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Intra-annual Variability of Carbon and Nitrogen Stable Isotopes in Suspended Organic Matter in Waters of the Western Continental Shelf of India : Volume 8, Issue 2 (18/04/2011)

By Maya, M. V.

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Book Id: WPLBN0004005837
Format Type: PDF Article :
File Size: Pages 29
Reproduction Date: 2015

Title: Intra-annual Variability of Carbon and Nitrogen Stable Isotopes in Suspended Organic Matter in Waters of the Western Continental Shelf of India : Volume 8, Issue 2 (18/04/2011)  
Author: Maya, M. V.
Volume: Vol. 8, Issue 2
Language: English
Subject: Science, Biogeosciences, Discussions
Collections: Periodicals: Journal and Magazine Collection (Contemporary), Copernicus GmbH
Publication Date:
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications


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Naik, H., Roy, R., A. Naqv, S. W., Maya, M. V., Shenoy, D. M., & Karapurkar, S. G. (2011). Intra-annual Variability of Carbon and Nitrogen Stable Isotopes in Suspended Organic Matter in Waters of the Western Continental Shelf of India : Volume 8, Issue 2 (18/04/2011). Retrieved from

Description: National Institute of Oceanography, Council for Scientific and Industrial Research, Dona Paula, Goa – 403004, India. The Δ13C and Δ15N of water-column suspended particulate organic matter (SPOM), elemental carbon and nitrogen concentrations, and C/N ratios in SPOM, along with ancillary chemical and biological variables including phytoplankton pigment abundance, were determined every month, with the partial exception of the southwest (SW) monsoon period, from March 2007 to September 2008 at a fixed site located off Goa (central west coast of India). The results reveal significant shifts in isotopic signatures, especially Δ15N, of SPOM before and after the onset of the SW monsoon. Very low Δ15N values, reaching a minimum of −4.17‰, are found during the pre-monsoon period. Although the average Δ15N values for the SW monsoon (6.55‰) and post-monsoon (6.19‰) are substantially higher, these values are lower than expected from a region that experiences intense water-column denitrification, as well as those reported previously from the open Arabian Sea. Our results provide the first direct evidence for the addition of substantial amounts of isotopically light nitrogen by the diazotrophs, especially Trichodesmium, in the region. The Δ15N of SPOM is generally lower than the mean value (7.38‰) for surficial sediments in the region, presumably because of diagenetic enrichment. The results support the notion that sedimentary Δ15N may not necessarily reflect denitrification intensity in the overlying waters due to diverse sources of nitrogen and variability of its isotopic composition. The observed intra-annual variability of Δ13C of SPOM is small (seasonal averages: pre-monsoon: −21.40‰, SW monsoon: −20.41‰ and post-monsoon: −22.15‰). Phytoplankton production and probably species composition could drive the observed changes. Occasional shifts in Δ13C toward more negative values are suggestive of terrestrial inputs, but by and large the SPOM in the region seems to be of marine origin with relatively low and constant C/N ratios (5.8–6.5) occurring throughout the study period.

Intra-annual variability of carbon and nitrogen stable isotopes in suspended organic matter in waters of the western continental shelf of India

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