent in haline variability. Horizontal thermohaline structure of the KB is inhomogeneous, where the upstream boundary region is warmer and less saline than the mouth region. Changes in the meteorology disturb the thermohaline structure of KB. Rainfall and associated river influx cause large haline stratification in the mouth region, in which a ap1-4 m thick layer of low salinity water (ap0-2 psu) floats on the surface.