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Decadal Variations in Oceanic Properties of the Arabian Sea Water Column since Geosecs

Published online by Cambridge University Press:  26 July 2016

Ravi Bhushan*
Affiliation:
Geosciences Division, Physical Research Laboratory, Ahmedabad 38009, India
Koushik Dutta
Affiliation:
Geosciences Division, Physical Research Laboratory, Ahmedabad 38009, India Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, USA
Rajesh Agnihotri
Affiliation:
Geosciences Division, Physical Research Laboratory, Ahmedabad 38009, India Radio and Atmospheric Science Division, National Physical Laboratory, New Delhi 110012, India
R Rengarajan
Affiliation:
Geosciences Division, Physical Research Laboratory, Ahmedabad 38009, India
Satinder Pal Singh
Affiliation:
Geosciences Division, Physical Research Laboratory, Ahmedabad 38009, India
*
2.Corresponding author. Email: bhushan@prl.res.in.

Abstract

This article reports temporal changes in the measured oceanic geochemical properties of the Arabian Sea and the equatorial Indian Ocean by reoccupying six stations investigated during the GEOSECS expedition in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in the environment and climate that have occurred in response to natural or anthropogenic processes. The depth profiles of major parameters such as dissolved oxygen, ΣCO2, major nutrients (silicates, nitrates, and phosphates), and radiocarbon in dissolved inorganic carbon were measured during the cruises between 1994 and 1998 along with temperature and salinity. Most stations in the Arabian Sea show an increase in salinity by ∼0.2 to 0.3 salinity units in the top 400 m, whereas one station in the equatorial Indian Ocean showed a decrease in salinity by ∼0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The ΣCO2 increased by an average of 8 μM within the top 1200 m of the Arabian Sea. The depth profiles of nitrates and dissolved oxygen for the central Arabian Sea stations show significant variations, while only marginal changes are seen for silicates and phosphates relative to the GEOSECS data. The decrease in Δ14C of surface waters is due to the steady decrease in atmospheric 14C concentration since GEOSECS, and the Δ14C increase in subsurface waters is attributed to the downward vertical diffusion of bomb 14C interpreted in terms of atmosphere to ocean transfer and lateral advection of water masses.

Type
Articles
Copyright
Copyright © 2014 by the Arizona Board of Regents on behalf of the University of Arizona 

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