A study of the seasonal changes in the dissolved oxygen of the surface waters of the sea on the Malabar Coast

Abstract

There is wide recognition at the present day of the importance of hydrographical investigations, particularly in association with biological studies of the marine environment. A knowledge of the physics and chemistry of sea-water is essential for a scientific approach to the fundamental problem of organic production in the sea and, in certain instances, greatly helps in the solution of specific problems connected with fisheries. Investigations on the distribution and seasonal variations of temperature, salinity, dissolved oxygen, pH and of various inorganic compounds of phosphorus, nitrogen and silicon, —usually referred to as " nutrient salts,"—have been carried out in many countries abroad largely in temperate latitudes (Harvey, 1945). Work in tropical waters has not been on the same scale and most of it is of recent date. Studies carried out in India and Australia would be found in the publications of Sewell (1925-32), Orr (1933), Dakin and Colefax (1935), Thompson and Gilson (1937), Bal et al., (1951), Chidambaram et al. (1951, 1954), Jayaraman (1951, 1954), Prasad (1952) and Ramamurthy (1953, 1953 a). In regard particularly to dissolved oxygen, mention may be made of the attempts of Cooper (1933) and others to derive an index of organic productivity of an area from values of oxygen production and consumption. " In nature, the oxygen accumulates in the layers of organic production and thus its fluctuations in time and space give a measure of the intensity of phytoplankton outbursts. It can provide only minimal values because the exact quantity of oyxgen produced is obscured by the respiratory activity of animals and bacteria, and in case of surface supersaturation some oxygen is given off" to the atmosphere" (Sverdrup et al, 1942, p. 934). The above quotation makes evident the usefulness of oxygen values when they are available in required detail. A simple series of values derived from analysis of surface samples such as is presented below, has interest from another angle revealing as it does the broad features of the changes in composition of the sea-water from season to season and year to year.