, ., /" Indian Journal of Marine Sciences Vol. 28, December 1999, pp. 375-379 Alkali and alkaline earth metals in surface sediments off Bhimunipatnam-Amalapuram, central east coast of India (Bay of Bengal) Nittala S Sarma & M Umamaheswara Rao* Marine Chemistry Laboratory, School of Chemistry, Andhra University, Visakhapatnam-530 003, AP, India Received 19 June 1998, revised 5 August 1999 The alkali and alkaline earth metals both major (Na, K, Mg, Cal and minor (Li, Rb, Cs, Sr) were analyzed in 75 surface sediment samples from an area covering the continental shelf, slope and the deep sea regions. Lithium, Rb, Cs and Sr averaged 7.2, 42.5, 12 and 27.2 ppm respectively. Rubidium and Sr showed north-south trends. Starting from the northern sector, the former increased and the latter decreased towards the mouth of R. Godavari. This behavior is explained by th e dissolved transportation index (DTI) according to which the transport of Rb takes place mainly in the particulate and th at of Sr in the dissolved phases. Lithium and Rb are correlated well to K suggesting a detrital origin for the elements. The alk ali and alkaline earth metal distribution of the study area revealed a strong signature of R. Godavari. Strontium showed a good anticorrelation with the biogenic fraction of Mg (Mg B ). It attained peak concentrations in th e carbonate sa nd s of th e northern outer shelf which according to previous reports are of the late Pleistocene age. Sediments although rich equally in carbonate and from proximate stations, contain variable concentrations of Sr probably due to a differential time-dependent leaching of the metal as these carbonate deposits may have been formed at different stages of the regressive - progressiv e cycle of the late Quaternary sea level. The alkali (Li, Na, K, Rb and Cs) and alkaline earth metals (Be, Mg, Ca, Sr, Ba and Ra), although are electronically similar belonging to the s-block of the Periodic Table of Elements, are wide apart in terms of involvement in the biological and geological reactions . In marine sediments, the origin of alkali metals is considered mostly as detrital and/or hydrothermal. Their enrichments are a reflection of the source rock, its weathering and maturity (detrital origin) and hot extraction or basalt precipitation (hydrothermal origin). The alkaline earth metals on the other hand, are influenced by the biological enrichment mechanism. A study of these metals together can throw light on the relative importance as well as interplay of various natural processes. Of these, Na, K, Mg and Ca being major, have received considerable attention in the world oceans'·2 including the coastal and offshore sediments off the Indian coasts. 3 - 6 But the metals Li, Rb, Cs and Sr (and Ba) are trace and reported scarcely.2-7 No reports are particularly available from the Bay of Bengal sediments, even though the Bay is uniquely characterized by a bottom covered with sediments derived mainly from fluvial inputs. The two groups of *Present Address: Geological Survey of India (Marine Wing) Chemical Laboratory; MIG 3, Lawsons Bay Colony, Visakhapatnam - 530 017, AP, India. elements (for which a detrital source is the common can indeed be helpful in investigating the extent of detrital character of sediments. Hence, as a continuation of earlier report of the major elements 8 , present study is on trace alkali and alkaline earth metals of 75 surfacial sediments that were collected from 80,000 km 2 area in Bhimunipatnam to Amalapuram coastal area off the central east coast of India. Materials and Methods The sampling stations (around 75; Figs I, 2) occur in the three physiographic domains of continental shelf (29 stations), slope (6) and deep (40). The surface sediment samples were collected by Van , Veen grab (during Fe_bruary 1988 to February 19 89 . on board R. V. Samudra Manthan ) and " _ representative samples dried (at 40°C) and powdered . to pass through 100 mesh. A small sample (250 mg) of each, in duplicate, was digested with the digestion mixture (25 ml) prepared from cone. HN0 3 , HCI0 4 and HF (40 0/0 ) in the volume' ratio of 1: '1:3 . These digested masses, extracted into 3.5 N HNOl used for the AAS (Varian Tecbtron Spectrr AA-300) determination in the absorption mode (Rb) and , emission mode (Mg, Ca, Sr, Cs) using air-acetyleHe flame ?, Na, K and Li were estimated by flame