ALBERT

Description: The present volume gives the observed physical and chemical data obtained by R. V. "Meteor" in the Indian Ocean during her cruise 1964/65. The tables are based on the computations made by the National Oceanographic Data Center (NODC) in Washington. In addition to the normally communicated data, the tables contain four chemical parameters: alkalinity, ammonia, fluoride, and calcium.

Description: In this paper the sections for temperature and salinity are presented, which were obtained during the cruise of R. V. "Meteor" in the Indian Ocean (1964/65). The hydrographic observations in the Arabian Sea, had the aim to provide information on the influence of the NE-monsoon on the distribution of salinity and temperature off the east coast of Africa and off the west coast of India. Special attention was given to the spreading of highly saline water from the Red Sea and the Persian Gulf. The track of the expedition was layed out according to these plans and is presented in figure 1. The data were collected by means of hydrographic casts with newly developed water bottles, and by means of "in-situ" measurements with the "bathysonde", an instrument for the continuous recording of electrical conductivity, temperature and pressure. This paper only deals with the data of the casts which are presented in a special publication together with the chemical data. The hydrographic conditions off the east coast of Africa are characterised by a rather complicated distribution of salinity within the first 1000 m of depth with several intermediate maxima and minima (hydrographic sections III-IX). This is due to the spreading of highly saline water mainly from the Red Sea, which can be traced southwards at least as far as 4° N (figure 9). Similar complicated conditions were found off the west coast of India (sections XI-XVI). Here the cause can be traced back to watermasses from the Persian Gulf. In depths below 2 000 m the TS-relation is virtually the same at both sides of the Arabian Sea.

Description: The present investigatioh concerns itself with two problems: First it is investigated with the aid of the hydrographic data available until medio 1965 from the Indian Ocean, whether due to the varying actions of the monsoons a large scale seasonal shift in the distribution of the isohalines occurs at the level of intermediate salinity maxima ( depth range about from 300 to 800 m). Furthermore it is investigated by means of two theoretical models whether advection or horizontal mixing dominates in the large scale distribution of the salinity in the Arabian Sea. In the treatment of the first problem, distribution charts for the water from the Read Sea and the Persian Gulf were made with the aid of the core layer method for both monsoon periods. The core layer of Red Sea water lies at about 600 to 800 m depth. The watermasses from the Persian Gulf sink from 200 to 500 m while moving from north to south. In both seasons the observable limit of extension lies at about 3° N. Seasonal variations occur apparently only in the northern part of the basin and at its margins. The observed distribution of salinity shows at all levels (300, 400, 500, and 600 m) an east-west pattern (fig. 7 to 10). In no case a tongue form appears in the isohalines. The observed distribution is satisfactorily interpreted by means of a model which considers only horizontal mixing and the natural boundary conditions (Dirichlets problem for the rectangle). A further model which includes advective terms does not corroborate the observations. The investigations lead to the conclusion that the existing stationary distribution of salinity in the central part of the Arabian Sea is maintained essentially by large scale mixing processes. Further theoretical considerations, which are based upon observations at the 800 m level, suggest that the distribution of salinity at the margins of the basin strongly influences the salinity of the inner part. A change in the marginal distribution on the other hand, may be caused by means of horizontal movements of relatively small width. In further investigations on the circulation of the Arabian Sea one has therefore to consider especially the processes at the margins of the basin.

Description: Although vertical velocities are very small, they are of great importance with regard to chemical and biological processes in the sea. A study of the circulation phenomena of down- and upward moving watet masses is not possible experimentally. Therefore, the vertical velocities were determined by means of a theoretical model using empirical data obtained by R. V. "Meteor" in the Arabian Sea, during the period of tbe NE-monsoon 1964/65. Based upon the observed data for the density the physical topography of the sea level was calculated by means of the dynamic method. The wind registrations during the hydrographic stations of R. V. "Meteor" show a very constant wind distribution of the NE-monsoon. The data of wind distribution, shapes of sea level and pycnocline were used in a simple two dimensional two layer model with two constant densities and two constant vertical eddy coefficients. The main results are presented in horizontal charts for four levels from O to 300 m for the African and for the Indian coast (plate 6 and 7). The charts show alternative strips of weak upward and downward movements parallel to the coast. The width of the strips varies from 30 to 80 km. There are three areas of intensified vertical velocities: south of the island of Socotra (profile III), south of the equator near the coast of Mombasa (profile VIII), and southerly from Karachi (profile XV). These results of stripwise distribution of upward and downward velocities are compared for one case with the distribution of particulate carbon, which shows a similar alternative distribution of minimum and maximum values (plate 8). Maximum velocities of 2 · 10-4 cm/sec occur in profile XV, in the layers between 100 and 200 m. On the other profiles velocities are less than 10-5 cm/sec. In all cases it was found that the vertical velocities reach a maximum well below the pycnocline, in order to decrease in either direction.