Distribution patterns of Recent pteropods in surface sediments of the western continental shelf of India

Arun Deo Singh,Neelakantan Ravindran Nisha,Thadickal Viswanathan Joydas

doi:10.1144/jm.24.1.39

Arun Deo Singh, Neelakantan Ravindran Nisha + Show 1 more

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https://doi.org/10.1144/jm.24.1.39

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Abstract

Abstract. This paper is the first contribution to the knowledge of pteropods in surficial sediments of the entire western continental shelf of India. Both qualitative and quantitative analyses of pteropod assemblages were carried out on 50 coarse fractions (>125 μm) of topmost portions of grab samples recovered along 12 transects covering the inner shelf to the upper slope (30–200 m water depths). The distribution of eight significant species was mapped. The resultant maps were correlated with the bathymetric, hydrographic and aragonite preservation conditions in the investigated area. This study reveals a bathymetric control over the distribution of Limacina inflata, Creseis acicula and Creseis chierchiae across the shelf. Furthermore, a marked difference in vertical salinity gradient from south to north along the shelf appears to have a profound influence on the abundance of these species. The pteropod shells in sediments of the northern offshore region with anoxic bottom conditions are generally well preserved, unlike the southern region, where oxygen concentration of the bottom water is relatively high enough to cause dissolution or even elimination of many shells of the most susceptible pteropods like C. acicula and C. chierchiae. The variation in the intensity of the oxygen minimum zone along the western continental shelf of India has significant influence upon the distribution pattern of Clio convexa.

Highlights

Pteropods are widely distributed in oceans and marginal seas but abundant in those shallow basins and along those continental margins with high temperature and salinity (Sverdrup et al, 1942)
Several studies have been carried out on living, as well as dead, pteropod assemblages in marginal seas to understand the relationships between their distribution pattern and environmental conditions (Rosenberg-Herman, 1965; Reiss et al, 1980; Weikert, 1982; Almogi-Labin, 1984; AurasSchudnagies et al, 1989)
Previous studies on living pteropods reveal that the distribution of pteropods in the water column is greatly influenced by the variations in hydrographic conditions and diurnal vertical migration in certain species (Chen & Bé, 1964; Van der Spoel, 1967; Bé & Gilmer, 1977; Wormuth, 1981; Almogi-Labin et al, 1988)

Summary

INTRODUCTION

Pteropods are widely distributed in oceans and marginal seas but abundant in those shallow basins and along those continental margins with high temperature and salinity (Sverdrup et al, 1942). The North Equatorial Current (low-salinity water) sets in during the NE monsoon and moves upward into the southeastern Arabian Sea. The annual mean sea-surface salinity and temperature of shelf-slope waters vary approximately between 34‰ and 36‰ and 28(C and 26(C, respectively, from south to north along the coast (Fig. 2). The outer shelf sediments along the northern part of the west coast (north of 18(N Lat.) consist of non-skeletal components (ooids, grapestones, pelletoids and lithoclasts) (Hashimi & Nair, 1976)

MATERIAL AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS