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Seminar on "Carbon and Nitrogen Stable Isotopic Studies in coastal waters around Goa, India" 
Monday, 04 February 2013,  3:00 -  4:30
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The delta13C and delta15N composition of Suspended Particulate Organic Matter (SPOM) from coastal waters

especially along the western continental shelf of India (WCSI) and the adjacent Mandovi Zuari estuarine

system were studied. The principal objective of this study was to understand how the delta15N and delta13C of SPOM

is affected by seasonally varying processes of organic matter production and respiration, and how it relates to

the delta15N of sedimentary organic matter. The use of carbon isotope data and C/N ratios were used to gain

insight into the sources of organic matter. This issue is also of considerable importance as the area studied

receives large runoff from the Mandovi-Zuari rivers during the SW monsoon and the associated terrestrial

organic matter inputs may possibly play a role in biogeochemical cycling of coastal systems.

Elemental carbon and nitrogen concentrations, C/N ratios in SPOM, along with ancillary chemical and

biological variables including phytoplankton pigment abundance were determined on a seasonal basis (from

March 2007 to September 2008), with the partial exception of the southwest (SW) monsoon period. The results

reveal significant shifts in isotopic signatures, especially delta15N, of SPOM before and after the onset of SW

monsoon. 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 delta15N of SPOM is generally lower

than the mean value (7.38 per thousand) for surficial sediments, presumably because of diagenetic enrichment. The

results support the view that sedimentary delta15N 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 delta13C of SPOM during the pre-monsoon and post-monsoon period is

generally small. The largest changes (depletion of delta13C and increase in C/N) appear to occur during the pre

and post-monsoon seasons, presumably through episodic deposition of terrestrial organic matter from the

atmosphere.

Location : Conference Hall, C-MMACS New Building
Contact : Krishna Mohan, T. R.
Speaker: Elizabeth Maya, M. V., Chemical Oceanography, National Institute Of Oceanography, Dona Paula, Goa 403004

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